The Importance of Energy Storage

By Ryan Shubert

Greenhouse gases are currently one of environmental scientists’ top concerns. Made through both natural and anthropogenic processes, these gases trap heat in the atmosphere and contribute to global climate change. In 2010, 25% of anthropogenic global greenhouse gas emissions came from electricity and heat production. An additional 10% came from other energy-sector activities like extracting and processing fuel, and 14% came from the transportation sector.¹ If nothing is done, the growing population ensures that greenhouse gas emission will increase. With 70% of global greenhouse gas emissions coming from activities within cities,² the path to overall global sustainability starts at achieving sustainability at the city level. In fact, the best area to focus on is energy storage.

The primary source of greenhouse gases emitted by humans is fossil fuel combustion, especially in the electricity and heat production and transportation sectors. For electricity and heat production, cities need a consistent, reliable source of energy able to support the high density of people and businesses. It is primarily because of this that renewable energy sources have not yet penetrated electrical grid systems. Typically, the energy comes from the burning of fossil fuels to heat up water, turning it into steam that will turn a turbine. In the US, almost half of the electricity produced is from coal burning, yet this is responsible for 80% of the nation’s greenhouse gas emission from power plants.³ For transportation, current electrically powered methods are not up to par with fuel based methods.  They have less range, take much longer to recharge, and there is hardly any infrastructure for them- there are not sufficient numbers of charging stations. Because of this and the economic advantages of fossil fuels, 95% of the world’s transportation is powered by the burning of petroleum based fuels,¹ which is the source of almost all anthropogenic greenhouse gas emissions. Both of these emission problems stem from the fact that the renewable, sustainable alternatives to current practices are currently not practical or plausible. The issues slowing the growth of these sustainable practices- the intermittency of renewable energy sources and the overall insufficiency of electric vehicles- have a common factor that, if improved, could greatly decrease these issues. This factor is energy storage.

In the majority of current power grids for cities, the amount of electricity able to be produced over short periods of time is relatively constant, even though demand varies.⁴ This creates problems on two end of a spectrum- on one side, if energy consumption is high and the supply cannot match the demand, there is a blackout. On the other side, if energy consumption is relatively low, there is a redundancy in electricity produced and it is usually wasted. This problem, along with the large amount of greenhouse gas emissions, can be solved through the combination of a smart grid and energy storage technologies. A smart grid is essentially an computerized electrical grid. It uses two-way communication between the source of electricity and the consumer and data from many sensors and meters to efficiently produce and deliver electricity.⁵ The communication will raise consumer awareness of how much energy they are using, and it could also act as a warning for when there will be an electrical demand peak. Ideally, this will help smooth out the peaks by notifying consumers of predicted spikes and recommending different times to use the electricity, known as load balancing. This demand-side energy management will have an overall effect of decreased redundancy in electricity produced, so that less will be wasted, and improved utilization of electrical generators, which will in turn lower energy prices.⁶

If this smart grid technology were to be combined with effective, grid-scale energy storage technologies for a city, then renewable alternatives become much more practical. The variability of renewable energy sources would no longer make them unreliable as the energy they produce could be stored for later use. Also, the demand peak curtailment and load balancing of smart grids could mediate large, unexpected spikes in demand while the stored energy easily suffices them. In a power system like this, rather than a redundancy of electricity produced, you could have a redundancy of electricity stored.

A good candidate for this city power grid storage is the liquid metal battery developed at MIT by Dr. Donald Sadoway and his team. This battery is unique because all three components- the anode, the cathode, and the electrolyte exchange layer- are in the liquid state. The three layers separate into the necessary order by their density, and the heat generated by the operation of the battery alone is enough to keep the metals in the liquid state. The batteries are made of relatively earth-abundant, inexpensive materials, and have a longer lifespan than other feasible candidates. Furthermore, they are made in a compartmentalized design so they are easily scaleable to meet the needs of whatever they are powering.⁷ This liquid metal battery working with a smart grid is the key to city-wide, sustainable dependence on renewable energy sources.

On a smaller scale, energy storage again has the potential to largely decrease greenhouse gas emissions. In the United States in 2014, over one-fourth of the total carbon dioxide from the United States was put into the atmosphere by the transportation industry.⁸ Cities already have an advantage in fixing this as they are typically denser than other areas and biking or walking as a mode of transport is more plausible. But not everyone who lives in a city works in the city, and in that case one of the best solution for reducing emissions lies in electric vehicles (see more about Energy Consumption in Transportation).These vehicles, though, have many problems, arguably the two most influential ones being the low range and the long recharge time. Both of these characteristics, luckily, lie in the same realm- the strength of the battery in the car. A better battery means longer life and quicker recharge. Currently, the best candidate for an electric vehicle battery is the Lithium-ion battery. When compared to its competition, lithium-ion batteries have a higher energy capacity, need little maintenance, and have a low self-discharge, internal chemical reactions in the battery that decrease the stored potential. However, the battery’s components are fragile and requires a protection circuit which limits maximum voltage.⁹

Although in the fight against greenhouse gas emissions and general sustainability energy storage is typically seen secondary to renewable energy sources, it is really of equal or even more importance. If cities fund the research and development of batteries and energy storage in general, then renewable energy as a city’s energy source becomes feasible, and those cities would vastly decrease their greenhouse gas emissions.