Learn About Battery Storage

What is energy storage?

Energy storage is any technology that can store energy over time and discharge that energy when it is needed. A battery is an example of an energy storage technology.

What benefits can energy storage provide to the electric grid?

Electric grid operators have traditionally had to balance the amount of electricity needed (load) with the amount of electricity generated (supply) at every given instant. Energy storage allows some wiggle-room between load and supply: If there is more supply than is needed by load, energy storage can absorb the excess supply. If there is more demand from load than there is supply, energy storage can release some electricity to cover the gap.

Energy storage can also provide other benefits like mitigating high costs during times of high demand, helping to adjust various qualities about the electricity to optimize grid performance and efficiency, and prevent the need for costly enhancements to the poles, wires, and substations that make up our electric grid.

Can energy storage reduce energy costs?

Energy storage can lead to reduced costs. Our energy bills are essentially composed of two costs: the cost of electricity supply and the cost to deliver that electricity to your home or business. Energy storage can reduce supply costs by storing electricity produced at lower cost (like during times when demand is low and the most efficient, cheapest generation sources can be used) and discharging that electricity during times when it is most expensive to generate electricity (like the hottest summer days when everyone is running their air conditioners on high). Energy storage can reduce delivery costs by storing electricity generation in close proximity to where that electricity is needed. Doing so can reduce the need for costly upgrades to wires and substations.

Does energy storage provide environmental benefits?

Energy storage provides environmental benefits. First, energy storage can store electricity generated by renewable energy sources for use at another time. This makes it easier to integrated renewable energy onto the electric grid, thereby reducing the need for fossil-based generation sources. In this way, energy storage can help Rhode Island reduce its greenhouse gas emissions and meet its climate goals. Second, energy storage can help with resilience during extreme weather events or power outages. Place that have both renewables and energy storage can essentially act like their own ‘microgrid’ and run even when the main electric grid is down.

Why is energy storage important for the state of Rhode Island?

Energy storage is one technology that can help the state meet its clean energy goals. Energy storage can help match the timing of renewable energy generation with the timing of when we need electricity, particularly on the days when we use the most electricity. Energy storage can also help Rhode Islanders manage our energy consumption, our energy costs, and can play a role in enhancing energy resilience in our communities.

What is the difference between the terms: energy storage system, battery energy storage system, battery system, energy storage facility, and battery energy storage facility?

An energy storage system is an umbrella term that encompasses all technologies that have the ability to store and return energy. A battery energy storage system is a subset of energy storage technologies that use chemical technologies to store energy. A battery system is a shorthand term for battery energy storage system, typically used when referring to residential and commercial use cases. An energy storage facility is the set of energy storage technology and all ancillary equipment, including inverters, HVAC system components, fire suppression equipment, battery management system, and site ground preparation. A battery energy storage facility is an energy storage facility that uses battery technology. Storage facilities typically reference utility-scale use cases, as smaller systems need less ancillary equipment and are typically packaged into only one or two component parts.

What are the components of a battery energy storage system?

A cell is the basic unit of a battery energy storage system. A cell houses the chemicals that store electrical energy. A standard lithium-ion cell is slightly larger than an AA battery. Larger battery systems are composed of thousands of individual cells, housed in racks.

Battery systems also contain a Power Control System, which consists of an inverter to transform the alternating current electricity that we use into direct current electricity for storage, and vice versa. It also contains the switches, transformer, and equipment necessary to interconnect the battery system with the electric grid. The Power Control System is sometimes called a pack.

Battery systems rely on two main software components. The Energy Management System internally manages the battery to make sure that it performs within its specifications and monitors the system. The Site Management System serves as the communication link between the battery system and the electric grid.

Finally, a battery system has additional infrastructure components, which are generally referred to as Balance of Plant. This infrastructure includes things such as a building to house the battery system, heating and cooling systems, and fire protection systems.

What happens to these facilities and their battery technologies after they have served the full extent of their useful life?

Any battery energy storage system should have a decommissioning plan before installation. Alternatively, once a facility has reached its end-of-life, it could potentially be equipped with new technologies to serve a similar function. There is also the potential to recycle battery materials to make new batteries.

I might be interested in installing a battery system for my home or business – what is my next step?

Congrats! We recommend contacting at least three installers and asking for quotes and a turn key contract to review. Make sure you talk about your needs and typically energy consumption patterns with the installers, so they can put together a proposal that makes sense for you. You may also consider whether you want to pair the battery system with a solar PV system or other clean energy source. Good luck!

What are the tradeoffs between a traditional generator and a battery system?

The primary tradeoffs include fuel type, noise, cost, and duration.

• Fuel: A traditional generator runs on fossil fuel, like gasoline or propane, and emits greenhouse gases and particulate matter when its running. Local air quality and emissions standards may limit when and for how long a generator may be used. Energy storage systems do not consume fuel, so their associated emissions will depend on the resources that are charging them. Because the process of converting energy from electric to chemical and back to electric results in losses, a battery will lose anywhere from 10 percent to as much as 40 percent of the energy it takes in, depending on the type of battery and how it is used.
• Noise: Because a generator uses an engine to run, it makes a significant amount of noise. Because the battery system does not have moving parts like an engine does, it is much less audible than a generator.
• Cost: Up front, a diesel generator costs much less than a comparably sized battery system. However, the ongoing operational costs, such as fuel and maintenance, are much higher for a generator than for a battery system. For home and business owners interested in backup power, determining which technology is the better investment will depend on many complicated factors, such as how much backup power is needed, how long it is needed, utility rate structures, and local ordinances. Home and business owners should work with a trusted provider to understand their options and how they compare.
• Duration: As long as a generator has fuel, it can produce energy. A battery, however, is energy limited, which means that it can only output the energy that it has stored, and cannot generate more on its own. Home and business owners should carefully identify their needs when considering their options for backup power, such as which devices the backup power will be expected to support and for how long.

