Solar thermal captures sunlight to produce heat, not electricity. Flat-plate collectors on rooftops warm water for homes and pools. Concentrated solar power plants use mirrors to focus sunlight onto a receiver, generating high-temperature heat that drives steam turbines.

The distinction matters. Photovoltaic panels convert light directly to electricity. Solar thermal converts light to heat first. That heat can be stored in molten salt or oil and used later, which gives concentrated solar plants an advantage: they can generate power after sunset.

Solar thermal is simpler and cheaper for low-temperature uses. A rooftop water heater pays for itself in a few years in sunny climates. Concentrated solar power is more complex and expensive. It works best in deserts with direct sunlight. Some plants have failed financially. Others, like those in Morocco and California, continue to operate.

Common types

• Flat-plate collectors
• Evacuated tube collectors
• Parabolic troughs
• Solar power towers
• Dish Stirling systems