All about battery storage

All about battery storage

Learn how this zero-carbon energy source works, its history and future while Duke Energy builds more renewables

Editor’s note: This article is part of a series on renewable energy. Read the others about solar and wind here.

The United States has roughly 1.7 gigawatts of battery storage – that’s enough to store the electricity generated from more than 5.4 million solar panels. By 2050, experts predict the country to have 10 times as much.

Duke Energy has been using batteries since 2012 when it built multiple projects including what was the country’s largest battery at a wind farm in Texas. They've been expanding the technology since.

The company plans to invest more than $600 million in batteries by 2025, which will help Duke Energy support its growing renewables portfolio as it works to reach net-zero carbon emissions by 2050. By then, the company estimates renewables will be its largest generation source supported by an upgraded grid, natural gas and nuclear power to keep electricity affordable and reliable.

Here’s a look at how batteries work, their history, and their future.

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Batteries can store electricity generated from solar panels for use on a cloudy day or from wind turbines for when it’s not so windy, but they also strengthen the grid by providing backup power for remote areas and controlling the flow of electricity in power lines.

As clouds move over solar panels and winds change throughout the day, the amount of electricity generated from renewables varies. This causes swings in voltage and frequency, too. It’s challenging for grid managers because the grid was designed for electricity to match customer demand at all times. A slight change in voltage or frequency can cause a power outage or flickering lights.  

But batteries can help. They react almost instantly to these changes and smooth the swings to stabilize the flow of electricity. 

How do they work?

There are several types of batteries, but at the simplest level, batteries store electrical energy as chemical energy so it can be converted back and released when needed. Batteries have two electrodes – an anode (positive) on one side and cathode (negative) on the other – with an electrolyte in between. The electrodes work together to initiate a chemical reaction that releases electrons, and the electrolyte – usually a liquid – makes it possible for the resulting electrical charge to flow between the two. From there, the electricity is directed from the battery’s terminals to the grid through a wire.

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Italian scientist Alessandro Volta invented the modern battery in 1800. His discovery led to the field of electrochemistry, and the volt – a unit of electric potential – was named in his honor. It wasn’t until the 21st century after years of research and development, that batteries were used for utility-scale projects.

Before batteries were an option, energy companies used other methods to store energy and manage power quality including flywheels, compressed air, thermal energy and pumped-storage hydroelectric plants. Pumped storage is a type of hydroelectric station where the water can be reused and strategically moved between an upper and lower reservoir. When demand for electricity is low, the plant can take excess generation and use it to pump water to the upper reservoir that can be released later when demand for electricity rises. 

Duke Energy has two pumped storage hydroelectric plants in South Carolina – one located inside a mountain – and is upgrading them so they will be more powerful to support its growing solar portfolio. When upgrades are complete in 2023, Bad Creek Hydroelectric Station will be able to produce about as much energy as some nuclear plants and power more than 1 million homes.

These hydro plants still make up the bulk of the nation’s energy storage, but most large-scale energy storage installations since 2003 have been batteries. As demand for electric vehicles and residential and utility-scale solar grows, the demand for batteries will grow, too.

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Today, the most widely used battery for utility-scale projects is lithium ion. The cost of lithium ion batteries has fallen 89 percent since 2010. They’re efficient and proven making them a popular choice, but researchers are testing other storage options and battery chemistries that might last longer and be better for the environment.

Last year, Duke Energy announced a study at Clemson University in South Carolina where it is working with Siemens to explore hydrogen energy storage and as a low-carbon fuel source.

The company has also been studying batteries and microgrids at its Emerging Technology Office since 2008. Microgrids are systems – usually a combination of renewables and batteries – that allow customers to disconnect from the energy grid and operate on their own. They can provide backup power in remote areas and improve power quality for critical infrastructure like hospitals, first responders or manufacturing facilities.

Their findings have led to microgrids and grid-connected batteries in several states. In North Carolina, Duke Energy built the state’s largest battery, a 9-megawatt lithium ion battery at a substation in Asheville, which will help power quality, and a microgrid in the Great Smoky Mountains National Park that uses solar panels and a battery to power communications equipment at the top of Mt. Sterling.

By 2022, Duke Energy will have at least 50 megawatts of battery storage in Florida, including a battery on Cape San Blas on the Gulf of Mexico. This battery will provide additional power capacity to the remote area as the population grows.

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Batteries have the potential to enable more renewables in the United States, but experts expect them to become even more valuable as the cost continues to fall and the technology improves. As Duke Energy adds more renewable energy and batteries to its fleet, it will continue to build a diverse generation mix and stronger grid, so its electricity is affordable, reliable and increasingly clean.

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