Re: [RE-wrenches] To insulate a battery bank

[frenergy]

  - Original Message - 
  From: Darryl Thayer 
  To: RE-wrenches 
  Sent: Friday, December 10, 2010 8:00 AM
  Subject: Re: [RE-wrenches] To insulate a battery bank


I have always been concerned with both high and low temperature.  On 
case of a battery bank failure it was insulated with 1.5 inch foam (no acid 
problems) but the battery melted I think from thermal runaway and 

--- On Fri, 12/10/10, bob ellison  wrote:


  From: bob ellison 
  Subject: Re: [RE-wrenches] To insulate a battery bank
  To: "'RE-wrenches'" 
  Date: Friday, December 10, 2010, 5:32 AM


  With the amount of lead in a battery bank it changes temperature very 
slowly. Both gaining and losing heat is a very slow process.

  I have never insulated battery banks, if in a cold area like here we 
size them larger for the slower reaction time in the winter anyway. Part of the 
reason being that I would bet that the acid would raise hell with the 
insulation! 

  We regularly see battery banks that are 40 degrees or so it presents 
no problem.

  If the exhaust fan is running in a 70 degree building all it does is 
draw the warm air over the top of the battery and not really warm them much 
anyway, in an unheated building it will probably not make much difference.

  The only way that I would put insulation in an unheated battery box 
is on the outside of the plywood, away from the acid and gasses. I would also 
make it removable in the summer.




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Re: [RE-wrenches] Tranformless inverter

[August Goers]

Helpful points, thanks Glenn. -August

On Fri, Dec 10, 2010 at 5:23 PM, Glenn Burt  wrote:

> I just did a review of the TL inverters by SMA for possible use.
>
> A few points that are relevant:
> They require the use of an external fused combiner (they also sell). It has
> support for up to 6 strings, with both + and – fuse positions provided.
>
> The integrated DC disconnect has no fusing – it will accept only two
> conductors
>
> The manual says these inverters are supposed to be installed in threes
>
> They only work on 208VAC
>
> Obviously they are lighter than their transformer based cousins
>
> There is a warning to beware of stray array capacitances in excess of 2
> micro Farads or more and 50mA from the cells to ground or the inverter will
> disconnect
>
> Obviously an EGC is still necessary from the frame of the array
>
> Required clearance around the inverter has been increased to 12” (36”
> below)
>
> Replaceable varistors are used to protect DC inputs from high voltages
> (inside DC disconnect)
>
> Still 600VDC upper limit
>
> AC max conductor diameter is 2AWG, min is #6
>
> DC conductors - #10 to #6
>
> They recommend operating the DC disconnect once a year, 10 times to keep
> the contacts clean
>
>
>
> FYI – thought I’d share.
>
>
>
> -Glenn Burt
>
>
>
>
>
> *From:* re-wrenches-boun...@lists.re-wrenches.org [mailto:
> re-wrenches-boun...@lists.re-wrenches.org] *On Behalf Of *August Goers
> *Sent:* Friday, December 10, 2010 3:50 PM
>
> *To:* RE-wrenches
> *Subject:* Re: [RE-wrenches] Tranformless inverter
>
>
>
> Hi Bill and Wrenches -
>
>
>
> For ungrounded arrays what specific fusing and or DC disconnect
> requirements are needed compared to grounded arrays?
>
>
>
> I'm trying to sort through the code but nothing is popping out at me
> besides what was already mentioned about needing to disconnect both the
> positive and negative lines on the DC side. In SMA's case I'm guessing that
> their new transformerless inverters with integrated DC disconnects and fuses
> may already take of all the requirements?
>
>
>
> Best,
>
>
>
> August
>
>
>
>
>
> August Goers
>
>
>
> Luminalt Energy Corporation
>
> 1320 Potrero Avenue
>
> San Francisco, CA 94110
>
> m: 415.559.1525
>
> o: 415.641.4000
>
> aug...@luminalt.com
>
>
>
>
>
>
>
> *From:* re-wrenches-boun...@lists.re-wrenches.org [mailto:
> re-wrenches-boun...@lists.re-wrenches.org] *On Behalf Of *Bill Brooks
> *Sent:* Friday, October 01, 2010 8:29 AM
> *To:* 'RE-wrenches'
> *Subject:* Re: [RE-wrenches] Tranformless inverter
>
>
>
> All,
>
>
>
> Transformerless inverters are simply a subset of ungrounded or resistively
> grounded PV systems covered by the NEC in 690.35 since the 2005 code cycle.
> Power-One has been marketing their ungrounded inverter in the U.S. for
> several years now. It was listed by CSA. The requirements for ungrounded
> systems in 690.35 are as follows:
>
>
>
> &bull  “Photovoltaic power systems shall be permitted to
> operate with ungrounded photovoltaic source and output circuits where the
> system complies with 690.35(A) through 690.35(G).
>
> &minus  *(A) Disconnects. *All photovoltaic source and output circuit
> conductors shall have disconnects complying with 690, Part III.
>
> &minus  *(B) Overcurrent Protection. *All photovoltaic source and
> output circuit conductors shall have overcurrent protection complying with
> 690.9.
>
> &minus  *(C) Ground-Fault Protection. *All photovoltaic source and
> output circuits shall be provided with a ground-fault protection device or
> system that complies with (1) through (3):
>
> &bull  (1) Detects a ground fault.
>
> &bull  (2) Indicates that a ground fault has occurred
>
> &bull  (3) Automatically disconnects all conductors or causes
> the inverter or charge controller connected to the faulted circuit to
> automatically cease supplying power to output circuits.
>
> &minus  *(D) *The photovoltaic source and output conductors shall
> consist of the following:
>
> &minus  (1) Nonmetallic jacketed multiconductor cables
>
> &minus  (2) Conductors installed in raceways, or
>
> &minus  (3) Conductors listed and identified as Photovoltaic (PV) Wire
> installed as exposed, single conductors.
>
> &minus  *(E) *The photovoltaic power system direct-current circuits
> shall be permitted to be used with ungrounded battery systems complying with
> 690.71(G).
>
> &minus  *(F) *The photovoltaic power source shall be labeled with the
> following warning at each junction box, combiner box, disconnect, and device
> where the ungrounded circuits may be exposed during service:
>
> WARNING
>
> ELECTRIC SHOCK HAZARD
>
> THE DC CIRCUIT CONDUCTORS OF THIS
>
> PHOTOVOLTAIC POWER SYSTEM ARE
>
> UNGROUNDED AND MAY BE ENERGIZED
>
> WITH RESPECT TO GROUND DUE TO
>
> LEAKAGE PATHS AND/OR GROUND FAULTS.
>
> &minus  *(G) *The inverters or charge controllers used in systems with
> ungrounded photovoltaic source and output circu

Re: [RE-wrenches] Tranformless inverter

[Glenn Burt]

I just did a review of the TL inverters by SMA for possible use.

A few points that are relevant:
They require the use of an external fused combiner (they also sell). It has
support for up to 6 strings, with both + and - fuse positions provided.

The integrated DC disconnect has no fusing - it will accept only two
conductors

The manual says these inverters are supposed to be installed in threes

They only work on 208VAC

Obviously they are lighter than their transformer based cousins

There is a warning to beware of stray array capacitances in excess of 2
micro Farads or more and 50mA from the cells to ground or the inverter will
disconnect

Obviously an EGC is still necessary from the frame of the array

Required clearance around the inverter has been increased to 12" (36" below)

Replaceable varistors are used to protect DC inputs from high voltages
(inside DC disconnect)

Still 600VDC upper limit

AC max conductor diameter is 2AWG, min is #6

DC conductors - #10 to #6

They recommend operating the DC disconnect once a year, 10 times to keep the
contacts clean

 

FYI - thought I'd share.

