The Challenge of Solar's Temporal Mismatch
The desert is an unparalleled reservoir of solar energy, but its gift is not evenly distributed in time. The glaring paradox of solar power is its peak generation during midday, often out of sync with demand peaks in the late afternoon and evening. While battery storage for electricity is advancing, the Arizona Institute of Desert Futurology is pioneering a broader, more integrated approach to solar utilization, focusing heavily on its thermal form. We view the sun not just as a source of electrons, but as a source of heat—a more fundamental and, in many ways, more versatile commodity. Our research explores systems that capture, store, and dispatch this thermal energy for electricity generation, industrial processes, building climate control, and even as a driver for chemical reactions, aiming to make solar a truly 24/7 resource.
Concentrated Solar Power (CSP) and Molten Salt Storage
Concentrated Solar Power, which uses mirrors to focus sunlight onto a receiver to heat a fluid, has a critical advantage over photovoltaics: inherent, low-cost thermal storage. Our work advances next-generation CSP systems. We are experimenting with supercritical CO2 as a working fluid in Brayton cycle turbines, which offers higher efficiencies and smaller footprints than traditional steam cycles. The cornerstone, however, is thermal storage. We use molten salts—mixtures of sodium and potassium nitrate—that can be heated to over 565°C and stored in insulated tanks for hours or even days. When the sun sets, the hot salt is used to generate steam and produce electricity. We are researching novel salt chemistries and encapsulated phase-change materials that can operate at even higher temperatures (700°C+), boosting efficiency and reducing storage volume. These 'solar batteries' made of salt are a cornerstone for grid-scale, dispatchable renewable power in desert regions.
Building-Integrated Thermal Systems
At the building scale, thermal management is a huge energy consumer. We develop building-integrated systems that turn structures into thermal batteries. One concept is the 'Trombe-Michel Wall,' an advanced version of the classic Trombe wall. It incorporates a selective surface that absorbs solar heat, a phase-change material (like salt hydrates or paraffin wax) that melts at a desired room temperature, storing latent heat, and a ventilated cavity managed by smart dampers. The wall absorbs excess heat during the day, melting the PCM and preventing indoor overheating. At night, as temperatures drop, the PCM solidifies, releasing its stored heat into the living space. Another project uses rooftop solar thermal collectors to heat a closed-loop water-glycol solution, storing it in large, underground borehole thermal energy storage (BTES) fields. In winter, this warmth is extracted for space heating; in summer, cool nighttime air is used to chill the storage for daytime cooling.
Solar Fuels and Process Heat
The highest-temperature solar heat opens doors to industrial applications and fuel production. Using heliostat fields to achieve temperatures above 1000°C, we can drive thermochemical reactions. One major research avenue is solar thermochemical hydrogen production. Metal oxides (like cerium or iron oxides) are heated to extreme temperatures, causing them to release oxygen. At a lower temperature, they are exposed to steam or CO2, grabbing oxygen from it and producing hydrogen or carbon monoxide (syngas, a building block for liquid fuels). This 'solar fuel' stores solar energy in chemical bonds, enabling long-term storage and transport. Similarly, high-temperature process heat can decarbonize industries like cement or steel production co-located in solar-rich deserts. By viewing the sun through a thermal lens, we unlock a spectrum of possibilities far broader than the electrical, moving toward a future where the desert's most abundant resource powers our electricity, heats our homes, and forges the building blocks of a circular economy.