Renewable energy

• 1. Introduction

  ›

  Renewable energy is energy made from natural resources that replenish on a human timescale. Between 2011 and 2021, it climbed from 20% of the global electricity supply to 28%. Solar and wind drove most of that, jumping from a combined 2% to 10%. Fossil energy slipped from 68% to 62% in the same span. By 2024, renewables supplied over 30% of the world's electricity. Werner Siemens saw this coming in 1885. Commenting on the photovoltaic effect, he wrote that the supply of solar energy is "both without limit and without cost, and that it will continue to pour down upon us for countless ages after all the coal deposits of the earth have been exhausted and forgotten." How did a source he could only describe in the future tense become the majority of new power capacity worldwide? What does it take to run a grid on sunlight and wind that come and go? And why does a clean technology depend so heavily on digging metals out of the ground?

• 2. Sun And Wind

  ›

  Solar power produced around 1.3 terawatt-hours worldwide in 2022, representing 4.6% of the world's electricity, with almost all of that growth happening since 2010. There are two mainstream ways to harness the sun. Solar thermal converts sunlight into heat using mirrors or lenses that concentrate light onto a receiver, which heats a water reservoir. Photovoltaics, or PV, convert light directly into electrical direct current via the photoelectric effect. PV is far more widespread, accounting for around two thirds of global solar capacity as of 2022. The first utility-scale solar power plant was built in 1982 in Hesperia, California by ARCO. The plant was not profitable and was sold eight years later. Over the following decades PV cells became far more efficient and cheaper. Global capacity rose from 230 GW at the end of 2015 to 890 GW in 2021. China added 560 GW between 2016 and 2021, more than all advanced economies combined. By 2025, four of the ten biggest solar power stations were in China, including the biggest, Talatan Solar Park. Wind tells an older story. Humans have harnessed it since at least 3500 BC, primarily to power ships, windmills and water pumps until the 20th century. Modern utility-scale wind turbines range from around 600 kW to 9 MW of rated power. The power available from the wind is a function of the cube of the wind speed, so stronger, more constant winds matter enormously. Offshore wind speeds average about 90% greater than on land. In 2015, wind met nearly 4% of global electricity demand, and in Denmark it met more than 40%. The cube law explains why engineers chase the windiest, most remote places on Earth.

• 3. Water Heat And Crops

  ›

  Water is about 800 times denser than air, so even a slow stream or moderate sea swell can yield considerable energy. Hydropower converts that flow to electricity at about 90% efficiency, the highest rate in renewable energy. Historically it came from large dams and reservoirs. The largest are the Three Gorges Dam, completed in 2003 in China, and the Itaipu Dam, completed in 1984 by Brazil and Paraguay. Small hydro systems typically produce up to 50 MW, and China alone runs more than 45,000 of them. Only a third of the world's estimated hydroelectric potential of 14,000 TWh per year has been developed, in part because new projects can require relocating communities and flooding habitats. Geothermal energy is heat extracted from the Earth's crust, much of it from the slow radioactive decay of minerals deep inside the planet. Extraction is viable mostly in countries on tectonic plate edges, where the hot mantle is closer to the surface. As of 2023, the United States had by far the most geothermal capacity at 2.7 GW, followed by Indonesia and the Philippines. In Iceland, which relies almost entirely on geothermal and hydroelectric resources, geothermal heats homes directly. In Kenya, geothermal accounts for 43% of electricity. Bioenergy works differently again. Biomass is biological material from living or recently living organisms, burned directly for heat or converted into a denser biofuel like ethanol. Wood is the most significant source as of 2012, with the biggest per-capita producers being heavily forested countries like Finland, Sweden, Estonia, Austria, and Denmark. Burning biomass still releases carbon, about 39 grams of CO2 per megajoule, compared with 75 grams for fossil fuels. Land use can take a stranger form. Agrivoltaics places solar panels and crops on the same land, but the shade demands plants that tolerate it, such as Polka Dot Plant, Pineapple Sage, and Begonia.

• 4. The Problem Of Intermittency

  ›

  Solar energy can only be captured during the day, ideally in cloudless conditions, and wind generation can swing not just day-to-day but month-to-month. The two most important renewables are therefore intermittent, with lower capacity factors than fossil, nuclear or hydropower plants that produce precisely what the grid demands. This poses a hard challenge when leaving fossil fuels behind, because demand is often higher or lower than what renewables can supply. In the medium term, that variability may mean keeping some gas-fired plants on standby until there is enough storage, demand response, grid improvement, or base load power from non-intermittent sources. Sector coupling adds flexibility. The transport sector can be coupled by charging electric vehicles and sending electricity from vehicle to grid. The industry sector can be coupled through hydrogen produced by electrolysis, and buildings through thermal energy storage for heating and cooling. Storage is the longer-term answer. Pumped-storage hydroelectricity accounts for more than 85% of all grid power storage, while batteries are increasingly deployed for grid services and domestic use. Green hydrogen is a more economical means of long-term storage in capital terms than pumped hydro or batteries. Building overcapacity for wind and solar helps guarantee output even in poor weather, though in optimal weather it may force curtailment when excess electricity cannot be used or stored. Where dispatchable power is more valuable than variable renewables, countries with large hydroelectric systems like Canada and Norway are spending billions to expand grids and trade with neighbors that have limited hydro.

