Where does solar energy get stored?

02 Apr.,2024

 

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Even the most ardent solar evangelists can agree on one limitation solar panels have: they only produce electricity when the sun is shining. But, peak energy use tends to come in the evenings, coinciding with decreased solar generation and causing a supply and demand issue. The thing is, solar panels often pump out more than enough energy during those lower demand hours when the sun is shining to meet peak demand later in the day. This means that efficient solar energy storage can open up a wealth of possibilities for homeowners and businesses alike.

In this blog, we’ll look at solar energy storage in-depth, its benefits, and even tools for modeling it on your solar installs.

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What are the benefits of storing solar energy?

Storing this surplus energy is essential to getting the most out of any solar panel system, and can result in cost-savings, more efficient energy grids, and decreased fossil fuel emissions. Storing solar energy has a few main benefits:

  • Balancing electric loads

    . If electricity isn’t stored, it has to be used at the moment it’s generated. Energy storage allows surplus generation to be banked for peak-use. As far as renewable energy is concerned, storing surplus power allows the lights to stay on when the sun goes down or the wind stops blowing. Simply put, energy storage allows an energy reservoir to be charged when generation is high and demand is low, then released when generation diminishes and demand grows.

  • Filling in the gaps.

    Short-term solar energy storage allows for consistent energy flow during brief disruptions in generators, such as passing clouds or routine maintenance.

  • Energy resilience.

    The energy grid is vulnerable to disruptions and outages due to anything from wildfires to severe weather.

    Solar energy storage creates a protective bubble during disruptive events by decentralizing where we get our energy from.

  • Reducing carbon footprint. With more control over the amount of solar energy you use, battery storage can reduce your property’s carbon footprint in areas with fossil fuel-based utility power. Large solar batteries can also be used to help charge electric vehicles and turn any appliance in your home into a “solar-powered” device.
  • Savings from electric bills.

    If you live in a state that has no solar net energy metering, or policies that don’t fairly compensate you for the solar energy you generate, battery storage can help lower your utility bills while consuming more of your own power. So, while you may not be compensated as much for excess energy sent to the grid, any additional solar power generated and stored throughout the day can be discharged from a battery at night or on cloudy days in the place of utility consumption.

  • California Net Billing Tariff (NEM 3) considerations. One of the big components of NEM 3 is that it has, “notably higher on-peak charges and lower off-peak charges” for electricity. Likewise, the export rate is lowest is the middle of the day, when solar energy is plentiful. Since “peak” hours are from 4pm – 9pm, this means, generally, that customers are exporting power to the grid when the rate they receive is the lowest, and using grid power at peak times, when it’s most expensive. Enter battery storage: Any solar energy that can be stored in a battery during non-peak hours and used during peak times will be much more valuable for the consumer. See Auroroa’s new battery self-consumption features by clicking the “Let’s go!” button in the image below, then learn more details in our blog: Explaining and modeling California’s Net Billing Tariff.

How is solar energy stored?

Solar energy storage can be broken into three general categories: battery, thermal, and mechanical. Let’s take a quick look at each.

What is battery storage?

Batteries are by far the most common way for residential installations to store solar energy. When solar energy is pumped into a battery, a chemical reaction among the battery components stores the energy. The reaction is reversed when the battery is discharged, allowing current to exit the battery. Lithium-ion batteries are most commonly used in solar applications, and new battery technology is expanding rapidly, which promises to yield cheaper, more scalable battery storage solutions. In fact, U.S. energy storage is expected to reach nearly 7.5 GW annually by 2025, a sixfold growth from 2020, representing a market worth $7.3 billion.

What is thermal storage?

Thermal energy storage uses various mediums — such as water or molten salt — to absorb and retain heat from the sun. This heated medium is stored in an insulated tank until the energy is needed, usually to boil water for energy generation.

What is mechanical storage?

Mechanical energy storage takes advantage of the potential energy of an object to generate electricity. Mechanical storage methods convert surplus electrical power into mechanical power, which is converted back into electricity for later use. There are three prominent mechanical energy storage systems:

  • Flywheel.

    This method uses surplus electricity to spin a flywheel, which later generates electricity to supply quick energy during peak demand times.

  • Pumped hydro.

    With pumped hydro, water is pumped uphill to a reservoir located above turbine generators. The water is allowed to flow through turbines and generate electricity when demand is high.

  • Compressed air.

    With this energy storage system, compressed air is pumped into large vessels such as a tank or underground formation. The air is released to generate electricity during peak demand.

Click above to download the Storage Sales Cheat Sheet.

The best way to store solar energy

There’s no silver bullet solution for solar energy storage. Solar energy storage solutions depend on your requirements and available resources. Let’s look at some common solar energy storage options for commercial and home applications. 

Commercial solar energy storage

Utility companies and other businesses generally have bigger budgets than individual households, making mechanical and thermal storage viable options. Though costs for these storage methods can be high, they help utilities keep up with peak energy demand.

  • Grid energy storage with next-generation batteries. 2020 was a record year for new energy storage in the United States. In the third quarter alone, the nation

    deployed

    476 MW of new storage, a 240% increase from the record-breaking previous quarter. Most of the new deployments are one-hour front-of-the-meter (FTM) storage solutions, but nonetheless offer a promising look into the future of commercial solar energy storage.

