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FOCUS Technology Snapshot - Yale University's High-Temperature Dual-Junction Topping Cells

The Yale/NREL/SolAero team aims to demonstrate an efficient and reliable dual-junction concentrator photovoltaic (CPV) cell that can operate at temperatures as hot as the inside of a brick oven. While CPV cells efficiently convert much of the solar spectrum directly into electricity, they become significantly less efficient upon heating — an inevitable side effect of absorbing highly concentrated sunlight. In addition, any heat generated during the photovoltaic energy conversion process and any light not absorbed by the cells must be rejected as waste.

Unlike CPV cells, which maintain their efficiency by dispersing the heat away, our team will design and fabricate cells from III-V materials that can generate electricity reliably at temperatures exceeding 400 °C. This “hot CPV cell” will be integrated with a solar thermal collector that absorbs the unused portion of the solar spectrum as well as excess heat from the cells. The otherwise-wasted energy will be transferred to high-temperature fluids that can be used to power a steam turbine and generate electricity in a manner analogous to concentrating solar power (CSP). The high-temperature fluids can also be economically stored so that the heat energy can be dispatched when the sun is not shining or whenever electrical demand rises. This method of storing solar energy is projected to be significantly more cost-effective than battery storage.

The current high cost of storing solar electricity in batteries, combined with the natural variation of available sunlight, will weaken the economic drive for photovoltaic market growth unless novel solutions are developed. The Yale/NREL/SolAero project addresses both these challenges by combining the high efficiency of CPV with the low-cost energy storage offered by CSP.