Let the Sun Shine In

Monday, August 20th, 2007

In Let the Sun Shine In, Greg Blonger notes that “too much energy is wasted by converting it”:

Sometimes the best solutions to the energy crisis are the simplest, and often they’re right in front of our eyes. Consider the use of solar power to light a home. Even the most advanced photovoltaic solar panels convert just 20% of the available sunlight to electricity. The resulting direct current (DC) then must undergo conversion to alternating current (AC), losing another 20%. If that AC goes on to light an incandescent bulb, which is only 5% efficient, you end up using a fraction of 1% of the original sunlight as room light. (Even switching to compact florescent bulbs, which are 15% efficient, makes little difference in overall energy efficiency.) But if you were to simply leave sunlight as light—via proper skylights, window orientation, and louvers—nearly 80% of the light ends up as illumination.

Or take the multiple conversions required to produce alternative biofuels. The efficiency of converting sunlight into plants such as corn and switch grass and then into ethanol or biodiesel is one-tenth of 1%, or less. Algae looks like it will perform slightly better, but at these rates, why bother? The best way to convert plants to energy, frankly, is to eat them.
We could begin by siting new buildings for optimal exposure to sunlight and properly designing them to best capture daylight via skylights and windows. Though still a rarity in the U.S., such design practice has become much more common in Europe. With proper insulation, such structures also require very little energy to heat.

Similarly, we could install heat exchangers—simple, low tech devices that operate with 90% efficiency—much more widely. Office building architects, for example, increasingly use heat exchangers to help separate sources of heat and cold, thus eliminating double heating and cooling. Banks of server computers, now routinely walled off from office space, use heat exchangers to transfer the hot air they generate out of the building during summer and into the building during winter. Less-expensive versions for the home can do the same for refrigerators or stoves (why use electric energy to cool food when the outside temperature is 30 degrees Fahrenheit?) and hot water generated for showers (why lose all that heat down the drain?).

Even if you can’t avoid mulitiple conversions entirely, there are ways to minimize the number of conversions. For example, we could also find more opportunities to break the DC/AC conversion cycle. Refrigerators and other appliances that operate on DC are becoming available and, with the certain arrival of economical LED lighting, which operates on DC, direct DC solar-power-to-DC-end-use shortly will become much more practical.

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