Solar Thermal Storage

Renewable energy is hard to store. Wind and sun come and go. The electricity they generate must be consumed by the electricity grid immediately.

But concentrating solar power creates heat as its primary energy source, not electricity. As a result, this heat energy can be "stored" and released as needed. This storage capability is a major advantage of concentrating solar power.

It means solar energy generated during morning hours when grid demand is low can be released during the afternoon and early evening hours when grid electricity demand is greatest. If the afternoon demand peak is high, stored solar thermal energy can be released to provide near instantaneous power. If the afternoon peak is small, stored heat can be held over and released into the evening. If evening demand is low, stored heat can be used to power desalination, base load power, or both, reducing fossil fuel use. If electricity grid demand remains low all day long, desalination can be powered exclusively by solar energy all day long and into the night using the stored energy. Combining concentrating solar power, solar thermal storage and desalination offers huge flexibility in meeting a community's power and water needs.

How does solar thermal storage work?

Heat energy is created by focussing and magnifiying sunlight to create 400-1,000C temperatures. Specialised salts and oils are then used to absorb the heat. These are then transferred into insulated storage tanks such as those in the photo below left, taken in California. The graph to the right indicates how concentrating solar power and solar storage typically work during a 24-hour period. In the morning, solar heat creation rises more rapidly than grid demand so the "extra" solar energy is placed into storage.

During the afternoon and early evening hours as solar heat output reaches its maximum for the day and begins to decline, real-time solar heat energy and stored solar heat energy can both simultaneously be turned into electricity, "doubling-up" the output to meet peak grid demand. By offering the ability to meet short-lived afternoon peaks in demand, concentrating solar power and solar thermal storage can lower consumer electricity bills through reducing the amount of expensive traditional generating capacity that must be kept running merely to meet peak demand.

Solar thermal storage tanks	Solar thermal storage allows solar energy production to be aligned to electricity demand
Source: US National Renewable Energy Laboratory	Source: US National Renewable Energy Laboratory

"Concentrating Solar thermal power stations can deliver power on demand, making use of thermal storage capability and hybrid operation with fuels. They are the natural link between the fossil system and the other renewables."       European Union

"Australia needs to significantly accelerate our conversion to the low emissions practices and technologies of the future." Council of Australian Governments, 2006

Significant investment will be required in new energy generation capacity if growing peak demands are to be reliably met. Electricity Supply Industry Planning Council (South Australia), June 2006