by Apurva Govande
figures by MacKenzie Mauger

North Africa’s vast, arid Sahara Desert region covers 3.5 million square miles, which is just about the size of the United States. Sunlight hits the Sahara an average of 3,000 hours every year. Covering less than 1% of the Sahara with solar panels would generate enough energy to power the globe. Some solar energy can be used right away – to power indoor lighting, or to heat water for cooking, for example. However, the real potential of solar and other renewable energy resources lies in their ability to supplement the electric grid by storing energy for later use, at a time or location where it is more useful. Currently, green energy reduces demand on sources like oil, gas, and coal, but energy storage in batteries is still fraught with environmental costs. Policies that encourage renewable energy resources need to be coupled with technologies that reduce the environmental burdens of energy storage.

Energy and Climate Change

Global energy consumption is increasing every year, and most energy still comes from sources like oil, gas, and coal. The energy stored in these types of fuels is energy from millions of years ago, from the organisms that once lived and used it for their own survival. Burning these fuels releases the energy for use but also adds greenhouse gases to our atmosphere, contributing to global warming. Renewable sources of energy aim to reduce the release of greenhouse gases to combat climate change, but storing these resources has associated environmental costs and ethical concerns. During the 21st century, we’ve successfully developed several carbon neutral sources to generate energy, including solar and wind energy (Figure 1). Cleanly and efficiently storing that energy for later use is the next hurdle; this will require an overhaul of our battery technology.

Figure 1. Renewable sources of energy: Solar, hydro, and wind power are all renewable energy sources that reduce our dependence on coal and fossil fuels. Renewable energy sources convert energy from the sun, water, and air into electricity for human use.

Batteries convert and store energy for later use          

A battery is a device that charges with excess energy and stores it for future use, bridging the gap between energy supply and energy demand. Current battery technology is used to power our devices, homes, businesses, and electric vehicles.  The most widely used batteries employ lithium or cobalt ions to electrochemically store energy. When these batteries are charged, liquid state ions move from areas of positive charge, usually metals, to areas of negative charge, usually graphite. When the battery is being used, these ions flow back from the negative region to the positive region, and this movement of ions creates an electrical current that can be used to power electric devices. These kinds of batteries can be used to store large amounts of power, like for electric vehicles, as well as small amounts of power, like for portable devices such as cellphones. However, environmental and ethical concerns around lithium and cobalt mining and the increasing demand on these resources highlight the need for battery technology that doesn’t rely solely on these materials.       

The simplest and most widely used renewable energy “battery” is the hydroelectric dam (Figure 2). Energy, either from solar or wind power, is used to pump water uphill for storage in a reservoir. Later, this water can be let down the hill and used to power turbines or pumps that will generate energy when it is necessary. While hydroelectric power is a great source of potential energy, it’s difficult to implement widely in areas without significant sources of water or elevation nearby, and it’s not very portable. Further, research on how hydroelectric dams create disruptions to river ecosystems underscores the current trade-off between storage of renewable energy to reduce greenhouse gas emissions and the additional environmental burdens they cause.   

Figure 2. The hydroelectric dam: Hydroelectric power is a “battery” that stores potential energy in water. The battery is “charged” by pumping water uphill for storage in a reservoir and used by letting water flow downhill in a controlled environment, powering turbines that generate electricity.

Another green method for storing energy, one that is a cost-effective, high-density alternative, is molten salt or sand, which converts solar energy to thermal energy for later use (Figure 3). Solar power is used to heat up salt or fine grain sand to temperatures over 1000°F, which is then stored in an insulating tank. When the energy is required, the heat is used to generate steam that can power turbines, generating electricity. This type of battery is useful for residential power, like houses or apartment buildings.

Figure 3. Molten storage: Solar energy is stored by heating molten salt or sand. Salt or sand reservoirs are “charged” by sunlight, storing thermal energy. The “battery” can be used by using the superheated storage to generate steam, powering turbines and generating electricity.

However, it’s still difficult to develop a small, portable battery, such as ones we use almost every day in smaller devices, without the associated environmental costs like those associated with traditional lithium/cobalt ion batteries. To get around this, technologies that make battery storage more efficient can be useful and can address multiple problems in the raw materials supply chain for battery manufacturing. More energy storage with fewer materials reduces the environmental burden and lowers the demand for controversial sources of raw materials, such as with existing lithium-ion batteries. The overall goal must be battery technology that improves efficiency gains and lowers costs of manufacturing, while increasing portability. This is the focus of policies addressing battery technology.

Policies encouraging clean storage 

Over 2019 and 2020, several states increased their focus on renewable energy. California, Oregon, and Colorado, among other states, built legislation that increased monetary allocations for energy storage and projected targets for physically increasing residential storage. The Biden Administration has focused their attention on wind energy, aiming to expand offshore wind turbines in the Atlantic.

The private sector is also interested in investing in energy storage. The Energy Storage Association, a national trade organization of over 200 diverse companies exploring energy storage, compiled its recommendations to Congress for the future of energy storage in 2021. Their recommendations included making energy storage technology eligible for income tax credits to incentivize new technological developments.

The Advanced Research Projects Agency – Energy (ARPA-E) from the Department of Energy has provided $47 million for novel energy technology projects and funds applied research and technology in the energy sector. These include new developments in lithium-ion battery technology that use fewer materials with higher density, reducing manufacturing costs and decreasing the amount of copper, aluminum, lithium, and cobalt that goes into building a battery. Lowering the demand on these materials is one way to reduce mining and mitigate environmental damage. Another way is through solid state battery technologies, which unlike lithium-ion batteries, use a solid material ion to carry charge and eliminate the explosive and chemical risks of lithium batteries while also improving overall energy density, or how much energy a battery can store in a limited volume of material. Overall, the goals of the ARPA-E grants are to provide early funding, especially for novel technology that could disrupt the energy sector in the next few years. Ideally, increased private sector investment could then drive these technologies forward.

Renewable Technology for a greener future

The future of green energy depends on advances in energy storage technology. For renewable energy sources to be economically viable, the cost of storing energy must decrease and the efficiencies must increase. New technology developments are hoping to address both of these goals. Currently, the most promising new technology from ARPA-E funding is advancements in solid-state batteries using materials like silicon that increase the energy density and allow more storage with fewer materials. State and government policy must also consider the environmental and humanitarian impacts of renewable energy storage. To reduce our dependence on burning coal, oil, or natural gas, the way forward depends on reconciling environmental conservation policy and renewable energy storage to find better ways of taking the energy produced by carbon-neutral sources and storing it for an efficient future (Figure 4).

Figure 4: The balancing act: Renewable energy sources can also have environmental costs. Policies encouraging renewable energy sources must also be cognizant of the humanitarian and environmental burdens of energy production.

Apurva Govande is a recent graduate of the Virology Program at Harvard

MacKenzie Mauger is a second-year Ph.D. student in the Biological and Biomedical Sciences program at Harvard Medical School, where she is studying the role of condensate formation in epigenetic memory. You can find her on Twitter as @MacKenzieMauger

Cover image by Pexels from Pixabay

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