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New innovations of old technologies: Renewable energy storage systems

New innovations of old technologies: Renewable energy storage systems

Enel assesses the importance of renewable energy storage technologies. We reveal the high-impact potential of upgrading old technologies and the investment opportunities for startups.


  • Innovative companies are redesigning energy storage technologies for a more sustainable grid.
  • Investment in long duration energy storage (LDES) is key to developing renewable energy.
  • In the race for renewable energy storage systems, startups mustn’t overlook the high-value potential of upgrading existing technologies like pumped hydro.
There’s no doubt a sustainable future depends on renewable energy, and investment needs to catch up. According to the IEA, the world must triple clean energy investment by 2030 to curb climate change. Renewable energy storage systems are a key part of this investment.

While there’s been a proliferation of energy storage innovations, two of the most common systems have demonstrated their energy capacities over the years: pumped hydropower and electrochemical batteries. Now, these two stalwarts are getting upgrades.

Enel wants to take a deep dive into the new innovations of old technologies to show that innovation doesn’t always mean reinventing the wheel. Startups can improve existing technologies to meet the needs of a sustainable future.


Why is it important to invest in renewable energy storage?

It often costs more to store energy than it does to produce it. So, even though renewable sources like solar and wind are cheaper than coal and gas, they are more expensive to store than fossil fuels. Moreover, renewable energy sources tend to fluctuate – while you can burn coal whenever you want, you can’t control when the sun shines or the wind blows. Cheap, efficient and renewable storage is imperative.

Long-duration energy storage (LDES), a system that can store energy for more than 4-8 hours, is crucial to developing a grid that can run off intermittent renewable energy sources. This is important for the environment and for investment. A study by McKinsey estimates that by 2040, LDES deployment could result in a decrease of 1.5 to 2.3 gigatons of CO2 equivalent per year, or around 10 to 15 percent of today’s power sector emissions. In the United States alone, LDES could reduce the overall cost of achieving a fully decarbonized power system by around $35 billion annually by 2040.  

The race is on for developing innovative energy storage systems, and there’s no shortage of contenders, including flywheel, thermal energy, compressed air, and mechanical systems, to name a few. The problem is that none of these technologies check all the boxes: low cost, scalable, and energy efficient.  

While some companies are searching for new ways to store energy sustainably, others are looking for ways to improve existing technologies. Two technologies – pumped hydro and electrochemical batteries – have already proved their energy-storage capacities. Now, it’s time to make them even better.


Renewable energy storage #1: Pumped hydro

Pumped hydro storage is truly the unsung hero of LDES. In 2021, pumped hydro storage accounted for 96% of global storage power capacity and 99% of global storage energy volume. This is only expected to increase. According to the IAE, pumped hydro storage will account for more than half of new hydropower capacity additions in Europe by 2025, which will play a critical role in decarbonizing the power system and plugging gaps in energy demand.  

While pumped hydro storage may seem like a ground-breaking technology, these systems have been around since the 1980s. This technology relies on two reservoirs at different elevations. After water is pumped from the lower reservoir to the higher reservoir, it then flows back down to the lower reservoir, spinning turbines to generate electricity.                                                

Pumped hydro storage is so popular because it’s large scale, cost effective, and sustainable. However, it also has some downsides. First of all, it isn’t a completely efficient system: only about 80% of energy is regained from when it is pumped up to when it is released. Second, there are geographic complications. Pumped hydro storage systems are typically built in or near rivers, and sometimes seas, meaning that not all locations are suitable. When they are, they are often expensive and difficult to build. It’s hard to imagine a pumped hydro system with sprawling lakes in urban settings like New York City or Rome. Startups that innovate ways to overcome these scalability and accessibility challenges will gain a competitive edge in the marketplace.


Renewable energy storage #2: Electrochemical Batteries

It’s hard to talk about energy storage without talking about electrochemical batteries. Even though batteries have been an energy storage staple for decades, that doesn’t mean interest in them is waning. On the contrary: the battery energy storage market is projected to reach $31.20 billion by 2029. While lithium-ion batteries are highly efficient and have become much cheaper in recent years, they still pose significant environmental and supply-chain risks. Among electrochemical technologies, there are innovative, sustainable alternatives: iron redox flow batteries and metal/air batteries.

MIT Technology Review named iron batteries as one of the top ten breakthrough technologies of 2022. Instead of relying on cobalt like their lithium cousins, iron batteries are made from safe, cheap, and sustainable materials –iron, water, salt, and air – meaning that they are scalable. They are projected to cost only $20 per kilowatt-hour, about one fifth the price of lithium-ion batteries.

Of course, iron batteries don’t come without their own problems: they are typically less energy efficient than their traditional chemical counterparts, meaning that some of the energy that’s put into them is lost. Even so, they’re more durable. While conventional chemical batteries can last 7-10 years, iron flow batteries could last for 20 years or more.

Enel is currently collaborating with two companies that are developing this exciting grid potential. ESS has developed patented electrode design and control systems that make these long-duration iron redox flow batteries some of the most durable, efficient, and sustainable on the market. Alongside Enel Green Power España, they are installing these batteries in a solar farm in Spain to transform the local grid. Form Energy is also developing an ultra-low-cost, long-duration metal/air battery for sustainable energy storage. In partnership with Enel, their goal is to design a fully renewable electric grid with zero CO2 emissions.            


Renewable energy storage #3?

If you are a startup, entrepreneur, or investor who is passionate about sustainability, renewable energy storage is the niche for you. Pumped hydro and iron flow battery storage are just some of the many opportunities to create a positive impact on the world.

Enel Open Innovability® is here to support you on this adventure. We are constantly on the lookout for new ways to build a sustainable future. If you have an idea for renewable energy storage systems, check out these two challenges:

  1. Energy storage systems. We are searching for new sustainable technologies, architectures and control strategies to lower energy storage costs and improve how our energy storage assets are built, operated and maintained.
  2. Renewable energy technology. This challenge is for the improvement of existing technologies, including the integration of renewable power in anthropized environments and the use of new renewable resources.

Remember, innovation doesn’t always have to be a completely new design. Companies that are shaking up existing systems like pumped hydro and electrochemical batteries are taking important steps toward creating a more sustainable energy grid. If you have an idea with similar potential, join us today!