• 5. Why It Is Winning

  ›

  The main reason to choose renewables over fossil fuels is to cut greenhouse gas emissions, which cause climate change. Renewables also cause far less air pollution, improving public health, with potential worldwide savings in health care costs estimated at trillions of dollars annually. Cost is the other engine. From 2013 to 2022, installation costs for solar PV, onshore wind, and offshore wind dropped by 69%, 33%, and 45% respectively. In some places, photovoltaic solar or onshore wind is now the cheapest new-build electricity. The International Renewable Energy Agency stated that about 86% of renewable capacity added in 2022, some 187 GW, cost less than fossil-generated electricity. That same agency reported that capacity added since 2000 reduced 2022 electricity bills by at least $520 billion. Money has followed. From 2020 to 2022, solar technology investments almost doubled, from US$162 billion to US$308 billion, with PV accounting for 90% of the total. China and the United States were the main recipients, together making up about half of all solar investment since 2013. The energy sector now receives roughly US$3 trillion each year, with US$1.9 trillion directed to clean energy technologies and infrastructure. Jobs have followed the money. Renewables employed about 12 million people as of 2020, with solar PV the largest employer at almost 4 million. Yet as of February 2024, the supply of solar workers lags far behind demand, because universities still produce more graduates for fossil fuels than for renewables.

• 6. The Dependencies Beneath

  ›

  Like all mining, extracting the minerals for renewable technologies damages the environment. Lithium mining uses around 65% of the water in the Salar de Atacama desert, forcing farmers and llama herders to abandon ancestral settlements. Wind power needs large amounts of copper and zinc, plus smaller amounts of the rarer metal neodymium. Batteries demand copper, nickel, aluminum and graphite. Demand for lithium is expected to grow 42-fold from 2020 to 2040, with nickel, cobalt and graphite rising by a factor of about 20 to 25. For each key mineral, one country dominates mining: copper in Chile, nickel in Indonesia, rare earths in China, cobalt in the Democratic Republic of the Congo, and lithium in Australia. China dominates the processing of all of them. That concentration carries a second risk. About 90% of the photovoltaic supply chain sits in a single country, China, and mass-installed solar inverters with remote control and security vulnerabilities can be hit by cyberattacks. Such an attack could disable generation from millions of decentralized panels, erasing hundreds of gigawatts from the grid in one moment. Similar attacks have targeted wind farms through their remote control and monitoring systems. The European NIS2 directive responds in part by extending cybersecurity regulations to energy generation. Renewable infrastructure is also exposed to the very climate change it aims to limit. In 2023, hydropower production in Sudan and Namibia dropped by more than half after rainfall collapsed, while heatwaves and clouds cut solar output and melting glaciers disrupted hydropower.

• 7. An Old Source Made New

  ›

  Before coal arrived in the mid 19th century, nearly all energy used was renewable. The oldest known use is traditional biomass to fuel fires, dating back more than a million years. Harnessing the wind to drive ships came next, traceable some 7000 years to vessels in the Persian Gulf and on the Nile. Geothermal hot springs served for bathing since Paleolithic times and for space heating since ancient Roman times. The earliest verified windmill designs date to Iran, between 700 and 900 CE. The modern turn began with ideas before machines. Max Weber noted the end of fossil fuel in the closing paragraphs of The Protestant Ethic and the Spirit of Capitalism, published in 1905. A 1911 article in Scientific American predicted that in the far distant future, with natural fuels exhausted, solar power would remain as the only means of existence of the human race. The theory of peak oil was published in 1956. In the 1970s, environmentalists promoted renewables both to replace eventually depleted oil and to escape dependence on it, and the first electricity-generating wind turbines appeared. Solar panels stayed too costly to build solar farms until 1980. New spending, regulation and policy helped the industry weather the 2008 financial crisis and the Great Recession better than many other sectors. The International Renewable Energy Agency was formed in 2009, with 75 countries signing its charter, and by April 2019 it had 160 member states. The International Energy Agency estimates that to reach net zero emissions by 2050-90% of global electricity will need to come from renewables, a pace the world, including the G7 and the EU, is still far from matching.