Solar Panels vs Solar Panels

When I was starting out, solar panels were those rooftop contraptions which used sunlight to heat water for the house. Solar panels contained row after row of copper or pvc pipes, painted black, all in a frame behind a sheet of glass. The idea was to create a small chamber where the pipes heated up from sunlight faster than they lost heat to the air. Many were custom-built by ecologically-minded amateurs with Whole Earth Catalogs, and looked suitably low tech. Some didn’t deal with freezing temperatures well. Some leaked, but some are still working.

For about ten grand, you can now get very complete solar hot water systems by companies like Velux, which started out making roof windows – a cross between skylights and windows for attic spaces. Their solar water panels aesthetically mimic their roof windows. To deal with freezing temperatures, Velux runs a propylene glycol solution (antifreeze) through its panels, then exchanges heat with the domestic water supply. A Green Building Advisor contributor raved about his unit.

When solar panels are mentioned in today’s news, the reporter is probably talking about photovoltaic (PV) panels, which turn the energy of the sunlight into electricity. PV panels used to be horribly expensive, but after over a decade of government subsidies, prices have come down from Lotus to Porsche range. (It may also be the case that the same declining demand that is pushing down oil prices is pushing down PV and battery prices.) Some PV panel companies offer lease deals, where the cost is spread out over decades and supposedly paid for by the energy savings. But some of these deals have escalation clauses tied to the price of electricity, and electricity is actually the smaller and less important part of your energy budget compared to heating. You may find yourself trying to wring savings out of electricity while your heating bill is killing you.

Electric vehicles have also progressed from do-it-yourself projects to mainstream cars like the Nissan Leaf or luxury cars like the Tesla Model S. The Leaf has found success as a short range car among people who can drop $35K on a second family car, while the Tesla is selling well to people who can choose to spend $100K on a full range electric car and charging station instead of on a liquid-fueled supercar or limo.

With his SolarCity project, Elon Musk is hoping to sell other sorts of batteries to those same people who can swing an EV. One sort would be storage batteries for a rooftop photovoltaic array. Since the sun only shines during the day, and most of us expect electricity all the time, having a big battery would allow PV owners to rely less on the grid as backup.

I think buying batteries will work out fine for the crowd who can afford it. The rest of us will be better off designing our homes around passive solar principles and going to bed when it gets dark. It sounds straightforward to make sunlight into electricity, and use that for everything, but it is actually five times more efficient to use the sun to heat water, and lots more efficient again to use sunlight to heat your home through an arrangement of windows and well-insulated walls.

Our house was poorly sited for passive solar, so we’ve put our money into insulation, caulking, weatherstripping, thermally-efficient windows and a garden.


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