Solar radiation has a great deal of heat content. There are many ways to use solar heat to produce electricity. Achieved via thermal energy storage (TES) systems, these units deliver heating using renewable energy, rather than burning fossil fuels.
TES works by using high-pressure liquid storage tanks connected to the photovoltaic system. Instead of using electricity or a battery, the system stores potential electricity. The use of heat to generate electricity is nothing new. Solar thermal power systems have been active since the 1980s. But, concentrated solar energy requires the use of mirrors and a receiver, often in the form of:
Linear Concentrating Systems:
Long, rectangular, U-shaped mirrors focus sunlight onto tubes that run along the mirrors’ length. The fluid that runs through these tubes gets heated concentrated sunlight. Entering a heat exchanger, the water is boiled in a steam-turbine generator. The two types of concentrator systems are:
- Parabolic Troughs
A long parabolic-shaped reflector focuses the sun’s energy on a receiver pipe at a strategic focal point (magnifying its intensity up to 100x). As the sun moves throughout the day, the collector tilts to follow it and direct sunlight onto the receiver. Such a facility is located in California’s Mojave Desert.
- Linear Fresnel Reflectors
Here, mirrors concentrate sunlight onto a receiver as well. But, in this case the Fresnel lens effect occurs, allowing for mirrors with a shorter focal length. This concentrates the sun’s energy up to 30x. This configuration is also found in more compact forms that use many absorbers/receivers to improve efficiency.
Solar Power Towers
Heliostats, or sun tracking mirrors, concentrate sunlight (up to 1,500x) onto a receiver located on a tower. The preferred heat-transfer fluid is often water. However, experiments have used molten nitrate salt, as it is highly effective at heat transfer and energy storage. The system is even able to produce electricity at night or in cloudy conditions.
A structure, similar to a large satellite dish, is covered in mirrors to direct and concentrate sunlight (by up to 2,000x). The heat transfers to a receiver that absorbs and collects it. It is then transferred to an engine and converted to mechanical power. The mechanism, in turn, runs a generator or alternator that produces electricity.
How to Make Solar Thermal Power Workable
Various improvements have been made over the years. It has become possible to store solar thermal energy and produce electricity using the following configurations:
Two-Tank Direct Systems
Solar thermal energy is collected and stored by a heat-transfer fluid. One tank stores low temperature fluid. The second stores heated fluid that has passed through the solar collector. The heated liquid goes to a heat exchanger, where steam is produced. The steam turns into electricity with the help of a generator. Returning to the low temperature tank, then recycles the fluid.
Two-Tank Indirect Systems
Different types of heat-transfer fluids are used, and they’re usually more expensive and not stored the same way as indirect systems. An additional heat exchanger is used to pass low temperature fluids through. However, the process works in a similar way to direct systems.
Single-Tank Thermocline Systems: Store thermal energy in silica sand or another solid. Different parts of the solid are kept at low or high temperatures, forming a temperature gradient. Energy storage is achieved by moving hot fluid into the top of the tank (which cools as it descends) and exits at a lower temperature. Reversing the process generates steam and in turn electricity.
Contact Sunworks USA
As you can see, there are various ways to take the sun’s energy and convert it into solar heat and electricity. Sunworks USA makes solar power accessible to more homeowners in California, Nevada, Oregon, Florida, and Texas as well as on a national scale. To learn more, contact us on the web or call 866-600-6800.