From selenium to space based power stations: the history of solar power

Photo by Nuno Marques on Unsplash

The birth of the solar cell

In 1952, Bell Labs — the research branch of the Bell Telephone Company in New Jersey — asked engineer Daryl Chapin to solve a problem.

The company wanted to extend its network of telephones in remote tropical regions. However, the standard batteries used at the time were unsuitable, as they degraded too quickly in the hot humid conditions. Chapin was asked to look into other power sources, and immediately thought solar power might be the answer.

Humans have been using the sun for power for thousands of years. Greeks and Romans used mirrors reflecting the sun used as torches, and in 1767 a scientist called Horace de Saussure constructed a glass box which functioned as the world’s first solar oven. French scientist Edmond Becquerel discovered the photovoltaic effect in 1839, and French mathematician August Mouchet designed a solar powered steam engine in the 1860s.

Solar cells which could convert sunlight into electrical current were themselves invented in the late 1800s. However, the earliest were too inefficient to be of much use.

The solar cells on the market in the early 50s were made from selenium. But these produced just five watts per square metre — converting less than 0.5% of the incoming sunlight into electricity, and not strong enough to power everyday items.

So Chapin asked Calvin Fuller and Gerald Pearson, who at the time were developing transistors made from silicon, for their help. Pearson and Fuller were experimenting with introducing different impurities into the silicon to boost its conductivity.

As an experiment, the pair used gallium to give the silicon a positive charge and then dipped it into hot lithium to create a negative charge. They attached an ammeter — a device for measuring current — and switched on a desk light. The ammeter recorded the highest current flow yet seen in a solar cell, and Pearson immediately told Chapin to focus on silicon for his solar cells.

The trio worked on their technology until they had a reliable cell that could convert 6% of solar energy into electricity. Chapin believed that up to 23% should be possible, but it took more than a year to reach the 6% target.

The cell was demonstrated to journalists for the first time on April 25, 1954. Page one of the following day’s New York Times called it “the beginning of a new era, leading eventually to the realization of one of mankind’s most cherished dreams — the harnessing of the almost limitless energy of the sun for the uses of civilization.”

Adam Gasson/UKRI

Modern solar cells

Today’s solar cells are much more efficient, exceeding even Chapin’s predictions. In 2020, Oxford PV — a spin out company from the University of Oxford — set a world record with a cell that can convert 29.52% of solar energy into electricity.

The solar cells made by Oxford PV are coated with a thin film of a material called perovskite to boost conductivity. Thirty-five kilograms of perovskite generates the same amount of power as seven tons of silicon,

The company has teamed up with scientists at the University of Oxford to produce a solar cell with 37% efficiency within five years. The first products, designed for residential roofs, will generate 20% more power from the same number of cells than current solar cells on the market.

Solar panels in space?

One of the challenges in achieving Net Zero by 2050 is how we meet our energy demands with renewable energy sources that can be intermittent. Could giant solar power stations orbiting the earth be the answer?

Space-based solar power (SBSP) has one significant advantage over terrestrial solar panels — a station could orbit the Earth so as to always face the Sun. Energy could be ‘beamed’ back from space to any part of the globe, and the solar panels would get more of the Sun’s light than those inside the Earth’s atmosphere.

It sounds like science fiction — a solar power station is even the setting for one of Isaac Asimov’s Robot short stories — but in September 2021 the UK government announced the results of an independent feasibility study into which concluded SBSP is technically feasible and affordable, along with its intention to fund an innovation programme looking at the technology we would need to create such a power station.

Researchers at the University of Liverpool are already using 3D printing techniques to print ultra-light solar cells onto solar sails used to propel spacecraft. A ‘swarm’ of such sails could be assembled into a space solar power station — potentially providing energy for generations to come.

Want to know more?

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