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Where I now work there is a solar array of 17KW going into a suitably sized invertor.

We use a ton of energy and we’re trying to find a way of reducing our use as well as generating more. We get big bills.

I’ve been tracking our energy use over the year to see how much we use and when, and how much is generated from the solar PV array.

This week is has been a very clear, no clouds or haze, and sunny in London. According to local weather stats this month should be peak sunshine for the year. I would expect our array to be producing the maximum it could at certain times of the day.

The array is on the roof of a 3 story building, nothing overshadowing it. The panels I believe are unobstructed. They are angled in a particular direction (I assume the most efficient direction). I assume the installation was competent (back in 2014).

We’re generating a maximum of 10.5KW at the peak of the day on one of the sunniest days of the year. I understand we won’t get the full 17KW, but is 10.5 the max we should expect? This is the most it’s generated at any point of the year, so far.

We’re thinking of expanding or replacing our existing set up once we’ve sorted some issues. The array hasn’t been serviced or attended to at all (ownership of it is complicated). Does it need looking at? Do we need overprovision panels by a lot of achieve maximum output?

Thanks.

Hi @solarbob , what is the inverter spec? You will find that the older panels are not as efficient and they do also reduce output when they are hot (a conundrum of course as the sun heats them!). 

Have the panels been cleaned at all? I would expect that if there has been no maintenance, it will be mostly down to the age/dust/temperature components. A simple washing will suffice - nothing that special required. Then it will be down to the inverter settings which might also be restricted depending on the install and the requirements of the local DNO.

Thanks for replying.

It’s a Goodwe GW17K-DT invertor with a Max PV-generation power: 17500W. 

I was thinking cleaning might make a difference, but I read that it wouldn’t make too much of a difference with the output. Not enough to warrant paying someone to do it. We have that down to be done by someone inhouse. As you suggest a simple wash. I’ll prompt them.

I get that new panels are much improved. Were panels this old never likely to reach anywhere near 17KW then? I’ve read newer panels maybe produce 20% less than the specified output.

We very very rarely output anything to the grid the entire time we’ve had it. We use almost everything produced from the array. Which is perhaps good, but we still use a lot of grid power.

It does depend on the panels and inverter settings - there are scenarios where the inverter is restricted to 50% or 75% of its output so that’s worth looking into. 
https://nl.goodwe.com/Ftp/EN/Downloads/User%20Manual/GW_SDT%20G2_User%20Manual-EN.pdf

I would expect a clean (especially if they’ve not had one for several years) to give maybe a 10% improvement but as I say, the inverter setup needs looking at first. 
Someone also needs to check on the installation detail as there can be restrictions made due to that. 
All that said, I would expect a 17k array to be able to produce more than 10k at peak 

So the restriction of 50/75% to the output might be there so we never output 17KW to the grid in the event we’re using no energy? They can handle 10 from us but not 17. Something the local DNO might require? But this also means we can never produce more than that for use internally.

I guess if we wanted to expand our system this would be a hurdle to doing that.

Is that was the case is it any more likely now (rather than in 2014) that the output capacity could be raised (after negotiating appropriately) as the grid might be more capable now in our area? Are DNOs more keen now for energy from solar PV arrays?

Yes, it’s all about the install spec and whether it was installed under G98 or G99,

https://connections.nationalgrid.co.uk/g99-connection-procedures/

coupled with the loading of the rest of the hardware, breaker capacity and such like.
For the DNO, it’s more related to their capacity to transport the energy should they need to match other feeds and local load requirements. I believe there is more capability/desire to use renewables more and so your DNO might well be agreeable to an increase but the full connection system needs to be capable of safely running with the load

That’s useful info. Thanks.

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