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 Sunday at 12:41 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 Sunday at 13:31 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 Sunday at 13:34 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. 

[mk1_man]

For my situation installing the inverter and batteries has been far more beneficial than installing solar, something I have yet to do.  The time when I need the most electric is during the winter when I am using the ASHP the most.  Last winter I ran the heat pump and rest of house 24 x 7 at 5p per kWh (TE) and monthly costs were a 1/5 of previous year.  The batteries (6 x 5kWh) and inverter (Sunsynk 5kW) were self installed so costs were what I considered very cost effective working out at £120 per kWh.  I reckon ROI will be less than 3 years.  You can do something similar with a build yourself Seplos 16 kWh battery @ £1500 ( or just £93.75 /kWh)  :  https://www.fogstar.co.uk/collections/seplos-mason-kits/products/seplos-v4-kit-and-x16-mb31-314ah-grade-a-bundle

[JamesPa]

@dilsue @mk1_man thanks for those very helpful comments which I will certainly factor into my personal choice. 

 

Im thinking that if I self install  (unless I self install it definitely doesnt cost in.) I cant DC couple, because to DC couple requires changing the generation meter and inverter on the existing PV and that requires MCS to retain FiT payments.  However DC coupling and a hybrid inverter means that one inverter controls the export so it can remain within G98.

 

But if I AC couple, which means I can leave the existing PV alone and thus potentially self install, I need G99 unless I can find a certified way to link the PV inverter and the battery inverter to ensure that, together they, remain within the G98 export limit (even though in practice they certainly will).  I wonder if any battery inverter supports that.

 

 

 

Alternatively I can wait until the solar inverter fails and I am forced to replace anyway.  They were guaranteed for only 10 years but mine is still going strong, I wonder what the practical lifetime is in the real world.

Edited Monday at 12:10 by JamesPa

[Dillsue]

5 hours ago, JamesPa said:

Im thinking that if I self install  (unless I self install it definitely doesnt cost in.) I cant DC couple, because to DC couple requires changing the generation meter and inverter on the existing PV and that requires MCS to retain FiT payments.  However DC coupling and a hybrid inverter means that one inverter controls the export so it can remain within G98.

I dont believe that MCS is required for any alteration or repairs/replacement to a FIT system. As an example, if you extend a 4 kw system by 4kw to give an 8kw system you get paid FIT rates on the original 4kw. If the 4kw extension element is MCS installed you can claim SEG on the extension. If the 4kw extension isn't MCS certified then you can't claim SEG but you could get paid under a PPA by the likes of Octopus. It's all in here https://www.ofgem.gov.uk/sites/default/files/2024-09/Guidance_for_FIT_Generators_V18.pdf

[SteamyTea]

56 minutes ago, Dillsue said:

As an example, if you extend a 4 kw system by 4kw to give an 8kw system you get paid FIT rates on the original 4kw.

That is the way I understand it.

 

You should be able to get a better yield and newer PV modules are more efficient at lower light levels and if the right inverter is chosen, then that can be taken advantage of.

Generally, natural daylight follows an inverse square law.  So you get a lot of sub 100 W.m^-2 light, then half that between 100 and 200 W.m^-2, half again between 200 and 300 W.m^-1 and so forth.  Very little at the greater than 700 W.m^-2.

 

[JamesPa]

2 hours ago, Dillsue said:

I dont believe that MCS is required for any alteration or repairs/replacement to a FIT system. As an example, if you extend a 4 kw system by 4kw to give an 8kw system you get paid FIT rates on the original 4kw. If the 4kw extension element is MCS installed you can claim SEG on the extension. If the 4kw extension isn't MCS certified then you can't claim SEG but you could get paid under a PPA by the likes of Octopus. It's all in here https://www.ofgem.gov.uk/sites/default/files/2024-09/Guidance_for_FIT_Generators_V18.pdf

Hmm, interesting (and thank you). 

 

This is a later version of the guidance than the one I have previously read, and does indeed seem to omit many references to MCS. 

 

However the requirement to pro-rate based on total installed capacity seems to depend on the definition of the latter, which is apparently given on Page 65 in a way that involves certification by either MCS or Roofit. 

 

I think this might mean that you can install a DC coupled battery without MCS (because, although the metering requirements will change, the TIC doesn't) but you cannot increase the solar export capacity without MCS (because the TIC does change).  If so that would, in itself, be very helpful.  I may need to read this document a few more times to understand whether swapping an inverter (which, practically speaking, potentially changes the TIC) does (in terms of the rules) change the TIC in the circumstance that the inverter has the same limit (eg G98).

