Gas Technology Institute (GTI)

There are two primary methods for capturing and using sunlight today: direct conversion of sunlight to electricity using photovoltaic (PV) solar panels, or focusing sunlight onto a fluid that is used to drive a steam turbine in concentrated solar power (CSP) systems. Storing hot fluid in CSP systems is a less expensive way to generate electricity when the sun is not shining compared to storing electrical energy from PV in batteries. However, PV uses just part of the solar spectrum at high efficiency, while CSP systems use the entire solar spectrum but at low efficiency. Combining the best elements of these two technologies could provide a means to get the most out of the full solar spectrum, generating both electricity and storable heat (for later use) within the same system. Developing hybrid solar energy systems that perform both functions at the same time could provide electricity at cost comparable to traditional sources, whether the sun is shining or not.

Gas Technology Institute (GTI) is developing a hybrid solar converter that focuses sunlight onto solar cells with a reflective backside mirror. These solar cells convert most visible wavelengths of sunlight to electricity while reflecting the unused wavelengths to heat a stream of flowing particles. The particles are used to store the heat for use immediately or at a later time to drive a turbine and produce electricity. GTI’s design integrates the parabolic trough mirrors, commonly used in CSP plants, into a dual-mirror system that captures the full solar spectrum while storing heat to dispatch electricity when the sun does not shine. Current solar cell technologies capture limited portions of the solar spectrum to generate electricity that must be used immediately. By using back-reflecting gallium arsenide (GaAs) cells, this hybrid converter is able to generate both electricity from specific solar wavelengths and capture the unused light as heat in the flowing particles. The particle-based heat storage system is a departure from standard fluid-based heat storage approaches and could enable much more efficient and higher energy density heat storage. GTI’s converter could be used to provide solar electricity whether or not the sun is shining.

If successful, GTI’s hybrid solar converter could simultaneously generate electricity and dispatchable heat even while the sun is not shining.