Some people mistakenly think of solar energy as an area-intensive energy production technology that requires much more space than traditional fossil fuel-fired power plants.
The world’s population is 8 billion, so 0.5 million square kilometers of solar panels are needed for a wealthy, energy-intensive world that is completely carbon-free with solar electricity alone. In perspective, this is 1% of the surface area devoted to agriculture (50 million km2). Areas with lower per capita energy consumption and areas with significant wind or water resources require much smaller solar panels per person.
Solar panels can be installed on roofs, solar farms in connection with agriculture (agrivoltaics), dry areas, inland lakes (floating PV) and calm sea waters. Agrivoltaics and floating solar power are growing rapidly, but on a much smaller base than more traditional rooftop or ground-mounted solar power.
Agrivoltaics combined with grazing costs almost the same as traditional ground-mounted solar, except that the rows of panels can be wider. The farmer benefits from the leasing payments and the cattle benefit from the shade of the panels. A solar farm company benefits from free lawn management. Agrivoltaics in combination with farming usually requires higher panel supports and other adaptations that increase costs.
The cost of floating PV is about 20% higher than rooftop PV, but can be similar to tracked, ground-mounted PV with bifacial modules. This bodes well for future rapid growth. Although the cost of floating solar power is currently higher than that of rooftop and ground-mounted solar power, it has great potential in countries with high population density. Many countries have large inland basins that can host large solar power plants.
The possibilities of floating solar power at sea are huge. In Indonesia’s calm, tropical inland sea, there is 0.7 million km2 of seascape, where there is never any wind and waves over 15 m/s and 4 m high, enough for all the solar energy a prosperous and completely carbon-free world needs.
The world has 1.3 TW of hydropower capacity, which will be surpassed by global solar capacity during 2023. This consists of a combination of run-of-river systems with small reservoirs and large storage tanks. Covering a hydroelectric storage lake 100% with solar panels typically produces much higher power capacity and annual energy than a hydroelectric system.
One of the world’s largest hydroelectric plants is Itaipu in Brazil, with a flood area of 1350 km2 and an installed capacity of 14 GW. The 50-year-old factory was part of the country’s foreign debt for decades ($63 billion – the last installment paid off recently!). Due to water restrictions and eutrophication, only 66 TWh of electricity was produced in 2021 (in 2016, a record of 103 TWh). If Lake Itaipu were completely covered with solar modules, this gigantic solar power plant would have an installed capacity of 270 GW (almost 20 times the installed capacity of Itaipu) and would produce approximately 350 TWh of electricity per year (more than five times the 2021 output of Itaipu), which is equivalent to more than 70% of Brazil’s annual electricity consumption.
Itaipu took 10 years to build and another 10 years to get it to full capacity. Fifty years after the Itaipu agreement was originally signed, it is the largest “battery” in the country, with rooftop and ground-level solar power benefiting enormously from this large base-load modulator. Brazil only allowed solar to be connected to the grid in 2012, and 10 years later almost twice the installed capacity of Itaipu was achieved (18 GW of rooftop solar and 8 GW of large-scale ground-mounted solar by February 2023). .
Roof solar energy
Rooftop PV is the fastest growing segment in the global energy market. Rooftop PV is behind the energy meter and competes with retail electricity prices, which are typically much higher than wholesale prices. Households and companies are responsible for financing and take the risk, thereby avoiding public debt.
In Australia, about a third of homes have solar power on their roofs. Rooftop solar power is expected to continue to grow rapidly, as most houses and commercial buildings will eventually install solar power systems. An important trend is making previous systems more efficient: houses are upgrading solar power systems from 2 kW to 4 kW to 8 kW to 15 kW. Large-scale home storage to increase self-consumption is available in the form of electric vehicle batteries, home batteries and hot water tanks. Australia’s electricity grid remains very stable despite the dire predictions of ten years ago.
High conversion efficiency of solar electricity is key to reducing both prices and land use. Efficiency has improved approximately fourfold since the 1950s. The first practical Si solar cell was introduced in 1954, with an area of about 3 cm2. It had an efficiency of about 6% (60 Wp/m2 at STC) and cost US$286/Wp, more than a thousand times the current price of surface solar modules.
Nearly 70 years later, the best individual Si solar cells have an efficiency of nearly 27%, and commercially available Si PV modules have an efficiency of nearly 24% (240 watts/m2). Commercial Si modules may increase to 26% in 2030. Tandem cells have higher efficiency than Si cells. However, there are huge technical and commercial hurdles, including unstable equipment efficiency. If they can be overcome, 30% efficient tandem cells may become available. The required solar panel area of a completely carbon dioxide-free, energy-intensive economy would drop from 60 m2 to 45 m2 per person.
The demand for electricity in developing countries is much lower than in developed countries (Bolivia, Brazil and Chile respectively 1.6, 2.5 and 4.1 MWh per person per year). For many reasons, it is questionable whether and when energy consumption will reach the level of wealthier countries. Important factors of future clean energy consumption are private vehicles, electrification of industrial heating, production of hydrogen atoms for the metal and chemical industry, and production of synthetic aviation fuels. Solar electricity can be the energy source for all of this, and in most countries there are no regional restrictions.
Authors: Professor Andrew Blakers (ANU) and Professor Ricardo Rüther (UFSC).
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ISES, the International Solar Energy Society, is a UN-accredited member organization that was founded in 1954 and strives towards a world where 100% renewable energy is used efficiently and wisely for everyone.