Thanks. Could you explain in more detail how and under what conditions (location, type of system) a 4500W panel system generates 70/.11 = 636 kWH of power each month?
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...
http://www.sunelec.com/comparisons_of_grid_tie_systems_price...
Optimal tilt just refers to the tilt the panels are installed at, no tracking.
Total hardware costs are currently about $1.75 watt for panels, inverter and hardware. Fed Tax rebate is 30%.
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?
(I do think you're right about the confusion and exploitation of the difference between peak power and average power.)
5 hr * 4.5 kw * 30 days/month = 675 kwh/month
http://rredc.nrel.gov/solar/calculators/PVWATTS/version1/US/...
It might become reasonable in Seattle at some point, depending on the costs of installing a system with tracking. One should also factor in that peak output decreases over the life of the panels in figuring out lifetime cost/benefit, and not just look at output numbers from the first year.
It's important to establish what specific area we are talking about in these discussions and what particular sorts of systems we mean and their actual complete costs. Not everyone lives in Florida or Hawaii and my understanding is that tracking systems are quite rare and have their own issues. I've only seen one tracking system myself, it was at a school installation that was done in a field. I have not yet seen them on rooftop installs. There is little information about them but often estimates include numbers assuming tracking.
Given the rate solar PV panel prices are falling, however, PV in Seattle-type climates (and in Germany like the OP discusses) may be economic much sooner than many people expect.
This is not strictly correct, tracking does help as the numbers from the DOE calculator show. However, the cost of purchasing, installing, and maintaining a tracking system will cancel out some, or possibly all of the gain. How much so is not clear.
In this case, a 4500Wp fixed angle installation, which appears to be available for around $12,000 not including installation or installation brackets generates 4364kWh per year in Seattle, saving the homeowner $279.30 in annual electric costs given the alleged 6.4¢/kwH rate in Seattle (which seems very low to me). This is equivalent to a 2.3% return on the investment, with, unlike in savings, the principal is non-recoverable and expires after 25 years as the panels reach their end of life.
The numbers are better for other cities true. The DOE calculator gives 5491 kWh/yr for a 4500Wp fixed angle installation in Hawaii, with 18.1 cent electricity. Over a year, the electricity value is $993.87, an 8.2% annual return, but again, with the principle not returned and the investment expiring after 25 years.