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Comment by droithomme | Hacker News Reader

Thanks. For optimal tilt that implies a sun tracking system, correct? Do most installations track? Do the sun trackers use much energy to rotate all the panels? Are they reliable, or do they add maintenance costs. The system costs we are talking about here do not include trackers or installation of trackers, correct? How much would that add.

Florida gets a lot of sun. I agree with you that a tracking array of new panels in Florida gives those numbers.

For people in other parts of the country and without trackers I find this site that has monthly solar radiation numbers to be useful for estimating output.

http://rredc.nrel.gov/solar/calculators/PVWATTS/version1/

Looking around I see that a 4500W system, no installation, no tracking, runs about $20,000.

http://www.infinigi.com/4500w-solar-grid-tie-system-20-sanyo...

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$20000 isn't a good price. Check here to see more competitive pricing:

http://www.sunelec.com/comparisons_of_grid_tie_systems_price...

Optimal tilt just refers to the tilt the panels are installed at, no tracking.

No tracking system. Here are some average numbers of hours of peak energy a day for a fixed system Portland Or 4.0, Chicago 4.4, Tampa 5.3, San Francisco 5.4

Total hardware costs are currently about $1.75 watt for panels, inverter and hardware. Fed Tax rebate is 30%.

Do these installations just pick the best single angle and stick to it all year? It seems like you must be able to get a reasonable benefit by adjusting your panels say, once a month.

Yield from that isn't very big, and far outweighed by the cost of making the whole installation moveable. If you're going to put everything on a moveable frame anyway, it's better to have it servo-controlled so that it's at least adjusted continually.

Thanks. Ok, your peak equivalent hours number for Portland OR using a fixed position is 4, implying an average of 365 * 4 * 4.5k = 6570kWh/year, correct?

The federal DOE site calculator for the same 4.5kWh fixed tilt plant gives 4580 kWh/yr for Portland (http://rredc.nrel.gov/solar/calculators/PVWATTS/version1/US/...), ranging from 142 kWh/mo in December to 578kWh/mo in July. What accounts for the discrepancy between the two calculations?

A good bit of the discrepancy is that the calculator assumes that the DC to AC conversion is only 77% efficient (see "DC to AC Derate Factor" in the calculator), while the naive calculation assumes 100% efficiency of conversion, right?

fed tax rebate turns into a tax credit at the end of this year, btw! Move fast!

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