Solar Thermal Energy

solar thermal

Technology has led to more innovations and improved standards in our way of living. However, with the advancing technology also comes the increasing demand for power. Electrical devices that needed to be connected to an outlet to work became cordless and portable. Electricity within a household need not only be sourced from the grid but can now be harnessed from the sun. Solar panels, for example, can now be installed on roofs and be used to power up an entire home.

Further research in this technology has led to another innovative solution, solar thermal energy. We often hear about solar panels and how they are a great way to save money on utility bills and get tax incentives from the government. However, we don’t often hear of the latter. What does this technology do? This article will look at the technology, its use in power plants, and the differences with plain solar panel technology.

What is Solar Thermal Energy?

Solar thermal energy is a technology that utilizes solar energy to collect thermal energy (heat) or electrical energy for residential or commercial consumption. This technology uses solar collectors, and these collectors can be classified as low, medium, or high-temperature ones. Different classes of collectors generate energy for use in different industries.

Since the energy it generates is not limited to just electrical energy, it has more uses than the regular solar panels. Low-temperature collectors are uncoated or unglazed, and they are typically used for heating up swimming pools or ventilation air. This technology goes to less than 100 degrees Celsius in temperature.

Medium-type ones are used for residential and commercial industries. With their flat-plate design, they are utilized for heating water or air, which means that they can be used to supply hot water to homes. They are about 100 to 250 degrees Celsius in temperature. They are also used for cooking in the form of a solar oven, a device that has a specifically-shaped reflector for focusing the sunlight on the cooking apparatus.

High-temperature collectors have a temperature of more than 250 degrees Celsius. This temperature is achieved through high-concentration mirrors that harness solar radiation at greater levels. As you can imagine, it is used for powering high-energy requirement machines such as steam or gas turbines, commercial concentrating solar thermal power plants, or CSP plants.

Like solar panels, this source also produces power using renewable energy. However, instead of using the light or photons from the sun to generate electricity only, it collects heat to transfer or converts it to electricity. This emission-free source is therefore set up at different levels depending on its use.

This technology can be used in the home either through active or passive heating. For homes, it can provide passive or active heating with active heating being slightly more difficult to set up for better heating benefits. Active heating means that the collectors will be stored on the roof and the collected heat will be transferred for home use through piping or by using a heat exchanger depending on its intended purpose.

On the other hand, passive heating will not require any equipment. Instead, a heat collector (in the form of windows and the like) will be positioned at a sun-facing angle to allow the heat to enter the home and provide warmth.

Solar Thermal Power Plants

One of the biggest uses of thermal solar technology is power plants. As you may already imagine, they are huge enterprises that produce large amounts of electricity and heat. Specifically, these facilities use equipment that harnesses and concentrates sunlight to produce a copious amount of heat.

With this, they use a reflector that allows the sunlight to be drawn into the receiver. These systems may also use heat to transfer liquid and have it circulate in the receiver for steam production.

Power plants that are sun-powered are high-temperature systems and utilize a technique called concentrated solar power. By focusing the sunlight on the collector, the plants do not need large-scale land or increased collector sizes to achieve its target temperature.

This reduces expenditure as well as the environmental impact of its operation. While regular solar panels, the efficiency increases with the amount of sunlight received by the cells, thermal solar plant power increases with higher temperatures.

Depending on the achieved temperature, the technology that the yield of the system is applied to may change. With a temperature of 600 degrees Celsius and below, steam turbines achieve about 41% efficiency. Over 600 degrees Celsius, gas turbines may be more suitable. With temperatures higher than 700 to 800 degrees Celsius come a problem with application and maintenance, so various materials and techniques may be required to achieve ideal efficiency.

CSP plants are further classified into linear concentrating, solar power towers, and solar disk engines. A linear concentrating CSP’s method of collection of the sun’s heat is through its long, rectangular, curved (U-shaped) mirrors.

These mirrors target the sun’s rays into its receiver tubes and allow the fluid in these tubes to be heated and flow naturally into the heat exchanger to enable water boiling in the steam-turbine generator, which then generates electrical current. This CSP type can either be designed as a parabolic trough or a linear Fresnel reflector.

Solar power towers utilize a field of heliostats – flat sun-detecting mirrors for sunlight reflection and concentration onto the receiving mechanism at the tower tip. The heat transfer can either be done through a heated fluid or through molten nitrate salt for more advanced structures. Two well-known solar tower facilities in the United States that were recently built are Ivanpah in Dry Lake, California, and Crescent Dunes in Tonapah, Nevada.

Solar dishes or engines utilize a satellite-like dish that is built with small, flat mirrors fashioned into the said shape. Its surface then focuses the sunlight onto its receiver, which enables it to be heated and for the heat to be moved to the engine generator. This generator uses mechanical power to generate electrical current.

Solar Thermal vs Solar PV

Solar panel technology uses light in the form of photons and collects them through the photovoltaic cells to become a source of direct current, or through an inverter, alternating current.

However, how does thermal solar energy differ from solar technology through photovoltaic cells? First of all, solar panels are pretty standard. They may differ in sizes, shapes, or capacities, but the mechanism is similar. The solar cells collect photons from the sun, which then provides direct current.

If used with an inverter, it can also supply alternating current, the type of current used for most home appliances. If a battery is connected to the system, then the battery can be charged through the sun and the equipment to which the battery is connected can work without needing to be hooked up to a wall outlet.

There are also portable PV systems on the market now and they are perfect for use during outdoor trips or sailing. Most PV systems are expensive to install, but they provide long-term savings through grid-independence and tax incentives from governments who applaud this sustainable energy source.

It is also quite easy to find installers and solar providers as it’s starting to become mainstream technology around the world. Once installed, this technology provides practically free energy.

Concerning large-scale use, thermal ones have solar plants while PV ones have solar farms. The yield and efficiency of solar plants are greater than that of solar farms. The former also requires a bigger land area and only works for typically hot locations.

Regarding residential use, passive solar thermal heating can reduce the need for in-house heating. However, if active thermal heating is required, the household must evaluate if it’s better to build a PV system instead. After all, a PV system can provide more than just heating and can reduce overall energy expenses after a few years of installation. It also provides energy even during the winter as it is not reliant on the sun’s heat but on the sun’s light.

This is why PV systems are often chosen over thermal ones if the reason for acquiring one is for home use and convenience. This is especially true now that more and more governments are supporting this alternative energy source and providing tax incentives for those who go solar. Since there are numerous solar panel producers, the prices are also quite competitive now and have become more affordable even for an average earner.

Concerning installation, solar thermal systems can be complex for home use but can be of great value for businesses as they do not require very expensive systems to operate. This heat-based system is primarily used to operate gas or steam turbines.

For example, hotel businesses can utilize a solar thermal system for water heating instead of using electric-based machines. With both solar thermal and solar panel technologies, one can contribute to the preservation of these resources.


The sun is a powerful and free resource. With the light it emanates, it can supply electricity to a household or even a business. With its heat, it can provide unlimited heating. Two technologies that harness the sun’s power are solar thermal and solar PV systems.

Solar thermal systems collect the sun’s heat and use heat transfer technologies and mechanisms to supply water heating. This type of system can be low, medium, or high-temperature depending on the amount of heat it can collect.

PV systems are more widely known for residential and commercial use. This type collects light particles or photons from the sun and supplies direct current to a system. If more and more people choose either of these two methods, then we can make use of our non-renewable resources more efficiently and conservatively.

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