Hi all from the UK - Looking to design and install a complete PV + Battery solution for 2024

[di_sjo]

Hi all,

I just joined up on the forum after many months, maybe years, or watching @Will Prowse on YouTube. I have a long history/interest in electronics and engineering, so it's probably about time I modernised the energy supply & storage in our 2019-built house. I'm in the UK, which feels a bit limiting when it comes to sourcing things like batteries, but I have just come across the merchant Fogstar (@Ben@Fogstar) which may be my answer of bridging the gap, so to say.

Brain dump:

• Want solar
• Want batteries
• Want to get AC installed, possibly heating too (split inverters)
• May be getting an air source heat pump (possibly the new Octopus Cosy 6 (or bigger when released)) which will consume more power over the winter when solar generation is low (estimated 10% generation compared to peak summer - tbc!)
• Want to charge the car overnight from low cost energy or batteries (typically 16-18kwh per night (mostly Mon-Fri), charging between 00:30-04:30 on Octopus Go)
• Would like to earn some money back using Octopus Flux in the future
• Don't want to burn my house down, or my neighbours
• Solar panels to be mounted on faces A and B on the diagram (possibly C but evening sun/limited generation)
  I think I can fit around 5 kW of solar panels
• Don't mind building DIY, but don't want to be changing anything out in 1, 2, 5 maybe even 10 years (otherwise the ROI will drop significantly)
• Concerns about feasibility of doing any of this, in this way, when MCS certification is required to tie into grid (yes I know Octopus apparently have a way round this, but my sparky doesn't think so, and is familiar with the policy - he's not MCS though)

Facts

• Have a single 100A 240v mains input from DNO
• Have a Myenergi Zappi v2 for charging our Nissan Leaf (30 kWh battery)
• Currently using Octopus Go (as above)
• May be upgrading EV or getting a second EV seriously ramping up evening usage
• Last month used 813 kWh of electricity, 398 kWh of which was EV charging, so roughly 50% of total consumption.. so an average of 13-14 kWh per day, each for house and EV

I haven't done any real calculations yet, but budget would allow for three of the Fogstar 15.5 kWh kits, which I am hoping would enable me to get a decent ROI based on Octopus Fluxm, supported by additional earnings from PV generation in the warmer months. These kit batteries seem to be a _considerably_ cheaper option than any of the 'big brand' batteries installed by all the opportunistic cowboys, and a long way from something like a Tesla powerwall. However, I am conscious of my point above about not burning down my house.

I welcome any opinions or experience relative to what i'm trying to achieve above. Appreciate it's mostly a brain dump, but hopefully some of you will be on a similar wavelength.

Thank you




Roof Layout




Energy Usage Split

 

[di_sjo]

Appreciate any opinions, or re-direction if there's a more UK-centric discussion forum.

 

[zanydroid]

Most of your questions are very UK centric (regulations, allowed hardware options esp for batteries, min maxing the compensation schemes). There are people here from UK very familiar with it, you might try tagging.

I’d say the most important questions you need are to understand the equipment options/tradeoffs (for instance in the US you save a lot with uncertified ESS; previously also saved a lot using hardware that’s not compliant with unique US safety rules but the current generation is much better) and what the DIY tie in regulations are. And maybe also semi-legal options, which are very commonly used in the U.S.

I personally wouldn’t mind if you changed this to more of a build experience thread and created a new focused post on the specific starting out questions.

Good luck.

 

[SeaGal]

Welcome!

I'll get back with more (UK specific) detail in the morning

 

[SamDeleted]

That's an interesting roof layout , it's good , more panels on the south W side for evening production (when most people use power)

 

[OffGridForGood]

Essex UK - I used Chelmsford as a proxy for your likely solar available plugged into PVWatts (maybe you have another calculator more specific to UK) I used 5kW of PV, 30-degree tilt (depends on your roof slope) and I didn't try to split the PV into SE and SW, I just used due South.
PVWatts shows you getting 101 kWh in December - worst month, and 600kWh per month May-June-July (wow, 6:1 seasonal spread)
December 101kWh/31 days = 3.25kWh per day on average.
May-July 600kWh/30.5 = 19.7 kWh per day on average.
You can expect to get less than these numbers with the E/W split in the winter months.

