DNO output reduction

spud

So our supplier (Light Renewables) quoted a 20 x 500w system across three aspects E/S/W) with 8kw inverter and applied to the DNO. Heard yesterday that they have said must be less than 8kw so options presented are:-
1. Drop to 6kw inverter and keep all panels as unlikely to clip given the three aspects.
2. Drop to 6kw and drop a few panels (maybe from East aspect).
3. Add a 7.5kw limiter at extra cost

ive asked for some modelling to help determine but does anyone have other thoughts on the likely best decision?

thanks all.

pete-20-11

Doesn't the inverter have a setting for export limit? 

It's the export that matters usually. If you can use some of the power as it is generated and export the rest, great. If not, it should throttle back to meet the export limit? 

Magnitio

A 6kW inverter is likely to clip at this time of year during the middle of the day, but I doubt you'll be losing a lot of generation. Will it be a hybrid inverter with battery storage? If so, some of the excess above 6kW can be used to charge the battery.

Does the proposed inverter have 3 MPPT's, one for each aspect?

spud

Not sure about the limit setter? It’s a solar edge SE8000 wave inverter with edge optimisers if that helps. No battery. Intent was to export all we don’t use and add battery further down the road (annual usage approx 4100kw).

Martyn1981

Hi spud. If you are happy to have some clipping then Solaredge's home wave inverters can manage 200% of rating on the DC side. So you could put the 10kWp of panels through their 6kW model.

I think some of their other models have 150% DC side rating, so the 8kW model will be fine to around 12kWp, so long as it can be set to 6kW AC side max by the installer.

I may be wrong about this, but I think they may also be able to monitor import/export, and thus limit generation to that, rather than inverter output, thus allowing for home consumption too.

I say this, because I've noticed that when I tell my 3.68kW unit to discharge (edit - it has DC side batts (and 6.725Wp of panels), it will do so at 3.68kW early in the day, but then dials down when my WNW array (which is separate) is generating well in the afternoon. So I think it's capping export, not production.


Can I ask, have you been offered a 6kW limit, or possibly 7.5kW as your point 3 suggests? If 7.5kW and the 8kW model can be limit set, then I'd suggest your 3 aspect set up won't see any clipping.

spud

Thanks. Martyn1981 I had a brief conversation yesterday - only those 3 options offered inc the 7.5kw limiter. I’m expecting a call later today so have a few more questions now based on the responses. Though it does sound like If I had to have a 6kw inverter worse case it would still make sense to retain the 20 panels. 

Screwdriva

spud said:

ive asked for some modelling to help determine but does anyone have other thoughts on the likely best decision?

Out of curiosity, what is your annual consumption? The reason I ask is that a PW3's built in inverter allows for a 7kW inverter size, has 3 string inputs for each of your aspects (assuming there is no shading?). 

If you've ruled that option out and want to stick with SolarEdge, your best option is to add a limiter (#3). 

I believe a 6kW inverter will lead to severe clipping(I have a 7.3kW triple aspect bifacial panel SolarEdge system and am still clipping with a 5kW inverter).

Martyn1981

spud said:

Thanks. Martyn1981 I had a brief conversation yesterday - only those 3 options offered inc the 7.5kw limiter. I’m expecting a call later today so have a few more questions now based on the responses. Though it does sound like If I had to have a 6kw inverter worse case it would still make sense to retain the 20 panels. 

Yeah, with regard to the worst case 6kW example - it may seem strange to miss out on the peak power, but if you have space, then the bigger system will be generating more than it otherwise would be, at all times generation is under 6kW. So better to have too much PV kWp on your roof, but of course it's not my money to spend, it's yours.

Infuriating to lose some peak and export income, but on the other hand, it will generate more at times when you need the generation most (poorest 6 months of the year), and losses will be when you tend to have too much.

Bit of straw clutching now, but what pitch are your roofs, since the steeper they are, the less clipping you'll get in the summer compared to a flatter roof(s) when the sun is high and shining down.

NedS

spud said:

So our supplier (Light Renewables) quoted a 20 x 500w system across three aspects E/S/W) with 8kw inverter and applied to the DNO. Heard yesterday that they have said must be less than 8kw so options presented are:-

Do you know how much less than 8kW? What inverter size and export limit are the DNO prepared to offer?

spud

Update. The modelling provided showed a 0.2% estimated loss due to clipping. Appreciate that’s an estimate but based on that ballpark in which case we’ve opted for the 6kw which save a few hundred quid to go toward an EV charger. To answer the other questions, generation limit was set to less than 8, export to 4 (which the supplier is going to challenge and confident of that going to 5). 

NedS

Gary does Solar (on YouTube) has just published a video looking at clipping, which is timely given this discussion:

https://www.youtube.com/watch?v=rra6LGjAjZE