A new energy boom is taking shape in the oil fields of west Texas, but it’s not what you think. It’s solar. Solar power has gotten so cheap to produce—and so competitively priced in the electricity market—that it is taking hold even in a state that, unlike California, doesn’t offer incentives to utilities to buy or build sun-powered generation. Pecos County, about halfway between San Antonio and El Paso and on the southern edge of the prolific Permian Basin oil field, could soon host to several large solar-energy farms responsible for about $1 billion in investments, according to state tax records. On a recent day, contractors for OCI Solar Power LLC erected posts for a solar farm that will be the size of more than 900 football fields. First Solar Inc. FSLR -5.51 % was negotiating to lease an adjacent property, its second project in the county. […]