Hi Ben,
What SRPs CEO knows and you will find out is you are diving into a
rabbit
hole. It is not a rational world down there, yet.
I will just talk about batteries.
It is important to know what your present and future power needs are.
For
instance, I just has a six week period this past July and August where
my
PV system made an average of 8kWh a day - I use 23kWh. As I write this
it
is completely dark and gray outside and raining once again. Obviously,
my
5.6kW system is not big enough to span the time I may need more power
than
I can reasonably make even with battery storage. A good month where I
break
even with Duke Energy, I make 23 to 30 kWh a day. To go off grid have
to
guess what I will need to save for my location and it is probably at
least
3 days worth of average use - based on current needs (no EV to charge)
-
round up to 100kWh at 120 and some 240VAC.
You need to be brutally honest about your weather, how you feel about
your
use of power, and your willingness to go with far less power or without
completely for some periods of time. I see you live in a sunny place,
AZ,
but be honest - is it ever not sunny, and how well will your system
deal
with the worst case. How well will your wife an daughters, and so on.
How
have to design for the worst case and decide what you can manage.,
In this way the grid is worth something to us all.
On the battery front - you live an a place that gets quite hot, it get
hot
when have a lot of sunlight. This means you will subject your batteries
to
the worst possible conditions for their life - high heat and high state
of
charge. You should know that Leaf batter packs are proving to be very a
lot of trouble in AZ and SoCal where they get hot, and Nissan did not
make
provisions to col them. Some packs have lost 27% of their capacity in a
year and lawsuits are in process. The heat is killing them. You are
going
to need to cool the system actively. You need to know what the exact
cells
are in it and their particular needs. A mixed pack will need to have
climate control for the worst cells in it.
Consider this LiFePO4 cells start to have real problems at 40°C (104°)
and
high states of charge. NMO at 35°C.
This is a fascinating lecture in Li Ion batteries. [The fellow giving
it
Dr. Jeff Dahn, really knows what he is talking about (he has been
working
on Li ion since 1978, one of his main collaborators is now the head
engineer at Tesla for battery life, and another is building and selling
high precision cell test equipment for Bosch, Tesla (Panasonic), ATL,
and
others)]
https://www.youtube.com/watch?v=pxP0Cu00sZs
A list of Electorchemical papers is here:
http://www.dal.ca/diff/dahn/publications.html The 1st one
chronologically
is #422, and search on A.J Smith and J.C Burns for subsequent ones.
In a nutshell the lecture says that most Li Ion battery testing in the
past
has been unable to evaluate long term performance. What happened to
Nissan
is liable to crop up with any EV packs out there (except perhaps
Tesla),
and you need to account for this with any home storage plan. If you try
to
use PbSO4 then they are more forgiving, but still a very expensive and
tricky proposition.
In truth every Li ion chemistry, electrolyte package, manufacturer, and
form factor is a little unknown world unto itself, and the data on how
to
manage them for longevity is not yet available. You make a mixed pack
from
used EVs and you are asking for trouble.
The questions is, are you offended by SRP so much that you would drop
$10k
to $20K to make a reliable home storage system? Or would you rather
send
the to SRP in little monthly bits for 30 years?
Here is how it would look for me -
Duke Energy charges me $19.50 a month when I net to no power use for
them.
Applying no time value of money - that is about 500 months before I
break
even on a $10K storage system.
Roughing it out further, I would need to at least double my PV capacity
(I
have already gotten all the tax credit I can get, so I would spend $30K
for
an additional 6kW system with really quality components (Sunpower has
the
best chance of actually lasting 30 years) to meet my worst case needs,
And
I would probably be having some times of very low available power with
this system when I would have to be very conservative in my use of
stored
power. If I charge an EV I need even more. The storage system is
probably
$20K. $50K out of pocket.
I am not happy with my utility, but I like my money more. In 30 years I
can triple that $50K with conservative investing practices. The
heartache
of and time going into design a home storage system is not appealing
either. It will be risky and if you get it wrong the extra cost high.
I believe simply waiting 10 or 20 years to see how all this shakes out
is a
smart move. Maybe buy some stock in Tesla and SolarCity - or similar.
Domestic storage is coming, doing it DIY right now sounds like a
foolish
and costly endeavor.
I suspect that SRP and Duke have done their home work on this. I bet
they
know that tripling the grid use fee to you is actually what the market
will
bear. Be careful assuming they have done this wrong.
MIke
On Sun, Dec 21, 2014 at 3:24 PM, Ben Goren via EV <ev@lists.evdl.org>
wrote:
So, I have my roof covered with solar panels. And Salt River Project,
my
utility, is threatening to at least triple monthly "basic connection
fees"
for solar "customers."
I've decided that's not an option for me. Before I pay such Danegeld,
I'll
get a bunch of batteries and drop off the grid entirely. (And I wrote
as
much in a letter to SRP's CEO.) The rate increase is still in the
proposal
stage and there'd be a period of some years before it'd go into place
for
existing "customers"...but, still, now is the time to start planning.
As I see it, I have two main reasonable options for the battery:
nickel-iron or something discarded from an EV.
Nickel-iron would either be expensive to purchase or a significant
investment in time to make, but it should last forever.
A few surplus / used / whatever EV batteries would presumably be much
cheaper, but have a much more limited lifespan.
Part of me would be inclined to go the nickel-iron route and never
have to
deal with it again.
Another part suggests to do things as cheaply as possible, even if it
only
lasts a few years, because battery technology is improving so
rapidly.
So...can anybody offer any suggestions? For example, what to expect
to pay
for EV batteries that're no good for use in an EV but still hold
enough
charge to be worth putting at the back of a closet?
I'm assuming the battery output will go into the DC input on the
inverter
I already have for the PV panels, and that, in turn, means that I
don't
have to worry about matching voltages from different batteries. That,
for
example, I should be just fine getting a surplus Leaf battery from
here and
a Tesla battery from a wrecking yard there and so on until I've got
enough
amp-hour capacity for my needs, and that I can add and remove
batteries
later as the fancy tickles me. Is that a valid assumption?
Anything else I should consider or start thinking about?
Thanks,
b&
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