Graetzel’s TiO2 with dye semi-transparent cell. This PV does not gain us anything in efficiency (it’s 10%), however it is much easier (and hence cheaper) to make than silicon PV. It relies on chemical processes in standard chemical reactors rather than on vacuum vapor deposition (a-silicon) or labor intensive crystal growing and cutting (crystalline PV). It is so easy to make that kits for students to make their own will be on the market in less than one year (Direct Gain, Inc.). The most interesting application of this type of PV will be to apply it so windows and walls. Large glass fronted buildings will then be able to generate 10s of kilowatts of power. Martin Green’s 21.5% efficient thin film silicon cell This cell holds the promise of being a high efficiency, cheap to manufacture PV. There are several types of high efficiency PV, but they are all still in the S200/W and up range. Thin films are typically much cheaper to manufacture because they use less material (they are less than 50 microns thick) and are made with automated processes (less labor). While the details of how this PV is made are scarce (proprietary) some commercial interests have already begun work to commercialize it. That is rare, because cells made in the lab are often hard to manufacture in quantity. Apparently, this is not the case for this PV. GalnP/GaAs cells have been demonstrated to be 30.2% efficient. These are very expensive to manufacture, but may catch on in concentrator systems where much less PV is needed. Copper Indium Di-selenide and Copper Indium Phosphide are two new types of thin film PV that are being commercialized now. They are over 10% efficient and being thin films, promise to be cheaper to make than crystalline PV. Materials science and engineering are in a Golden Age right now. A lesson to be learned from the development of PV manufacturing is that cost of manufacture is often more important that cell efficiency. It the cost to manufacture a new type of PV is 4 times lower, this is equivalent to making a cell 4 times more efficient for the same manufacturing cost, as long as the physical space the PV takes is not a very big consideration. Along the same vein, we are not likely to see a 50% efficient multi-junction PV cell come on the market if it is extremely expensive to manufacture. For SSP, the additional amount sunlight received (1300 W/m2 ) and higher availability does not necessarily mean space power will be preferable, if the price is not right. People will pay double for peak power over baseload, but probably not 10x. Storage One of the big difficulties with using solar energy is that power is often needed when the sun either not up or obscured by clouds. In higher latitudes, the hours of useful sunlight per day varies from 2 to 6 hours. Even at the equator, there are only about 10 hours of useful sun per day. This means that, if one wants lights after dark or power on cloudy days, then storage is required. Traditional storage includes batteries and water pumping (at the scale of the utility power plant). New storage methods might include generating hydrogen with a solar electrolyzer that could be used in fuel cells or spinning up flywheels. Batteries The most common and inexpensive batteries for large capacity storage are the lead-acid type. These come in all sizes, from the portable power pack (7 Ah) to the industrial storage sizes (2000 Ah). The cost per
RkJQdWJsaXNoZXIy MTU5NjU0Mg==