Advice on best system setup

Hi,

I'm about to order a new solar/battery system, I'm new to the whole solar thing but I'm learning fast about the different options available. I'm after some advice on the best setup for our situation.

After a visit from a local installer they have recommended installing 2 panel arrays on our garage roof which has an east/west facing roof with a very shallow pitch, they said this should provide good generations as it's so shallow. We can fit about 4kW of panels on the garage roof.

Our garage is about 10m away from the house, we are planning on installing the battery and inverter etc. in the garage. Our main board is in the house.

After some research I see it's suggested the optimal size of solar is about 30% of your daily usage, which for us would be 5.1kW. We do have the option of putting 3-4 more panels on a south facing roof of the house which would bring us over the 5.1kW target but that would be about all we could fit on there.

Other than the usual things of wanting to save money on bills etc. is that we want to have an automatic backup in the event of power cuts as we live in the sticks and get relatively frequent power cuts. These usually last a few hours at a time.

I've been looking at the EPS documentation and believe the 4th method of installation is what we would want as it has automatic backup of the whole house. My concern would be if we would exceed the kW output of the system and cause it to shut off which it says can permanently damage the inverter if this happens too often. I'm not sure how to work out if this would be a risk for us or not. We have a 5 bedroom detached house with fairly standard appliances other than we have a couple of computer servers running 24/7 and we have air con.

Given all of that would we be best going for an AC coupled inverter or a hybrid one?

Our installer has currently specified the Gen2 5kW Hybrid and the 9.5kWh battery system. We would have 2 solar arrays very close to the inverter/battery that are on the garage roof, but we would also have a 3rd array that is about 10m away on the roof of the house, I'm not sure if that makes a difference to the best setup for us at all?

Thanks for any help

ZmGahH6yQBe There's lots of things to think about. The first one for me (having had our installation in January this year) is that there are plenty of people on this forum wishing/planning to add extra panels. The panels are relatively inexpensive to add when there's a whole array going in but costly if adding later because of scaffolding etc. I've never heard anyone say they wish they hadn't bothered adding those extra two panels. If there's lots of light about but no sun directly on your panels, you will still generate and the more panels you have, the more you can capture. It also extends the season where you are reliably able to generate later into the autumn and earlier in the spring.

With an E/W orientation, it might make sense to have the E panels on one string and the W panels on the other string. This should optimise the output of each array to your inverter which will make best use of the available PV on each string. In this scenario, you could put in way more PV than your the inverter capacity because there would only be limited generation one one string when the other has the maximum available. If the total PV power available exceeds the inverter's capacity, it will just clip the output to reduce the throughput. The inverters do this anyway when the battery is fully charged and the house load is low and the grid export is capped.

You could add panels on the S-facing roof but since it would be generating at a different time from the other two strings, it'd be difficult to know how best to connect them. I'm unsure of the overall affect of putting panels with a low voltage output onto a string with panels having higher output. Maybe others can advise?

ZmGahH6yQBe optimal size of solar is about 30% of your daily usage

Not sure about this. We decided we were going to install solar and covered the roof with panels since we were going to pay for installation once. That drove the inverter and battery size but I recognise that not everyone has a south facing roof large enough to take 32 panels, nor the budget to do that either. But we have been self-sufficient since March (including EV charging) with grid import less than 1kWh/day. We're hoping to import off-peak just during December and January, but this is our first year so we don't know the likelihood of this yet.

What you could do with your S-facing roof is to install another inverter and battery and then, if available to you use the inverter to charge the battery overnight off-peak and consume during the day, topped up by whatever PV is available. This would be a costly exercise, but if it means you can shift your electricity import from daytime to off-peak, then you could save quite a bit per kWh of consumption. EdF have withdrawn their EV tariff now, but we were able to lock in at 39p/kWh peak and 4.5p/kWh off-peak. We don't actually import anything yet but will do when generation tails off in the autumn.

ZmGahH6yQBe AC coupled inverter or a hybrid one

AC coupled if you have no PV panels or hybrid if you do have PV panels.

Tim Thanks for the info, that is very helpful, and thank you for taking the time to respond in detail. You must generate loads of power with 32 panels! We can only fit 12 on the garage roof, and maybe 8 on our main roof, but that would have to be split over 3 different aspects.