 

-Glenn Burt

 

 

From: re-wrenches-boun...@lists.re-wrenches.org
[mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of August Goers
Sent: Friday, December 10, 2010 3:50 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] Tranformless inverter

 

Hi Bill and Wrenches -

 

For ungrounded arrays what specific fusing and or DC disconnect requirements
are needed compared to grounded arrays? 

 

I'm trying to sort through the code but nothing is popping out at me besides
what was already mentioned about needing to disconnect both the positive and
negative lines on the DC side. In SMA's case I'm guessing that their new
transformerless inverters with integrated DC disconnects and fuses may
already take of all the requirements?

 

Best,

 

August

 

 

August Goers

 

Luminalt Energy Corporation

1320 Potrero Avenue

San Francisco, CA 94110

m: 415.559.1525

o: 415.641.4000

aug...@luminalt.com

 

 

 

From: re-wrenches-boun...@lists.re-wrenches.org
[mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Bill Brooks
Sent: Friday, October 01, 2010 8:29 AM
To: 'RE-wrenches'
Subject: Re: [RE-wrenches] Tranformless inverter

 

All,

 

Transformerless inverters are simply a subset of ungrounded or resistively
grounded PV systems covered by the NEC in 690.35 since the 2005 code cycle.
Power-One has been marketing their ungrounded inverter in the U.S. for
several years now. It was listed by CSA. The requirements for ungrounded
systems in 690.35 are as follows:

 

&bull  "Photovoltaic power systems shall be permitted to operate
with ungrounded photovoltaic source and output circuits where the system
complies with 690.35(A) through 690.35(G).

&minus  (A) Disconnects. All photovoltaic source and output circuit
conductors shall have disconnects complying with 690, Part III.

&minus  (B) Overcurrent Protection. All photovoltaic source and output
circuit conductors shall have overcurrent protection complying with 690.9.

&minus  (C) Ground-Fault Protection. All photovoltaic source and output
circuits shall be provided with a ground-fault protection device or system
that complies with (1) through (3):

&bull  (1) Detects a ground fault.

&bull  (2) Indicates that a ground fault has occurred

&bull  (3) Automatically disconnects all conductors or causes
the inverter or charge controller connected to the faulted circuit to
automatically cease supplying power to output circuits.

&minus  (D) The photovoltaic source and output conductors shall consist
of the following:

&minus  (1) Nonmetallic jacketed multiconductor cables

&minus  (2) Conductors installed in raceways, or

&minus  (3) Conductors listed and identified as Photovoltaic (PV) Wire
installed as exposed, single conductors.

&minus  (E) The photovoltaic power system direct-current circuits shall
be permitted to be used with ungrounded battery systems complying with
690.71(G).

&minus  (F) The photovoltaic power source shall be labeled with the
following warning at each junction box, combiner box, disconnect, and device
where the ungrounded circuits may be exposed during service:

WARNING

ELECTRIC SHOCK HAZARD

THE DC CIRCUIT CONDUCTORS OF THIS

PHOTOVOLTAIC POWER SYSTEM ARE

UNGROUNDED AND MAY BE ENERGIZED

WITH RESPECT TO GROUND DUE TO

LEAKAGE PATHS AND/OR GROUND FAULTS.

&minus  (G) The inverters or charge controllers used in systems with
ungrounded photovoltaic source and output circuits shall be listed for the
purpose.

 

We now have several products newly on the market to include on the list such
as the SMA and Exeltech products. Ungrounding the array requires additional
fusing and disconnects, but the most significant difference is that the
module wiring and all external cable must be PV Wire/Cable. Therefore only
modules with PV Wire/Cable can be used in thes

Re: [RE-wrenches] Driving Point Impedance of the Point ofConnection of a Grid-tied PV System

[Peter Parrish]

Hi Bill,

There are many places to take this measurement and we pick the terminal lugs
on the solar breaker for convenience. Another obvious point (as I mentioned)
is the L1-L2 terminals on the inverter output. A third would be the load
jaws of the meter.

>From my way of thinking, 

(1) the service transformer, service wiring, meter, service disconnect
constitute one (active) impedance

(2) the distribution buss and its house loads constitute a second (passive)
impedance

(3) the inverter output circuit including AC wiring, AC disco and back-fed
breaker constitute the third impedance.

It is a combination (series-parallel) of all three that determine the
impedance seen from the inverter side.

Another reason for making the measurement at the back-fed breaker terminal
lugs, is that the voltage drop if the inverter output circuitry is not
included. If one is interested in the condition of the distribution panel
buss, and utility side of the system, this is where one wants to make the
measurement.

If you want to include the AC output wiring, then the L1-L2 terminals on the
inverter output are the best place to make the measurement.

I am glad to hear that dV~3V-ac is nominal for 4000 kW-ac and relatively new
200A service.

- Peter
 

 
Peter T. Parrish, Ph.D., President
California Solar Engineering, Inc.
820 Cynthia Ave., Los Angeles, CA 90065
CA Lic. 854779, NABCEP Cert. 031806-26
peter.parr...@calsolareng.com  
Ph 323-258-8883, Mobile 323-839-6108, Fax 323-258-8885

 

-Original Message-
From: re-wrenches-boun...@lists.re-wrenches.org
[mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Bill Brooks
Sent: Friday, December 10, 2010 2:53 PM
To: 'RE-wrenches'
Subject: Re: [RE-wrenches] Driving Point Impedance of the Point ofConnection
of a Grid-tied PV System

Peter,

Are you making your measurement before and after the inverter breaker? I
believe what you are attributing to the breaker is actually the voltage rise
from the service transformer, through the service conductors, through the
service panel. A 3-Volt drop is common when adding a 4kW load to a
distribution transformer. 

Actually, without knowing the load on the transformer to start with, you
have several variables. What is likely happening is that the transformer is
providing power to the grid on a sunny day before turning off the inverter
at say, 2kW. Turn off the inverter, now you instantly turn the inverter from
2kW sourcing to the grid to a 2kW load. The voltage drop, just on the
transformer can be a volt or two in the direction of power flow (transformer
losses).

Let me know if you took the service transformer out of the equation.

Bill. 

-Original Message-
From: re-wrenches-boun...@lists.re-wrenches.org
[mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Peter
Parrish
Sent: Friday, December 10, 2010 9:07 AM
To: 'RE-wrenches'
Subject: [RE-wrenches] Driving Point Impedance of the Point of Connection of
a Grid-tied PV System

I wanted to share with the Wrenches a post-install measurement that we make
and file along with the other routine measurements (e.g. V(+) to V(-), V(+)
to Gnd, V(-) to Gnd, Pac, time or date, date, ambient temp, etc).

This is the AC voltage at the distribution panel with and without the
inverter operating. For example, let's say we have a 5.5 kW PV system. A
clear day in late Fall around Noon might result in 4 kW-ac. We measure the
voltage at the distribution panel with both system(s) operating and then
throw the AC disco and re-measure. We typically see something around 3 Vac
difference.

Among other things this measurement provides evidence that a grid tied
inverter raises its output voltage/current to the point needed to inject its
AC power through the back-fed circuit breaker onto the panel (and from there
into the house loads and possibly the grid). 

One can calculate the "effective resistance" at the backfed breaker, using
the formula:
R=(2*Vac*dV/dP), where Vac~240V, dV~3V and dP~4000W. In this example the
result is 0.36 ohms. And this is close to what we see for relatively new
200A 120/250 split phase panel.

>From our way of thinking, this number represents the impedance seen at the
back-fed solar breaker which is in turn a function of the resistance of the
breaker, the contact resistance of the breaker-buss connection, the
resistance of the panel distribution buss, the total resistance of the house
loads and the utility feed. The lower this number is the better. We have
seen as much as 1.2 ohms in an old 100A Zinsco panel, and this causes us
concern.

