How much can I practically/legally DIY, and other newb questions

[nowty]

I've said it before and I'll say it again, especially if you are paying someone to get them up for you.

Get as many as will fit and consider paying extra for higher efficiency panels if space is tight.

You won't overload the inverter as it will current / power limit.
Just don't go over voltage on a string.

You might want to check out this handy solar comparison page on itstechnologies before you finally decide on the panel of your choice.
https://www.itstechnologies.shop/pages/ ... comparison

[dangermouse]

If you have the room it might be worth getting the 10 panels if the inverter will safely restrict the input power - worth checking this, not all will. In the UK 125% oversize is good because acheiving full output is comparatively rare and it will give you more output under typical winter conditions when you most need it. Victron say the amount of curtailment is only 1% of total generation so worth it overall.

Appreciate this advice from you and others (Nowty) - I could get 10 panels on, maybe, but I'd be looking at about a 10cm border top and bottom, and that's (in my mind) too close for comfort. Plus I have to buy the panels in advance, if I buy 10 and can only get 8 up there then I've got 2 panels surplus.

Here's my roof - It's 420cm wide and about 540cm in the sloping dimension, although I had to estimate this by measuring the depth of the house and the vertical distance in the roof void.



As you can see it's not huge. I could go 3x3 in portrait mode and get 9 of the 295W panels. I doubt having more peak power than the inverter can draw will be a problem, because as you say it will only draw what it can use - unless anyone knows differently? It's a Sofar HYD3600ES.

Bearing in my what Nowty says, the more expensive 410W panels from Bimble would fit in a 2x4 landscape pattern and give me 3.28kW, and have a better £/watt ratio despite being pricier.

Don't much fancy solar limpets, they need accurate location of the joists, require drilling through the tiles/slates and rely on mastic rather than gaskets for sealing. There is an earlier thread on them somewhere. But I guess if your man prefers them as he is used to them you may not have much option.

What is your roof covering? I think they were developed for tiles and may be better on them than on slates.

Also I was told they will only sell them to people who have undergone their supervised training regime, so after a lot of back-and-forth Callidus could not supply them for my installation kit. They are also boxed in 25s IIRC, I didn't find anyone else who stocked them or who would split boxes.

Roof is slate. I share your concerns but it's what the installer wants, so as you say I'm not sure there's much choice. The installer has done the limpet training course, I may have to get him to buy them instead.

Thanks for the advice.

[AE-NMidlands]

Carrying on the thought experiment (aka planning - or daydreaming)

I ought to be able to put pv on 3 roof aspects, so that means 2 (hybrid?) inverters as I believe each only handles 2 pv arrays/inputs. One day I might even put a vertical array on the s-facing wall for winter top-ups using the spare input on the second inverter...

Now, to storage: why do people have parallel battery banks? Is it so that you have 2 inverters so you can get double the output from them at any one time? If we are going to progressively transfer heating loads from gas to various electric devices (Induction hob, AS/A2A HP, instantpots etc) I guess we are at risk of needing more kW from the batteries than 1 inverter can deliver...

Comments please
A

[nowty]

@AE-NMidlands, if two of your aspects can have the same number of panels, you can parallel up the two strings into the same MPPT input. So it may be possible to do three aspects on a twin MPPT inverter.

[Krill]

You could easily fit 6 of these in a 3x2 array for 3.6kwp. Shame that they had larger panels that would have allowed 3.9kwp but would have fit your roof space great. Don't work with that inverter though due to the higher Isc though.

https://www.bimblesolar.com/solar/large ... olar-panel

[Oldgreybeard]

I can make an observation of sizing an inverter to run the house partially from batteries, based on my experience and the way we've adapted over a couple of years to running mostly off batteries, although I'm not sure it will help, as we all have different needs.

First the loads. Our house is all-electric, so electric heating (via a 6kW to 7kW output power heat pump), electric water heating (3kW element directly heating a thermal battery) and electric lighting etc (all the lights are LEDs, no outdoor lights left on as we're in a Dark Skies area). We have an induction hob that is rated at an unbelievable 7.35kW, a fan oven rated at 3.2kW, plus a 1kW microwave and an air fryer/mini oven rated at 2.4kW. We also have a relatively high baseload, as we have heat recovery ventilation running 24/7 that draws around 50W and a sewage treatment plant that draws about 40W 24/7. There's also a 600W water pump for all our water, but that only runs for around 10 minutes to 15 minutes per day, usually.

