Energy Storage Solutions for Renewable Energy: An Overview

Renewable energy is reaching new heights. As it grows, though, some cracks are starting to emerge that could stand in the way of large-scale adoption. The need for cost-effective, reliable energy storage solutions is one of the most pressing of these challenges.

Energy storage is helpful in any grid, as it minimizes waste and improves resilience. However, it’s essential for grids powered by renewable energy. If grid-scale renewables are to become a reality, they need effective power storage first.

Why Renewables Need Energy Storage Solutions

The need for renewable energy storage solutions stems from renewable power’s inconsistency. Unlike conventional power plants, renewables cannot produce energy on demand. How much electricity they generate depends on fluctuating conditions like sunlight or the wind.

Renewables’ peak generation times often don’t align with peak consumption, creating surpluses and shortages at different times of day. When people use the most energy, renewables often produce the least. Similarly, they produce the most when demand is lowest. This “duck curve” makes an entirely renewable-powered grid unviable, but power storage poses a solution.

If grids could store excess power, supply fluctuations wouldn’t be as impactful. They’d prevent waste during high-production but low-consumption hours by storing the surplus. Then, when demand rises, but generation falls, they could transfer this stored energy back into the grid to avoid blackouts.

Types of Renewable Energy Storage Solutions

While the concept behind renewable energy storage is simple, its implementation isn’t. These systems must produce minimal losses and be highly responsive and cost-efficient to be viable grid-wide. That’s challenging, but there are several potential solutions.

Batteries

Batteries are the most straightforward energy storage solutions — at least on the surface. These systems work like the rechargeable batteries powering household electronics, only on a much larger scale.

Tesla’s battery energy storage system (BESS) in Moss Landing, California, showcases this concept in action. The facility uses hundreds of lithium-ion battery packs to store up to 730 megawatt-hours (MWh) of electricity. While this specific installation manages excess power from natural gas, the same concept could apply to renewables.

The biggest advantages of battery storage are that it’s energy-dense, easily scalable and switches on and off quickly. Unfortunately, it’s also expensive. Some battery technologies — like lithium-ion systems — also degrade over time, introducing more costs and maintenance concerns. Many researchers are working on improving battery technology, but these obstacles remain for now.

Hydrogen

Hydrogen is a less common but promising energy storage method. In these setups, excess renewable electricity powers electrolysis, which separates water into hydrogen and oxygen. When demands rise, grids use fuel cells to turn that hydrogen back into electricity without emissions.

This method has several advantages. First, hydrogen has the highest energy density of any fuel, so grids can store much power in a relatively small space. Fuel cells are also highly efficient, so the conversion process involves minimal waste. It’s also emissions-free, so this conversion ensures renewable grids don’t include any greenhouse gases.

Like batteries, fuel cells are expensive, which can be problematic at scale. Storing hydrogen can also be complicated, as the gas is highly flammable. Converting it into ammonia makes it safer to store, but introducing another step means these systems become less efficient and more costly.

Pumped Hydro

Another possible solution is to use pumped hydroelectric power. While water itself doesn’t store electricity in the traditional sense, grids can take advantage of its potential mechanical energy.

Pumped hydro storage uses surplus electricity to pump water to an above-ground reservoir. When grids need more power than renewables are currently generating, the reservoir opens. The water then flows down due to gravity and passes through a turbine to generate clean electricity. Like fuel cell storage, this conversion produces no emissions.

The biggest advantage of pumped hydroelectric storage is its cost-effectiveness, which stems from it being relatively simple. It’s also easy to implement. Many areas already use hydropower — it accounts for 60% of all renewable energy today. However, not every area has sufficient space to implement these facilities. 

Compressed Air

Compressed air is a similar energy storage solution. Instead of using excess power to pump water, these systems use it to compress air into low-volume storage areas. When the grid needs more electricity, it releases this compressed air to turn a fan, thus generating electricity through mechanical force.

It’s possible to store compressed air in tanks, but these facilities typically use natural underground formations. Empty natural gas reservoirs and salt mines are among the most common. While not every area has these spaces readily available, they offer a low-cost storage solution where available.

Like pumped hydro, compressed air energy storage is highly cost-efficient. Compressed air can also last far longer than batteries or similar high-tech solutions. However, it has a relatively low energy storage density, so it may not be sufficient for larger grids.

Thermal Energy Storage

Another way to store excess renewable power is to convert it into thermal energy. These energy storage solutions work differently than others in using stored power for a specific purpose instead of general-use electricity. Whereas most alternatives convert the stored medium back into electricity, thermal systems use it directly for heating or cooling.

Thermal energy storage starts with heating or cooling a medium — often a refrigerant or water — with excess power. Then, when buildings need to heat or cool a room, they use this stored medium to do so. Thermal management systems either transfer heat away from or toward an area for emissions-free heating and cooling.

While thermal energy storage doesn’t tackle the whole grid, it helps by reducing overall demand. Thermal applications account for 50% of all energy use in buildings. Consequently, by using surplus power to provide emissions-free heating and cooling, these systems lead to considerable energy savings.

Energy Storage Solutions Are Key to Sustainable Power

These five energy storage solutions aren’t the only possibilities but represent the most promising technologies. Because each has unique advantages and disadvantages, there’s no one ideal system. Instead, grids must determine which is best for their needs or combine multiple systems.

As energy storage becomes a more widespread practice, renewable power will become more viable. Grids will be able to transition away from fossil fuels without worrying about reliability issues or waste.