Is anyone aware of an article which discusses the effective circuit model of
a back-fed, grid-tied PV system? Or the inferences that one can make from
this measurement? What is the normal range of this impedance; or any other
similar measurements (such as taking these measurements at the L1-L2
terminal bock of the inverter proper which would include the voltage drop
for the

Re: [RE-wrenches] feed-in imbalance

[Bill Brooks]

Jamie,

 

The 6kVA imbalance limit, as you point out, is for 120V/240 split phase 
services, not 3-phase. It comes from California’s Rule 21 interconnection rules 
adopted by each California utility. As the technical facilitator of the 
development of Rule 21, I had a lot to do with the 6kVA number. It was based on 
the largest 120-Volt inverter that could be placed on the smallest available 
service. It JUST happened to coincide with the size of my Trace Engineering 
SW5500 inverter—funny how that works out.

 

Bill.

 

From: re-wrenches-boun...@lists.re-wrenches.org 
[mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Jamie Johnson
Sent: Friday, December 10, 2010 12:14 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] feed-in imbalance

 

Marco,

 

I believe some of the discussions in the past had to do with the old 6kW 
imbalance limit that is used by several utilities on a 120/240 small 
residential single phase transformer. (don't remember the CA utility that came 
up with this)

I had this discussion with our local utility (FPL) recently and they look at it 
on a case by case basis due to the many variables involved with 3 phase power 
distribution, such as the size and type of transformer(s), 3 phase loads on the 
premises, the harmonic distortion if any on a shared 3 phase transformer, core 
saturation, load balancing, etc.

 

If you install a system in the FPL service area that is not balanced and either 
the harmonics or voltage is out of spec as a result (yes, they do test them), 
then you basically have 2 choices, balance the system or pay to upgrade the 
service drop and transformer.

 

There has been talk of testing various 3 phase transformer(s) to determine the 
maximum/safe out of balance configuration by our local utility, however, again 
there are a lot of variables, so it would be difficult to cover every scenario. 
 And this usually is only an issue on small 3 phase transformer(s).

 

I think that the 8,9,10TL 208v inverter has a load limiting ability that is 
incorporated in the inverter when you install 2 or more inverters, and it is 
programmable to limit the output of a single inverter to 6kW.  I believe you 
have to purchase the additional communication cables from SMA (cables available 
after the first of the year? or so I have been told).  Also, the design 
parameters seem a bit limited on the TL's.

 

Jamie

 



 

 

 Original Message 
Subject: [RE-wrenches] feed-in imbalance
From: "Marco Mangelsdorf" <  ma...@pvthawaii.com>
Date: Fri, December 10, 2010 2:00 pm
To: "'RE-wrenches'" <  
re-wrenches@lists.re-wrenches.org>

Now that SMA has come up with their new 8, 9 and 10 kW transformerless line of 
single-phase 120/208V inverters, it brings up the question once again about how 
practical and wise it is to have one or two of these inverters feed into a 
three-phase service.  That is, is such an unbalanced feed much, if any, of a 
big deal?

 

I spoke to my consulting E.E. about this and he said that the large majority of 
utility-provided transformers are so large these days that an unbalanced feed 
of, say, a 10 kW inverter that only has output power through L1 and L2 should 
not present a problem.

 

Any other thoughts out there on this matter?

 

Thanks,

marco 

 


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Re: [RE-wrenches] Tranformless inverter

[Bill Brooks]

August,

The conductor should be labeled "PV Wire" or "PV Cable", and the
documentation should show that it has been evaluated according to UL4703.

Bill.

-Original Message-
From: re-wrenches-boun...@lists.re-wrenches.org
[mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of August Goers
Sent: Friday, December 10, 2010 1:30 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] Tranformless inverter

Thanks, Dave.

Anyone have clarification on what exact marks to look for in "PV Wire?"

For example, the cables I see on a batch of Suntechs I have in the shop are
listed as "H+S RADOX SMART cable 4.0 mm" on the spec sheet but the only
listing I see on the wire themselves is RHH/RHW-2.

NEC Table 310.13(1) doesn't seem to mention PV Wire.

Thanks again for all your help.

Best,

August

-Original Message-
From: re-wrenches-boun...@lists.re-wrenches.org
[mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Dave Click
Sent: Friday, December 10, 2010 1:11 PM
To: re-wrenches@lists.re-wrenches.org
Subject: Re: [RE-wrenches] Tranformless inverter

I believe it's just:
Fusing on the +/-
disconnects break both + and -
Need your modules to use PV wire
labeling per 690.35(F)

Square D discos are UL'd for ungrounded systems- and I just noticed that
there's a June 2010 revision of the Square D disconnect guide. A bit of
clarification since the 9/09 edition I had.
http://ecatalog.squared.com/pubs/Electrical%20Distribution/Safety%20Switches
/Solar%20Disconnect%20Switches/3110DB0401.pdf

August Goers wrote:
> Hi Bill and Wrenches -
>
> For ungrounded arrays what specific fusing and or DC disconnect
> requirements are needed compared to grounded arrays?
>
> I'm trying to sort through the code but nothing is popping out at me
> besides what was already mentioned about needing to disconnect both the
> positive and negative lines on the DC side. In SMA's case I'm guessing
> that their new transformerless inverters with integrated DC disconnects
> and fuses may already take of all the requirements?
>
> Best,
>
> August
>
> August Goers
>
> Luminalt Energy Corporation
>
> 1320 Potrero Avenue
>
> San Francisco, CA 94110
>
> m: 415.559.1525
>
> o: 415.641.4000
>
> aug...@luminalt.com 
>
> *From:*re-wrenches-boun...@lists.re-wrenches.org
> 
> [mailto:re-wrenches-boun...@lists.re-wrenches.org
> ] *On Behalf Of *Bill
> Brooks
> *Sent:* Friday, October 01, 2010 8:29 AM
> *To:* 'RE-wrenches'
> *Subject:* Re: [RE-wrenches] Tranformless inverter
>
> All,
>
> Transformerless inverters are simply a subset of ungrounded or
> resistively grounded PV systems covered by the NEC in 690.35 since the
> 2005 code cycle. Power-One has been marketing their ungrounded inverter
> in the U.S. for several years now. It was listed by CSA. The
> requirements for ungrounded systems in 690.35 are as follows:
>
> *"Photovoltaic power systems shall be permitted to operate with
> ungrounded photovoltaic source and output circuits where the system
> complies with 690.35(A) through 690.35(G).
>
> -*(A) Disconnects. *All photovoltaic source and output circuit
> conductors shall have disconnects complying with 690, Part III.
>
> -*(B) Overcurrent Protection. *All photovoltaic source and output
> circuit conductors shall have overcurrent protection complying with 690.9.
>
> -*(C) Ground-Fault Protection. *All photovoltaic source and output
> circuits shall be provided with a ground-fault protection device or
> system that complies with (1) through (3):
>
> *(1) Detects a ground fault.
>
> *(2) Indicates that a ground fault has occurred
>
> *(3) Automatically disconnects all conductors or causes the inverter or
> charge controller connected to the faulted circuit to automatically
> cease supplying power to output circuits.
>
> -*(D) *The photovoltaic source and output conductors shall consist of
> the following:
>
> -(1) Nonmetallic jacketed multiconductor cables
>
> -(2) Conductors installed in raceways, or
>
> -(3) Conductors listed and identified as Photovoltaic (PV) Wire
> installed as exposed, single conductors.
>
> -*(E) *The photovoltaic power system direct-current circuits shall be
> permitted to be used with ungrounded battery systems complying with
> 690.71(G).
>
> -*(F) *The photovoltaic power source shall be labeled with the following
> warning at each junction box, combiner box, disconnect, and device where
> the ungrounded circuits may be exposed during service:
>
> WARNING
>
> ELECTRIC SHOCK HAZARD
>
> THE DC CIRCUIT CONDUCTORS OF THIS
>
> PHOTOVOLTAIC POWER SYSTEM ARE
>
> UNGROUNDED AND MAY BE ENERGIZED
>
> WITH RESPECT TO GROUND DUE TO
>
> LEAKAGE PATHS AND/OR GROUND FAULTS.
>
> -*(G) *The inverters or charge controllers used in systems with
> ungrounded photovoltaic source and output circuits shall be listed for
> the purpose.
>
> We now have several products newly on the market to include on the 

Re: [RE-wrenches] feed-in imbalance

[Bill Brooks]

Marco,

 

All 3-phase services, and single split-phase services has imbalances from
time to time. The question of whether the imbalance is problematic depends
on the size of the imbalance relative to the service transformer. Since
3-phase services are generally larger, a 10kW phase-to-phase connected
single-phase inverter in unlikely to cause an imbalance problem unless it is
indiscriminately placed on the service on the most lightly loaded phases.

