Underspecifying an inverter

[st3ve]

It depends very much on the roof angle. You can use PVGIS to give the max clear sky irradiance level for the max month of May or June. I ran it through PVGIS assuming NNE and a standard roof angle of 35 degrees. In June it only shows a max of a little over 500 w/m2, so you could use 50%.

However, if the angle is shallower, it will be more. For example I am planning on putting some panels on my NE facing shed roof which has an angle of less than 10 degrees. For that I get about 800 w/m2 or 80%.

Edit - My calcs are also based on the south coast, so it also depends on where the installtion is.

You need to be careful on this one, nowty...
PVGIS may give the stats you quoted (50%) for May/June, but this is the overall average return compared to for example facing South.
What I need to be mindful of, is the maximum possible output at any one time on any one date as I need to know the maximum possible power generation to specify my underspec'd inverter correctly.

The equivalent %age for this is around the 70% mark, in, as you say May/June.
Additional complication is that the peak power on each of my 2 roofs will occur at different times of day and maybe even dates!

I have therefore had to model the 2 daily and hourly output curves and combine them 'out of synch' so to speak, to deterrmine the maximum possible combined output to spec the inverter correctly whilst not wasting peak capacity. Phew.

 

[nowty]

No !,

I used the Daily Radiation tab in PVGIS to find the MAX clear sky irridance level in w/m2, not the usual average PV estimation tab to give average return. As the max amount I found at a particular day and time in May/June was circa 500w/m2, that is 50% of the 1000w/m2 that solar panels are rated at.

But yes, you will have to model both aspects and add them together to find what the max peak of both roofs in w/m2 will peak at.

 

[st3ve]

Nowty,

Am about to find out what the actual output is across the 2 roofs..... Installation and commissioning due to begin today Weds 18th July....

Will be interesting to compare against the theoretical values

 

[Earthstore]

Looking out of my window you will get very little...
but at least they will get the dust washed off them...

 

[st3ve]

I now know what happens when the input power exceeds the inverter capacity... See this link for a 5k280 panel system (South facing, no shade, in Exeter area) into a 4000W Sunny inverter... (NB. not my system)

Dan's PV 5.280kW | Live Output

:teeth_smile:
Steve.

 

[Worcester]

They must have put the (optional) 16 A limit on. I'd be suprised if the 4000TL would limit like that otherwise

 

[SolarCity]

The 4000TLs can't be limited to 16A - the power can be limited, but not the amperage.

 

[Gavin A]

They must have put the (optional) 16 A limit on. I'd be suprised if the 4000TL would limit like that otherwise

why not?

it's limiting at the maximum output limited for the inverter that's set as standard, not 3680W, so is exactly what I'd expect it to do.

 

[Worcester]

You are of course correct. it an be set at 3680W manually (or any other figure) so I was just suprised to see it so flat topped at exactly the specified output.