Module efficiency and kWh/yr

[Obbit]

Hi people

Does any one include module efficiency when working out kWh/yr generation.

We never have, and wasn't sure how to include it in the MCS calcs.

I ask, as a competitor as quote a much higher generation total then we have for the same 35kWp, and the only difference I can see is they have used LG mono (17.4%) over our poly (15.32%) quote.

Cheers

 

[Gavin A]

module efficiency is irrelevant, but if they've used pv-sol or similar then this will include inverter efficiency and other factors that can make the panels produce more per kWp, and have a more geographically accurate data than MCS regionalised data.

All systems aren't created equal, and all locations across a massive region aren't equal either, so their performance estimate may well be more accurate... or they could just be fudging the figures, hard to say without seeing them really.

Alternative methods are allowed in addition to the MCS method.

 

[Obbit]

Cheers for that.

Obviously the client hasn't let me see the other quote, so only have his rough figure. My figures are the MCS calcs, location is London:

Installed capacity of the system	35 kWp
Orientation of the PV system – degrees from South	10 ° °
Inclination of the system – degrees from horizontal	20
Postcode region	1
Calculations:​
kWh / kWp (Kk) from table	945 kWh / kWp
Shade factor (SF)	1
Estimated annual output (kWp x Kk x SF)	33,075 kWh / year

The client said they got 40,000 something kWh. I believe your fudging conclusion may be correct.

Cheers

 

[whinmoor]

I agree with 33,075 using the MCS method but a PV-Sol report may well give a higher reading.

 

[The Solar King]

I use PVSol for every job. PVGis-SAF climate data is imported as it is location specific taking more account of Albedo levels especially in coastal locations. A cross check is also done using the database in the software.

I have never seen an output figure in the range being quoted by your competitor. You would need to be in Plymouth in a very good year to get this kind of output.

If you PM me the postcode, exact make of panel, exact model and number of inverters, number of strings per inverter, I'll quickly run it through the 2D model and give you an output figure.

There are other things such as cable losses (where you have long runs) that can be taken into account on a larger array, but they tend to be marginal if every effort is made to minimise them in the design.

If there is still a significant variance, you can go back and challenge the other quote.

 

[Gavin A]

unless they're using higher efficiency panels to actually give eg a 40kWp system for the same number of panels, then there's no way that other prediction is going to be right.

 

[SibertSolar]

LG Neon 285Wp panels have a 17.4% efficiency - have they quoted for the same TIC or qty of panels? If it's qty then it's as Gavin has indicated. If it's TIC then I'm struggling to see why there's such a discrepancy unless they've tweaked the variables a good bit