 

If the above inverter is placed on the two most heavily loaded phases (since
it is a negative load), it will often reduce imbalance rather than increase
imbalance. A load recorder placed on the service before construction can
gather data so that when it comes time to choose the most heavily loaded
phases, there is plenty of data to make that decision.

 

The inverter in question has the same imbalance impact as a 10kW
single-phase water heater on a 3-phase service. If the service utility
requires a load analysis to add a water heater, then doing the same for PV
is justified. If they don't require it, they should not require the analysis
of the PV inverter.

 

Bill.

 

From: re-wrenches-boun...@lists.re-wrenches.org
[mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Marco
Mangelsdorf
Sent: Friday, December 10, 2010 11:01 AM
To: 'RE-wrenches'
Subject: [RE-wrenches] feed-in imbalance

 

Now that SMA has come up with their new 8, 9 and 10 kW transformerless line
of single-phase 120/208V inverters, it brings up the question once again
about how practical and wise it is to have one or two of these inverters
feed into a three-phase service.  That is, is such an unbalanced feed much,
if any, of a big deal?

 

I spoke to my consulting E.E. about this and he said that the large majority
of utility-provided transformers are so large these days that an unbalanced
feed of, say, a 10 kW inverter that only has output power through L1 and L2
should not present a problem.

 

Any other thoughts out there on this matter?

 

Thanks,

marco 

 

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Re: [RE-wrenches] Driving Point Impedance of the Point of Connection of a Grid-tied PV System

[Bill Brooks]

Peter,

Are you making your measurement before and after the inverter breaker? I
believe what you are attributing to the breaker is actually the voltage rise
from the service transformer, through the service conductors, through the
service panel. A 3-Volt drop is common when adding a 4kW load to a
distribution transformer. 

Actually, without knowing the load on the transformer to start with, you
have several variables. What is likely happening is that the transformer is
providing power to the grid on a sunny day before turning off the inverter
at say, 2kW. Turn off the inverter, now you instantly turn the inverter from
2kW sourcing to the grid to a 2kW load. The voltage drop, just on the
transformer can be a volt or two in the direction of power flow (transformer
losses).

Let me know if you took the service transformer out of the equation.

Bill. 

-Original Message-
From: re-wrenches-boun...@lists.re-wrenches.org
[mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Peter
Parrish
Sent: Friday, December 10, 2010 9:07 AM
To: 'RE-wrenches'
Subject: [RE-wrenches] Driving Point Impedance of the Point of Connection of
a Grid-tied PV System

I wanted to share with the Wrenches a post-install measurement that we make
and file along with the other routine measurements (e.g. V(+) to V(-), V(+)
to Gnd, V(-) to Gnd, Pac, time or date, date, ambient temp, etc).

This is the AC voltage at the distribution panel with and without the
inverter operating. For example, let's say we have a 5.5 kW PV system. A
clear day in late Fall around Noon might result in 4 kW-ac. We measure the
voltage at the distribution panel with both system(s) operating and then
throw the AC disco and re-measure. We typically see something around 3 Vac
difference.

Among other things this measurement provides evidence that a grid tied
inverter raises its output voltage/current to the point needed to inject its
AC power through the back-fed circuit breaker onto the panel (and from there
into the house loads and possibly the grid). 

One can calculate the "effective resistance" at the backfed breaker, using
the formula:
R=(2*Vac*dV/dP), where Vac~240V, dV~3V and dP~4000W. In this example the
result is 0.36 ohms. And this is close to what we see for relatively new
200A 120/250 split phase panel.

>From our way of thinking, this number represents the impedance seen at the
back-fed solar breaker which is in turn a function of the resistance of the
breaker, the contact resistance of the breaker-buss connection, the
resistance of the panel distribution buss, the total resistance of the house
loads and the utility feed. The lower this number is the better. We have
seen as much as 1.2 ohms in an old 100A Zinsco panel, and this causes us
concern.

Is anyone aware of an article which discusses the effective circuit model of
a back-fed, grid-tied PV system? Or the inferences that one can make from
this measurement? What is the normal range of this impedance; or any other
similar measurements (such as taking these measurements at the L1-L2
terminal bock of the inverter proper which would include the voltage drop
for the inverter-panel circuit)?

- Peter


 
Peter T. Parrish, Ph.D., President
California Solar Engineering, Inc.
820 Cynthia Ave., Los Angeles, CA 90065
CA Lic. 854779, NABCEP Cert. 031806-26
peter.parr...@calsolareng.com  
Ph 323-258-8883, Mobile 323-839-6108, Fax 323-258-8885

 

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Re: [RE-wrenches] To insulate a battery bank

[Nick Soleil]

Hello Wrenches:
I have always insulated my battery boxes (or the battery room).   I have 
built hundreds of battery boxes, and insulated them all with 1-1/2" rigid foam. 
 
I have never seen the foam deteriorate, with 15+ years experience on many 
sites.  As you know, the capacity of the batteries is much lower when the 
batteries get cold, so adding insulation will certainly improve the performance 
of the battery.
Unfortunately, I have seen thermal runaway occur on one battery bank in 
2002, but that was due to other circumstances. However, the insulation probably 
didn't help the batteries cool, in that one instance.  When I got to the site, 
the generator had been running for 3 very hot days, continuously pumping 
current 
into DRY batteries that should have been flooded.  The batteries had begun to 
melt, and some had become blobs of maroon plastic.  Those L-16s were only five 
years old at the time.
Nick Soleil
Project Manager
Advanced Alternative Energy Solutions, LLC
PO Box 657
Petaluma, CA 94953
Cell:   707-321-2937
Office: 707-789-9537
Fax:707-769-9037





From: Allan Sindelar 
To: re-wrenches@lists.re-wrenches.org
Sent: Fri, December 10, 2010 8:36:00 AM
Subject: Re: [RE-wrenches] To insulate a battery bank

Bob,
Extruded polystyrene ("blueboard" or "pinkboard", depending on brand) is 
designed for direct-burial use, and is unaffected by direct and continuous 
contact with battery acid. It's also strong enough to directly support the 
weight of the batteries. So it's a useful material to use, if you have need 
of insulation.

I'll use it if an otherwise tempered space for the batteries has a cold 
slab 
or dirt floor, in order to inhibit long-term conductive heat loss. 
Otherwise, I agree with the others here about the lack of benefit of 
insulation in battery enclosures. Fundamentally, insulation just retards 
the 
rate of heat transfer from a warmer space to a cooler one. Batteries don't 
generate significant heat at times when the heat is most needed, so they 
will eventually maintain the same average temperature as their immediate 
environment. 


If batteries are directly exposed to sunlight through a window, insulation 
is called for, to prevent the cells directly exposed to the sun's heat from 
warming more than the shaded cells. 


