I want to talk about solar systems, and I will thus begin by mentioning that the solar powered Mars Spirit spacecraft, now operating (as of this writing) on its 1,811th Martian day on the surface of Mars, recently experienced an energy surge, when the Martian wind blew dust off its solar panels.
The Spirit Rover, according to the press release now produces 240 Watt-Hours of electrical energy per Martian day, up from 210 watt-hours. The craft - my kind of spacecraft since I love space robots - requires 180 watt-hours a day to survive, so it now has an extra 60 watt-hours with which to play.
Speaking of watt-hours, you can read all about the solar system installed on the roof of the Massachusetts Museum of Contemporary Art by clicking on this link.
The system, we learn by clicking, is 52 kilowatts we are told by the Museum, which describes the system as massive.
How "massive" is it? The average American, according to the EIA, the 'average' American consumes about 335 million BTU a year. Translating this to familiar units of electricity as power - although it includes stuff like dangerous gasoline for cars and dangerous natural gas for heating - and dangerous coal for generating electricity - one can see that this translates to an average power consumption of about 11,200 watts per person per year, or 11.2 kilowatts, since a day contains 86400 seconds and a year 365.25 days.
Thus, in theory the "massive" solar system installed on the roof of the Massachusetts Museum of Contemporary Art would - operating 24/7/365.25 produce as much energy as is required for five people to do everything people do in the United States on average.
But does it?
The Massachusetts Museum of Contemporary Art has installed on its "massive" solar system, a product that allows every single person with access to a computer to look at the power and - more importantly - energy the system produces.
Not "peak" power, but actual power, not theoretical energy, but actual energy.
Now click on "view data."
A new window pops up. Adjust the start date to Jan 1, 2008. Choose "span of one year - energy by month" and click on the "table" button.
The total energy produced by the Mass MoCA solar system will come up as a table that may be imported into a spreadsheet program and summed.
The total for 2008 is 47,514.3 kWh of electricity actually produced by the "massive" system. There are 8766 hours in a year (24 * 365.25). A power system of any type that is one "kilowatt" will, in theory, operating continuously thus produce 8766 kWh. A "51.6 kw" system will thus produce therefore, in theory, 452,000 kWh per year. Dividing this number into the actual energy output gives the capacity factor - or how reliable the system is.
For the Mass MoCA system this figure is thus, by direct calculation 10.6% meaning that the Mass MoCA system on average produced the energy needs of one half of one American.
According to the website Solar Buzz as of this writing the average cost of a solar installation in the United States is $4.81 per "watt" meaning that an average system the size of the Mass MoCA system would cost about $250,000 - but I'm sure there's a volume discount.
But maybe I'm wrong...let's see...oh, yes...here it is: The grant was $700,000.
Screwing around with the very interesting data page we can quickly learn what the actual "peak" power of the Mass MoCA "51.6 kw" solar system was in 2006.
It's best performing months in 2008 were in May and in July. The best day in July of 2008, July 26, 2008 the system peaked at 40.367 kw. Looking at the graph for that day, it was over 40 kw for about 10 minutes, and below it for the rest of the 24 hour period.
Let's look at the best day in May 2008 in energy terms. On May 28, 2008, the system produced the maximum for a single day in May, 349.2 kWh. Since a day has 24 hours, and the system is claimed to be 51.6 kw (theoretical 1,238 kWh at 100%) the actual best capacity utilization of the system was 28.2% on that best of all days in may for system performance.
On June 21, 2008, the first day of summer, the system produced zero energy, although on June 23, two days later, it produced 560.8 kWh, one of two days in the entire year where it produced more than 500 kWh. The record day for the entire year was June 13, 2008, when it produced 632.0 kWh. This is a capacity factor - for a single day - of 50.1%.
On the first day of winter of 2008, Dec 21, the system produced zero energy, and had a capacity factor of zero. It produced zero energy on December 20, zero energy on New Year's Eve day, zero energy on Dec 17.
The best day in December of 2008 was December 8, 2008, when it produced 108 kWh, or 8.8% of its nominal capacity.
At no point did the system ever produce peak power levels of 51.6 kw. The highest peak power level for the entire system in 2008 occurred on June 1, 2008 when the system briefly produced 43.491 kw. Looking at the graph for that day, it was that high for about 5 or 10 minutes, maybe even less, depending on how the software works.
Thus it is fair to say that the claim of a "51.6 kw" power plant is misleading at best, and an outright lie at worst.
As I write the power output of this system is 12.51 kw, at the total power generated by the system during its entire existence is 86893.9 kWh.
The average cost of power in Massachusetts is given by the EIA, and the commercial rate for 2006 was one of the highest in the nation an astounding 15.54 cents per kWh. Thus over it's life - assuming that this record setting price of electricity prevails in Massachusetts indefinitely into the future, the solar PV system for the Mass MoCA has produced $13,500 worth of electricity.
It would probably be unfair to attribute the entire $700,000 grant to the solar system. However, to recover the cost of this grant, the system would need to operate flawlessly for 51 years - and that's not counting interest on the money and any maintenance. Actually though, solar PV systems degrade over time, an effect known as the Stabler-Wronski effect.
(To be fair, this effect in amorphous silicon cells slows after about 1000 hours of solar irradiation, and is probably no longer a major consideration for the Mass MoCA system described here. c.f. Compaan, "Photovoltaics Clean Power for the 21st Century" Solar Energy Materials & Solar Cells 90 (2006) 2170–2180. However it is well known that roofing materials exposed to the elements do degrade from wind, rain, heating, cooling etc. There is no evidence that this solar PV system will be operating at a level as high as 10% capacity factor in 50 years, if it is operating at all.)