‘Solar energy is the “clean” source of power [meaning no carbon dioxide is belched into the atmosphere to create the energy] based on harnessing the sun for generating electricity. Light is converted into power via a photovoltaic cell, or solar cell. The effect was discovered by physicist Edmund Becquerel in 1839 but built on by scientists at Bell Laboratories in the 1950s who produced 4% efficiency. Modern laboratories can produce 25% efficiency, (‘Clean energy rush’, by Terry Macalister, The Guardian, Wednesday June 13, 2001).
Potential: ‘Every 75 minutes enough sunlight reaches the earth to power all the world’s electricity, vehicles, boilers, furnaces and cooking stoves for a year. Yet solar power produces under 1% of the world’s commercial energy,’ (The Economist 16 April 2016).
Two types of solar energy: Solar energy ‘comes in two forms. The more widespread form of solar energy [is] electricity produced by photovoltaic (PV) cells. The smaller (accounting for around a tenth of existing solar capacity) is thermal storage, in which sunlight is concentrated as heat, for example in molten salt. That can be used to produce steam for power turbines, (‘Renewables–We make our own?’ The Economist Special Report–Energy & Technology January 17th 2015, p6-8).
How it works: ‘Two layers of ultra-pure (99.9999%) silicon, each doped with an additive to make it semiconducting, absorb light and use the energy from this to move electrons across the junction them, thus generating an electric current,’ (‘Solar’s new power’, The Economist 23 May 2020, p.68-9).
‘Solar cells work by the action of light on electrons. An electron held in a chemical bond in the cell absorbs a photon (a particle of light) and, thus energised, breaks free. Such electrons can move about and, if they all move in the same direction, create an electric current. But they will not all travel in the same direction without a little persuasion. With silicon, this is achieved using a secondary electric field across the cell. Non-silicon cells usually have a built-in “electrochemical potential” that encourages the electrons to move away from areas where the are concentrated and towards places where they have more breathing space. Most commercial solar cells are made from silicon, and silicon is expensive. Cells can be made from other, cheaper materials, but these are not as efficient as those made from silicon,’ (‘Solar power, Thou orb aloft full-dazzling,’ (The Economist October 15th 2011 p16).
Investment: In 2015, for the first time, the world invested more in photovoltaic cells than in coal- and gas-fired power generation combined (The Economist 02 April 2016).
Home solar makes sense: Putting a solar panels on the roof of one’s house means ‘electricity is generated where it is consumed, easing the strain on transmission lines and power plants. The average price of a residential solar-power system is less than half its level in 2010,’ (‘Solar eclipsed’, The Economist December 22nd 2018 p87).
Efficiencies: ‘Standard solar panels using silicon-based solar cells typically convert 17-19% of the sun’s energy into electricity. More exotic solar cells that make panels 40% efficient can cost around $300 a watt compared to just under $1 for some silicon versions. Hence the better panels are used in specialist roles, such as powering spacecraft. Now, a middle way seems to have been found. Insolight, a startup from the Swiss Institute of Technology in Lausanne, has developed a panel that uses expensive high-efficiency solar cells, but does so in such a fashion that should make its panels competitive with the standard silicon variety. The new panel has been confirmed in independent tests to be 29% efficient. Insolight employs so-called multi-junction solar cells, which are similar to those on spacecraft. These capture energy from a much broader spectrum of sunlight by using a stack of different materials, such as gallium arsenide and gallium indium phosphide. Fabricating such cells is complex and costly. Insolight, though, is extremely parsimonious in their use. Instead of spreading them across an entire panel, they are spaced well apart in a grid that covers just 0.5% of the surface. The panel is then covered with a protective glass layer that contains optical lenses above each cell. This way sunlight falling on the panel is concentrated onto the cells below. To ensure maximum exposure, a mechanism moves the position of the panel by a few millimetres horizontally, enough to follow the trajectory of the sun. Such panels would still cost a bit more than standard silicon ones, but as Laurent Coulot, Insolight’s chief executive, points out, what matters is the final cost of the electricity they produce. He reckons that in mass production his panels will work out cheaper, going well below silicon’s $1 a watt to 30-40 cents a watt. Moreover, a hybrid panel could be made using the Insolight system and silicon cells covering the remaining 99.5% of the panel’s surface. Such a panel would help harvest diffuse light in places where conditions are often cloudy,’ (‘Gathering the rays,’ The Economist 30 March 2019).