When asked, I recommend either putting batteries indoors (with proper 
sealed 
enclosure with controlled ventilation to the outdoors) or in a separate 
insulated, sun-tempered space, such as a power shed, with passive solar 
glazing and mass storage, but with no auxiliary heat. Of course, what works 
here in the sunny Southwest wouldn't work as well in your region.
Allan


 
AllanSindelar
al...@positiveenergysolar.com
NABCEP Certified Photovoltaic Installer
EE98J Journeyman Electrician
Positive Energy, Inc.
3201 Calle Marie
Santa Fe, New Mexico 87507
505 424-1112
www.positiveenergysolar.com
On 12/10/2010 4:32 AM, bob ellison wrote: 
 
>With the amount of   lead in a battery bank it changes temperature 
>very slowly.   Both gaining and losing heat is a very slow process.
>I have never   insulated battery banks, if in a cold area like 
>here 
>we   size them larger for the slower reaction time in the  
> 
>winter anyway. Part of the reason being that I would bet   that 
>the 
>acid would raise hell with the insulation! 
>
>We regularly see   battery banks that are 40 degrees or so it 
>presents no   problem.
>If the exhaust fan   is running in a 70 degree building all it 
>does 
>is draw the   warm air over the top of the battery and not really 
>warm   them much anyway, in an unheated building it will probably  
> 
>not make much difference.
>The only way that I   would put insulation in an unheated battery 
>box is on the   outside of the plywood, away from the acid and 
>gasses. I   would also make it removable in the summer.
> 

 
>No virus found in this message.
>Checked by AVG - www.avg.com
>Version: 10.0.1170 / Virus Database: 426/3305 - Release Date: 12/09/10
> ___ List sponsored by Home Power 
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Re: [RE-wrenches] Tranformless inverter

[August Goers]

Thanks, Dave.

Anyone have clarification on what exact marks to look for in "PV Wire?"

For example, the cables I see on a batch of Suntechs I have in the shop are
listed as "H+S RADOX SMART cable 4.0 mm" on the spec sheet but the only
listing I see on the wire themselves is RHH/RHW-2.

NEC Table 310.13(1) doesn't seem to mention PV Wire.

Thanks again for all your help.

Best,

August

-Original Message-
From: re-wrenches-boun...@lists.re-wrenches.org
[mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Dave Click
Sent: Friday, December 10, 2010 1:11 PM
To: re-wrenches@lists.re-wrenches.org
Subject: Re: [RE-wrenches] Tranformless inverter

I believe it's just:
Fusing on the +/-
disconnects break both + and -
Need your modules to use PV wire
labeling per 690.35(F)

Square D discos are UL'd for ungrounded systems- and I just noticed that
there's a June 2010 revision of the Square D disconnect guide. A bit of
clarification since the 9/09 edition I had.
http://ecatalog.squared.com/pubs/Electrical%20Distribution/Safety%20Switches/Solar%20Disconnect%20Switches/3110DB0401.pdf

August Goers wrote:
> Hi Bill and Wrenches -
>
> For ungrounded arrays what specific fusing and or DC disconnect
> requirements are needed compared to grounded arrays?
>
> I'm trying to sort through the code but nothing is popping out at me
> besides what was already mentioned about needing to disconnect both the
> positive and negative lines on the DC side. In SMA's case I'm guessing
> that their new transformerless inverters with integrated DC disconnects
> and fuses may already take of all the requirements?
>
> Best,
>
> August
>
> August Goers
>
> Luminalt Energy Corporation
>
> 1320 Potrero Avenue
>
> San Francisco, CA 94110
>
> m: 415.559.1525
>
> o: 415.641.4000
>
> aug...@luminalt.com 
>
> *From:*re-wrenches-boun...@lists.re-wrenches.org
> 
> [mailto:re-wrenches-boun...@lists.re-wrenches.org
> ] *On Behalf Of *Bill
> Brooks
> *Sent:* Friday, October 01, 2010 8:29 AM
> *To:* 'RE-wrenches'
> *Subject:* Re: [RE-wrenches] Tranformless inverter
>
> All,
>
> Transformerless inverters are simply a subset of ungrounded or
> resistively grounded PV systems covered by the NEC in 690.35 since the
> 2005 code cycle. Power-One has been marketing their ungrounded inverter
> in the U.S. for several years now. It was listed by CSA. The
> requirements for ungrounded systems in 690.35 are as follows:
>
> *"Photovoltaic power systems shall be permitted to operate with
> ungrounded photovoltaic source and output circuits where the system
> complies with 690.35(A) through 690.35(G).
>
> -*(A) Disconnects. *All photovoltaic source and output circuit
> conductors shall have disconnects complying with 690, Part III.
>
> -*(B) Overcurrent Protection. *All photovoltaic source and output
> circuit conductors shall have overcurrent protection complying with 690.9.
>
> -*(C) Ground-Fault Protection. *All photovoltaic source and output
> circuits shall be provided with a ground-fault protection device or
> system that complies with (1) through (3):
>
> *(1) Detects a ground fault.
>
> *(2) Indicates that a ground fault has occurred
>
> *(3) Automatically disconnects all conductors or causes the inverter or
> charge controller connected to the faulted circuit to automatically
> cease supplying power to output circuits.
>
> -*(D) *The photovoltaic source and output conductors shall consist of
> the following:
>
> -(1) Nonmetallic jacketed multiconductor cables
>
> -(2) Conductors installed in raceways, or
>
> -(3) Conductors listed and identified as Photovoltaic (PV) Wire
> installed as exposed, single conductors.
>
> -*(E) *The photovoltaic power system direct-current circuits shall be
> permitted to be used with ungrounded battery systems complying with
> 690.71(G).
>
> -*(F) *The photovoltaic power source shall be labeled with the following
> warning at each junction box, combiner box, disconnect, and device where
> the ungrounded circuits may be exposed during service:
>
> WARNING
>
> ELECTRIC SHOCK HAZARD
>
> THE DC CIRCUIT CONDUCTORS OF THIS
>
> PHOTOVOLTAIC POWER SYSTEM ARE
>
> UNGROUNDED AND MAY BE ENERGIZED
>
> WITH RESPECT TO GROUND DUE TO
>
> LEAKAGE PATHS AND/OR GROUND FAULTS.
>
> -*(G) *The inverters or charge controllers used in systems with
> ungrounded photovoltaic source and output circuits shall be listed for
> the purpose.
>
> We now have several products newly on the market to include on the list
> such as the SMA and Exeltech products. Ungrounding the array requires
> additional fusing and disconnects, but the most significant difference
> is that the module wiring and all external cable must be PV Wire/Cable.
> Therefore only modules with PV Wire/Cable can be used in these systems.
> You must confirm from the manufacturer that they have made the switch.
> Hopefully all manufacturers will be instal

Re: [RE-wrenches] Tranformless inverter

[Dave Click]

I believe it's just:
Fusing on the +/-
disconnects break both + and -
Need your modules to use PV wire
labeling per 690.35(F)

Square D discos are UL'd for ungrounded systems- and I just noticed that 
there's a June 2010 revision of the Square D disconnect guide. A bit of 
clarification since the 9/09 edition I had.

http://ecatalog.squared.com/pubs/Electrical%20Distribution/Safety%20Switches/Solar%20Disconnect%20Switches/3110DB0401.pdf

August Goers wrote:

Hi Bill and Wrenches -

For ungrounded arrays what specific fusing and or DC disconnect
requirements are needed compared to grounded arrays?

I'm trying to sort through the code but nothing is popping out at me
besides what was already mentioned about needing to disconnect both the
positive and negative lines on the DC side. In SMA's case I'm guessing
that their new transformerless inverters with integrated DC disconnects
and fuses may already take of all the requirements?

Best,

August

August Goers

Luminalt Energy Corporation

1320 Potrero Avenue

San Francisco, CA 94110

m: 415.559.1525

o: 415.641.4000

aug...@luminalt.com 

*From:*re-wrenches-boun...@lists.re-wrenches.org

[mailto:re-wrenches-boun...@lists.re-wrenches.org
] *On Behalf Of *Bill
Brooks
*Sent:* Friday, October 01, 2010 8:29 AM
*To:* 'RE-wrenches'
*Subject:* Re: [RE-wrenches] Tranformless inverter

All,

Transformerless inverters are simply a subset of ungrounded or
resistively grounded PV systems covered by the NEC in 690.35 since the
2005 code cycle. Power-One has been marketing their ungrounded inverter
in the U.S. for several years now. It was listed by CSA. The
requirements for ungrounded systems in 690.35 are as follows:

•“Photovoltaic power systems shall be permitted to operate with
ungrounded photovoltaic source and output circuits where the system
complies with 690.35(A) through 690.35(G).

−*(A) Disconnects. *All photovoltaic source and output circuit
conductors shall have disconnects complying with 690, Part III.

−*(B) Overcurrent Protection. *All photovoltaic source and output
circuit conductors shall have overcurrent protection complying with 690.9.

−*(C) Ground-Fault Protection. *All photovoltaic source and output
circuits shall be provided with a ground-fault protection device or
system that complies with (1) through (3):

•(1) Detects a ground fault.

•(2) Indicates that a ground fault has occurred

•(3) Automatically disconnects all conductors or causes the inverter or
charge controller connected to the faulted circuit to automatically
cease supplying power to output circuits.

−*(D) *The photovoltaic source and output conductors shall consist of
the following:

−(1) Nonmetallic jacketed multiconductor cables

−(2) Conductors installed in raceways, or

−(3) Conductors listed and identified as Photovoltaic (PV) Wire
installed as exposed, single conductors.

−*(E) *The photovoltaic power system direct-current circuits shall be
permitted to be used with ungrounded battery systems complying with
690.71(G).

−*(F) *The photovoltaic power source shall be labeled with the following
warning at each junction box, combiner box, disconnect, and device where
the ungrounded circuits may be exposed during service:

WARNING

ELECTRIC SHOCK HAZARD

THE DC CIRCUIT CONDUCTORS OF THIS

PHOTOVOLTAIC POWER SYSTEM ARE

UNGROUNDED AND MAY BE ENERGIZED

WITH RESPECT TO GROUND DUE TO

LEAKAGE PATHS AND/OR GROUND FAULTS.

−*(G) *The inverters or charge controllers used in systems with
ungrounded photovoltaic source and output circuits shall be listed for
the purpose.

We now have several products newly on the market to include on the list
such as the SMA and Exeltech products. Ungrounding the array requires
additional fusing and disconnects, but the most significant difference
is that the module wiring and all external cable must be PV Wire/Cable.
Therefore only modules with PV Wire/Cable can be used in these systems.
You must confirm from the manufacturer that they have made the switch.
Hopefully all manufacturers will be installing PV Wire/Cable soon so
that this will not be a problem anymore.

It is a good call to use up your USE-2 and order PV Wire/Cable from now on.

Bill.

*From:*re-wrenches-boun...@lists.re-wrenches.org

[mailto:re-wrenches-boun...@lists.re-wrenches.org
] *On Behalf Of *Exeltech
*Sent:* Friday, October 01, 2010 6:39 AM
*To:* RE-wrenches
*Subject:* Re: [RE-wrenches] Tranformless inverter

Transformerless grid-tie inverters are permitted under the National
Electric Code as of 2008. The Nationally Recognized Testing Laboratories
(UL, ETL/Intertek, CSA, etc.) took a while to develop the testing
procedures for testing to UL1741, which was the basis for most of the delay.

SMA isn't the only company with transformerless grid-tie inverters. I
know

Re: [RE-wrenches] Tranformless inverter

[August Goers]

Hi Bill and Wrenches -



For ungrounded arrays what specific fusing and or DC disconnect requirements
are needed compared to grounded arrays?



I'm trying to sort through the code but nothing is popping out at me besides
what was already mentioned about needing to disconnect both the positive and
negative lines on the DC side. In SMA's case I'm guessing that their new
transformerless inverters with integrated DC disconnects and fuses may
already take of all the requirements?



Best,



August





August Goers



Luminalt Energy Corporation

1320 Potrero Avenue

San Francisco, CA 94110

m: 415.559.1525

o: 415.641.4000

aug...@luminalt.com







*From:* re-wrenches-boun...@lists.re-wrenches.org [mailto:
re-wrenches-boun...@lists.re-wrenches.org] *On Behalf Of *Bill Brooks
*Sent:* Friday, October 01, 2010 8:29 AM
*To:* 'RE-wrenches'
*Subject:* Re: [RE-wrenches] Tranformless inverter



All,



Transformerless inverters are simply a subset of ungrounded or resistively
grounded PV systems covered by the NEC in 690.35 since the 2005 code cycle.
Power-One has been marketing their ungrounded inverter in the U.S. for
several years now. It was listed by CSA. The requirements for ungrounded
systems in 690.35 are as follows:



*  "Photovoltaic power systems shall be permitted to operate with
ungrounded photovoltaic source and output circuits where the system complies
with 690.35(A) through 690.35(G).

-  *(A) Disconnects. *All photovoltaic source and output circuit
conductors shall have disconnects complying with 690, Part III.

-  *(B) Overcurrent Protection. *All photovoltaic source and output
circuit conductors shall have overcurrent protection complying with 690.9.

-  *(C) Ground-Fault Protection. *All photovoltaic source and output
circuits shall be provided with a ground-fault protection device or system
that complies with (1) through (3):

*  (1) Detects a ground fault.

*  (2) Indicates that a ground fault has occurred

*  (3) Automatically disconnects all conductors or causes the
inverter or charge controller connected to the faulted circuit to
automatically cease supplying power to output circuits.

-  *(D) *The photovoltaic source and output conductors shall consist of
the following:

-  (1) Nonmetallic jacketed multiconductor cables

-  (2) Conductors installed in raceways, or

-  (3) Conductors listed and identified as Photovoltaic (PV) Wire
installed as exposed, single conductors.

-  *(E) *The photovoltaic power system direct-current circuits shall be
permitted to be used with ungrounded battery systems complying with
690.71(G).

-  *(F) *The photovoltaic power source shall be labeled with the
following warning at each junction box, combiner box, disconnect, and device
where the ungrounded circuits may be exposed during service:

WARNING

ELECTRIC SHOCK HAZARD

THE DC CIRCUIT CONDUCTORS OF THIS

PHOTOVOLTAIC POWER SYSTEM ARE

UNGROUNDED AND MAY BE ENERGIZED

WITH RESPECT TO GROUND DUE TO

LEAKAGE PATHS AND/OR GROUND FAULTS.

-  *(G) *The inverters or charge controllers used in systems with
ungrounded photovoltaic source and output circuits shall be listed for the
purpose.



We now have several products newly on the market to include on the list such
as the SMA and Exeltech products. Ungrounding the array requires additional
fusing and disconnects, but the most significant difference is that the
module wiring and all external cable must be PV Wire/Cable. Therefore only
modules with PV Wire/Cable can be used in these systems. You must confirm
from the manufacturer that they have made the switch. Hopefully all
manufacturers will be installing PV Wire/Cable soon so that this will not be
a problem anymore.



It is a good call to use up your USE-2 and order PV Wire/Cable from now on.



Bill.



*From:* re-wrenches-boun...@lists.re-wrenches.org [mailto:
re-wrenches-boun...@lists.re-wrenches.org] *On Behalf Of *Exeltech
*Sent:* Friday, October 01, 2010 6:39 AM
*To:* RE-wrenches
*Subject:* Re: [RE-wrenches] Tranformless inverter



Transformerless grid-tie inverters are permitted under the National Electric
Code as of 2008.  The Nationally Recognized Testing Laboratories (UL,
ETL/Intertek, CSA, etc.) took a while to develop the testing procedures for
testing to UL1741, which was the basis for most of the delay.

SMA isn't the only company with transformerless grid-tie inverters.  I know
of one American manufacturer with transformerless models on the market as
well.

Transformerless inverters are smaller, much lighter, and tend to be more
efficient than transformer-based units.  No transformer also means lower
product cost, and less shipping expense.  Win-win-win.