From the daily use and EV charging you listed, you can expect to run the house loads during the summer, and some spare for EV charging, if the car is not parked at your home while it is sunny, you will need sufficient battery storage to hold the solar collected until the car is at the house. I expect you will generally still need to charge the EV at night. During good solar you will just need a top off charge, and during poor solar days you will be stuck with charging the EV from the utility.
For winter, based on 5kW of PV panels , don't expect to run much of the house, and none of the EV charging. The super low PV potential during winter suggests you go for the highest efficiency inverters you can get, so the inverter-standby doesn't eat up the bit of solar power you will be able to collect each day.

In my own set up, I use my EV as a dump load during sunny summer days, once my ESS (batteries) are fully charged. During Winter or a string of cloudy days in summer the EV is charged off-peak ToU when the utility rates are about half price here.

 

[rpdom]

Essex UK - I used Chelmsford as a proxy for your likely solar available plugged into PVWatts

Nice place.

 

[rpdom]

Some rough initial thoughts.

It looks like area C will get some shading from B that may affect output at certain times of day.
I've got 3kW of panels (8x385W) on my small SSW facing roof. I have had 4kW peak out of them on a bright cold day. I think you'll be able to get more than 6kW of panels on yours, although size is hard to judge from the picture.
Many batteries is good. I wish I had enough in my budget for more than my 4.8kWh of Pylontechs at the time.
You're looking at an inverter rated at over 3.68kW, so you'll need G99 approval before installing to connect that to the grid.
Get a big inverter to handle those loads. If I exceed the 3kW output of mine the rest has to come from the grid and at night that goes down to 2.5kW for me because that is the maximum my batteries can supply. Another 2.4kWh battery and I could get the full 3kW.
You'll want either one inverter with at least three MPPT inputs - one for each array - or one hybrid with two MPPTs and one grid tied. The hybrid should detect the surplus from the grid tied and use that to charge the batteries if needed.
MCS is required for export payments (we'll see what Octopus can do. I'm keeping an eye on what they are up to. They seem to be challenging the system on a number of things). G98/99 are required for connection.

There are many more things to consider as well. I may add some later. Feel free to ask questions. I've had my system for 14 months now so should be able to provide some real world generation figures for a location close to you.

If anyone thinks I've got something wrong, please correct me

 

[SamDeleted]

(wow, 6:1 seasonal spread)

I think what people forget is just how northerly the UK is ,


London (south UK) is on the same latitude as Newfoundland, Canada

the Highlands of Scotland (north UK) are just about level with Anchorage, Alaska

 

[SamDeleted]

Nice place.

If you gel your hair up, like fake tan, fast cars, loose women.. then yea it's great


Thinking about it, it's only really the accent letting you lot down ?

 

[MisterB1959]

where in Essex, i am in Clacton and have assembled my own Fogstar battery. Happy to share my experience so far, which has been excellent - i have a Sunsynk 5kw inverter, 14.3kw self assembled Fogstar battery (plus a 3.6kw Power One Aurora inverter and 4kw of PV installed under the FiT scheme) i charge the battery overnight on the Octopus cheap rate and use pretty close to its storage capacity at the moment late October.

we also have Dimplex Quantum storage heaters and an immersion water heater, also charged up during the cheap period.

My next step is to install either more solar or more battery.

i am leaning more to and more to adding additional solar - which will not feed the grid so as not to impact the FiT payments and will just add charge to the battery. if i can squeeze another 5 or 6kw per day for free then it would really make a difference, or the alternative is to increase battery capacity and pay 2 or 3 pounds a day.

at an initial outlay of @£2400 for batteries and then £2/3 per day through the winter or £400 for second hand panels and no ongoing costs, the solar option would pay for itself in a year or so (cost of charging the battery would 180 days @ an average of £2 per day = £360 ) - so on pure maths its not difficult to work out until however of course i consider that i am not always going to get an additional 5 or 6 kw per day !!

 

[SeaGal]

All good input above from @OffGridForGood, @rpdom & @MisterB1959

You're in good position in UK (I'm East Anglia too) for maximising what sunshine we get (like today )

I have a long history/interest in electronics and engineering,

Overall, I'd say your plans sound good. My main thought, though, is the use of electricity for heating and EV charging will consume far more than the solar you'll be able to produce apart from in peak summer time. But if you're looking at 45kWh+ of battery storage to charge at cheap rates, together with solar you'll make a very significant impact in your electricity bills.

Few random thoughts on other aspects...

