The sun has captivated our hearts and imaginations for millennia. Every organism on Earth is powered by the sun. Even our energy sources — coal, natural gas, wind, hydroelectric — are indirectly generated through solar power. But what really excites me is solar power itself. Humans have used solar-thermal power to make fire or heat or pump water since the 7th century B.C. We figured out how to convert solar energy directly into electricity in 1839, with the first photovoltaic cell. These three technologies have evolved and entered the market at wildly different paces and success rates.
Ancient hot-water solar panels evolved into rooftop hot-water solar panels, famously installed on the White House by President Jimmy Carter in 1979, and also into concentrated solar power panels (CSPs), first developed in 1968 by Professor Giovanni Francia. CSPs use sophisticated mirrors to concentrate sunlight to heat liquids to extreme temperatures. Through additional processes, these hot liquids can be converted to electricity or stored for future use. Unlike CSPs, photovoltaics (PVs) convert solar energy directly into electricity. The most common type of PV is crystalline silicon, which dominates 90 percent of the solar cell industry. However, PVs raise the problem of intermittence — the amount of available sunlight varies with time of day and weather conditions. This means that PVs cannot meet electricity demand in real-time without battery storage. Battery chemistry further complicates this process, introducing additional barriers of costs, production and waste. It is for this reason that the photoelectrochemical cell (PEC) model is particularly exciting. PECs convert solar power directly into chemical fuels. The most common type of PEC cell is a hydrogen fuel cell, which converts water into hydrogen fuel. This hydrogen fuel can be stored and transported until needed to generate electricity. This process works by employing a hydrogen fuel cell: Hydrogen fuel passes through a platinum catalyst and mixes with oxygen to produce electricity and water. In this process, new complications emerge concerning the cost of catalysts and the design of safe, reliable fuel cells. Regardless, the PEC model eliminates the need for battery storage and overcomes the intermittence of PVs.
Despite these exciting technologies, solar energy only makes up 1.5 percent of energy production in the United States. One of the biggest challenges has been the cost (which is measured in cents per kilowatt hour), with fossil fuels clocking in around five cents per kWh. However, solar energy is starting to compete with fossil fuels. Utility-owned silicon PVs have dropped in cost from 23 cents per kWh in 2010 to an average of six cents per kWh in 2017. The cost of utility-owned solar panels will typically remain lower than the decentralized alternatives — solar panels on residential or commercial buildings. However, an attractive alternative is a power purchase agreement (PPA), where a utility company purchases electricity from a third party that owns the solar panels. The cost of solar PPA has also dropped significantly over the years, to less than three cents per kWh in 2018 with some geographical variance. Every state has a unique energy profile, though none are dominated by solar power.
Of course, all is not lost. Solar research has promoted rapid growth of solar capacity: The U.S. saw a 16 percent increase in installed PV capacity in 2018 to 626,000 megawatts. Globally, we’re projected to achieve a terawatt (or one million megawatts) of PV capacity by 2023. CSPs in the U.S. reached an installed capacity of 1,815 megawatts in 2018. PECs are not quite ready for commercialization due to strict material demands and limitations in hydrogen fuel cell technology. CSP, PV and PEC solar cells demonstrate benefits and limitations concerning energy storage, material input and waste production. The market disproportionately favors silicon PV solar cells which does not accurately represent the wealth of knowledge and advancement in the solar cell field. Our ability to capture solar power is a marvel; it’s what makes us human. And we’re not slowing down anytime soon.
Desi Dikova is a senior in the College of Literature, Science & the Arts and can be reached at firstname.lastname@example.org.