Our PV system can deliver up to 6kW, but in reality rarely gives more than about 5kW, and at this time of year it tops out on a good day (like today) at maybe 4kW, and then only for a short time. Our battery inverter tops out at about 3kW and charges at more or less the same power. We've not run out of battery power at all this year, I think the lowest I've seen is an SoC of around 20% once, most of the time the SoC doesn't get lower than about 40%. The battery charges to 80% SoC overnight at this time of the year, if there hasn't been enough PV during the day. During the summer I reduce that to 55% SoC, to give more headroom for storing PV power. We have about 21kWh of battery capacity, of which a bit under 18kWh is usable.

So far this year we have used 46kWh of grid energy at the peak rate (most of that in the winter) and 3,255kWh at the off peak rate (again, most of that in winter). A fair bit of the off-peak electricity is charging the car, roughly half of it. We self-use about 97.5% of our PV generation, and that averages about 6,000kWh/year, so most of our energy comes from PV (about 64% of it), about 35.995% comes from off-peak grid energy and about 0.005% comes from peak rate electricity.

The key thing to take from this is that 0.005% of peak-rate usage, as that is wholly the usage when the 3kW battery inverter cannot supply enough power for the house, so we need to import it. If I was to increase the size of the inverter so that we never used any peak rate electricity then I would need to pretty much double it's power output. Doing that would add around £1,000 to the inverter cost, so the sums just don't stack up. The 46kWh of peak rate electricity costs us under £16/year, so the additional cost of the bigger inverter would take around 60 years to recover.

The key thing seems to be to work out what the sweet spot is between what's a sensible investment and what's not. I suspect that, for most people, around 3kW or so makes sense, and that anything over about 5kW is unlikely to ever recover the additional cost.

[Countrypaul]

Carrying on the thought experiment (aka planning - or daydreaming)

I ought to be able to put pv on 3 roof aspects, so that means 2 (hybrid?) inverters as I believe each only handles 2 pv arrays/inputs. One day I might even put a vertical array on the s-facing wall for winter top-ups using the spare input on the second inverter...

Now, to storage: why do people have parallel battery banks? Is it so that you have 2 inverters so you can get double the output from them at any one time? If we are going to progressively transfer heating loads from gas to various electric devices (Induction hob, AS/A2A HP, instantpots etc) I guess we are at risk of needing more kW from the batteries than 1 inverter can deliver...

Comments please
A

If looking at hybrid inverters then presumably you are looking at battery storage, in which case why not just one hybrid inverter and one array directly charging the battery via a charge contoller? - unless Nowty's suggestion would be appropriate.

[dangermouse]

You could easily fit 6 of these in a 3x2 array for 3.6kwp. Shame that they had larger panels that would have allowed 3.9kwp but would have fit your roof space great. Don't work with that inverter though due to the higher Isc though.

https://www.bimblesolar.com/solar/large ... olar-panel

Thanks but a 3x2 of those panels gets a bit too close to the roof edge for my liking - maybe I'm being over cautious but it would only give me just over 10 cm at the sides.

[nowty]

You could easily fit 6 of these in a 3x2 array for 3.6kwp. Shame that they had larger panels that would have allowed 3.9kwp but would have fit your roof space great. Don't work with that inverter though due to the higher Isc though.

https://www.bimblesolar.com/solar/large ... olar-panel

Thanks but a 3x2 of those panels gets a bit too close to the roof edge for my liking - maybe I'm being over cautious but it would only give me just over 10 cm at the sides.

They are also very large and very heavy.

[Oldgreybeard]

They are also very large and very heavy.

This is a very good point, I'm currently waiting for a friend who's coming to stay and who has agreed to help me get the panels up on our second system, as having tried to do it on my own I felt that there was a fair chance of damaging a panel or causing myself harm, and that is with modestly sized 400W panels being fitted to a wall frame that's only abut 12ft up the wall at it's highest point.