Starting from scratch, new design for grid-tied PV system, 8.5kW panels, 14.5kWh storage, 8kW inverter. G99 Form

[Smallholder]

The update to our previous electricity tariff has given me the push I needed, to crack on with getting solar on our house.

I've made off grid solar systems before, but never done anything grid tied, and never anything of this scale. So I'm not completely clueless, but also realise I have a lot to learn. Please go easy on me!

The system I am planning will sit on a flat roof. Panels sitting at about 15 degrees. Thinking I'll use 20x 425W panels. The reason for this being, it's the max I can fit on the roof.

Then I was thinking of using 3x PylonTech US5000 4.8kWh 48v batteries, and a Victron Quattro inverter (either 10,000VA or 15,000VA).

I was really keen to be able to export, but now see I would need MCS cert... I assume that the additional cost of getting the install done by a professional, would be greater than I'd ever get back from feeding in. Despite having to pay VAT if I do the job myself.

We currently have gas for DHW and heating, but interested in switching to electric. We have 2x EV's. Current we are consuming about 20kWh per day, with 50-60% of that off-peak (EV charging)

So my questions are:

1 - Is it possible to install a system like this on your own. Not in terms of technical ability, but in terms of regulations etc.

2 - In term of the system spec, do you think I'm heading in the wrong direction with any part of the spec?

3 - Any advice on filling in the G99 form? Are there any good resources online, ideally with example applications?


Many thanks in advance!

[Stinsy]

1) You can install yourself. However connecting the new circuit to your CU (fuse box) has to be done by an electrician who pays an annual fee to one of the money-making schemes. (Lots of people ignore this, but you should be aware of the rules even if you’re breaking them).

2) Panels and batteries are fine (You’ll probably want to add more batteries when funds allow 3x your kWp in kWh is a good rule of thumb). Why do you need such a big inverter? 3.6kW is perfect for most normal households, 5kW if you have a big heat pump. Victron is great quality stuff, expensive and complex though, and you’re not using the key benefit whereby you can integrate a load of components together, so why spend the money? You’d be better off with a made-in-China hybrid inverter from Solis/Solax/SoFar or whoever.

Plan to export as little as possible. A DHW tank and BEVs are perfect places to put excess power. Have a look at MyEnergi products (Zappi and Eddi) for a really good system to self-consume.

3) DNOs vary in how helpful they are. Expect them to be unhappy about you hooking a huge inverter to a single-phase connection if you’re rural.

[Krill]

Couple of questions, before the people who know these things turn up to answerbyour questions.

Where in the country are you (for DNO purposes)?

Have you looked at PVGIS to look at probably generation figures? https://re.jrc.ec.europa.eu/pvg_tools/en/ and suncalc to look at possible shading problems? https://www.suncalc.org/#/52.9946,-2.23 ... 0:45/5.5/1


Do you have any other locations where you could put more panels/additional strings?

What is your peak load like? Is there flexibility to shift use around?

Are there multiple car chargers or just one, and how often are the cars present during the day so they can charged?

Would you consider building your own battery? There are many people on this forum who have done it and it costs about half the amount for equivalent Pylontech storage (I have three US5000 and can't fault them though) https://camelot-forum.co.uk/phpBB3/view ... =14&t=1194

How much time do you have to do all of the wiring? I ask this because when I had my system installed last month, if I was as skilled as the workers (I'm not) it would have taken me two months in equivalent man hours just to do the work.

Is this a forever home or would you consider moving, in which case you will need paper work for buyers solicitors.


What some people have done is get an AC tied system installed profesionally for the MCS certificate and then built a further DC coupled system as DIY that directly feeds the batteries and this does not need any DNO signoff. Pergolas seem to be good for this.

The Flux import/export tariff is starting to gain some traction though, as it can payback alot for excess production but if you self consume everything (and two EVs can help that) then export may be unlikely without further generation capacity.

[Smallholder]

1) You can install yourself. However connecting the new circuit to your CU (fuse box) has to be done by an electrician who pays an annual fee to one of the money-making schemes. (Lots of people ignore this, but you should be aware of the rules even if you’re breaking them).

2) Panels and batteries are fine (You’ll probably want to add more batteries when funds allow 3x your kWp in kWh is a good rule of thumb). Why do you need such a big inverter? 3.6kW is perfect for most normal households, 5kW if you have a big heat pump. Victron is great quality stuff, expensive and complex though, and you’re not using the key benefit whereby you can integrate a load of components together, so why spend the money? You’d be better off with a made-in-China hybrid inverter from Solis/Solax/SoFar or whoever.