 

Am I right in thinking (as I did with the previous version of the guidance) that there is nothing to stop you increasing the capacity of the panels above the output capacity of the inverter, and thus claiming FIT on the generation as clipped by the inverter (even though this will be greater in aggregate than the generation with the original panel capacity), on the grounds that the 'total installed capacity' is set by the inverter limit.  

 

 

Complex this stuff!

 

Edited Monday at 19:38 by JamesPa

[JamesP]

7 hours ago, JamesPa said:

Alternatively I can wait until the solar inverter fails and I am forced to replace anyway.  They were guaranteed for only 10 years but mine is still going strong, I wonder what the practical lifetime is in the real world.

We have a Fronius IG-TL 4, nearly 15 years old but both my brother and father had theirs replaced under a 20 year warranty due to failure.

 

@mk1_man Thanks for this, I would consider a battery option to be charged on a decent night rate tariff to then consume during the day.

If possible being able to top up with any excess PV after the PV diverter to DHW has maxed out.

Think the cost would take 2-3 years to recover.

 

[Dillsue]

4 hours ago, JamesPa said:

However the requirement to pro-rate based on total installed capacity seems to depend on the definition of the latter, which is apparently given on Page 65 in a way that involves certification by either MCS or Roofit. 

Page 65 is within the section on eligibility criteria for FlT installations/payments and I read that as applying only to the FIT accredited part of your installation??

 

The section on extensions talks about accredited and non accredited installations and the tariff rates you are entitled to on p23 section 3.18. It gives 3 scenarios which I read as follows-

Original accredited installation-MCS, entitlement to FIT tariff(80% in their example)

Extension accredited installation-MCS, no FIT entitlement but entitled to SEG tariff(20% in their example)

Extension non accredited installation- non MCS, no FIT or SEG entitlement. (20% in their example) You may get PPA from Octopus and Co.,  but no entitlement  to anything. These 3 senarios suggest to me that self installed/non MCS extensions to a FIT system are allowable

 

5 hours ago, JamesPa said:

I may need to read this document a few more times to understand whether swapping an inverter (which, practically speaking, potentially changes the TIC) does (in terms of the rules) change the TIC in the circumstance that the inverter has the same limit (eg G98).

An inverter swap may impact DNC but not TIC which is driven by the panel capacity, as I read it!

5 hours ago, JamesPa said:

Am I right in thinking (as I did with the previous version of the guidance) that there is nothing to stop you increasing the capacity of the panels above the output capacity of the inverter, and thus claiming FIT on the generation as clipped by the inverter (even though this will be greater in aggregate than the generation with the original panel capacity), on the grounds that the 'total installed capacity' is set by the inverter limit. 

You'd be increasing the TIC if you added panels so wholly notifiable as an extension. From what's on our original MCS cert the G98 limit is what defines the DNC. Our FIT install has 4kw of panels and a declared TIC of 4 kw. The inverter is limited to 16amp so the DNC is declared as 3.68kw.

5 hours ago, JamesPa said:

Complex this stuff!

Yep!!

[JamesPa]

@Dillsue thanks for the comments.

 

It's going to take a few more read throughs before I respond with any confidence. 

 

In fairness to the people drawing up the regs they seem to be trying really hard to allow as much flexibility as possible without compromising the integrity of the initial FIT scheme.  

 

It does make me wonder whether they should just offer a buy out option, basically (eg) 90 pc of the remaining expected fit revenues in return for no ongoing commitments on either side.  I can however understand why this would create all sorts of complications given that it's government sponsored.

 

This does also highlight how complex 25 year contracts are in a landscape where the technology is forever shifting!  I genuinely don't envy the people constructing contracts with wind farms and nuclear power stations, with perhaps a 50+ year life expectancy.  The only certainty is that whatever the context is now, it will be totally different by the time the half way point is reached (even without the politics)

Edited Tuesday at 18:40 by JamesPa

[SteamyTea]

14 hours ago, JamesPa said:

where the technology is forever shifting

PV technology has not changed in 40 years.

Only gradually improving module efficiency and large price decreased have happened.

 

When governments created long-term contracts, they usually look to be poor value, so you are right when you say that you would not want to be negotiating them.

The original FiTs was classic, people are still whining that they cannot get 41p/kWh, but fail to remember that a 4 kW_p system could cost £20k+.

Same system can be self installed for less than a fifth of that now.