I managed to speak to one of the directors at the installer who was very knowledgable and was able to answer all of my technical questions.

He said that the hybrid inverter can only handle 2 strings and so if we wanted to add panels on the roof of our house we would need to switch the whole system to something like micro inverters to accommodate this and in turn we would need to switch to AC coupled to do this. Interestingly he said that with AC coupled you only get 3kW during a power outage and even though you can technically add multiple inverters and batteries to get more than 3kW this is not supported by GivEnergy officially and you often find that one inverter will be working much harder than the other resulting in uneven battery charge/discharge.

Regarding the EPS he said that you generally won't be able to run a whole house during a power cut and advised choosing which circuits we want to have operating during a power cut and have them on their own EPS mainboard.

This all sounded very sensible to be, he basically talked me out of getting anything extra on top as he said they would be happy to do it but for the additional costs we wouldn't see that much benefit. He said if we could fit 12 or so panels on the south roof then it would make more sense, but as we can only fit about 4 the additional benefit doesn't justify the extra cost in his opinion.

Does that all sound sensible?

ZmGahH6yQBe
I agree with Tim to get the most panels you can at time of installation. Our installer recommended 12 panels and with a battery was going to be about £9.1k. I asked to go with 16 panels as we could fit those on our roof and the actual cost was just under £9.9k (2020 prices)

We therefore ended up with a 33% increase in generation for an extra 8% on the cost.

We didn't have our EPS connected when we had our installation, but I am thinking of doing so now in case we start to get "power rationing" in Winter. In order to avoid the cost of splitting out all the circuits I would want to stay live in the event of a power cut which is in the region of £1k, I am looking at having the 3rd method installed with a manual change over switch. This will allow me to ensure there are no heavy loads running at that time, and therefore we would stay within the EPS limit with fridge/freezer, lights, TV, broadband and central heating pump being used.

The only issues I can see with that are if the power goes off overnight then we wouldn't know about it, and also we wouldn't be aware of when the mains power resumes.

Our roof is SE facing and a more West orientation would be better as we would get generation later in the days which is when we use most power for cooking and at present we exceed the 2.6kW output from the battery. The sun is still shining strongly on our neighbours east facing roof. The solar would keep us under the 2.6kW.

Martyn The only issues I can see with that are if the power goes off overnight then we wouldn't know about it, and also we wouldn't be aware of when the mains power resumes.

This is something I wanted to avoid, if you have to manually switch over you loose some of the benefit, like if you're away from the house you don't come back to a defrosted freezer. And as you say you don't know when the power will come back on.

Ideally we would like to have fridge/freezer, lights and power to the internet and tv. I'm not sure it would be good to have out boiler on the EPS as it's on the same circuit as our washing machine and dryer.

Martyn I agree with Tim to get the most panels you can at time of installation. Our installer recommended 12 panels and with a battery was going to be about £9.1k. I asked to go with 16 panels as we could fit those on our roof and the actual cost was just under £9.9k (2020 prices)

We therefore ended up with a 33% increase in generation for an extra 8% on the cost.

From what I understand we would pay amount extra for only a small gain in production. The max we can fit on our garage is 12 panels and this is the largest area available to us. The roof of our house doesn't have any large faces as its essentially 3 roofs arranged in a U shape with a valley in the middle and lots of bits to get in the way of solar panels. We can only fit maybe 9 in total on the roof but that would be split over 3 different arrays. So the cost would be quite high. If we had one large section to out panels on I think it would be a different story.

ZmGahH6yQBe fridge/freezer, lights and power to the internet and tv

If these are your priority, I'd suggest a mini consumer unit fed by EPS which supplies spurs to dedicated EPS sockets for your freezer and internet/tv (and boiler if it's oil or gas). That way, those circuits will always be fed whatever the state of the grid. You could also feed lighting from the EPS consumer unit but I reckon that's a lot of work. If there's a power cut, you've got your fridge/freezer etc sorted. Just use torches as you currently would in a power cut or switch the TV on and catch up on some box sets.

ZmGahH6yQBe

1. The optimum size for solar is as many panels as will fit on the roof. No such thing as too much generation.
2. Your garage is detached, you will need 2 power cables to the garage if you want EPS. Look at the diagrams closely, grid power and EPS power. I suspect you only have one already.

