Inverter downsizing - Looking for advice

gefnew

Hi you could try this for summer.
Cooling down PV panels with water – pv magazine International (pv-magazine.com)

QrizB

gefnew said:

Hi you could try this for summer.
Cooling down PV panels with water – pv magazine International (pv-magazine.com)

I've thought about that sort of thing now and then but we've got hard water and I can imagine my solar panels scaling up

I guess if it's a commercial system there's a chance to use water softeners or pH adjustment to keep the carbonate levels down.

2nd_time_buyer

QrizB said:

gefnew said:

Hi you could try this for summer.
Cooling down PV panels with water – pv magazine International (pv-magazine.com)

I've thought about that sort of thing now and then but we've got hard water and I can imagine my solar panels scaling up

I guess if it's a commercial system there's a chance to use water softeners or pH adjustment to keep the carbonate levels down.

Ideally you would have coils of pipes behind the panels sending water to the hot water tank. Win win. 

Meatballs

It's difficult to say, you should get better low light performance across the winter months by having an undersized inverter, but you miss some peak generation in summer which invariably you may export anyway.

I have a 6kW SE inverter for an 8.8kW array across 3 elevations E S & W. I sometimes hit 6kW for short periods when the panels are cool and the sun comes from behind a cloud but generally it may sit around 5-5.5kW between 12-3.

I think there are plenty of supply issues at the moment so they may have lumped for 3.8 due to availability. Maybe the G99 was rejected but I suspect they should have informed you if so...

Thinking about it the SolarEdge design platform should be able to give you performance output estimates for the 3.68kW and show the clipping amount as well as the 5kW inverter so maybe ask for that?

gefnew

But if you supply from rainwater harvest should be ok.

flyinggoose

So i spoke to the installer today, despite telling me they would be seeking G99 approval when they came for the initial survey they now seem to have forgotten about this, the reason for the 3.68kw inverter is because it falls within G98 they're saying, whereas G99 approval could take six months (weird because they didn't mention this on the initial survey and the job was booked in for about a month or two later, they also didn't mention it, but from what i've read G99 approval costs more aswell? And it could be rejected of course).

They seem to be quite confident that there won't be many clipping issues because the panels are over three roofs and the sun won't be hitting all three roofs at once for large periods of time so the 3.68kw inverter will be more efficient than a higher rated one.

I have checked the quote and there's nothing on there concerning G98/99 approval or anything about DNO in writing, i suppose it's not the end of the world or anything, if they're correct about the six month delay then that's lost generation/money in the summer months and it might not even get approved, so maybe it's better this way.

The only other issue i've found with G98 is that the Tesla Powerwall will be restricted when it comes to it discharging to the grid, from 5kw to about 3.6kw i believe, but that doesn't bother me because from my understanding you cannot discharge the powerwall to the grid manually and it's something Tesla/Octopus would do on the Tesla Energy Plan if i was to sign up to it so wouldn't really affect me i guess.

I appreciate all the advice given in this thread, i'll just go ahead with the 3.68kw inverter since i can't be doing with any more delays, just wish the installer had clarified all of this from the beginning.

Spies

I didn't notice you said North west for one of your arrays, how many kwp in each orientation are you to have?

flyinggoose

Spies said:

I didn't notice you said North west for one of your arrays, how many kwp in each orientation are you to have?

So they've confirmed 14 panels (360w per panel) will be the max I can get up there, so the end result should be:

South East Roof - 4 panels - 1.44kwp
South West Roof - 6 panels - 2.16kwp
North West Roof - 4 panels - 1.44kwp

2nd_time_buyer

flyinggoose said:

Spies said:

I didn't notice you said North west for one of your arrays, how many kwp in each orientation are you to have?

So they've confirmed 14 panels (360w per panel) will be the max I can get up there, so the end result should be:

South East Roof - 4 panels - 1.44kwp
South West Roof - 6 panels - 2.16kwp
North West Roof - 4 panels - 1.44kwp

I think you'll be fine with that split.

Have you considered the 10kwh Solaredge battery? It will be cheaper than the Powerwall. It is it DC coupled so will be more efficient as you are going DC to AC rather than DC to AC to DC to AC. It will also minimize clipping as it can store what otherwise would be clipped.

[Deleted User]

You may appreciate this already but a PW2 will not discharge to the Grid unless you sign up to the Tesla Energy Plan via Octopus Energy. My understanding is that all AC batteries require DNO approval as their inverters are treated as generators. I have a 6.35kWp array on two roofs with SolarEdge. My inverter is limited to 5kWs. Inverter limits not only have to take into account maximum power but also power outputs during the Winter months. Yes, at times my maximum output flatlines but as I am getting about 20% more than the predicted annual output, I am convinced that my installer’s modelling has got it right.