California’s home solar mandate, which says that newly constructed homes must have panels on the roofs, is now in effect. In a state known for its sunshine, that seems like a sensible idea, but it’s been a contentious path putting this law into place. Builders say that at $8,000 to $10,000 per house, solar energy will drive up prices, potentially making the housing affordability crisis even worse. Advocates say the expense will be offset by lower bills, and then there are the environmental benefits. But some are already looking for loopholes, including an option in the law to build so-called community solar projects, piping in energy from remote solar installations.