Dan


--- On *Fri, 10/1/10, Drake * wrote:


From: Drake 
Subject: Re: [RE-wrenches] Tranformless inverter
To: "RE-wrenches" 
Date: Friday, October 1, 2010, 6:58 AM

I also received this advertisement.  Previously I had investigated the
smaller SMA transformerless inver

Re: [RE-wrenches] feed-in imbalance

[Jamie Johnson]

Marco,
 
I believe some of the discussions in the past had to do with the old 6kW imbalance limit that is used by several utilities on a 120/240 small residential single phase transformer. (don't remember the CA utility that came up with this)
I had this discussion with our local utility (FPL) recently and they look at it on a case by case basis due to the many variables involved with 3 phase power distribution, such as the size and type of transformer(s), 3 phase loads on the premises, the harmonic distortion if any on a shared 3 phase transformer, core saturation, load balancing, etc.
 
If you install a system in the FPL service area that is not balanced and either the harmonics or voltage is out of spec as a result (yes, they do test them), then you basically have 2 choices, balance the system or pay to upgrade the service drop and transformer.
 
There has been talk of testing various 3 phase transformer(s) to determine the maximum/safe out of balance configuration by our local utility, however, again there are a lot of variables, so it would be difficult to cover every scenario.  And this usually is only an issue on small 3 phase transformer(s).
 
I think that the 8,9,10TL 208v inverter has a load limiting ability that is incorporated in the inverter when you install 2 or more inverters, and it is programmable to limit the output of a single inverter to 6kW.  I believe you have to purchase the additional communication cables from SMA (cables available after the first of the year? or so I have been told).  Also, the design parameters seem a bit limited on the TL's.
 
Jamie


 
 

 Original Message Subject: [RE-wrenches] feed-in imbalanceFrom: "Marco Mangelsdorf" Date: Fri, December 10, 2010 2:00 pmTo: "'RE-wrenches'" 



Now that SMA has come up with their new 8, 9 and 10 kW transformerless line of single-phase 120/208V inverters, it brings up the question once again about how practical and wise it is to have one or two of these inverters feed into a three-phase service.  That is, is such an unbalanced feed much, if any, of a big deal?
 
I spoke to my consulting E.E. about this and he said that the large majority of utility-provided transformers are so large these days that an unbalanced feed of, say, a 10 kW inverter that only has output power through L1 and L2 should not present a problem.
 
Any other thoughts out there on this matter?
 
Thanks,
marco 
 

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[RE-wrenches] feed-in imbalance

[Marco Mangelsdorf]

Now that SMA has come up with their new 8, 9 and 10 kW transformerless line
of single-phase 120/208V inverters, it brings up the question once again
about how practical and wise it is to have one or two of these inverters
feed into a three-phase service.  That is, is such an unbalanced feed much,
if any, of a big deal?

 

I spoke to my consulting E.E. about this and he said that the large majority
of utility-provided transformers are so large these days that an unbalanced
feed of, say, a 10 kW inverter that only has output power through L1 and L2
should not present a problem.

 

Any other thoughts out there on this matter?

 

Thanks,

marco 

 

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Re: [RE-wrenches] Driving Point Impedance of the Point of Connection of a Grid-tied PV System

[Jeff Irish]

We usually measure this input resistance into the grid (it's not a full 
impedance measurement) at the MSP lugs.  Experience has shown that less than 
150 mohm is usually OK, above 250 mohm starts to get troublesome.  The cause 
for a high resistance is most often undersized conductors from the utility 
transformer to the meter and MSP.  Depending on your utility and area, these 
conductors may be the responsibility of the homeowner or the utility.  If the 
resistance is much above 250 mohm you'll find the voltage seen at the MSP will 
vary widely with load, whether or not a PV system is present.

Jeff Irish

-Original Message-
From: re-wrenches-boun...@lists.re-wrenches.org 
[mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Peter Parrish
Sent: Friday, December 10, 2010 12:07 PM
To: 'RE-wrenches'
Subject: [RE-wrenches] Driving Point Impedance of the Point of Connection ofa 
Grid-tied PV System

I wanted to share with the Wrenches a post-install measurement that we make
and file along with the other routine measurements (e.g. V(+) to V(-), V(+)
to Gnd, V(-) to Gnd, Pac, time or date, date, ambient temp, etc).

This is the AC voltage at the distribution panel with and without the
inverter operating. For example, let's say we have a 5.5 kW PV system. A
clear day in late Fall around Noon might result in 4 kW-ac. We measure the
voltage at the distribution panel with both system(s) operating and then
throw the AC disco and re-measure. We typically see something around 3 Vac
difference.

Among other things this measurement provides evidence that a grid tied
inverter raises its output voltage/current to the point needed to inject its
AC power through the back-fed circuit breaker onto the panel (and from there
into the house loads and possibly the grid). 

One can calculate the "effective resistance" at the backfed breaker, using
the formula:
R=(2*Vac*dV/dP), where Vac~240V, dV~3V and dP~4000W. In this example the
result is 0.36 ohms. And this is close to what we see for relatively new
200A 120/250 split phase panel.

>From our way of thinking, this number represents the impedance seen at the
back-fed solar breaker which is in turn a function of the resistance of the
breaker, the contact resistance of the breaker-buss connection, the
resistance of the panel distribution buss, the total resistance of the house
loads and the utility feed. The lower this number is the better. We have
seen as much as 1.2 ohms in an old 100A Zinsco panel, and this causes us
concern.

Is anyone aware of an article which discusses the effective circuit model of
a back-fed, grid-tied PV system? Or the inferences that one can make from
this measurement? What is the normal range of this impedance; or any other
similar measurements (such as taking these measurements at the L1-L2
terminal bock of the inverter proper which would include the voltage drop
for the inverter-panel circuit)?

- Peter


 
Peter T. Parrish, Ph.D., President
California Solar Engineering, Inc.
820 Cynthia Ave., Los Angeles, CA 90065
CA Lic. 854779, NABCEP Cert. 031806-26
peter.parr...@calsolareng.com  
Ph 323-258-8883, Mobile 323-839-6108, Fax 323-258-8885

 

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[RE-wrenches] Driving Point Impedance of the Point of Connection of a Grid-tied PV System

[Peter Parrish]

I wanted to share with the Wrenches a post-install measurement that we make
and file along with the other routine measurements (e.g. V(+) to V(-), V(+)
to Gnd, V(-) to Gnd, Pac, time or date, date, ambient temp, etc).

This is the AC voltage at the distribution panel with and without the
inverter operating. For example, let's say we have a 5.5 kW PV system. A
clear day in late Fall around Noon might result in 4 kW-ac. We measure the
voltage at the distribution panel with both system(s) operating and then
throw the AC disco and re-measure. We typically see something around 3 Vac
difference.

Among other things this measurement provides evidence that a grid tied
inverter raises its output voltage/current to the point needed to inject its
AC power through the back-fed circuit breaker onto the panel (and from there
into the house loads and possibly the grid). 

One can calculate the "effective resistance" at the backfed breaker, using
the formula:
R=(2*Vac*dV/dP), where Vac~240V, dV~3V and dP~4000W. In this example the
result is 0.36 ohms. And this is close to what we see for relatively new
200A 120/250 split phase panel.

>From our way of thinking, this number represents the impedance seen at the
back-fed solar breaker which is in turn a function of the resistance of the
breaker, the contact resistance of the breaker-buss connection, the
resistance of the panel distribution buss, the total resistance of the house
loads and the utility feed. The lower this number is the better. We have
seen as much as 1.2 ohms in an old 100A Zinsco panel, and this causes us
concern.

Is anyone aware of an article which discusses the effective circuit model of
a back-fed, grid-tied PV system? Or the inferences that one can make from
this measurement? What is the normal range of this impedance; or any other
similar measurements (such as taking these measurements at the L1-L2
terminal bock of the inverter proper which would include the voltage drop
for the inverter-panel circuit)?

