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?
In Tampa FL with optimal tilt and no shade a panel rated at 1 peak watt would generate 5.3 watts a day X 30.4 days a month * 4500w panels = 725 Kw per month
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.
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%.
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?
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.
It took me some thinking to decode it as well. He has ratings numbers per watt-peak of the rating. Watt peak is a normalized output rating for a panel under some conditions and doesn't actually mean it's producing that in a given condition. He has numbers that a brand new 1 watt-peak panel gives 5.3 watts a day of power in a certain location with a certain configuration. He has a 4500Watt peak installation. So he multiplies the 4500 watt peak by the watts per day per watt-peak. The watt-peaks cancel out, giving watts per day. Multiplying further by days per month gives the average watts per month (average per year) for the 4500Wp installation in the given location. Basically, it's correct, but one has to understand that the W, typically called Watts, in the panel rating is not Watts, but a normalized Watt-peak rating of the panel. It is worth noting that solar salesmen will often intentionally confuse the two, leading homeowners to believe that their new installation has much higher capacity than it actually does.
It's not a matter of decoding-- it's wrong. Watts are a rate of energy usage. It's like saying that my car can drive 60 MPH per day. Doesn't make any sense.
(I do think you're right about the confusion and exploitation of the difference between peak power and average power.)
Thanks. It looks like a 4500W fixed tilt system in Seattle would generate 150 to 572 kWh, depending on the month. 4364 kWh per year, which is not too bad. 1 axis tracking brings it to 5492kWh, 2 axis tracking to 5819kWh.
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.
Tracking is only helpful in sunny areas, certainly not in a cloudy place like Seattle.
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.
"Tracking is only helpful in sunny areas, certainly not in a cloudy place like Seattle."
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.
