The link between solar energy and thermal storage
September 7, 2016
Thermal energy storage on a broad level
There are two main categories of thermal energy storage. One technology group is grid level, meaning purchased and operated by the utilities. The other type is a distributed energy resource (DER). DERs are smaller power sources, owned and operated by property owners. DERs can be aggregated to supply power for the grid or serve the building alone and are becoming more important as they help facilitate a transition to more renewable energy resources, micro-grids and the smart grid. In New York for instance, the REV (Reforming the Energy Vision) plan will outline how the state will modernize their grid and develop best practices to encourage DERs.
Grid scale thermal energy storage
On the grid level, Concentrating Solar Power (CSP) plants, use mirrors to direct sun energy to boil water. The water is used to power steam engines that generate electricity. These power plants are becoming more widespread as interest in the investment of renewable energy grows. However, when the sun doesn't shine, the electrical generation at the CSP plant is curtailed. According to a study conducted by the Concentrating Solar Power Alliance (CSPA), these plants are able to bring reliability to the national grid, but only through effective energy storage.
With thermal energy storage able to store the solar energy in the form of salts or oil, CSPs can improve their response time to around 10 minutes, Renewable Energy World reported. The thermal energy storage will allow these plants to replace older traditional forms of peak power plants more reliably, and facilitate greater grid penetration of renewable energy.
Distributed thermal energy storage
While adoption to incorporating thermal energy storage onto CSPs is important for collection of solar energy outside major cities, the insight into the challenges of grid scale solar power plants provides a glimpse into how property owners and tenants can make more effective use of solar panels on their own buildings.
At the distributed level, thermal energy storage resources store energy in the form of ice to cool building spaces. Similar to how CSPs work, solar panels on a building rooftop provides power to buildings. However, the solar energy is curtailed by weather. In order for solar resources to be more effective on buildings, thermal energy storage is needed. In order for solar resources to be more effective for the grid or micro-grid, thermal energy storage is needed to reduce electric demand.
Energy storage resources like batteries can store energy in the form of electricity to run lights, elevators, etc. However, thermal energy storage resources play a very direct role in storing energy in the form that it will be used. Thermal energy storage meets demand for energy by only storing cooling. Why address cooling specifically? First, cooling demand is the largest contributor to peak demand. To meet summer demand for cooling, utilities call on their most polluting and expensive "peaker" plants. As a result, peak demand charges in the summer are mainly driven by air-conditioning and make up to 70% of electricity bills. Second, it would be highly inefficient and costly to store energy in a battery only to be transformed yet again to create instantaneous cooling.
Storing solar for a more sustainable energy future
The future of a more reliable grid rests in multiple energy storage technologies. Don't forget, however, thermal energy storage. Ice storage is not sexy but it is proven to work affordably for years over several hours each day with little or no cycle degradation. Ice cooling energy storage has the ability to minimize the effects of intermittent solar power during the day and capture wind generation at night. The grid reliability burden caused by a shift to renewable energy generation doesn't just fall on utility providers to provide grid scale solutions, building owners and operators can help support these efforts by installing distributed energy resources. The incentive for installing ice storage for example, is cooling system flexibility, resiliency, and lower peak demand which lowers operating costs. As the transition to net-zero buildings hastens, the need for policy makers, architects, engineers and facility energy managers to incorporate distributed thermal energy storage will as well.
Architects will need to have a plan B for when solar energy is curtailed. Net-zero buildings use a lot of solar energy however, net zero facilities are still connected to the grid, which means net-zero buildings are actually drawing from the grid's fossil fuel resources and need back up resources. Thermal storage, batteries, backup generation and passive design strategies like daylighting and natural ventilation to reduce peak demand will be critical to getting to zero.
