In an interview with Wired Magazine, Microsoft Founder Bill Gates talks about work being done to meet the world’s energy needs. The wide ranging talk covers the public safety issues of power generation (including coal and nuclear plants) as well as the economics and politics of energy.
Mr. Gates dismisses rooftop solar as “cute” – a deep insult in the nerd-world implying that it’s not a serious solution. He suggests that the only practical use of solar energy would be in large desert installations and points out that there’s a problem with generation during the nighttime periods:
I think people deeply underestimate what a huge problem this day-night issue is if you’re trying to design an energy system involving solar technology that’s more than just a hobby. You know, the sun shines during the day, and people turn their air conditioners on during the day, so you can catch some of that peaking load, particularly if you get enough subsidies. It’s cute, you know, it’s nice. But the economics are so, so far from making sense.
Again with the geek insults, in the tech world “hobby” is another cut saying it’s not a practical endeavor. In reality rooftop solar makes economic sense even now in parts of the world with expensive electricity like California and Japan. Because I saved money by installing my rooftop PV system myself, I’m already at “grid parity” (the cost to generate electricity is the same as the cost to buy it from the utility) so I’m not spending one extra dime to harness the sun’s power and reduce my carbon footprint.
Of course, Mr. Gates may be coming from a biased perspective: he’s a major investor in a company that’s promoting a new type of nuclear reactor. It’s a bit harder to be impartial about a race when you’ve got money riding on one of the horses.
In reality, there are currently two different solutions to the day/night problem with power generation. In large-scale desert solar installations, mirrors are used to focus the sun’s light onto a collector. Rather than create electricity directly as in a photovoltaic system, the power is used to heat a liquid in an enclosed system. That liquid (usually molten salt) is then used to heat water and spin turbines to produce electricity. To spread out the power generation over 24 hours, the molten salt can be stored in large tanks for use during the nighttime.
Another method for taking excess power generation and banking it for later use is gravitational storage. Also referred to as Pumped-storage Hydroelectricity, the system takes electrical power and uses it to pump water uphill into a holding pond. When more power is needed, the water is released downhill through a turbine generator. This works just like a hydroelectric dam except that instead of harnessing a river, water is actually pumped uphill to fill the reservoir. (Yes, it sounds odd but this technique is in use today to balance loads on the electrical grid)
While solar power is still improving, it’s already a practical means of electrical generation and one of the least harmful to the environment. Local rooftop microgeneration is a practical, reliable and cost effective way of meeting our increasing power needs while lowering our impact upon the environment.