What is Solar Thermal Technology?

PrintEmailSave

Main Image: 

We are fortunate enough to live in nations where we do not suffer much from lack of electricity. We take it for granted when fans above our heads rotate, or lights come on with a touch of a switch. We do not consider at what expense we are getting electricity to operate our appliances. Most of our energy is generated by burning fossil fuels like oil, coal and natural gas. They are dwindling sources of energy and have contributed to pollution. The rest of the energy is produced from renewable energy sources.

We are fortunate enough to live in nations where we do not suffer much from lack of electricity. We take it for granted when fans above our heads rotate, or lights come on with a touch of a switch. We do not consider at what expense we are getting electricity to operate our appliances. Most of our energy is generated by burning fossil fuels like oil, coal and natural gas. They are dwindling sources of energy and have contributed to pollution. The rest of the energy is produced from renewable energy sources.

We are fortunate enough to live in nations where we do not suffer much from lack of electricity. We take it for granted when fans above our heads rotate, or lights come on with a touch of a switch. We do not consider at what expense we are getting electricity to operate our appliances. Most of our energy is generated by burning fossil fuels like oil, coal and natural gas. They are dwindling sources of energy and have contributed to pollution. The rest of the energy is produced from renewable energy sources. One of the clean renewable sources of energy is solar energy. In solar thermal energy the heat of the sun is used to heat water. The heated water turns into steam and is used to rotate the turbine to generate electricity from the generator coupled to it. Solar energy is being used as solar photovoltaic energy where photovolaics or solar thermal energy.

What is the background of Solar Thermal Technology?

United Stated had built nine solar thermal power plants in California’s Mojave Desert between 1984 and 1991. Even today, the plants produce about 354 megawatts every year. It powers 500,000 homes in California. In the year 2008 these thermal plants stabilized the condition in California during peak demand load periods. The conventional power grid buckled while this plant ran at 110 % capacity. But after the year 1991, prices of natural gas dropped suddenly and as a result the power industry shifted its focus from solar thermal technology to natural gas. But today the U.S. National Renewable Energy Laboratories estimates, that this technology if harnessed properly, can produce more than hundred Giga watts of electricity. This is more than 10% of the demand in United States.

What are the differences between Solar Thermal Technology and Solar Photovoltaic Technology?

To begin with, let us understand that Solar thermal technology has nothing to do with the solar panels that you see on the rooftops of many homes. In the solar photovoltaic system, electricity is generated directly from the sun’s rays or the photons which is a DC current and is converted to AC current that can be used to run any appliance in a household or business but in solar thermal, the rays of sun are converted using mirrors that are directed to recieve maximum sunlight which is transferred into heat, which is used to generate steam and eventually run the turbines, to produce electricity. But definitely in both the processes, carbon based and sulfur based pollutants are not released into the atmosphere. They are both environment friendly technologies.

How does the Solar Thermal Technology work?

Since the sun is an abundant source of energy, atleast until the next 5- 7 billion years, we can definitely say that solar thermal technology is a reliable source of energy. Thermal energy storage (TES) systems are very effective except for days when there is a cloud cover. Solar thermal systems are used along with high pressure liquid storage tanks in the plants. Off peak storage is very important because that determines how effective a solar thermal power plant is. Three technologies of TES have been tested so far since the 1980s. The three technologies that were tried are two-tank direct system, two-tank indirect system and a single tank thermocline system. We shall take a look at all these systems one by one.

