Life on Earth could not survive without the sun. It provides light and heat, the seasons and the day and night cycle necessary for life to have evolved. Today, we’re exploiting the energy from the sun to power our lives and experts say one day, this source of energy may be all we need. But, behind the headlines what exactly is solar power and how do we harness it?
What is solar power?
There are two main types of solar energy: photovoltaics and concentrated solar power (CSP), also known as concentrated solar thermal.
Solar energy accounts for around 1% of global electricity generation, but it is predicted to play a much greater role in the future. It is a renewable energy source, which produces no greenhouse gases or toxic waste, and it relies on light from the sun, which reaches all corners of Earth. It generates electricity using photovoltaic solar cells, typically fitted into solar panels, which convert sunlight into energy on an atomic level.
Solar panels: how do they work?
Solar cells make use of a property called the photovoltaic effect, which describes the process of a photon, or a particle of light with the right wavelength, hitting the cell and causing an electron to flow. This effect was first noticed in 1839 by Henri Becquerel, a French physicist and Nobel laureate.
Most photovoltaic cells are made of a thin film of semiconductors, which creates an electric field. In the most basic terms, when an electron is excited by the light striking the cell, it will flow from one side of the semiconductor to the other, creating a current.
One of the benefits of using solar cells is their size does not matter when it comes to efficiency. For example, a 10 square metre array of PV cells is just as efficient as a 10 square kilometre array – which is why the development of off-grid solar cells for people’s homes and businesses is taking off. This is unlike any other renewable energy. By comparison, if you built a wind turbine in your back garden it would be ten times smaller than one in a wind farm and nowhere near as efficient.
Solar power across the globe
Countries like China are leading the way when it comes to large-scale solar development. The Chinese National Energy Administration (NEA) released statistics on solar energy production earlier this year, revealing production doubled in 2016 and reached a gargantuan 77.42 gigawatts by the end of the year. China Merchants New Energy Group (CMNE), one of the country’s largest clean energy operates, also built a panda-shaped solar plant last month as part of an effort to interest kids in renewable energy.
The problem with using photovoltaics is they can only generate electricity when the sun is shining, so would not be able to power anything at night. There is currently no efficient way to store electricity on a large scale, making it the most significant challenge for renewable energy companies.
Tesla CEO Elon Musk has promised to build a 100MW lithium ion battery storage farm in Australia, which would be the biggest of its kind if completed. Musk said the system would be installed and working within 100 days of signing a contract.
Beyond solar panels
Aside from photovoltaics, there is another method of solar power generation that is often overlooked but can already be stored in some way. CSP plants use mirrors to concentrate the light from the sun. This generates heat, which warms a certain type of oil. The oil heats water which drives steam turbine engines, creating electricity. This thermal energy can be stored and used to provide electricity whenever it is needed. However, storing energy as heat is inefficient.
The challenges facing solar power
In order for solar power to become widely adopted, we will need to find a way to store the energy generated by the sun more efficiently.
A report published in 2015 by physicists at Massachusetts Institute of Technology found solar power has the potential to meet the world’s electricity needs.
“Silicon based photovoltaics have the demonstrated capacity, the reliability, and the available resources [to power the world], and also to provide electric power for a large fraction of ground and sea transport,” Robert Jaffe, MIT physicist and co-author of the report, told us.
But we’re not there yet. “The one missing ingredient at present is large-scale, robust, and cheap electrical energy storage,” Jaffe added. “And there are no obvious candidates at present.”