A photovoltaic cell is a simple thing: a square piece of silicon 160-185 millimeters on a side and 0.2 millimeters thick, with thin wires on the front and an electrical contact on the back. If illuminated with light and a circuit connected between the front and back, direct sunlight can provide about seven watts of electrical power. About 70 billion solar cells will be manufactured worldwide this year, most of them in China, and installed in panels that incorporate 60-72 cells each. These panels will supply power to single-family homes, local energy communities, industrial facilities, and large power grids; we see them installed on rooftops, in deserts, and in almost every other setting imaginable. Once installed, they will remain there for decades, making no noise, emitting no smoke, using no resources, costing almost nothing, and expending no energy while producing it. It’s a revolution that doesn’t bother you and that you barely notice, but it is still a revolution.
- It grows and grows and grows…
By 2023, the world’s solar cells, whose panels currently cover less than 10,000 square kilometers, will produce about 1,600 TWh of energy (1 TW = 1012 W). This represents approximately 6% of the electricity generated in the world and just over 1% of the primary energy consumed on the planet, a figure that is still very modest.
What makes solar energy revolutionary is the pace of growth that has brought it to this situation. Michael Liebreich, an analyst of the technology and economics of clean energy, explains it like this: in 2004, it took the world a whole year to install 1 GW of solar power (1 GW = 109 W); in 2010, a month; in 2016, a week. In 2023, there was only one day when one GW was installed worldwide. Throughout 2024, between 520 and 655 GW of capacity are expected to be installed: that is, two 2004 years every day.
Photovoltaic power installed and accumulated on the planet, for the period 2010-2023
And the prospects for evolution in the coming decades are spectacular. The Economist magazine recently showed this in a graph, which shows that, in a “rapid transition scenario”, solar energy will be the main source of energy in the world in 2040.
In the rapid transition scenario, solar energy will be the dominant source of energy in 2040
- Reasons behind explosive growth
This extraordinary growth is due to the interaction of three simple factors. When industries make more of a product, they make it cheaper. When things are cheaper, their demand increases. When demand grows, more is made – and back again. This is the “virtuous circle” of any technology. In the case of solar, demand was initially created and maintained by government subsidies early this century long enough for the price drop to be noticeable and, soon after, predictable. The positive feedback loop that drives exponential growth is happening on a global scale. And it shows no signs of stopping, or even slowing down.
Investment in installing solar panels is currently the largest source of investment in electricity generation, with the International Energy Agency (IEA) forecasting $500 billion this year, not far behind the amount invested in oil and gas. Installed capacity doubles every three years. Solar power is on track to generate more electricity than all the world’s nuclear power plants by 2026, all wind turbines by 2027, all dams by 2028, all gas-fired power plants by 2030, and all coal-fired power plants by 2032. Under a scenario that sees net-zero carbon dioxide emissions by mid-century, solar power will become humanity’s largest primary energy source (and not just electricity) by the 2040s. In a paper published in 2022, scientists from academic institutions in Britain, the US, and Australia showed that, under their “rapid transition” scenario, the world could get more energy from solar cells by 2070 than from all energy sources combined last year (2023).
Obviously, at some point, demand or supply faces an unavoidable constraint; a graph that was rising exponentially begins to take the shape of an elongated S. There may be several reasons: bankruptcy of manufacturers, inability of solar farms to connect to grids, lack of stability of solar-powered grids, etc. The growth of the railway during the last century in Europe is a good example of this.
Growth and spread of the railway in Europe during the 19th and 20th centuries
- An unstoppable path
Over the past 20 years of solar energy growth, year-on-year installations have repeatedly exceeded forecasts. In 2009, when total installed solar capacity worldwide was 2.3 GW, energy experts at the IEA predicted that within 20 years to 2030 it would rise to 244 GW. That milestone was reached in 2016, only six of the 20 years had passed. For most of the 2010s, actual solar installations exceeded the IEA’s five-year forecasts by 235% (see figure below). The closest to reality has been environmentalists at Greenpeace, who also in 2009 predicted 921 GW of cumulative solar capacity by 2030. But even that was an underestimate. Global solar capacity reached 1,419 GW last year.
Forecasts and reality of solar growth year on year. The yellow lines show forecasts for annual installations and the black line shows installations completed each year. Now that solar is a significant part of the global energy mix, the world as a whole is going to continue to see the energy used in many applications become increasingly cheaper. Innovation aimed at making the most of this bonanza will change the way many existing industries work and create new ones more or less from scratch. It will be the biggest drop in the price of one of the basic factors of production that the global economy has ever seen.
Ignacio Mártil Professor of Electronics at the Complutense University of Madrid and member of the Royal Spanish Society of Physics
