Solar rays that enter the earth are a direct source of solar energy. Two technologies that can collect them are solar photovoltaics (also known as solar PV) and solar thermal systems. The Sun is the ultimate light source. The fact is primarily responsible for the growth of the renewable energy industry. The majority of renewable technologies in use today harvest solar energy, either directly or indirectly. Wind, low grade geothermal (used in ground source heat pump systems), tidal, and wave are all indirect solar energy sources that are either widely used (wind) or under development (low grade geothermal) (tidal and wave).
The distinguishing factor between solar PV and solar thermal is their operational standards. Solar PV is dependent on the photovoltaic effect, which occurs when a photon (the basic unit of light) collides with unique material and causes an electron to be released. On the other hand, solar thermal heats a solvent using sunlight (depending on the particular application, it can be water or other fluid).
The photovoltaic effect occurs only in a small number of materials known as semiconductors (such as silicon -monocrystalline, polycrystalline, and amorphous- and cadmium telluride), which enable the generation of an electric current when exposed to light after undergoing complex chemical procedures. These semiconductors are formed into thin layers that make up the heart of solar cells, which are the essential component of a solar PV device and contain direct current.
Solar cells are built into larger structures called solar panels, which allow for the desired current and voltage to be achieved. The use of an inverter is needed for grid-connected systems (which account for a significant portion of the market) (to convert DC generated by cells into AC, used in the grid). Solar thermal systems have a more straightforward operating principle than photovoltaic systems, but they are almost as effective at generating usable electricity. It works by heating water (or other fluids) directly with sunlight. Depending on the temperature range at which the working fluid is heated, this energy transfers to different devices.
Flat plate panels or evacuated tubes may be used as low and medium-temperature collectors. Concentrated solar systems, such as PV panels, Fresnel reflectors, dish Stirling, and solar towers, are examples of high-temperature collectors.
The first step is to distinguish small, residential solar systems from power plants, PV, and thermal in their usage. The following sections go into how they are used in the home.
In terms of power plants, all PV and thermal systems have the same goal of producing electricity. If PV systems produce electricity directly from sunlight, thermal systems heat a fluid (water, oil, salts, air, etc.) to power a steam engine, gas turbine, or other similar devices. The electricity is fed into the grid in AC form and at the appropriate voltage.
The largest photovoltaic power plants have capacities of over 500 MW, while the largest thermal power plants have less than 400 MW capacities. In many parts of the world, both types are expanding rapidly, with many under construction and more planned.
Solar energy is directly converted into DC power in residential PV installations. Grid-connected and “off-grid” or “stand-alone” residential PV systems are the two types accessible. The first provides the option of using an inverter to feed the grid (which is encouraged by financial incentives). The latter is solely for self-consumption (lighting, ventilation, water heating, and so on) and involves battery banks to distinguish consumption from generation.
Water heating is the primary use of residential solar thermal systems. They are typically used in conjunction with central heating systems (gas or oil) that kick when the water tank’s temperature drops below a predetermined level. As a result, even in cold climates, these devices will supply hot water all year. Should you use up all of the water, thermodynamic systems will heat it with the built-in compressor; this way, you can have a fossil-free system. You can also use solar thermal systems to heat the building’s interior (this is relatively common in Sweden).
Most significant advantages of solar PV:
- PV design is much simpler than thermal design when it comes to power plants. Many solar panels are connected in parallel and in series to create a PV power station. On the other hand, solar thermal electricity generation entails transferring energy from a hot fluid to a generator. As a result, various and complex designs have emerged, some of which have already been listed.
- Domestic PV systems are more robust than thermal systems on a smaller scale since they can fuel various appliances (solar thermal is limited to space and water heating). They have a longer lifetime as well.
Most notable advantages of solar thermal:
- Since thermal power plants do not transform solar energy directly into electricity, and domestic thermal systems often have a water tank where heat can be deposited, it can store the energy produced. PV systems, on the other hand, have built-in intermittency due to sunlight patterns. Electricity storage is typically not considered a viable solution due to energy losses that render it ineffective. As a result, thermal power plants can provide a more consistent and stable source of electricity.
- Solar thermal technology is much less complicated than solar PV for domestic use. It is worth noting that electricity generation for residential purposes ranges from thermal to photovoltaic (PV) systems. Thermal energy is used to produce heat, while PV energy is used to generate electricity. Thermal panels often take up less room.