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THE TRUTH ABOUT SOLAR PANELS October 2007
Or
PHOTOVOLTAIC ARRAYS ONLY BREAK EVEN AFTER 20 YEARS!
by Geoff Fernald-
Author of Not In a Thousand Years
Graduate of UC Berkeley in Electrical Engineering, BSEE, MSEE 1968.
There is a great deal of effort and money going into alternate, cleaner energy sources. One of the recently popular with consumers and the media is the solar panel or photovoltaic array. It is made up of panels that are about three feet on a side and contain several hundred photo-cells each. These panels are connected to one another in series and placed on your roof or other south-facing surface that receives unobstructed sunlight. There are frequent advertisements suggesting your electric bills will drop significantly if you buy one of these arrays. Solar arrays are, however, costly to install. In this article I will lay out some of the pro’s and con’s of such arrays in more detail than provided in most media articles to illustrate both the positive as well as the unsavory aspects of these popular and Green-correct devices
The main downside that jumps out at you is the twenty to forty year break-even time for the initial investment. This can be a bad thing if the array doesn’t function longer than the break-even point or longer than the lifetime of the roof that the array is installed on. In addition PV array durability has not yet been proven; whether it will outlast its payback time. Several government test setups have lasted for thirty to forty years but that doesn’t mean consumer versions will last as long. Since roof replacement tends to be needed every forty or so years you might wish to install any solar array at the same time.
The great thing about the consumer feast on solar arrays is that solar panel manufacturers have a chance to sell them in larger quantities reducing the price and allowing them to debug new designs and to find cost reduction techniques that eventually may allow future buyers to break-even within the normal expectation of five years. We all love an early adopter in situations like this. If you want to spend twenty thousand to eighty thousand dollars for a solar array, betting that electricity rates will rise more quickly than predicted, please do. Or, if you just want to be part of the ‘greening of America’, this is a good way to start.
Finally, if you believe you will recover the capital costs of your solar array when you sell your house (not a sure thing at all for the moment) the time to break even is much shorter. You can just add to your home loan the cost of the array and make payments on that loan over the time you live in the house which is hopefully shorter than the useful life of the array.
HIDDEN FACTORS:
Let’s look at a few hidden factors that are important before we become carried away with the romance of being green:
1. Any dark shade (trees) that covers as little as 3% of your panels during any day or time of year will cause the panel’s power output to drop by 50%. Beware of your trees, you may have to cut them back severely.
2. The best payback occurs only if your electricity consumption rises to the 200-300% of baseline energy-use bracket, in that bracket your utility rates rise to around 35cents/kwhr; three times that of baseline. This means your monthly electric bill should be higher than $200 for the faster payback. You can optimize the cost benefit of a solar array by sizing it to shave off only the top of your electricity usage where rates are highest. At the baseline usage an array does not make sense at the present 12 cents per kilowatt-hour.
3. The credits you receive when you produce more solar electric energy than you use in your own home (primarily during the summer) can be used to pay for electricity you use later in the year when the sun is not out as much. If you have credits left over at the end of the year, however, those credits are zeroed out. There is no carryover. So the array must be sized to generate less than your annual use, and preferably, as mentioned, only enough to remove you from the top energy-use pricing bracket.
4. Finally, even with a solar array you aren’t as green as you might expect because the utility peak power need in a residential district occurs late in the afternoon and in the early evening, a time when your solar power is less effective than it otherwise would be. Solar arrays make more sense for businesses located in a mixed residential/industrial area where utility energy requirements peak in late morning and stay high until late afternoon, the perfect time to help them out with solar.
To feel calibrated on what a kilowatt-hour means think of your refrigerator which consumes 500+kwhrs/ year, or think of your stove that eats 2 kwhrs during dinner preparation, or imagine a house with 10 100-watt light bulbs on all at once consuming 1 kilowatt in an hour.
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