Quote from: velacreations on July 04, 2013, 07:38:57 PM

Quote from: Vycid on July 04, 2013, 07:25:21 PM

The 3 year ROI on solar is based on typical US costs for electricity at ~$0.15/kWh. Friedcat gets ~$0.06/kWh. His solar ROI is too far out to make sense, especially since he's going to need to have a bunch of UPS so he can switch back over to the grid at night without everything going down.

(By the way, the 3 year ROI is really good - something I'd consider for my own home. Can you get me a source for that? Last I'd heard was 9-10 years, with subsidy.)

Cost of solar in China is $500/kW.
His cost is $.06/kWh

So, he needs 8,333 hours for ROI. @ 7 hours a day for sunlight, that's 1190 days, or 3.26 years.

If he buys in bulk, he can get it considerably less than $500/kW, cause those are retail prices, and for a data center, he can get wholesale. If he does a wind/solar hybrid in a suitable location, the ROI will be closer to 2 years.

For buying for your home in the US, this site has a decent cost comparison: http://www.ecobusinesslinks.com/surveys/free-solar-panel-price-survey/

Ahhhh... I see the problem, here. You assume that for all 7 hours of sunlight, the power output will be at the maximum possible. This is false, of course. The workaround is to use insolation times area times external quantum efficiency.

http://en.wikipedia.org/wiki/Insolation

So we'll use the Canadian Solar panel from the website you linked as an example. It has an EQE of 15.23% (here: http://www.solarsystems-usa.net/solar-panels/#.UdXTxPm1Eqg). Its area is (60 cells x 156 × 156 mm), or 1.46 m². You said $0.5/W, so we'll stick with that; the cost of the panel is $166/panel in bulk, for a cost of $0.72/W; we'll assume serious bulk and Chinese discounts, so the actual cost will be computed $166 * 0.5/0.72 = $115.28. Hopefully you agree that price is reasonable.

So here are the characteristics so far:

Area: 1.46 m²
EQE: 15.23%
Price per 1.46 m²: $115.28

Now, we look up the insolation in Shenzen province, China.

http://www.greenrhinoenergy.com/solar/radiation/empiricalevidence.php

This looks like about 1500 kWh/m²-year to me. If you can find a better source, that'd get a more accurate calculation.

So, the energy output per year is

1.46 m² * 1500 kWh/m²-year * 0.1523 = 333.537 kWh/year

Now, since we're using a power cost of $0.06/kWh,

333.537 * $0.06 = $20.01 worth of power per module per year.

At a cost of $115.28 per cell, that's on the order of 6 years.

Insolation is enormously important in any solar calculation. If you use maximum wattage all the time, you're gonna end up getting screwed by people looking to sell you solar power.

I also am compelled to point out that I assumed your figure of $0.50 was correct. If we used the original $0.72/W value, the ROI would be about 9 years, like I thought (also: installation is not free).

EDIT: Found a better map. I'm sticking with 1500 kWh/m²-year.

http://solargis.info/doc/_pics/freemaps/1000px/ghi/SolarGIS-Solar-map-South-And-South-East-Asia-en.png