Energy Sciences

Solar

Solar energy is energy that comes from the sun. It is free, renewable, virtually limitless and has a low environmental impact. The sun delivers enough energy to the Earth in one hour to provide all the energy consumed by the entire human population in one year.³² Solar energy does not produce air pollutants or carbon dioxide. However, solar energy does have limitations and inherent challenges. The amount of sunlight on Earth is not consistent, being dependent on location, time, season and weather conditions. The key to harnessing solar energy lies in capturing, storing and then distributing all of that energy. There are several types of solar energy, including solar thermal, solar photovoltaics and solar biomass.

Solar thermal utilizes the energy from the sun for heating or electricity production. Typically, there is an active system that utilizes “fans or pumps to circulate heat-carrying fluids.”³³ Examples include swimming pool heating systems, which are often roof-mounted and circulate the pool water through the panels to heat them. There can also be passive systems which have no mechanical parts. Examples include heating or cooling systems that capture or reflect solar energy like a greenhouse or a solar oven. There are also high-temperature solar thermal systems that use mirrors to concentrate solar power (CSP) that are able to reach the temperatures necessary to create “steam which turns turbines, driving a generator to produce electricity.”³⁴ Solar thermal power is low maintenance and emission free, but is susceptible to problems of intermittent sunshine and less-than-ideal location.

Solar photovoltaic (PV or solar cells) energy uses technology to convert sunlight into electric currents using semiconductors. When a photon from the sun hits the semiconductors (PV cells), usually made of silicon, electrons are freed. The layers of silicon in the PV cells are specially treated or doped with phosphorus, creating a positive charge, and with boron to create a negative charge. This doping allows the freed electrons to flow in one direction through the solar cell and generate an electric current. Metal plates on the sides of the PV cells collect the electrons and transfer them into wires where they can flow as electricity to power devices. An advantage to PV cells is that the electricity produced is scalable depending on how many cells are used. The semiconductor system can be set up to operate within the existing electrical grid or work independently.³⁵

One problem inherent in solar power is the risk of storing large amounts of energy during peak solar production. In California, there has been a periodic overabundance of solar power. In order to avoid damaging its energy system from overload, the state has had to pay other states to take its excess power, shut off portions of its solar power collection or even pay its customers who generate solar energy to stop temporarily. “California has so much surplus electricity [from solar] that existing power plants run, on average, at slightly less than one-third of capacity. And some plants are being shuttered earlier than planned.”³⁶ Recent technological advances in lithium ion battery storage methods have the potential to minimize or eliminate the problems inherent in solar energy peak generation or in a lack of generation at night or during cloudy days. Officials in Los Angeles, where these issues are most prevalent, have recently brokered an unprecedented deal to address the problem of solar storage with one of the world’s largest battery manufacturers. Implementation will begin by hitting an expected overall solar energy source target of 7% of all electricity for the entire city by 2023.³⁷

Solar biomass contains energy stored from the sun. It is organic material that comes from either plants or animals and it is a renewable source of energy. When biomass is burned, the chemical energy in biomass is released as heat. A common use of biomass is wood burning for heat. Agricultural crops, food and other biowaste can be burned as biofuels also. Ethanol is an example of a biofuel from crops of corn or sugar.