Move Off the Grid with Solar Energy

New technology in photovoltaic power has improved the world of solar energy. Learn abut: new power sources and cell technology.

| August/September 1995

Perhaps no other endeavor has captivated the 0minds of MOTHER readers as much as living independently, free of the indentured servitude of the electrical grid. For nearly half a century, the photovoltaic cell, generating DC power solely from the rays of the sun, has represented one of the best avenues to that independence. At long last, developments in those renewable energy systems have made it easier for us to live within our solar income while maintaining our quality of life ...and without first obtaining a degree in electrical engineering. As appliance energy-efficiency continues to improve, better appliances made more easily available to energy-conscious buyers, and new equipment for managing homegrown energy (and selling the excess to the local power company) finally taking the intimidating learning curve out of system installation, the dream of decentralized generation is now. Off-the-gridders are being joined by nations and municipalities in declaring this to be the year renewable energy becomes the people's power choice.

Can a home PV system, designed to be integrated into and complement your existing grid power, ever pay for itself? Yes, if the utilities agree to pay you for the excess power you produce at the same rate that they charge you for their own power. The chart assumes modest to moderate initial system cost of $6,000, a kilowatt-hour cost of 13 cents in the first year, and a conservative annual increase of 5 percent thereafter. For example, a kilowatt-hour of electricity in 2025, the endpoint of my projection, would cost 54.3 cents. Batteries for the system will need to be replaced every 10 years at a cost of about $1,000, and results in the saw-tooths in the break-even line.

Only a tiny fraction of a percent of American homes-just over a hundred thousand-are off the electrical grid and renewably self-sufficient, but that trend is quickly changing. Programs designed to defrock the electric priesthood by demystifying electricity, once attended only by supposed environmental radicals, are now filled to near capacity by tens of thousands nationwide, who quickly learn how safe, simple, and rewarding it is to play productively in the energy game. At the same time, the stakes have never been higher: Electric rates poise on an uncertain brink, and no one predicts that they will ever fall again. The power brokers in this game of redefining our national energy resources will still be the utilities, but they will have to transcend their role as primary providers and eventually come to terms with the fact that power has to flow from where it is most naturally derived: from our south facing roofs, seasonal streams, and windy promontories where it is still free for the taking.

New Power Sources  

While awaiting a dramatic breakthrough in power-source technology, energy hobbyists and others who produce their own power have been happy to see incremental improvements in electrical source technology-smaller, quieter, affordable wind turbines, refined micro-hydro, and enhanced photovoltaic (PV) systems appearing in the past few months. Stepwise refinements in PV efficiency, yield, and packaging have decreased electrical cost per watt of installed systems-generation, control, and storage-by about a dollar from over five dollars a watt in 1993 to four dollars and change today. Systems that might produce a kilowatt-hour of electricity for 32 cents in 1992 may now produce a kilowatt-hour for less than 30 cents. Federal neglect for renewable energy programs continues to be, according to insiders, the secret strength of the alternative energy industry. Proudly unsubsidized, we get where we're going under our own power. Changes in PVs include minor tuning of module frames, larger cell size (up to six inches from four inches circa 1990), utilization of more of each cell, new collection strategies (vertical traces in laser-etched channels reduce the amount of cell shaded by the trace), and better antireflective coatings. Silicon, a material mastered because of transistor technology, remains the best material for large-scale development, and current technology approaches the practical limitation of that material's capabilities. Silicon cells are very good right now.

Current improvement efforts focus more on the way light gets to the cells than on improving photo-cells themselves. Higher efficiency cells can be made, but the cost of making them appears to be irreducible, so the challenge is to make these cells work harder. By using fresnel lenses and mirrors to concentrate sunlight as much as three hundredfold onto small, highly efficient photovoltaic cells, manufacturers have just begun entering the marketplace with concentrating modules which promise a breakthrough in yields, but do add to system complexity. Concentrators must be pointed squarely at the sun to within a degree or two to accomplish their light amplification, which pushes cutting-edge tracker technology to its limit. Since conventional flat-plane one-sun modules have encountered problems in their adhesives, coverings, and substrates when subjected to the stresses of collecting sunlight over a prolonged period extending to a half century, we can imagine how these problems will be compounded by several-hundred-sun modules whose cells absorb light and heat intensified by two orders of magnitude. Since production concentrator modules have yet to see a year in the field, pioneers who are installing these devices can only hope the problems have been well solved (see accompanying sidebar).

In Europe and Asia, a different strategy is being employed. In Germany, glass roofs and south-facing curtain walls of new buildings are now covered with photo-active materials. In Japan, low efficiency roofing tiles are making building tops into power farms. Swiss schools are graced with fanciful sculptures of PVs to introduce children to the inevitability of renewably harvested electricity. Observers of the global energy scene worry that America's fossil-fuel-only policies are hurtling us toward an inevitable wall.

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