Solar energy is a renewable source of electricity that uses sunlight’s energy to generate heat and light. It can be used to power many types of equipment, from small appliances to electric vehicles.
There are two main types: photovoltaic (PV), and solar thermal. Both systems use semiconductor materials that absorb sunlight and convert it to electrical energy.
Photovoltaic (PV)
A solar photovoltaic (PV) system is a power plant that converts the energy of sunlight directly into electricity. This power can then be used for household and/or utility-scale electricity production.
PV cells are semiconductor materials that absorb light and transfer it to an electrical current. This is the “photoelectric effects.” When photons of light strike a semiconductor material, electrons are detachable from their host atoms and are freed to act just like the electrons in a conducting material.
There are two main types: monocrystalline silicon or amorphous silicon. Both have different conversion efficiencies. This is dependent on the purity of the cells, but monocrystalline cells are generally more effective than amorphous.
Depending on the size and capacity of the cell, it can produce a few kilowatts up to hundreds of megawatts per year. Small photovoltaic cells are low-voltage and are used in household appliances like lights, calculators, and watches. Larger cells are used to produce utility-scale electricity.
A PV module’s cells can be connected in parallel or series to produce any voltage and current combination. These modules are often mounted in a supporting structure or frame and grouped into arrays to produce larger amounts of electricity.
The modules should face the sun at a 90 degree angle for optimal performance. Tracking systems can help you move the modules so that they face the sun continuously. Software can also be used to calculate the angle for a given place.
As a result, the overall efficiency of the system will vary with temperature and other variables. The conversion efficiency of crystalline silicon PV cells will decrease the higher the operating temperature.
Therefore, a well-designed and installed PV system should provide adequate ventilation behind the modules to dissipate heat. This will reduce the need for additional cooling and can increase the resulting efficiencies.
Grid-connected PV systems often have backup storage systems or batteries to meet peak load requirements at night or in cloudy weather. The solar panels can be charged with battery energy, which can then be used to power lights and other household appliances in the event of an outage or a failure of the grid.
This is especially important for rural and remote areas where diesel generators are expensive and electricity tariffs can be very low. Even in countries with low solar PV potential, such as Germany and Denmark, PV can offer a competitive alternative for grid-connected electricity.
The technology is currently developing rapidly. The world’s total capacity is expected to reach 515 gigawatts in 2018. This is 2% of the global electricity demand. As more countries and regions adopt the technology, it is expected that the total number of installations will continue to grow.
Concentrating Solar Power (CSP)
CSP, or concentrated solar power, is a form of renewable energy that uses a concentrated source of sunlight to generate electricity. It can be used in conjunction with photovoltaic and can reduce the need to store expensive electric energy in the grid.
It can also be used to replace fossil fuels for industrial heat applications like steel-making or cement. Although CSP is still more expensive that PV, the Department of Energy has set a goal of making CSP comparable to fossil fuels by 2030.
Parabolic troughs or power tower systems are the most common type CSP. These systems use mirrors to concentrate direct normal irradiance from the sun on a receiver, which is then used to generate electricity. Utility companies use power tower systems because they have a large footprint and can easily scale up to large capacities.
Some use steam to produce electricity while others use molten metals. They all have different efficiencies but can’t store the same amount of thermal energy as PV.
According to NREL the efficiency of a CSP system depends on a variety of factors, including the type of engine and receiver as well as the operating temperature and thermal losses. The most efficient CSP systems typically have a conversion efficiency of between 7 and 25%.
Technology advances will likely increase this cost. The DOE is currently working on reducing the cost for power tower and trough technologies.
CSP faces the most difficult challenges in financing, environmental concerns and land requirements. These issues can be particularly difficult in dry regions. Construction and operations can also have an impact on local flora or fauna.
Despite these challenges, many countries are making strides in the development of CSP. The United States has constructed the Ivanpah Solar Power Facility. Spain is home of the first commercial CSP plant in the world, PS10. This plant has a capacity to produce 392 MW. The country plans to double its capacity to 4.8 GW as part of its 10-year energy plan.
The Ouarzazate solar power plant in Morocco is one of the most powerful CSP plants with a capacity to generate 510 MW. The plant was completed in 2016 and is expected be used to power approximately 1.1million people.
It is also more sustainable than fossil fuels because it doesn’t emit carbon dioxide and can be used indefinitely. It can also improve air quality, and reduce greenhouse gas emissions.
CSP is more expensive than other renewable energy options. This is the main drawback. This is why CSP is often paired up with other forms electricity production to provide reliable and inexpensive power. It also has a lot to do with the environment, such as the need for large amounts if water to cool the system.
Solar Thermal Energy (STE)
One of the main forms of solar energy is solar thermal energy. Photovoltaic is another type that uses solar cells in order to convert sunlight into electricity. Solar thermal is the most popular form of solar power.
STE technology harnesses solar heat to produce thermal energy. It can be used for commercial and residential use as well as for crop drying, space heating, and solar cooking. Unlike photovoltaic technologies, which rely on the crystalline structure of silicon to convert light into electric current, STE uses lenses or reflectors to concentrate sunlight and heat fluids to high temperatures before they are converted to steam that drives a turbine, generating electricity.
There are many ways to capture and concentrate sunlight energy. The most popular is using parabolic or concentrating mirrors. Parabolic trough systems use curved mirrors to focus the sun’s energy onto a receiver tube that runs along the focal line of the trough. This system uses a high temperature heat transfer fluid such as antifreeze, synthetic oil, to absorb the sun’s heat. The heated liquid is then cycled through a heat exchanger to heat water and produce steam, which is then turned into pressured steam that pushes a turbine to generate electricity.
The molten salt plant is another type of solar power plants. This technology combines concentrated thermal thermal with a heat storage device to allow it to provide baseload as well as peak power generation. The molten salt is heated to nearly 300 degC before being piped through water and then through pipes that turn the water into steam. It can store energy even after it sets, which allows it to continue producing electricity during nighttime and overcast conditions.
This type of plant can only be used in areas that have adequate insolation (i.e. where the sun shines continuously) to produce large quantities of electricity at high efficiency. This plant is an excellent choice for areas where there are not enough hydroelectric power sources or where existing coal- and natural-gas-fired power plants exist.
Many STE systems combine a traditional fossil fuel-fired, steam turbine generator with an auxiliary system for solar heat collection and storage. Installing the thermal storage and solar collectors on a roof can accomplish this. The storage system will provide hot water for the building during the day, and can also be used to heat an energy storage tank that will then be used to generate electricity in the evening or during cloudy weather.
Other solar thermal power systems are based on towers that rely on solar heat to generate electricity without the need for water. The Commonwealth Scientific and Industrial Research Organisation of Australia (CSIRO), has created a solar power tower that uses 450 heliostats. It focuses the sun’s rays onto a 30-meter tall platform (98 ft high). This expands to heat compressed oxygen, which is then converted into steam to drive a 200-kW turbine that generates electricity.