25 Apr How Do Different Solar Technologies Work?
We’ve all heard about the benefits of solar technology, namely, lower energy prices and a greener planet. People used to dismiss the idea because of exorbitant installation costs, but these days, the initial investment is much more affordable. Solar electric systems have gotten about 50 percent cheaper and the price of solar PV panels has dropped more than 60 percent since 2010.1
Not only is solar energy attainable, but there are also many options to choose from, like photovoltaic (PV) systems, concentrating solar power (CSP) systems and solar water heaters. Each has its own distinct applications and benefits to consider.
Photovoltaic Systems
PV systems are what most people think of when they hear the term “solar energy.” These systems can be used residentially or commercially and are comprised of:
- Solar arrays – Collections of solar panels that house individual PV cells, which are no more than a few inches wide
- Mounting systems – Attach solar panels to the roof and prop them up at the perfect angle to catch the sun’s rays
- Inverters – Transform the electricity created by the panels into alternating current (AC) electricity that our homes can use
- Batteries – Allow us to use stored solar energy when it’s cloudy or dark out
At the most basic level, a PV system converts light energy directly into electricity. Sunlight is absorbed by the two-layer PV cells, which contain semiconductors made of silicon, cadmium telluride (CdTe), copper indium gallium diselenide (CIGS) or organic materials. As sunlight hits the semiconductor material, its photons strip the semiconductors’ electrons. These electrons then create an electric current due to the difference between the positive and negative layers of the PV cell, and the current is converted by the inverter for use on the power grid.
Concentrating Solar Power
CSP systems require an intermediate step. They harness thermal energy from sunlight first, and then use that heat to generate electricity.
There are four different types of CSP systems, and they are primarily used by plants or utility companies to produce large amounts of power.
- Linear concentrator system – The trough system, which is the most popular type of linear concentrator system, consists of a giant curved mirror and a receiver tube filled with heat-transfer fluid. Throughout the day, the trough reflects sunlight toward the tube, heating the fluid inside. This fluid is then transported to a water tank, where it turns the water into steam to power a generator, making electricity. No battery is needed, as the heated fluid can be stored in a tank for later use.
Another type of linear concentrator system is the Fresnel reflector system, where reflective panels lie flat on the ground and reflect sunlight upward toward the receiver tube.
- Power tower – Power towers work similarly to linear concentration systems but take a different form. An array of smaller mirrors, called heliostats, surround the tower and reflect sunlight up toward the receiver that sits on top. From there, the process is the same. Heated fluid transforms water into steam, powering a generator. Condensed steam and heat-transfer fluid are recycled so the system can run continuously.
- Dish/engine – These solar power systems look like giant satellite TV dishes. The mirrored dish, or “solar concentrator,” moves to track sunlight and reflects it onto a power conversion unit consisting of a thermal receiver and an engine. Sunlight heats the thermal receiver, and the engine then uses that energy to power a generator, making electricity.
Solar Water Heating
Solar water heaters are an energy-efficient way to warm water for home appliances and swimming pools. On occasion, they are also used for space heating.
There is significant design variation between heaters, including how they operate. Which type of solar water heater you choose will depend on the climate you live in and the level of energy efficiency you hope to achieve.
No matter which system you choose, the sunlight is first absorbed by a collector containing tubes with fluid inside. There are two main types:
- Flat plate collector – A rectangular panel with a black plate to absorb heat and a glass cover to allow sunlight in and trap heat inside. A layer of insulation prevents heat loss.
- Evacuated tube collector – A tube with two glass layers and a vacuum layer in between. The system works like a thermos. Sunlight penetrates the first glass layer and is absorbed by a dark coating.
Solar water heaters also differ in the way they heat and circulate water:
- Direct vs. indirect – Direct systems use sunlight to heat water directly. Hot water is then circulated throughout the house. Indirect systems use sunlight to heat a heat-transfer fluid, which travels to a heat exchanger to indirectly heat your home’s water. The water never goes to the solar collector.
- Active vs. passive – Active systems require pumps to draw and push water and heat-transfer fluid throughout the system. Passive systems work through natural physical processes like convection and gravity.
All systems operate on the same basic principle – sunlight is captured for its thermal energy, and this warms the water in your house.
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1 https://www.energy.gov/eere/solarpoweringamerica/solar-energy-united-states