My first PV set up - advice please !

[-rick-]

This Fogstar battery (https://www.fogstar.co.uk/collections/server-rack-batteries/products/fogstar-energy-seplos-48v-16-1kwh-solar-battery) is £109/kWh, they claim 8000 cycles with 80% discharge (I think 8000 cycles is quite a common claim these days).

 

If I've done my maths right thats:

109/0.8 = 136

136/8000 = 1.7p/kWh

 

The batteries themselves likely aren't an issue cost wise. Installation, age related capacity reduction, etc, makes things worse but still worth investigating.

 

Edited 5 hours ago by -rick-

[SteamyTea]

1 minute ago, -rick- said:

The batteries themselves likely aren't an issue cost wise

Yes, maybe I should have been clearer.  It is the total instal costs, not just the batteries.

 

I would be very wary of a claimed 8000 cycles.  After the halfway point, how much energy can you get out as a fraction of the energy in.  Generally as batteries age, they get warmer on both the charge and discharge cycles.  it is something I would like to see some decent data on.

[JamesPa]

1 hour ago, JohnMo said:

We get zero paid for export, so the financial case for a battery was pretty easy

I can easily believe that this case with zero export payment.

 

My current leccy prices are basically 7p from midnight-7am, 26p from 7am-midnight and 15p export.    Since the night time import rate <daytime export rate, I charge my EV, do my washing, breadmaking, washing up and water heating at night, and don't worry if I export during the day.  I don't currently bother with 'setting forward' my ASHP to benefit from the night rate, but neither do I set it back; bedrooms are just set to be a couple of degrees colder by adjusting the LSVs. 

 

For me at current electricity prices batteries would need to be <<£250/kWh installed to make sense, currently they are closer (at least in the South of England) to £400-£500.; In a few months time I will have  years worth of daily records of peak rather and night rate usage, which will enable me to d a more accurate calculation, but I can already tell that its not going to justify a 'professionally' installed battery just yet, but I am keeping my eye on self install prices.  One complication is that with solar already present any export by a separate battery inverter puts me into G99 territory.  Currently I have no realistic option other than to AC couple, given that I get FIT - ie generation - payments as well as export payments.

Edited 4 hours ago by JamesPa

[-rick-]

Good point about roundtrip efficiency. Went down a little rabbithole looking at this. Looks like >95% is what to expect new (with 98-99% commonly claimed). Given the cost of the battery, even if it only did 4000 cycles and efficiency dropped to 80% round trip near end of life, I suspect the cost is still easily below your 10p/kWh mark.

[-rick-]

6 minutes ago, JamesPa said:

For me at current electricity prices batteries would need to be <<£250/kWh installed to make sense, currently they are closer (at least in the South of England) to £400-£500.; In a few months time I will have  years worth of daily records of peak rather and night rate usage, which will enable me to d a more accurate calculation, but I can already tell that its not going to justify a battery just yet.

 

£400-500 kWh does seem crazy when the battery itself can be had for ~£110 (assuming you already had the inverter that supported adding a battery). The install is adding a few cables and configuring the inverter, it's half a days work for 1 guy at most. The battery itself comes with fuses and isolators I believe.

Edited 4 hours ago by -rick-

[JohnMo]

1 hour ago, SteamyTea said:

For how long?

Missed the 'h' should have said 5 kWh.

[Dillsue]

4 hours ago, JamesPa said:

Currently I have no realistic option other than to AC couple, given that I get FIT - ie generation - payments as well as export payments.

If your inverter supports it or you can change it for one that does, I believe you can DC couple within the FIT rules. If you can charge from the grid and potentially export it again through the generation meter then you need to replace your generation meter with a bi directional meter that gives a net reading so the net reading only represents the PV generation.