• Two Tank Direct System: The fluid used to collect the solar thermal heat is used for the storage of the thermal energy as well. The fluid is kept in two tanks divided equally. In one tank the temperature of the fluid is higher than the fluid in the other tank. The fluid stored at lower temperature is made to run through the solar collector of the power plant. In these collectors they are reheated and then sent to the tank where the fluid is stored at a higher temperature. The fluid stored at higher temperature is used to produce steam by making it pass through the heat exchanger. This steam is then used to generate electricity from the generator coupled to the turbine. After passing the liquid through the heat exchanger, it is again returned to the tank where it was maintained at a lower temperature.
• Two Tank Indirect System: In a two tank indirect system more than one type of heat transfer fluids are employed for heat transferring. It has a similar work principle as the direct system. This technology uses most expensive fluids. In order to overcome the problem of costs, the low temperature fluid is passed through an extra heat exchanger.
• Single Tank Thermocline System: In this system, no fluids are used for the storage of solar thermal energy. Instead a solid is used for the purpose of storing the heat. The solid employed is usually silica sand. The solid is maintained at both low as well as high temperature inside the single tank. This creates a temperature gradient. A heated fluid which is used for the heat transfer is allowed to travel over the top of the tank. When this liquid travels downward it loses heat and cools. It exits as low temperature liquid. This is the process used for storage. Now when steam generation is required, this process is reversed. It collects the heat from the silica sand instead of transferring heat to the sand. Solar thermal systems that make use of molten salts or minerals as the medium of heat transfer are considered to be very important for TES. Alternative fluids are being tried for heat storage which employs phase change materials. The concept of novel thermal storage is also being tried to reduce storage costs and improve the efficiency of the systems.

What are the Applications of Solar Thermal Technology?

Solar thermal power plants are not the only application of solar thermal technology. Apart from electricity generation the concept of solar thermal technology can be used for the generation of heat for solar water heaters, solar thermal chimneys or solar green houses. Solar thermal green houses can be made by using the right kind of materials for the construction of the home. If the roof of the home which is located in the northern hemisphere is tilted towards the south then it proves to be more effective in harnessing sunlight and vice versa for southern hemisphere homes. Heat sinks in the home can be created with water, water filled barrels, stone and cement. Pipes are made which are connected to the ground floor of the house. Air from the rooftop is collected in during the day, which goes down to the floor through the pipes to heat the floor. At night cool air is again brought down which gets heated by the warm floor and this is how it acts like a greenhouse. Solar thermal chimney is used to cool the house during summers. It makes use of convection for the transfer of heat. In this concept the hot air expands and rises up and it gets expelled from the top of the house while cool air comes down to take its place. Black and hollow thermal mass is employed for the making of the chimney. Solar thermal water heaters are exceptionally good. They are passive solar thermal technologies while electricity production is an example of active solar thermal technology. In a solar thermal water heater, thermosiphonic principle of water heating is used. To a large central tank collecting tubes are attached. These are placed at an angle to capture the heat from the sun. As soon as the water heats up, it rises up to the tank while cold water comes down to the tubes and gets heated. In this way a current is set up where the water keeps heating. This system is extremely efficient and much better than electric geysers. Utility bills can be cut drastically and break even can be reached within 2 or 3 years of use. The return on investment is calculated at around 12% to 30% depending upon the type of water heater used.

What are the advantages of Solar Thermal Energy?

Solar thermal energy is a clean source of power unlike the conventional fossil fuels. We can rely on the sun as a source of energy. Solar thermal can prove to be more efficient than the solar photovoltaic technology. It occupies less space to produce the same amount of heat at a far cheaper rate than PV systems. Solar thermal technology can be competitive when the oil price per barrel is $70 and it becomes even more economical when the price per barrel rises to $130. 30%. Federal tax credit is offered as incentive to those going the solar way in U.S.A. So this means that you can claim 30% of your investment if you wish to install a solar water heating system at your place. According to a report prepared by Ferrostaal, solar thermal power plants require significantly less space than traditional technologies to generate the same amount of electricity. Any kind of barren land will serve the purpose of a power plant construction site. 

What are the disadvantages of Solar Thermal Technology?

Solar thermal technology depends on the energy of the sun. Places characterized by higher rainfall are not ideal for harnessing solar thermal technology. The output comes down significantly on days when the sky is partly cloudy. Solar thermal energy undergoes double conversion to produce heat from the sun. It converts heat energy to mechanical energy and then into electrical energy. Ideally, energy losses involved in solar thermal should be more than that in solar photovoltaic. Apart from that, solar thermal technology cannot be implemented on a small scale for generation of power. Solar thermal technology is not ideal for small rural electrification projects or single households. Moreover, it is difficult to set up a solar thermal power plant. The initial investment costs are very high. As a result, investors often hesitate to invest on new and untried technologies.

Related Videos: 

Related Images: