Why Long Duration Energy Storage Matters for a Renewable-Powered Future

Wind and solar power can generate large amounts of electricity, but their output changes with the weather and time of day. Sometimes generation is higher than demand; at other times, electricity is needed when renewable output is low. Managing these longer gaps is one of the challenges of building a renewable-powered electricity system.

Long duration energy storage (LDES) can help by storing electricity when it is available and releasing it later. Unlike storage designed mainly for short periods, LDES is intended to deliver energy over longer durations. Its role is not to replace renewable generation or other grid solutions, but to add flexibility when supply and demand do not line up.

This article explains what long duration energy storage is, where it may be useful, and the factors that affect whether it is the right fit for a project or electricity system.

What Is Long Duration Energy Storage?

Long duration energy storage (LDES) refers to systems designed to store energy and deliver it over an extended period. They can charge when electricity is available and release it later, helping bridge gaps between generation and demand.

Two measures help explain how a storage system works:

• Power capacity is how much electricity it can deliver at one time, usually measured in kilowatts (kW) or megawatts (MW).

• Energy capacity is how much electricity it can store, usually measured in kilowatt-hours (kWh) or megawatt-hours (MWh).

The relationship between these measures determines how long a system can deliver power at its rated output. For example, a system with 10 MWh of usable energy capacity delivering 2 MW could supply that output for about five hours, assuming no losses or other operating limits.

There is no single definition of “long duration” used everywhere. The term generally distinguishes storage intended to supply energy for longer periods from systems designed for shorter, more frequent shifts. The important question is not just how much energy a system stores, but how long it needs to deliver it and what problem it is meant to solve.

Why Renewable-Powered Grids Need Longer-Duration Storage

Wind and solar generation varies with weather and time of day, while electricity demand continues around the clock. At times, renewable generation may exceed demand; at other times, output may fall while people and businesses still need electricity. Storage can help shift some available electricity to a later time.

Renewable generation doesn’t always match demand

Solar panels generate electricity during daylight, with output changing as sunlight and weather change. Wind generation depends on wind conditions and can rise or fall over different periods. These variations can create times when electricity is plentiful and times when supply needs additional support.

Long duration energy storage can charge during periods of available generation and discharge later. How much it can help depends on the amount of energy stored, its discharge capacity, and how long the supply gap lasts.

Short-duration storage has a different job

Storage systems are designed for different needs. Some are suited to responding quickly or shifting electricity over shorter periods. Long duration energy storage is intended to deliver energy for longer periods, which may be useful when a gap between generation and demand lasts beyond a few hours.

That doesn’t mean longer duration is always better. A system’s useful duration depends on the application, how often it will be used, and the alternatives available.

Longer gaps require a mix of solutions

Storage is one way to balance an electricity system. Renewable energy storage can help shift electricity from periods of surplus generation to times when it is needed, while transmission can move electricity between regions and flexible demand can shift when some activities use power. Different generation sources can also complement one another. 

The aim is to choose a mix that fits the system’s needs. Long duration energy storage may help with some extended gaps, but it does not generate electricity or remove the need for reliable infrastructure and careful planning.

Where Can Long Duration Energy Storage Be Useful?

Long duration energy storage can be useful when electricity needs to be shifted across a longer period not just from one part of the day to another. Its value depends on the length of the supply gap, the amount of energy the system can store, and what other resources are available.

Using more surplus renewable electricity

When wind or solar generation is higher than demand, some electricity may be available to store rather than use immediately. A long-duration system can hold some of that energy and release it later, when renewable output is lower or demand is higher.

This can help make better use of renewable generation, although the amount of energy that can be stored and returned depends on the system’s capacity and efficiency.

Supporting electricity-system flexibility

Electricity systems need to respond to changes in both supply and demand. Long duration energy storage can provide another option for managing periods when generation and demand do not align for an extended time.

It works alongside other flexibility measures, such as transmission, demand response and a mix of generation sources. The most suitable combination depends on local conditions and system requirements.

Meeting specific business or industrial needs

Some businesses use electricity in ways that make timing important. Depending on the site and operating pattern, storage may help manage when electricity is used, reduce exposure to certain periods of high demand, or provide support during planned interruptions.

These outcomes are not automatic. A project needs to be assessed against the business’s load profile, required discharge duration, connection limits and costs.

Serving remote or constrained locations

In some remote locations or areas with limited grid capacity, storage may help manage local electricity supply. Whether long duration storage is suitable depends on the local generation mix, demand pattern, available space, connection options and the alternatives.

The key point: long duration energy storage is most useful when it addresses a clearly defined, longer-lasting gap between electricity supply and demand. It is not necessary for every renewable-energy project.

What Technologies Can Provide Long Duration Energy Storage?

Long duration energy storage is not a single technology. Different systems store energy in different ways, and each has its own strengths, limitations and suitable applications. The right choice depends on how much energy is needed, how long it must be delivered, the site and the project’s costs.

Redox flow batteries

Redox flow batteries store energy in liquid electrolytes held in external tanks. During charging and discharging, the electrolytes circulate through a cell stack where electrochemical reactions take place.

Their design separates energy capacity from power capacity to a degree: larger electrolyte tanks can increase stored energy, while the cell stack affects how much power the system can deliver. This can make flow batteries worth considering for applications that need repeated, longer-duration discharge.

The technology still needs to be assessed for its efficiency, footprint, cost, operating requirements and suitability for the site. 

Pumped hydro storage

Pumped hydro stores energy by moving water between two reservoirs at different elevations. When electricity is available, water is pumped uphill; when electricity is needed, it flows back down through turbines to generate power.

It can provide large-scale storage, but it depends on suitable geography, water availability, infrastructure and project approvals. Its feasibility is therefore highly location-specific.

Other storage approaches

Other technologies including thermal storage and various mechanical or chemical systems can also store energy for later use. Their suitability depends on factors such as storage duration, scale, efficiency, site requirements and cost.

There is no universally best option. A useful comparison starts with the electricity-system need and then assesses which technology can meet it reliably and economically.

What Should Be Considered Before Choosing an LDES System?

Choosing a long duration energy storage system starts with understanding the need it must meet. A system designed for a short daily shift may not suit a situation where electricity is needed for many hours. Before comparing technologies, define the required performance and the conditions at the site.

How much power is needed, and for how long?

Estimate both the power the system must deliver and the length of time it needs to deliver it. These determine the system’s power and energy capacity. Be specific about whether the need is a few hours of support, a longer period of low renewable generation, or another operating requirement.

How often will it charge and discharge?

Some applications require frequent cycling, while others may need storage only during particular conditions. The expected operating pattern affects technology selection, system design and the project’s economics.

What are the site and grid requirements?

Available space, site conditions and grid connection capacity can limit which systems are practical. A project may also require network upgrades or other infrastructure, depending on where it is located and how it will operate.

What will the system cost over its lifetime?

Consider more than the initial purchase and installation price. Assess operating and maintenance costs, efficiency, expected service life, financing and any supporting infrastructure. Compare options against the service they are intended to provide.

What environmental and end-of-life factors matter?

Consider the materials used, land and water requirements, potential local impacts, and plans for maintenance and end of life. These factors vary by technology and project, so they should be assessed rather than assumed.

A suitable system is one that meets the required duration and operating needs while making sense for the site and the wider electricity system.

What Does Long Duration Energy Storage Mean for New Zealand?

New Zealand’s electricity system already uses substantial renewable generation, including hydroelectricity, geothermal energy and wind. As the mix changes, the system must continue balancing electricity supply with demand through different weather conditions and seasons.

Hydroelectricity is an important part of that picture, but water availability can vary. During periods of low inflows, hydro generation may be more constrained, increasing the value of having other ways to manage supply and demand.

Long duration energy storage could be one option for storing electricity when it is available and delivering it later. Its usefulness would depend on the length of the supply gap, the system’s capacity and cost, and how it works alongside hydro, other generation, transmission and flexible demand. Storage should not be presented as a complete solution to dry-year risk.

For New Zealand, the practical question is how long duration storage could fit into a wider set of measures to support a reliable, renewable-powered electricity system.

The Limits of Long Duration Energy Storage

Long duration energy storage can help manage extended gaps between electricity supply and demand, but it has limits. It stores electricity generated elsewhere; it does not create new energy.

It is not needed for every project. Some systems need only short periods of storage, while others may benefit more from transmission, flexible demand or a different mix of generation. The right approach depends on the problem being addressed.

Its performance depends on the technology and site. Storage duration, power capacity, efficiency, space, connection requirements and cost all affect whether a system is practical. A technology that suits one location or use case may not suit another.

It cannot replace wider electricity-system planning. Even a long-duration system must work alongside generation, networks and demand management. Storage can provide flexibility, but it is not a standalone guarantee of reliable electricity.

The main takeaway is that long duration energy storage is a useful option to assess—not a universal solution. Its value comes from matching the right system to a clearly defined need.

Conclusion

Long duration energy storage can help a renewable-powered electricity system manage periods when generation and demand do not align for extended periods. It can store electricity when it is available and release it later, adding flexibility alongside other solutions.

But it is not the right answer for every situation. The value of a system depends on the duration and scale of the need, the technology, the site and the overall cost. In New Zealand, it should be considered as part of a broader approach that includes hydro, other generation, transmission and flexible demand.

The takeaway: long duration energy storage can support a renewable-powered future when it is matched to a clear need and planned as part of the wider electricity system.

Frequently Asked Questions

What is long duration energy storage?

Long duration energy storage (LDES) stores electricity and delivers it over an extended period. It can help bridge longer gaps between when electricity is generated and when it is needed.

How is long duration energy storage different from a regular battery?

The key difference is the length of time the system is designed to deliver electricity. Some batteries are designed for shorter periods, while LDES systems are intended to supply power for longer durations. The right duration depends on the application.

Which technologies can provide long duration energy storage?

Options include redox flow batteries, pumped hydro, thermal storage and other approaches. Each has different requirements for location, scale, efficiency, operating pattern and cost, so no single technology is best for every project.

Can long duration energy storage make renewable electricity more reliable?

It can help by storing electricity when it is available and releasing it later. However, reliability also depends on generation, transmission, flexible demand and the wider design of the electricity system.

Is long duration energy storage suitable for New Zealand?

It may suit some applications, but suitability depends on the specific need, location, cost and available alternatives. In New Zealand, it would need to be considered alongside hydroelectricity, other generation, transmission and demand flexibility.

Does long duration energy storage generate electricity?

No. Storage holds energy produced elsewhere and releases it later. Some energy is lost during charging and discharging, so storage does not return all the electricity put into it.