Renewable thermal energy

This example system is "renewable" because the source of excess heat energy is a reliably recurring process that occurs each summer season.

Solar energy has been in use for centuries for heating dwellings and to produce hot water before low cost natural gas was discovered.

It gained attention during and after the oil embargo of 1973 as engineers investigated ways to produce thermal energy from a renewable source instead of fossil fuels.

High-temperature collectors concentrate sunlight using mirrors or lenses and are generally used for fulfilling heat requirements up to 300 °C (600 °F) / 20 bar (300 psi) pressure in industries, and for electric power production.

They use the Earth's near constant subterranean temperature to warm or cool air or other fluids for residential, agricultural or industrial uses.

Earth-air heat exchangers have been used in agricultural facilities (animal buildings) and horticultural facilities (greenhouses) in the United States of America over the past several decades and have been used in conjunction with solar chimneys in hot arid areas for thousands of years, probably beginning in the Persian Empire.

[9] Examples for district heating include Drake Landing Solar Community where ground storage provides 97% of yearly consumption without heat pumps,[10] The state of New York took a big step in September 2015 when it created a new office titled Director of Renewable Thermal.

[13] The report says: "State Renewable Portfolio Standard (RPS) programs have historically focused on electricity generation.

An industry public described on-site combustion as :responsible for 35 percent of fossil fuel greenhouse gas emissions in New York State.