Plan to export as little as possible. A DHW tank and BEVs are perfect places to put excess power. Have a look at MyEnergi products (Zappi and Eddi) for a really good system to self-consume.

3) DNOs vary in how helpful they are. Expect them to be unhappy about you hooking a huge inverter to a single-phase connection if you’re rural.

Thank you very much, good information.

1) Appreciated. I have someone that can do this part for me, so I may as well stay legit.

2) The plan is to get as much PV as I can on this roof, knowing I can add more batteries in the future without difficulty.
The inverter is an attempt to avoid using the grid when the PV and/or batteries are able to supply the load. One of our EV chargers is 7kW, and there will potentially be frequent times we're using that at the same time as other loads.
In an ideal world the big inverter would also allow us to maximise export, but I understand that's unlikely without MCS.
I've used Victron in the past, and got on well with it. That was the main reason for going that route. Plus I'd be confident rigging up some basic automation to charge EV or heat a water cylinder given certain conditions (S.O.C etc). Though this may be just as easy with cheaper kit.
I also quite like the idea of the MPPT function being split from the inverter. So if there are problems with one, just that component can be replaced.

3) I'm not sure what counts as rural, but we're in the middle of a small town. Am I right in thinking the DNO will either ask us to limit export to a certain amount, or possibly prevent any export at all?
Am I right in thinking that without MCS, we'll be able to export (with permission from DNO), but not get paid for it?

[Smallholder]

Couple of questions, before the people who know these things turn up to answerbyour questions.

Where in the country are you (for DNO purposes)?

Have you looked at PVGIS to look at probably generation figures? https://re.jrc.ec.europa.eu/pvg_tools/en/ and suncalc to look at possible shading problems? https://www.suncalc.org/#/52.9946,-2.23 ... 0:45/5.5/1


Do you have any other locations where you could put more panels/additional strings?

What is your peak load like? Is there flexibility to shift use around?

Are there multiple car chargers or just one, and how often are the cars present during the day so they can charged?

Would you consider building your own battery? There are many people on this forum who have done it and it costs about half the amount for equivalent Pylontech storage (I have three US5000 and can't fault them though) https://camelot-forum.co.uk/phpBB3/view ... =14&t=1194

How much time do you have to do all of the wiring? I ask this because when I had my system installed last month, if I was as skilled as the workers (I'm not) it would have taken me two months in equivalent man hours just to do the work.

Is this a forever home or would you consider moving, in which case you will need paper work for buyers solicitors.


What some people have done is get an AC tied system installed profesionally for the MCS certificate and then built a further DC coupled system as DIY that directly feeds the batteries and this does not need any DNO signoff. Pergolas seem to be good for this.

The Flux import/export tariff is starting to gain some traction though, as it can payback alot for excess production but if you self consume everything (and two EVs can help that) then export may be unlikely without further generation capacity.

Thanks for the info, really good stuff.

In terms of location, and DNO... I'm in Somerset, and our DNO is National Grid I think.

I have used the PVGIS tool to get some generation data, and it seems we could be electrically self sufficient for about 7 months a year with current consumption. It's an amazing tool!

The cars are potentially at home a fair bit of the time, enough to really maximise using PV for charging...
We have a fast L2 charger (7kW) and also slow L1 chargers (2.4kW).

I would certainly consider building my own batteries, though I'd not really thought of it as an option for this project. I like the plug and play aspect of PylonTech, having used them before. But if the costs stack up with doing the DIY route, then I guess why not. I'll have a look through the link you posted.

I'd not really considered the wiring time. Though having built my own off-grid system (2.5kW PV and 7kWh batteries), I feel I should have a vague idea of how much work is involved. Maybe I'm in for a surprise!

This it probably not a forever home. Again, not something I'd considered. If I've got permission from DNO, would that not be enough? I don't think MCS is really a requirement for home installed PV is it?

The MCS system plus DIY afterwards could work. I could use some of the roof for the first system, and then add more panels to the rest of the roof.
I might even be able to convince the installer to put in a larger inverter than needed!?

The system I'm looking at should generate more than we can use, for at least 5 months a year. Unless we alter consumption with shifting heating to elec. Export would be ideal if possible, but I'm not sure the costs would stack up in getting MCS vs DIY install.

Thanks again for your help, very much appreciated.

[nowty]

You say, never done anything grid tied,

But you say, “I've made off grid solar systems before, 2.5kW PV and 7kWh batteries, I feel I should have a vague idea of how much work is involved.”

I would say you have more than a vague idea and you understand both AC and DC, you also say you understand PVGIS.

MCS is not required for home installation, but it generally is if you want to export and get paid for it.