The Fogstar / Seplos kit does look like very good value. I also have 14.3kWh storage, using EVE cells purchased from Fogstar 15 months ago - mine is all DIY build, but happy with the cells & Fogstar ( & no connection, apart from being a customer of theirs).

Re doing it DIY, as @rpdom mentioned, you'll need to get G99 prior approval from UK Power Networks. UKPN may limit the amount you can export depending on your local network, but pretty irrelevant as I think you'll be consuming every little electron that you can excite anyway!

On the DIY front, see my posting here which summarises all the G98/G99, BS7671 and building regs part-P aspects of such a project..

Octopus Energy will no longer require MCS certification in the UK

https://gtec.co.uk/clause-5-8-octopus-opens-up-the-solar-pv-market-with-a-paragraph/ I'm not sure how exactly the UK's permitting and approval process works but this sounds like a major win for DIY.

diysolarforum.com

Re charging up at night... I think you'll need to seriously look at max load requirements. If I understand correctly, long term, you may be wanting to simultaneously charge 2 EV's, run an ASHP, partially charge up a 45kWh battery system, but all within a 4 hour cheap rate window. I haven't done the calcs, but even it it was a 7h 'economy 7' window that sounds to me like a lot of electrons you'll need to shift, so I'm wondering whether a 100A DNO cut-out rating be suffice? If not, you may need to pay for network reinforcement or maybe there is a possibility of getting a 3-phase supply installed where you are?

Similarly, you'll need to look at inverter ratings based not so much on your solar capacity but in terms of rate of charge / discharge to battery. Especially if you want to charge up at night, then use battery to power an ASHP and possibly charge cars during the evenings in winter.

Re your roof layout...
I'm assuming that budget is not that tight based on your planned purchases, esp. batteries. Therefore, with panels so cheap, don't dismiss the roof sides facing ENE. On cloudy days they'll produce probably as much as the WSW facing panels and will provide a good early morning boost, especially in spring / summer. For the price of panels, worth looking into IMHO.
Having said that, you'll then be looking at needing at least 3 MPPT inputs in total, but I suspect that with your high load requirements you may be needing to have more than one inverter anyway.

HTH. Any questions, do ask.

 

[di_sjo]

Most of your questions are very UK centric (regulations, allowed hardware options esp for batteries, min maxing the compensation schemes). There are people here from UK very familiar with it, you might try tagging.

I’d say the most important questions you need are to understand the equipment options/tradeoffs (for instance in the US you save a lot with uncertified ESS; previously also saved a lot using hardware that’s not compliant with unique US safety rules but the current generation is much better) and what the DIY tie in regulations are. And maybe also semi-legal options, which are very commonly used in the U.S.

I personally wouldn’t mind if you changed this to more of a build experience thread and created a new focused post on the specific starting out questions.

Good luck.

Thanks for your reply, I think it's a bit premature for a build thread, but as soon as I start to form a basis to move forwards on I am happy to document the build and learnings.

 

[di_sjo]

That's an interesting roof layout , it's good , more panels on the south W side for evening production (when most people use power)

Yes, annoyingly the previous version of this house design had a much more rectangular roof facing South which would have been preferable, maybe! Here is a drawing of my house, to give you all an idea of how (C) may work.

 

[di_sjo]

Essex UK - I used Chelmsford as a proxy for your likely solar available plugged into PVWatts (maybe you have another calculator more specific to UK) I used 5kW of PV, 30-degree tilt (depends on your roof slope) and I didn't try to split the PV into SE and SW, I just used due South.
PVWatts shows you getting 101 kWh in December - worst month, and 600kWh per month May-June-July (wow, 6:1 seasonal spread)
December 101kWh/31 days = 3.25kWh per day on average.
May-July 600kWh/30.5 = 19.7 kWh per day on average.
You can expect to get less than these numbers with the E/W split in the winter months.

From the daily use and EV charging you listed, you can expect to run the house loads during the summer, and some spare for EV charging, if the car is not parked at your home while it is sunny, you will need sufficient battery storage to hold the solar collected until the car is at the house. I expect you will generally still need to charge the EV at night. During good solar you will just need a top off charge, and during poor solar days you will be stuck with charging the EV from the utility.
For winter, based on 5kW of PV panels , don't expect to run much of the house, and none of the EV charging. The super low PV potential during winter suggests you go for the highest efficiency inverters you can get, so the inverter-standby doesn't eat up the bit of solar power you will be able to collect each day.

