Installed kWp way over inverters kWAC

[leovibroz]

Hello PVsyst forum users,

I'm participating at a solar plant project, and I would like to find out an optimal kWAC inverters power/ kWp installed power correlation.

For tracking systems, the recommendation is 15% more installed kWp than kWAC. Well, I would like to find a number myself, so I ran some tests using PVsyst and excel.

Admitting a fixed 4960 kWAC of inverter power installed, I started the first simulation with 4960 kWp, therefore the relation AC/Wp is 0%, or 100%.

Said so, in each new sample I increased 247 Wp approximately over 4960 Wp, that's about 5% more.

Great, in my head in some point between 30% and 40% AC/Wp, the extra production generated would drastically decrease, since most of the time the array power would be over the 4960 inverters kWAC, so the extra power would the thrown away. But, that's not what I observed.

I assumed that for each extra kWp installed, I would spend 1226 $ more, which means 1226 $/kWp for each extra kWp. And I also assumed, that I will sell this energy to the market for 0,16 $ each kWh, which means, 0,16 $/kWh.

So, in some point, the extra investment that I make to install some extra kWp, wouldn't be worth compared to the extra production the array would give me in 25 years, a basic IIR concept. And I've found this point, I just didn't realize this point would be so far from the recommended 15% AC/Wp, of course this is stricted realted to the prices I specified, but those are the prices from where I live converted to dollars.

 

 

That's the table I generated using Excel.

What I'm seeing then, even if I have 80 % AC/Wp, my system will still produce more energy than if I have like 15% AC/Wp, and it's worth the investment since my return in 25 years is higher than the investment. Does it make sense? I hope you guys understand what I'm trying to find here.

[André Mermoud]

I don't know how you have done your calculations.

PVsyst offers a powerful way for the estimation of the PnomPV / PnomAC ratio, named PNomRatio.

You can get this tool by clicking the button "Show sizing" in the "System" definition part.

Please also see the help "Project design > Grid-connected system definition > Inverter / Array sizing".

In practice, you don't have any overpower loss until a PNomRatio of 1.25 or even 1.3.

Due to the low price of the PV modules, and the limitation of grid inection, many people now use highly oversized PV array (with PNomRatio up to 1.5 - 1.6 or even more).

For such an optimiaztion you can use the PVsyst simulation, and evaluate separately the investment for the PV array and for the Inverter/connexions costs.