DNO is a legal requirement but some fly under the radar, even so many have successfully submitted a G99 application.

Your spec sounds good, but with that much PV, you will probably want a bit more battery capacity. Pylontech is easy but expensive. Build your own LIFEPO4 battery bank if you can like many on here have.

You just need a nudge, get back to us on progress with photos.

[Smallholder]

You say, never done anything grid tied,

But you say, “I've made off grid solar systems before, 2.5kW PV and 7kWh batteries, I feel I should have a vague idea of how much work is involved.”

I would say you have more than a vague idea and you understand both AC and DC, you also say you understand PVGIS.

MCS is not required for home installation, but it generally is if you want to export and get paid for it.

DNO is a legal requirement but some fly under the radar, even so many have successfully submitted a G99 application.

Your spec sounds good, but with that much PV, you will probably want a bit more battery capacity. Pylontech is easy but expensive. Build your own LIFEPO4 battery bank if you can like many on here have.

You just need a nudge, get back to us on progress with photos.

That's extremely encouraging, thank you very much indeed.
I'll work on finalising the system design, and get cracking with the G99 application.

[sharpener]

Two thoughts:

If you don't go down the MCS route for any of it you can DIY all the electrics under a Building Notice and get it signed off by LA Building Control, this will give you peace of mind now and paperwork that is useful when you come to sell.

Although it is historical I have found the combination of some AC and some DC-connected PV to be very handy, as during the day the AC can supply the loads directly (esp the EV) in addition to what is avaiable from the Victron Multi. So 5k is adequate for me and the 8k Quattro might be enough for your setup. You might also find like me that WPD (now NG) limit your inverter power anyway, so best to check that out before going too far.

[Stinsy]

1) You can install yourself. However connecting the new circuit to your CU (fuse box) has to be done by an electrician who pays an annual fee to one of the money-making schemes. (Lots of people ignore this, but you should be aware of the rules even if you’re breaking them).

2) Panels and batteries are fine (You’ll probably want to add more batteries when funds allow 3x your kWp in kWh is a good rule of thumb). Why do you need such a big inverter? 3.6kW is perfect for most normal households, 5kW if you have a big heat pump. Victron is great quality stuff, expensive and complex though, and you’re not using the key benefit whereby you can integrate a load of components together, so why spend the money? You’d be better off with a made-in-China hybrid inverter from Solis/Solax/SoFar or whoever.

Plan to export as little as possible. A DHW tank and BEVs are perfect places to put excess power. Have a look at MyEnergi products (Zappi and Eddi) for a really good system to self-consume.

3) DNOs vary in how helpful they are. Expect them to be unhappy about you hooking a huge inverter to a single-phase connection if you’re rural.

Thank you very much, good information.

1) Appreciated. I have someone that can do this part for me, so I may as well stay legit.

2) The plan is to get as much PV as I can on this roof, knowing I can add more batteries in the future without difficulty.
The inverter is an attempt to avoid using the grid when the PV and/or batteries are able to supply the load. One of our EV chargers is 7kW, and there will potentially be frequent times we're using that at the same time as other loads.
In an ideal world the big inverter would also allow us to maximise export, but I understand that's unlikely without MCS.
I've used Victron in the past, and got on well with it. That was the main reason for going that route. Plus I'd be confident rigging up some basic automation to charge EV or heat a water cylinder given certain conditions (S.O.C etc). Though this may be just as easy with cheaper kit.
I also quite like the idea of the MPPT function being split from the inverter. So if there are problems with one, just that component can be replaced.

3) I'm not sure what counts as rural, but we're in the middle of a small town. Am I right in thinking the DNO will either ask us to limit export to a certain amount, or possibly prevent any export at all?
Am I right in thinking that without MCS, we'll be able to export (with permission from DNO), but not get paid for it?

I’m not dissing Victron kit, and sure it can do all the fancy custom automations that the made-in-china inverters can’t. However your situation is very “standard” any hybrid inverter will shift power to and from batteries in real time depending on how bright the sun is and how much load you’re drawing. Zappi/Eddi will effortlessly heat your water and charge your car with excess solar right out of the box. You really don’t need anything fancy. What was hugely complex and custom a few years ago is basic functionality today.

[sharpener]

Usually the more panels the better and if there is space for 8.5 kW that's terrific. But the issue as I see it with a system of this size is choosing an inverter that will cope with the ouput while keeping on the right side of the DNO.

The other thing is the EPS option, is this required and if so how much of the house will stay connected? This is where the flexibility of the Victrons can be useful. But the 10kW Quattro is quite big for a normal domestic setup and their dual AC input capability is not necessary unless there is a backup generator as well.