Coal-fired electrical plants and other energy-producing and industrial manufacturing facilities, mostly built in the 1960s when “environmental stewardship” wasn’t in the mainstream lexicon, may actually hold the keys to the next generation of clean energy: waste heat.

Energy experts, from government agencies to university research programs and private companies, estimate that up to two-thirds of the heat generated by the creation of energy (e.g., fuels like coal burned to generate electricity) dissipates into the air via smokestacks and other vents—a waste stream that also outputs carbon dioxide, a greenhouse gas.

Somehow capturing that heat and either recycling it into a facility’s operation or putting it back on the power grid, however, has the potential to offset more energy consumption than solar and wind power. According to the EPA, comprehensive waste heat recycling from industrial, municipal, and agricultural uses would equal the energy generated by nearly 70 nuclear power plants.

Several solutions are emerging, including semiconductors that convert ambient heat from a steam or waste pipe into electricity to models like the Green Machine by Nevada-based ElectraTherm that uses pressurized waste heat and a small turbine to recycle energy to the grid.

Designed to scale up or down depending on the facility and amount of waste heat, the system ranges up to $200,000 per unit (other industrial waste heat system can be up to 100 times that) and returns its investment within five years, according to the company—perhaps less given applicable tax credits and utility rebates.