In my own set up, I use my EV as a dump load during sunny summer days, once my ESS (batteries) are fully charged. During Winter or a string of cloudy days in summer the EV is charged off-peak ToU when the utility rates are about half price here.

Thanks for the comprehensive reply. Yes I have been working to a very rough figure of winter generation being 10% of peak summer for my location. Of course, this will probably need some proving but I am sure there are ways to calculate this, which I will look into. I am just starting out with PV and so far have limited pretty limited exposure (pun somewhat intended).

Yes, the current EV is charged overnight, so would require battery to charge, however the current cost to re-charge from the grid is so low (£1.50/day) that it would take a LONG time to get a return on the battery investment, if just for that purpose, so that definitely wouldn't be a key driver or requirement for battery storage.

Whilst, at the moment, it seems possible for me to charge batteries during the cheap rate at night (00:30-04:30), and then sell it back to the provider at higher-demand periods (early evening), there will of course be a choke point on just how much energy I can transfer up and down the pipe within a short period of time (as @SeaGal correctly points out), so there will no doubt be a point of diminishing returns.

 

[di_sjo]

where in Essex, i am in Clacton and have assembled my own Fogstar battery. Happy to share my experience so far, which has been excellent - i have a Sunsynk 5kw inverter, 14.3kw self assembled Fogstar battery (plus a 3.6kw Power One Aurora inverter and 4kw of PV installed under the FiT scheme) i charge the battery overnight on the Octopus cheap rate and use pretty close to its storage capacity at the moment late October.

we also have Dimplex Quantum storage heaters and an immersion water heater, also charged up during the cheap period.

My next step is to install either more solar or more battery.

i am leaning more to and more to adding additional solar - which will not feed the grid so as not to impact the FiT payments and will just add charge to the battery. if i can squeeze another 5 or 6kw per day for free then it would really make a difference, or the alternative is to increase battery capacity and pay 2 or 3 pounds a day.

at an initial outlay of @£2400 for batteries and then £2/3 per day through the winter or £400 for second hand panels and no ongoing costs, the solar option would pay for itself in a year or so (cost of charging the battery would 180 days @ an average of £2 per day = £360 ) - so on pure maths its not difficult to work out until however of course i consider that i am not always going to get an additional 5 or 6 kw per day !!

Thanks, this is good info and I no doubt will reach out to you regarding the fogstar kit! I haven't really looked into inverters too much, yet, and I appreciate the are all-in-one devices that can handle DC<>AC, PV regulation and battery charging. Plenty of research to be done

 

[di_sjo]

Overall, I'd say your plans sound good. My main thought, though, is the use of electricity for heating and EV charging will consume far more than the solar you'll be able to produce apart from in peak summer time. But if you're looking at 45kWh+ of battery storage to charge at cheap rates, together with solar you'll make a very significant impact in your electricity bills.

Yes, and especially if we get a second EV, then the solar will be there purely to supplement either plain ol' grid supply or a grid/battery hybrid supply. I am under no illusion that I simply don't have the roof space to provide round the clock power, without getting some from the grid.

The Fogstar / Seplos kit does look like very good value. I also have 14.3kWh storage, using EVE cells purchased from Fogstar 15 months ago - mine is all DIY build, but happy with the cells & Fogstar ( & no connection, apart from being a customer of theirs).

Thanks for the vote of confidence in Fogstar. I came across their website by chance (not from this forum IIRC), and whilst the hardware costs are maybe 20% more than buying direct from China, having decent support/warranty etc. is potentially worth it. After all, this isn't a 1-2 year hobby for me, I want this to be relatively fit-and-forget for a decade or more. Appreciate I may need some spares on hand to support that dream...

Re doing it DIY, as @rpdom mentioned, you'll need to get G99 prior approval from UK Power Networks. UKPN may limit the amount you can export depending on your local network, but pretty irrelevant as I think you'll be consuming every little electron that you can excite anyway!

On the DIY front, see my posting here which summarises all the G98/G99, BS7671 and building regs part-P aspects of such a project..

