Ice-Storage and Other Thermal Storage-Related Systems (CABLE)

Growing concerns regarding the impacts of CO2 emissions and climate change have prompted both states and the federal government to promote the adoption of renewable energy sources. Combined with rapidly decreasing costs, the share of intermittent renewable energy generation on the grid, such as wind and solar, has increased rapidly. These intermittent energy sources do not necessarily align with periods of high electric demand, putting additional stress on the grid and requiring electric utilities to relay on high-cost, short-term, fossil-fuel power generation during peak demand. Furthermore, excess renewable generation capacity exists during specific periods, leading to curtailment of these resources. No significant grid-level storage technology has yet gained traction so utilities are attempting a market-based approach to shift electric demand away from peak periods with Time-of-Use (TOU) pricing. Consumers can easily shift some electric loads to off-peak periods, but heat and cooling (HVAC) systems must run at specific times of day when climate control is required. HVAC systems are the signal largest electrical load for most residential and commercial customers. As a result, they are not able to effectively able to shift their electrical usage and take advantage of TOU pricing. Mainstream and our partners at the National Renewable Energy Lab (NREL) will develop a low-cost thermal energy storage heat exchanger using water as a phase-change material (PCM). This PCM heat exchanger (PCM-HX) can be integrated into existing residential and commercial scale HVAC systems and will be produced with advanced materials and manufacturing techniques. During periods of low electrical demand, where prices are low, the system will be charged by freezing the water in the PCM-HX. During high demand periods the PCM-HX will be discharged, significantly reducing the electrical power required by the integrated HVAC system. This product will allow the consumer to shift their electrical usage to off-peak periods and take advantage of lower Time-of-Use prices. Adoption of this HVAC thermal storage technology will have significant benefits to individual consumers, grid stability, and the further adoption of intermittent renewable energy sources. Integrating this thermal storage scheme into HVAC systems will have a return on investment as low as 2 to 4 years depending on the Time-of-Use rates, which are likely to become more advantageous in the future. While not directly comparable to battery storage, Mainstream’s PCM-HX represents a significantly cheaper option for load-shifting compared to pure battery storage, which can cost $10,000 for even the most basic low-capacity systems. This technology could allow low-to-middle income households to participate in the green energy revolution that has thus far been limited to those who can finance solar and battery systems costing $10,000+. Additionally, shifting electrical loads reduces the costs incurred by utilities and customers due to peak electrical demand and the effects of intermittent renewable energy sources, benefiting all users. Finally, energy storage will be required to increase the share of intermittent renewable energy sources to the levels needed to combat climate change. This technology offers an alternative to grid-level energy storage schemes which have not yet gained significant market penetration.