10 kW Solar PV Setup Advice

[Aaron Brookham]

Hi Techies,

I am from Ontario and am looking to take advantage of the new Feed-in-Tariff being offered. The program looks at the 'nameplate' value of the system which they judge to be the lower value between the total STC Wattage or the maximum inverter wattage. This means that my limiting factor is the 10kW at the inverters.

My research has pointed me towards the following system.
44 x 260W Suntech panel (PTC 235.4W) = 10357.6 PTC Watts
2 x 5000W Sunny Boy SB5000US (95.5%) = 10000W Maximum output

Therefore my maximum wattage is 10357.6 x 0.955 = 9891.5 Watts (this does not take into consideration other system losses)

I have run the system analysis in PVwatts and RETscreen.

So here are my questions:
1. Have I truely optomized my systems potential?
2. Are wirewound inverters more durable/long lasting then HF inverters?
3. The most inverters that I looked at had a -25C temperature limit. This will be installed in an open barn. Does anybody have experience with semi outdoor inverter installations in cold climates?
4. Is 20% of system cost a fairly reliable estimation of installation costs?
5. I had an installer try to tell me that he was getting 190W AC(measured at an enphase inverter) from a 175W STC panel. He claimed monocrystaline panels work better up North. Whats the deal here?

Any help that you can offer would be greatly appreciated. Please do not post about the Feed-in-Tarif program as I have researched it to death. Thanks very much for the help!

[Mike90250]

All panels work better in cold temps. There is more "thickness" in the air, at higher latitudes, which filters out more of the suns rays.

The PTC spec, is generally 20% higher than real life, or the CEC spec.

Most electronics work better and more efficiently in the cold.
I have no idea of the measurement accuracy of the enphase inverters, many inverters read "high" to prevent lots of "My systems is not working well enough" calls.

No such thing as a "wirewound inverter". There are Transformer inverters, and Transformerless inverters. Some places require the transformer for isolation. When well designed, there is little difference, other than the weight of a 40# transformer.

[Aaron Brookham]

@ Mike

Thanks for the info! I was wondering if you confused STC with PTC. The CEC uses PTC which in some rare cases is 20% less then the STC. This would mean around a 40% loss from the STC value of the panel

STC -> PTC = 20% loss (rare case)
PTC -> real world = another 20% loss?

That seems extreme since it doesnt even factor in other system losses (shading, panel mismatch, AC/DC losses, etc.)

Please clarify. Thanks!

[Mike90250]

CEC is the closest number to delivered power. Alphabet soup acronyms sicken me.

There should be NO shading or mis-match losses. Those are solved by location and properly spec'ed panels.

[csteinman]

Hey Aaron,

I think that I might be able to answer a couple of your questions here:

1. Have I truely optomized my systems potential?
--> Perhaps not. You could actually get away with putting 24 panels on each of those inverters (depending on the panel). I have installed a couple of 11.04kW systems just north of Toronto on pairs of SunnyBoy 5000s using SolarWorld 230 monos. (I have a sweet deal on these monos -- hence the reason that I am not using polys -- drop me a note if you want details)
2. Are wirewound inverters more durable/long lasting then HF inverters?
--> I am not sure that I can answer that as, simply, the transformerless (or HF) units have not been in the field for that long. SMA's are very new -- though their claim is that they are lighter and higher efficiency. I am not sure how ESA or CSA will feel about them though -- given that they do lack that isolation characteristic.
3. The most inverters that I looked at had a -25C temperature limit. This will be installed in an open barn. Does anybody have experience with semi outdoor inverter installations in cold climates?
--> Yes. Generally the manufacturer will tell you that as long as it is not in the wide open, it will be OK. I have built custom enclosures (small sheds) for inverters w/o issue. Keep in mind that the coldest recorded temp in Toronto was -31C -- not far from the inverter rating. Worst that happens is that the capacitor dielectric freezes up in the night and has to thaw a bit before startup.
4. Is 20% of system cost a fairly reliable estimation of installation costs?
--> That is really low. After panels, inverter, racking and electrical you are looking at a system in the range of $3.50/W. If you use a commercial installer and/or electrician you are looking at another $1.00/W to $3.50/W depending on how much you do yourself and the installation difficultly (coring, trenching, etc.)
5. I had an installer try to tell me that he was getting 190W AC(measured at an enphase inverter) from a 175W STC panel. He claimed monocrystaline panels work better up North. Whats the deal here?
--> That is possible in Canada. Panels can produce much above STC if it is a cold, clear and midday. That is why you need to design with at least a 25% temperature coefficient in your string voltage calcs in Ontario.

I hope that this helps. Drop me a note if you have any other Qs.

Cam.