It’s getting harder to figure out whether converting your home to solar energy makes financial sense as utilities adopt new ways to pay customers who pump electricity into the electric grid.Most utilities buy homeowners’ excess solar power for the same price they sell power from the grid. This idea, called net metering, is easy to understand: Buyer and seller get the same price.But some utilities around the country complain that net metering doesn’t cover their costs of accommodating solar. With support from regulators, they’ve started paying for home solar at lower prices than grid power.Consumers need to pay attention to these changes. Most home solar systems export 40% to 60% of their electricity production back to the power grid, says Mark Dyson, a manager at the Rocky Mountain Institute, which studies alternate energy. Lower payments for that power have a big impact on whether home solar is cost effective.