J and D's Corner

From the Letters Archive

I support a continuing program of expanding use of non-fossil based energy, but at the same time am constantly irritated by the seemingly universal need to grossly over-hype the solar & wind options, both in terms of performance and true cost.  You can't make logical decisions without accurate data.

Interestingly, this letter actually got a well-written reply from a solar-equipped homeowner living in Las Vegas containing seemingly well documented performance figures for his hefty 10-KW system for the past year or so.  I unfortunately failed to save the reply letter but I do recall that the numbers he supplied indicated his actual yearly capacity factor was almost 22%.

Capacity factor, by way of explanation, is the actual production of power averaged over some significant period of time as a percentage of the peak capacity of a system.  In other words, if you have a "10KW" system that demonstrates an actual day-night, summer-winter production of 2KW  overall average, then you have a capacity factor of 20%.  This is the true power value of a system, and understandably is a figure you never, ever, see quoted by solar and wind advocates.

Anyway, the Las Vegas resident's 22% is significantly higher than my assumed 16% which I based on figures gathered over several years by a large commercial PV installation near Phoenix. The Phoenix plant averaged 19%, a number I downgraded to 16% for a roof-mounted panel in a Lancaster/Palmdale location based on the assumption that the commercial installation benefited from sun-tracking mounts and was operating in a less cloud-impacted location (Palmdale/Lancaster is subject to more general cloud cover than Phoenix, including local intrusion of the SoCal marine layer clouds during a significant part of the year).


To:  AV Press

Date: 07/2010

Re:  Home of the Future

One of my hobbies is attempting to discern truth from newspaper stories about ‘green’ and ‘alternate energy’ projects.  This is similar to the job of the CIA analyst who tries to estimate the probable actions of the Russian government from data he has on Kremlin budget figures for vodka and toilet paper.

Case in point is Lancaster’s “home of the future”, which Mayor Rex states is the “most energy efficient home in the world” (really?), producing “more than 100%” of its electricity needs, both of which claims caught my eye.

For data, we are told it has 18 solar panels, 220 watts each, presumably rated for high noon on a sunny day.  Since 18 times 220 is 3.96 kilowatts and the yearly capacity factor of small-scale PV solar in our area might reach, at best, 16%, we can conclude the panels will on year-round average deliver 15.2 kilowatt-hours of power per day, or 456 kilowatt-hours per 30-day month.

There is some confusing reference to batteries that can provide “10 kilowatts of power when fully charged”. Whether this means peak load capacity or that they can store up to 10 kilowatt-hours of power we don’t know.  Why batteries are installed in the first place is unclear to me unless they are needed to stabilize the system’s solar-to-grid interface, as utilizing battery storage decreases overall system efficiency and adds to cost. They do function as backup in case of grid system failure though.

The ‘home of the future’ has some LED lighting, which is helpful. Again on the plus side, the home looks to be small, maybe bordering on tiny, but also is air-conditioned, as evidenced by the picture of the home showing a seemingly standard A/C unit sitting outside the door.

It is suggested the overall concept includes charging an all-electric car while parked at the home. However, this part is somewhat vague and most definitely cannot be done as part of the available 456 KWh per month, so better drop the car from the energy budget.

So could a normal family of 4 truly & comfortably live in the home on less than the optimistically hoped-for amount of solar-supplied power, which is at least 37% below that used by an average Lancaster home (per SCE figures)?  Seems questionable.  My conclusion has to be that while it is a fine demonstration project, as always in alternate energy stories the so-called ‘most energy-efficient home in the world’ is being over-hyped.