- Peter


 
Peter T. Parrish, Ph.D., President
California Solar Engineering, Inc.
820 Cynthia Ave., Los Angeles, CA 90065
CA Lic. 854779, NABCEP Cert. 031806-26
peter.parr...@calsolareng.com  
Ph 323-258-8883, Mobile 323-839-6108, Fax 323-258-8885

 

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Re: [RE-wrenches] To insulate a battery bank

[Allan Sindelar]

  
  
Bob,
Extruded polystyrene ("blueboard" or "pinkboard", depending on
brand) is designed for direct-burial use, and is unaffected by
direct and continuous contact with battery acid. It's also strong
enough to directly support the weight of the batteries. So it's a
useful material to use, if you have need of insulation.

I'll use it if an otherwise tempered space for the batteries has a
cold slab or dirt floor, in order to inhibit long-term conductive
heat loss. Otherwise, I agree with the others here about the lack of
benefit of insulation in battery enclosures. Fundamentally,
insulation just retards the rate of heat transfer from a warmer
space to a cooler one. Batteries don't generate significant heat at
times when the heat is most needed, so they will eventually maintain
the same average temperature as their immediate environment. 

If batteries are directly exposed to sunlight through a window,
insulation is called for, to prevent the cells directly exposed to
the sun's heat from warming more than the shaded cells. 

When asked, I recommend either putting batteries indoors (with
proper sealed enclosure with controlled ventilation to the outdoors)
or in a separate insulated, sun-tempered space, such as a power
shed, with passive solar glazing and mass storage, but with no
auxiliary heat. Of course, what works here in the sunny Southwest
wouldn't work as well in your region.
Allan


  
  
  
  
  
  
  
  
Allan Sindelar
Allan@positiveenergysolar.com
NABCEP Certified Photovoltaic Installer
EE98J Journeyman Electrician
Positive Energy, Inc.
3201 Calle Marie
Santa Fe, New Mexico 87507
505 424-1112
www.positiveenergysolar.com
  


On 12/10/2010 4:32 AM, bob ellison wrote:

  
  
  
  
With the amount of
  lead in a battery bank it changes temperature very slowly.
  Both gaining and losing heat is a very slow process.
I have never
  insulated battery banks, if in a cold area like here we
  size them larger for the slower reaction time in the
  winter anyway. Part of the reason being that I would bet
  that the acid would raise hell with the insulation! 
We regularly see
  battery banks that are 40 degrees or so it presents no
  problem.
If the exhaust fan
  is running in a 70 degree building all it does is draw the
  warm air over the top of the battery and not really warm
  them much anyway, in an unheated building it will probably
  not make much difference.
The only way that I
  would put insulation in an unheated battery box is on the
  outside of the plywood, away from the acid and gasses. I
  would also make it removable in the summer.
 
  
  
  No virus found in
this message.
Checked by AVG - www.avg.com
Version: 10.0.1170 / Virus Database: 426/3305 - Release Date:
12/09/10
  

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Re: [RE-wrenches] To insulate a battery bank

[Darryl Thayer]

I have always been concerned with both high and low temperature.  On case of a 
battery bank failure it was insulated with 1.5 inch foam (no acid problems) but 
the battery melted I think from thermal runaway and 

--- On Fri, 12/10/10, bob ellison  wrote:


From: bob ellison 
Subject: Re: [RE-wrenches] To insulate a battery bank
To: "'RE-wrenches'" 
Date: Friday, December 10, 2010, 5:32 AM






With the amount of lead in a battery bank it changes temperature very slowly. 
Both gaining and losing heat is a very slow process.
I have never insulated battery banks, if in a cold area like here we size them 
larger for the slower reaction time in the winter anyway. Part of the reason 
being that I would bet that the acid would raise hell with the insulation! 
We regularly see battery banks that are 40 degrees or so it presents no problem.
If the exhaust fan is running in a 70 degree building all it does is draw the 
warm air over the top of the battery and not really warm them much anyway, in 
an unheated building it will probably not make much difference.
The only way that I would put insulation in an unheated battery box is on the 
outside of the plywood, away from the acid and gasses. I would also make it 
removable in the summer.
 


No virus found in this message.
Checked by AVG - www.avg.com
Version: 10.0.1170 / Virus Database: 426/3305 - Release Date: 12/09/10
-Inline Attachment Follows-


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Re: [RE-wrenches] To insulate a battery bank

[bob ellison]

With the amount of lead in a battery bank it changes temperature very
slowly. Both gaining and losing heat is a very slow process.

I have never insulated battery banks, if in a cold area like here we size
them larger for the slower reaction time in the winter anyway. Part of the
reason being that I would bet that the acid would raise hell with the
insulation! 

We regularly see battery banks that are 40 degrees or so it presents no
problem.

If the exhaust fan is running in a 70 degree building all it does is draw
the warm air over the top of the battery and not really warm them much
anyway, in an unheated building it will probably not make much difference.

The only way that I would put insulation in an unheated battery box is on
the outside of the plywood, away from the acid and gasses. I would also make
it removable in the summer.

 

  _  

No virus found in this message.
Checked by AVG - www.avg.com
Version: 10.0.1170 / Virus Database: 426/3305 - Release Date: 12/09/10

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Re: [RE-wrenches] 24v Battery Charger 80 Amps?

[bob ellison]

Why not just use a Magnum MS inverter as a 2nd charger? That way in an
emergency there is a 2nd inverter to cover a failure and it will balance the
loads with or without the PSX 240 most of the time.

I expect the transformer and 2 little chargers cost close to the same as the
inverter and not look as good on the wall either.

Want to speed up battery charging add more inverter / chargers. You could
probably add 2- 4024 Magnums as well as the SW to that large a battery bank
and be fine, but you would want to balance that one.. 

 

Later,

Bob Ellison

 

 

From: re-wrenches-boun...@lists.re-wrenches.org
[mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Dana
Sent: Thursday, December 09, 2010 11:24 AM
To: 'RE-wrenches'
Subject: Re: [RE-wrenches] 24v Battery Charger 80 Amps?

 

You could add a PSX 240 transformer to balance the generator output and then
add the IOTAs. The PSX240 I think has 6KW output.

 

 

Dana Orzel

Great Solar Works, Inc

E - d...@solarwork.com

V - 970.626.5253

F - 970.626.4140

C - 970.209.4076

web - www.solarwork.com

 

"Responsible Technologies for Responsible People since 1988"

Do not ever belive anything, but seriously trust through action.

 

From: re-wrenches-boun...@lists.re-wrenches.org
[mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Dave Palumbo
Sent: Thursday, December 09, 2010 9:13 AM
To: 'RE-wrenches'
Subject: Re: [RE-wrenches] 24v Battery Charger 80 Amps?

 

Wrenchsters,

 

Any recommendations on a generator fed Battery Charger for a large 24v
battery bank (1,800AH). It's an existing off grid system with one Trace
SW4024 (has a 120A battery charger). They are getting a larger generator
(14kW) to run shop tools and speed up battery charging. I want to balance
off the second leg of this new generators output with a battery charger that
puts out anywhere from 80 to 100 Amps into the 24v battery bank. 

 

I could use two Iota 24 volt 40 Amp chargers for the 80 Amp max total. 

 

Other options?

 

Dave Palumbo

Independent Power LLC 

www.independentpowerllc.com 

NABCEP Certified PV Installer

Vermont Solar Partner

802.888.7194 

 

 

  _  

No virus found in this message.
Checked by AVG - www.avg.com
Version: 10.0.1170 / Virus Database: 426/3304 - Release Date: 12/08/10

  _  

No virus found in this message.
Checked by AVG - www.avg.com
Version: 10.0.1170 / Virus Database: 426/3305 - Release Date: 12/09/10

 

  _  

No virus found in this message.
Checked by AVG - www.avg.com
Version: 10.0.1170 / Virus Database: 426/3305 - Release Date: 12/09/10

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