Scientists at Stanford University established that installing new solar and wind farms in order to meet the increasing energy demands in the U.S. requires large amounts of fossil fuels, which reduce the environmental benefits of these renewable sources.
According to Charles Barnhart, a postdoctoral fellow at Stanford’s Global Climate and Energy Project (GCEP) and lead author of the study published in Energy& Environmental Science, new storage devices such as lead-acid batteries, require much more energy to build and maintain. Such devices, however, are crucial if more energy is generated by renewable sources because it needs to be conserved for future usage.
Currently, only around 3% of the electricity generated in the U.S. comes from renewable sources. The scientists, however, made predictions for possible scenarios when 80% of the electricity comes from wind, solar or hydroelectric sources.
Sally Benson, one of the co-authors of the study, a research professor of energy resource engineering at Stanford and the director of GCEP stated that although these means of generating electricity produce limited amounts of carbon emissions, they fully depend on weather conditions. With the increasing electricity production of these sources, the demand for energy storage will increase to in order to balance the supply.
The study is the first of its kind, which quantifies the cost of grid-scale storage over time. The main goal of the study was to stimulate the development of technologies that are both environmentally friendly and practical. As Bernhart pointed out, these would significantly reduce the amount of greenhouse gas emissions that are currently produced by coal- and natural gas-fired power plants.
If the energy is stored on the power grid, then the consumers will be able to access it whenever they need to use it. Currently, the storage capacity of the grid is less than 1%, and it comes from pumped hydroelectric storage. The mechanism of this technology is relatively simple- when the demand is low, the “unneeded” electricity is used to power a water pump, which supplies water to the dam nearby. In their study, the scientists estimated the cost of constructing pump versus the cost of making five different battery technologies. The findings indicated that all five have high embodied-energy costs compared with pumped hydroelectric storage.
For the long-term estimates, Barnhart and Benson established a formula, which uses the amount of energy that can be stored and the amount of energy needed to build the technology. Following this, they estimated that Lithium-ion batteries performed best, while conventional lead-acid batteries should not be used for storage for the worldwide power grid.
The team also pointed out that the best way to reduce the enrgetic costs of a battery is to improve its cycle life, or the number of times it can be recharged over its lifetime. A technology like the pumped hydro storage can have more than 25,00 cycles, meaning that it could function well over 30 years, according to Bernhart. To compare these numbers with Lithium-ion and lead-acid batteries, the former can reach up to 6000 cycles, while the latter around 700.
According to the authors, the energetic constrains are much more limiting than material availability for new battery technology development.
By Le My
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