STORING THE SUNSHINE Balazs Striker explores the process of harnessing, utilising, and storing solar energy as well as the associated difficulties.
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ultiple methods of harvesting solar energy have been discovered and are already in use, but storing this energy remains a problem. Converting renewable energy into a reliable and transportable form is key to ending our reliance on fossil fuels. In 2019, only 11% of the world’s energy consumption came from renewable sources, with more than 84% sourced from fossil fuels such as oil, coal and natural gas. Fossil fuels have high energy densities (large amount of energy stored per unit volume, or mass) and release that energy rapidly so are ideal to power vehicles. Essentially, they store energy efficiently and make it accessible and cheap to utilise. To compete with fossil fuels, renewables must be equally reliable and transportable.
most efficient large-scale method to date, approximately 420 km. To travel this distance, suitable landscape is limited and its reputation a petrol powered car of similar weight would for environmental impact is bad. Also, the consume only around 32 kg (42 L) of fuel. stored energy is not transportable, so must be regenerated on. If you can’t beat fuel, make fuel! The electrochemical way of storing energy, batteries, is also widely used in stationary energy storage as well as in electric vehicles. The flagship, lithium ion (Li-ion) batteries, offer great energy density and reasonable power density. But the low charging speed, short lifetime, high cost and environmental
“In 2019, only 11% of the world’s energy consumption came from renewable sources, with more than 84% sourced from fossil fuels.”
Solar energy is a promising renewable source of energy, but as its performance depends on weather and the time of day, energy storage is needed for continuous supply. Most global electricity storage 96% in 2017 according to the International Renewable Energy Agency – is pumped storage hydroelectricity. Excess electrical energy from low demand periods is stored by pumping water to a higher altitude for release when demand increases. Despite being the
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concerns of the metals used are drawbacks. The biggest problem restricting use in vehicles is that the energy density is very low compared to fossil fuels; Li-ion batteries offer only 0.36– 0.88 MJ/kg compared to 44MJ/kg for petrol. A fully electric Tesla Model S with 85 kWh batteries has 540 kg of battery packs, a quarter of the car’s weight and providing power for
There is a growing interest in fixing solar or electrical energy in chemical bonds, the method plants use during photosynthesis. The artificial equivalents are photoelectrochemical processes turning water and carbon dioxide into more energetic molecules (H2, CO) that can be readily used as, or converted into, fuels. Another approach is electrolytically reducing these combustion products, without using sunlight directly. The drawback of the latter is a guaranteed loss of energy in the intermediate processes, but an advantage is that other renewable sources – for example wind electricity – can be used for fuel production. Hydrogen is a popular solar-to-fuel candidate. This light and abundant element can be directly used in fuel cells to generate electricity in vehicles or power plants. Its carbon-free production and utilisation make it a green alternative fuel. Unfortunately, storage is difficult; it is challenging to store this low-density gas in a way that yields high energy density. However, H2 can be used to make easy-to-handle organic fuels with the help of a friend made from an enemy: carbon monoxide.
