Probably not. The journalist didn't measure anything himself, and probably didn't compute anything himself. He simply reported pap, spoon-fed to him by the installer of the system who has a very vested interest in making it sound good. The 13.4 kW rating is almost certainly "high noon" power. The area of the roof is is about 171 m². At high angle and perpendicular incidence, sunlight is about 1 kW/m², and affordable solar cells are about 10% efficient. If the roof could be totally covered, perhaps 17 kW could be attained. Given standard size panels, 13.4 kW peak is reasonable. I estimate for a flat, non-tracking array, at optimum angle, he will get the equivalent of 4 h of peak power per day, or 54 kWh/day. (This will be "smeared" over more hours, but mostly lower power in bell shaped curve). My estimate is strongly at odds with the claim of saving $230000 over 25 years at current electric rate of $0.116/kWh. The implication of this statement is 217.3 kWh/day, roughly 4X my estimate. Time will tell. Note that this estimate requires 16 h of full power operation per day (average for the year. On average, how long is a day. It's not all full power either). :) As to the CO2 savings, the federal government uses a decade-old figure of 1.34 lb/kWh. I note that 48240 lb is EXACTLY the CO2 emission of 36000 kWh. However, the 36000 kWh number doesn't seem to relate to either power estimate above. As an annual estimate, it would apply to generating capability of 98.6 kWh/day (call it 100) more or less the geometric mean of the two estimate. The article is a pile of environmental voo-doo (or doo-doo) unlikely to translate to real results over the course of the year. However, the real problem is not the reporter's math ability but that all the "facts" came from the seller and there was no fact-checking or critical view of (very dubious) data. As to units, until we get AP to change the AP Style Guide, there is not a snowball's chance in hell of the units being all SI.
--- On Sun, 9/6/09, James R. Frysinger <[email protected]> wrote: From: James R. Frysinger <[email protected]> Subject: [USMA:45748] Can journalists be cured of their affliction? To: "U.S. Metric Association" <[email protected]> Cc: [email protected] Date: Sunday, September 6, 2009, 2:23 PM Journalists, as a rule, are terrible at dealing with measurements. Case in point, "Indiana Farmer Turns to Sun to Run Operation" Saturday, September 05, 2009 Associated Press http://www.foxnews.com/story/0,2933,547042,00.html The story describes a solar photovoltaic installation on a farm in Indiana. Comments: "The 66- by 28-foot roof supports 60 photovoltaic solar panels, each producing 224 watts of electricity. The panels are aligned in four rows, or two sub-arrays, with each sub-array producing 6.7 kilowatts, making the entire system produce 13.4 kilowatts of electricity..." The journalist should have said whether that claimed power output was the ideal, peak value (the most likely case) or the average over the length of a typical day. There is a huge difference, especially since power output must be zero at night! "The farm in southern Vigo County has at least 200 acres of electric fencing to contain a herd of beefalo..." Fencing is sold by length, not by area. Let's call 200 acres 80 ha (close enough), or 800 000 m2. If the field is 1 m by 800 000 m, then the fence around it would be 1600 km long. If the field is square, then 3.6 km of fencing would suffice. "The fencing itself uses 600 volts of power... Power is measured in watts, not in volts. "The Lovealls' system will avoid the release of 48,240 pounds of carbon dioxide into the atmosphere..." Is that per day, per week, per year, over the life of the system? There is a huge difference between 24 t of CO2 per day and 24 t of CO2 per score of years! Also, climatologists measure CO2 outputs in metric tons (symbol t), not in pounds. And it's not terribly leading edge to still be using feet, square feet, and acres. Since the electrical units which were misused in this article are SI units they should have stuck to the SI -- and should have used it properly. Not as a matter of measurement ignorance, but a lack of common sense: "The solar panels are part of a "phase one" project, Roberts said. A second phase for the Loveall farm will add more solar panels, plus move an existing 66-foot wind turbine next to the barn to produce wind power to allow the farm to be 100 percent energy independent. The farm would remain connected to Win Energy's power grid as a backup." You betcha they need that backup! What happens at night when the wind is not blowing hard enough to generate all their needs? The fallacy ignored by the green crowd is that systems such as this use the grid and its mainline nuclear and fossil fuel plants to serve as their energy surge reservoirs! Can journalists be cured of this affliction they have that prevents them from understanding how to measure things? And the news media wonders why we don't trust their reports! Jim -- James R. Frysinger 632 Stony Point Mountain Road Doyle, TN 38559-3030 (C) 931.212.0267 (H) 931.657.3107 (F) 931.657.3108