Do I need to pair a solar PV system with my battery?

You do not need to have a solar PV system in order to install a battery system. However, a battery system is a great way to ensure that the energy generated by your solar PV system is available for you to use even when the sun is not shining. If your desire is to have a resilient back-up, some way of charging the batteries will be needed, like a solar PV system. Another advantage to pairing solar PV with a battery system is making sure the inverters for the systems work optimally together. Consult your solar PV and battery system installers and manufacturers specifics for details on how systems may or may not be paired, and their ability to operate during power system outage.

What incentives are available to help offset the cost of the battery?

Rhode Island Energy customers may choose to participate in Connected Solutions, a demand response program which aims to reduce electric load during peak hours. Participating customers receive an incentive based on how much power their battery systems provide on average across all peak events in a year. Residential customers can learn more here. Commercial customers can learn more here.

How big should my battery system be for my home or business?

The size of your battery system should be determined by how you want to use that battery and by your unique energy consumption patterns. If you want to use the battery system for backup power for critical loads (like a refrigerator), then you may choose a smaller size. A home battery system for backup power may be 3-4 kW, 7-10 kWh in size. A battery system for a home or business that is intended to be able to run the entire home or business for a day or more would necessarily need to be bigger. Consult your battery installer for proper sizing based on your desired use and energy consumption patterns.

What does an inverter do?

Electricity delivered to your home from the electric grid comes in as alternating current (AC). AC is rapidly alternating between positive and negative; our grid works this way because traditional power plants (coal, gas, and nuclear) all work in the same fundamental way – spinning a magnet around an energized copper coil to generate voltage at a constant frequency. As the magnet spins, it generates positive and negative voltage.

PV and batteries are fundamentally different in that they do not spin. Instead, they are based on physical or electro-chemical reactions that result in a steady, non-alternating flow of current called direct current (DC). An inverter is the device that converts electricity between AC and DC, allowing DC devices to connect to the AC grid. For example, the “wall wart” plug-in adapter plug that some phones and many consumer electronics products use, and your laptop’s internal power supply have small inverters, allowing these devices to receive AC from your electrical outlet (plug), charge their batteries, and operate internally on DC power.

In addition to converting DC to AC, inverters make sure the electricity is appropriate to use in your home or business, and/or meet the performance requirements to export to the electric grid. “Smart inverters” are able to respond to grid conditions – either automatically or as directed by the grid operator – and actively control the flow of electricity between the grid and the DC device to provide grid support. All battery systems require an inverter.

How large is a battery system? What is the footprint?

A battery system size depends on the battery’s power and energy capacity, and type of technology used. Residential battery systems are the smallest, typically about a little larger than the door of a mini-fridge with a footprint that is only a few square-feet. An inverter is an additional necessary component and looks a bit like a traditional utility meter. The inverter is typically installed near the utility meter or near the solar PV inverter if there is one. Small businesses may choose battery systems that comprise one or more residential-sized batteries. Larger commercial and industrial businesses may choose to install a larger battery system that can be up to the size of a storage container unit, like those you see on cargo ships. The footprint for these batteries can be up to the size of a tractor trailer, and about as tall when accounting for the ancillary equipment like HVAC and inverters. Utility-scale battery systems, such as systems co-located with substations, are typically comprised of one or more storage container units, where each container houses rows of car-battery-sized cell packs.

What is the difference between a kilowatt (kW) and a kilowatt-hour (kWh)?

A kilowatt, abbreviated kW, is a unit of power at a given instant. A kilowatt-hour, abbreviated kWh, is a unit of energy, which is the amount of power transferred over time. A battery system is rated in both kW and kWh. Consider a simplified example of a battery system that is rated 2 kW, 6 kWh. This system can discharge at a maximum of 2 kW power at any given instant. The battery has a capacity of 6 kWh, so in theory it can discharge 2 kW for three hours (2 kW * 3 h = 6 kWh). In actuality, discharging a battery does result in some losses which will impact actual energy output. Consult with your battery installer and manufacturer specifications for more information.

What is the lifespan of a battery system?

The expected lifespan of a battery system is measured in cycles, where one cycle entails charging and discharging the battery system one time. The amount of years that a battery system is expected to last is therefore dependent on the number of cycles of charging and discharging the battery system does each year. For home battery systems that are used for demand response programs and backup power during power outages, the expected lifespan may be 8-10 years or more. Expected lifespan may differ for other use cases. Consult with your battery installer and manufacturer specifications for more information.

Are there any special considerations for new construction to integrate or be ready for a battery system?

New residential and commercial construction should consider the possibility of integrating battery systems during the design phase. Special considerations include battery use, electrical panel setup, battery location, and pairing with clean energy systems. For example, a new home design may consider installing a battery system for backup power and for participating in a demand response program. Design considerations may include setting up the electrical panel so that all circuits requiring backup power are able to be isolated from circuits that do not require backup power. The designer may also consider the location of the battery system in exterior design and landscaping, as well as preparing the roof and electrical panel for rooftop solar PV and electric vehicle charging. Rhode Island’s voluntary Stretch Codes provides additional guidance about residential and commercial building design.

State of Rhode Island

Office of Energy Resources