On 18.05.19 21:53, Nicklas Karlsson wrote:
> It might be worth looking a redox flow batteries, if they are
> available in suitable size somewhere. I think number of cycles and
> service life is good but did only spent a minute or so looking. I
> would expect they are a particularly good solution for long
> discharge/charge cycles but suspect short bursts of high power would
> be a problem.
I've made some mention of the Redflow "Z-Cell" ZnBr redox flow battery
on the "How come...." thread, which has been running the last few days.
It is the only small one I know of - just 240 kg, a quarter of a tonne.
The manufacturer boasts that it is "Theft resistant" - an asset in the
small remote telco installations in which it is popular. They're used in
the Pacific Islands, and usage in Australia and New Zealand is
increasing, in telco, business, and domestic installations. They're
starting to be sold into China and South Africa.
It's remarkably robust; can't be harmed by 100% discharge - in fact does
that itself once every 120 hrs pump² uptime, to regenerate. In that way
it does not lose capacity over a ten to fourteen year life, just an
efficiency fall (~1%/yr) which other battery technologies suffer
_in_addition_to_ capacity loss. (Schedule the regeneration to occur
during sunny daylight, and it is invisible downtime. Otherwise install a
second battery. If that's a Redflow (Z-Cell / ZBM2), then they'll take
turns by themselves.) If the household has quite a few occupants, then
one 10 kWh battery could be light on for grey wintry days, anyway.
It can also be left for months or years in a any state of charge,
without harm, and if left charged has little charge loss.
It won't catch fire like some lithium technologies - in fact the 190
litres of ZnBr solution would help to extinguish a fire if the tank were
breached.
The consumerised unit in an enclosure for external installation is:
Z-Cell: The enclosure measures about 1020mm long, 520 mm wide
and 1150 mm high and weighs around 290Kg.
https://www.zcell.com/
OK, what's less attractive? The darn thing is OK for cycle life cost,
but that makes the upfront cost substantial¹, because it lasts so long.
Input power: 2.5 kW (44A @ 57v) Must be externally limited.
Output power: 3 kW (5 kW for 30 min) Operating the ZBM at a
higher level will void any warranty claim.
The higher internal resistance of the ZBM compared
to other battery technologies is one of the reasons
why the ZBM is not ideally suited to high-power
limited-energy applications.
Like a number of other chemistries, initial energy retrieval efficiency
is 80%, falling about 1% per year of active use. A few extra solar
panels in the array is a cheap fix for that.
There's a folksy sort of review here:
https://www.solarquotes.com.au/blog/redflows-zinc-bromide-zcell-battery-may-have-the-edge-over-lithium-ion/
This page has links to product details and system integration info:
https://redflow.zendesk.com/hc/en-us
I figure it will do me for night-time power. The workshop can be run off
the array in daytime, and summer aircon similarly.
My preference is for installing it in a corner of the workshop or
garage, in an enclosure vented to the outside, as in extremis it can
emit a puff of bromine gas, and that pongs.
Erik
¹ Last time I looked. The price may be improving, by degrees.
(I don't dare look yet, as it's the best candidate for my off-grid build.)
² BLDC pumps, custom engineered for the product. Claimed to be designed
for long life.
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