Fool’s gold is an apt symbol for the future of sustainable energy, though not (we hope) in the obvious sense. It’s a case of less being more. There’s a growing recognition that many sustainable energy technologies are not always produced sustainably, particularly when it comes to key materials like platinum, lithium, indium and high-grade crystalline silicon. It comes down to scarcity, toxicity, costly processing or a combination. Researchers are beginning to look for less toxic, earth-abundant materials to generate and store energy. MIT’s Tonio Buonassisi is leading an effort to systematically search for safe, abundant semiconductor compounds for photovoltaics. Efforts like this aim to produce energy systems that have long-lasting supplies of raw materials, have minimal negative impacts on the environment, and lower the cost of producing clean energy. Researchers from UC Berkeley have taken the concept a step further. They’ve produced a study that shows that if our goal is to use photovoltaics to meet a large portion of our electricity needs, some of these abundant compounds are the best way to go based simply on the economics. Here’s where fool’s gold, which has fooled gold hunters for ages with its similar color and sheen, comes in. The Berkeley study looked at 23 compounds for the total potential electricity that can be generated from systems made with the known reserves and cost per watt. They combined the results to identify materials with the greatest long-term potential for generating electricity. The clear winner was pyrite, or fool’s gold. The runner-up was amorphous silicon, already widely used in the photovoltaics industry. The study counters the prevailing assumption that the best way to push photovoltaics into the mainstream is to improve device efficiency without increasing costs. We also need to look at lowering costs without sacrificing too much efficiency. It turns out that less efficient but markedly cheaper materials can be a better route to making solar a dominant source of energy. The study should bring encouragement to the many researchers working to make dye-sensitized, organic and nanostructured solar cells commercially viable. Maybe it’ll also spur a renewed interest in making solar cells from fool’s gold. Eric Smalley is editor of Energy Research News. He has written about technology since 1987 and has freelanced for many publications including Discover, Scientific American, Wired News and The Boston Globe on topics ranging from quantum cryptography to global warming.