Rubikcube @ZmGahH6yQBe Depending on the cable you already have to the garage, your installer may want to install a new one anyway. If new cable(s) are required, just ask them to run a couple of ethernet/cat6 cables at the same time. Just like solar panels, you can never have too much ethernet capacity and if you're getting a Gen 2 inverter, you'll be able to use ethernet to connect it to the internet and you'll want to run the Modbus from your main consumer unit meter (EM115) to the inverter, so at least two Cat5/6.

If you don't already have a smart meter, ask your energy supplier to install one before the solar system is installed.

Rubikcube Your garage is detached, you will need 2 power cables to the garage if you want EPS. Look at the diagrams closely, grid power and EPS power. I suspect you only have one already.

Tim Depending on the cable you already have to the garage, your installer may want to install a new one anyway. If new cable(s) are required, just ask them to run a couple of ethernet/cat6 cables at the same time. Just like solar panels, you can never have too much ethernet capacity and if you're getting a Gen 2 inverter, you'll be able to use ethernet to connect it to the internet and you'll want to run the Modbus from your main consumer unit meter (EM115) to the inverter, so at least two Cat5/6.

I need to dig a trench between the house and garage anyway, will be running water and waste. I know the electric cables will need upgrading anyway as the existing ones are quite old. I had been thinking about running network cable as well, not sure if it's a good idea to run the cat6 along the same line as the power though.

I have a reel of cat6 already, not external stuff though, not sure if I can run it in some kind of trunking or if it's better to get some external cat6 though.

Have you checked on what generating capacity your DNO will allow you to install? Don't forget that they base their permission on theoretical maximum output rather than the actual output. It varies from operator to operator but where I live it is rare for permission to install more than 3.68kWp to be granted.

Woodstock no I haven't checked, how would I go about doing that? I assumed the installer would know about and handle that, they are local.

The installer should both seek and get DNO approval for the proposed scheme before installation. You need to get hold of copies of both their request to the DNO and the approval (and I think there are both pre and post commissioning approvals) in order to get onto a tariff like Octopus agile outgoing. You will also need the MCS certificate. Make sure your installer understands (in writing) that you want copies of all these documents before you pay your final installment if at all possible - in other words make it a part of the contract. Once fully paid, installers can be lax in getting hold of them for you and that could cost you money. I had to plague my installer daily with multiple emails and phone calls before I got them.

ZmGahH6yQBe I have a reel of cat6 already, not external stuff though, not sure if I can run it in some kind of trunking or if it's better to get some external cat6 though.

I'd just run the ethernet you have in a 25mm flexible conduit next to the mains cables, as long as it's shielded twisted pair (STP), which won't be affected by noise from the mains cables. Make sure one run can get to wherever your router or home ethernet switch is and the other end can reach your inverter. Similarly, the other needs to reach wherever your installer is going to put the EM115 with the other end at the inverter. Actually, just dig the trench for your water and waste and ask the installer to sort out the ethernet cables (they'll know to use STP rather than UTP) and replace your existing garage supply cable and add in one for the inverter and another for EPS. They'll probably use SWA. Oh and if you think you might fit an EV charge point to the garage, either get a fourth cable installed at the same time, even if the ends are just left unconnected and capped for the time being, or ask them to make sure the garage supply is capable of feeding an EV charger in the future.

Another (fewer cables) scenario could be to replace your existing garage consumer unit and supply cable. If they connect the inverter to the new garage consumer unit via the MCS meter and then connect that consumer unit to the main house one, as long as the new cable between garage and house was sufficient to feed the potential load (think EV charging and and house battery charging at 3.6kW plus you've got a 3kW fan heater going in the garage or whatever), so a potential load of say 15kW, you'd need a 64A MCB in the house consumer unit and the cable would have to be probably 10mm or possibly 16mm SWA. Your installer would advise, but this option would reduce the number of power cable runs between house and garage (you'd still need the EPS one though). A new consumer unit in the garage would also facilitate the installation of an AC-coupled with battery in the future, should you wish to go that route.

Tim Thanks, thats very useful. I spoke to the installer and he said they can lay some extra 10mm cables and cap them as well as some network cables so we are future proofed as much as possible.

I've pulled the trigger and signed the contract, they will lay all of the cables in a couple of weeks time and then install the panels and batteries once they become available. 😀