Octopus Energy will no longer require MCS certification in the UK

https://gtec.co.uk/clause-5-8-octopus-opens-up-the-solar-pv-market-with-a-paragraph/ I'm not sure how exactly the UK's permitting and approval process works but this sounds like a major win for DIY.

diysolarforum.com

Thanks, regulation is one area i've not really looked into yet. In the scenario where there is no export, then it may seem logical to me to have an off-grid system, but if that was a good idea then I think it would omit me from certain tariffs from Octopus, e.g. Flex, so I suspect it will be tied to the grid and will require the right approvals. I will take a read of the link you shared. I haven't yet investigated to see how many MCS installers will be happy signing off something DIY........

Re charging up at night... I think you'll need to seriously look at max load requirements. If I understand correctly, long term, you may be wanting to simultaneously charge 2 EV's, run an ASHP, partially charge up a 45kWh battery system, but all within a 4 hour cheap rate window. I haven't done the calcs, but even it it was a 7h 'economy 7' window that sounds to me like a lot of electrons you'll need to shift, so I'm wondering whether a 100A DNO cut-out rating be suffice? If not, you may need to pay for network reinforcement or maybe there is a possibility of getting a 3-phase supply installed where you are?

Yes, this is a real concern. Charging two EVs could be 60 amps, and I think peak battery charge load (based on 200A BMS) could be topping 40 amps (or more depending on conversion efficiency). That's simply not going to work with the 100A tail. I haven't yet enquiried to see if that can be increased, or what the associated costs would be. Regarding 3 phase, this is a new build estate and I believe there are multiple phases run up the street, but as I live in a small cul-de-saq or 10 houses all three may or may not be present. I'd need to investigate. If it's not cost-effective, or feasible, then I will need to adjust the charging strategy to fit....

Similarly, you'll need to look at inverter ratings based not so much on your solar capacity but in terms of rate of charge / discharge to battery. Especially if you want to charge up at night, then use battery to power an ASHP and possibly charge cars during the evenings in winter.

Is this with regards to the inverter being AIO with a battery charging capability?

Re your roof layout...
I'm assuming that budget is not that tight based on your planned purchases, esp. batteries. Therefore, with panels so cheap, don't dismiss the roof sides facing ENE. On cloudy days they'll produce probably as much as the WSW facing panels and will provide a good early morning boost, especially in spring / summer. For the price of panels, worth looking into IMHO.
Having said that, you'll then be looking at needing at least 3 MPPT inputs in total, but I suspect that with your high load requirements you may be needing to have more than one inverter anyway.

Something I hadn't thought of, or at least didn't think it would generate any worthwhile returns.. Will research, thanks!

 

[OffGridForGood]

London UK is at 51.5 North Lat.
St. John Newfoundland is at 47.5
Toronto Ontario is 43.6 North Lat.
Anchorage AK is at 61.2 North Lat.
Northern Scotland (mainland) Dunnet Head is 58.4

Too bad temperatures of similar latatudes in Canada don't match up with UK temps of similar latatudes!

 

[OffGridForGood]

Thanks for the comprehensive reply. Yes I have been working to a very rough figure of winter generation being 10% of peak summer for my location. Of course, this will probably need some proving but I am sure there are ways to calculate this, which I will look into.

The PV Watts calculator predicts 6:1 or 16.7% (approx) for Chelmsford winter.
PV Watts doesn't take into account shading, ie for your garage roof area during low winter sun azamith angle, or trees, next door's roof shading your roof etc.

I am just starting out with PV and so far have limited pretty limited exposure (pun somewhat intended).

good one!
I would start with working out the PV that could fit the roof areas, and since you have half the year with high sun angle - nearly overhead - I wouldn't rule out any of the roof areas you have. Once you can determine the PV you can fit to the roof, this will set the limits for the rest of your system.
Another opportunity during long summer days, is using the EV's as part of you battery ESS, especially on weekends, if the cars typically would be parked at the house. There may be times when summer EV charging makes good sense for your system. I do this during summer in my system, since the EV has considerable storage capacty -Every bit counts.

 

[rpdom]

The PV Watts calculator predicts 6:1 or 16.7% (approx) for Chelmsford winter.
PV Watts doesn't take into account shading, ie for your garage roof area during low winter sun azamith angle, or trees, next door's roof shading your roof etc.

Here are my actual yield figures in kWh for Chelmsford on a 3kW array SSW facing, 30° roof.
Sep 22: 232
Oct 22: 301
Nov 22: 91
Dec 22: 68
Jan 23: 102
Feb 23: 162
Mar 23: 181
Apr 23: 351
May 23: 422
Jun 23: 493
Jul 23: 493
Aug 23: 374
Sep 23: 374