Solar Panel Guide Discussion

Cardew

orrery wrote: »

... which leads me to a further question:

So, under what conditions will I see the full 100% output?

How do you define the 'full 100% output'?

A PV system of say 16 x 250wp panels(4kWp) will produce 4kW under laboratory conditions of 'sunshine'(irradiance), temperature etc.

It depends on the latitude if a system will ever reach 4kW or indeed exceed 4kW, and even then the inverter will determine the output.

bjohnson

Today has been a beautifully sunny day but the combination of a lower sun (some unexpected shading from a next door tree which has yet to shed its leaves) and the shorter day has meant a total of only 11.20 kWh

grumpyoldsteve

bjohnson wrote: »

Today has been a beautifully sunny day but the combination of a lower sun (some unexpected shading from a next door tree which has yet to shed its leaves) and the shorter day has meant a total of only 11.20 kWh

What size system do you have?
Our 2.45kWp system produced 9kWh on an also beautiful day here. Yesterday however was dire, low cloud and drizzle all day, so only managed 1kWh.
I have yet to read the instructions fully on our generation meter, so not sure if or how I can get fractions of a kWh.

orrery

Cardew wrote: »

How do you define the 'full 100% output'?

I would have thought that it was obvious - I'm buying a 4kWp system.

Cardew

Originally Posted by Cardew
How do you define the 'full 100% output'?

orrery wrote: »

I would have thought that it was obvious - I'm buying a 4kWp system.

No it is not obvious at all - see my post above!

If you live in Cornwall you would expect it to exceed 4kW in you live in North Scotland it will not reach 4kW.

zeupater

orrery wrote: »

... which leads me to a further question:

So, under what conditions will I see the full 100% output?

In theory you'll only get 100% of your panel rated output when you receive over 1000W/sqm of irradiation (plus the inverter & system losses) and the panels are at 25C or cooler .... and of course, your inverter will need to be rated as being larger than the panels.

If the inverter can cope with the total array rating of the panels you are still only likely to see 100%, or >100%, when you have a bright day (no haze) with partial cloud. As panels warm above 25C they tend to lose efficiency at a rate of 0.5%/Degree C, so extended periods of sunlight warm the panels which reduces output. If a cloud has blocked the sun for a while the panels can cool, so when the clouds clear they are at their most efficient, but there is also what is known as 'cloud edge' effect, where as well as receiving direct sun the panels also collect light which is refracted through the cloud edge and reflected by the cloud walls thus boosting the collected light .... so you temporarily get somewhere over 1000W/sqm and achieve 100%(+), before the cloud edge moves away and the panel warms up again.

HTH
Z

zeupater

Cardew wrote: »

No it is not obvious at all - see my post above!

If you live in Cornwall you would expect it to exceed 4kW in you live in North Scotland it will not reach 4kW.

Hi

Whereas it is correct to say that an array in Cornwall would be expected to generate more energy over a year than one in North Scotland, it is probably incorrect to say that it's impossible for an appropriately configured array in North Scotland to receive somewhere over 1000W/sqm of irradiation on a temporary basis and therefore produce >100% of the array's rated peak power, even after allowing for inverter and other system losses .... (see cloud edge post above for details) .... although the temporary conditions which allow this are likely to only last for a few minutes.

HTH
Z

Cardew

Agreed. I was illustrating the point that 4kW is not 100% output from a 4kWp system. Inverter allowing, it could be well above 4kW especially if you lived on a mountain where it could be bright and cold.

They get pretty high outputs on the Space Station!

zeupater

Cardew wrote: »

Agreed. I was illustrating the point that 4kW is not 100% output from a 4kWp system. Inverter allowing, it could be well above 4kW especially if you lived on a mountain where it could be bright and cold.

They get pretty high outputs on the Space Station!

:rotfl:
Good point ! .... the space station is blessed by not having the atmosphere which gives them around 1400W/sqm of insolation though ... and then there are the clouds, which we look up at, but upon which they have a different perspective

Z

orrery

Cardew wrote: »

Agreed. I was illustrating the point that 4kW is not 100% output from a 4kWp system. Inverter allowing, it could be well above 4kW especially if you lived on a mountain where it could be bright and cold.

I agree, but what units were you expecting to see the answer in? A percentage was a good choice, as this removes any assumptions about system scaling.

The question you should have been asking was why the answers only went up to 80%. Hence my question 'When should I expect to see 100%?'. Presumably zeupater had a 100% in mind when he quoted the figures that he did.