  • Compressed air

    . The most

    recent government estimates calculate compressed air

    costs at $105/kWh, making it the most cost-effective mechanical storage option for large-scale applications.

  • Pumped hydro.

    Surplus solar energy can be used to pump water uphill, creating a massive amount of potential energy.

    Current pumped hydro costs

    are around $165/kWh, making it the second-best option for mechanical energy storage at scale. It’s only available in certain areas, however, as new pumped hydro involves high upfront costs and significant regulatory hurdles.

Home solar energy storage

Residential solar has myriad benefits, including resiliency, cost savings, and decentralization of electrical production (otherwise known as “virtual power plants”). But the commercial energy storage methods we discussed above are likely cost-prohibitive for the average homeowner. Thankfully, battery storage can now offer homeowners a cost-effective and efficient way to store solar energy.

Lithium-ion batteries are the go-to for home solar energy storage. They’re relatively cheap (and getting cheaper), low profile, and suited for a range of needs. Other batteries commonly available for residential use include saltwater batteries and lead-acid batteries.

Regardless of the battery type, home backup batteries allow homeowners to save energy during high production, low demand times (i.e. during the workday) for use during high demand periods when generation diminishes. Home solar energy storage inherits the same benefits of large-scale solar energy storage, translating into resiliency, uninterrupted energy, and cost savings. And these benefits go directly to the homeowner.

Technology to help design solar battery storage

Designing a storage system along with a solar installation used to be labor-intensive and include a fair amount of guesswork. Now, software like Aurora‘s includes battery storage as part of its offerings.

Using Aurora Solar’s Battery Storage Tool, solar installers can analyze load off-set, calculate the projected price of a project, forecast smart battery sizing recommendations based on customer priorities, and present it to the customer in a compelling, easy-to-understand way.

Aurora has also introduced battery self-consumption modeling. You can learn more here.

So, while the technology used to store solar energy may seem complicated or overwhelming to some customers, Aurora can help you break down the complexities for customers with interactive and easy-to-understand models of performance and savings. 

Click above to learn more about modeling battery storage for self consumption in Aurora.

How to Store Solar Energy: FAQ

Click here to learn more about Aurora’s battery self-consumption modeling capabilities.

Conclusion

The sun offers a limitless supply of clean power, but harnessing it can be a challenge. Thankfully, several options for commercial and residential storage offer proven solutions for storing solar energy, and emerging technologies are being developed daily. For commercial applications, mechanical storage options provide effective solutions to harnessing solar energy when it’s needed most, and grid-scale battery storage will likely become available soon. For residential solar, battery storage is the best option, with a variety of affordable units on the market. Together, these solutions provide an effective portfolio for storing solar energy and provide a compelling argument for further solar deployment in commercial and residential settings. 

To learn more, visit these resources:

To see battery self-consumption modeling in action, schedule a quick demo.

Sometimes two is better than one. Coupling solar energy and storage technologies is one such case. The reason: Solar energy is not always produced at the time energy is needed most. Peak power usage often occurs on summer afternoons and evenings, when solar energy generation is falling. Temperatures can be hottest during these times, and people who work daytime hours get home and begin using electricity to cool their homes, cook, and run appliances.

Storage helps solar contribute to the electricity supply even when the sun isn’t shining. It can also help smooth out variations in how solar energy flows on the grid. These variations are attributable to changes in the amount of sunlight that shines onto photovoltaic (PV) panels or concentrating solar-thermal power (CSP) systems. Solar energy production can be affected by season, time of day, clouds, dust, haze, or obstructions like shadows, rain, snow, and dirt. Sometimes energy storage is co-located with, or placed next to, a solar energy system, and sometimes the storage system stands alone, but in either configuration, it can help more effectively integrate solar into the energy landscape.

What Is Energy Storage?

“Storage” refers to technologies that can capture electricity, store it as another form of energy (chemical, thermal, mechanical), and then release it for use when it is needed. Lithium-ion batteries are one such technology. Although using energy storage is never 100% efficient—some energy is always lost in converting energy and retrieving it—storage allows the flexible use of energy at different times from when it was generated. So, storage can increase system efficiency and resilience, and it can improve power quality by matching supply and demand.

Storage facilities differ in both energy capacity, which is the total amount of energy that can be stored (usually in kilowatt-hours or megawatt-hours), and power capacity, which is the amount of energy that can be released at a given time (usually in kilowatts or megawatts). Different energy and power capacities of storage can be used to manage different tasks. Short-term storage that lasts just a few minutes will ensure a solar plant operates smoothly during output fluctuations due to passing clouds, while longer-term storage can help provide supply over days or weeks when solar energy production is low or during a major weather event, for example. 

Advantages of Combining Storage and Solar

  1. Balancing electricity loads – Without storage, electricity must be generated and consumed at the same time, which may mean that grid operators take some generation offline, or “curtail” it, to avoid over-generation and grid reliability issues. Conversely, there may be other times, after sunset or on cloudy days, when there is little solar production but plenty of demand for power. Enter storage, which can be filled or charged when generation is high and power consumption is low, then dispensed when the load or demand is high. When some of the electricity produced by the sun is put into storage, that electricity can be used whenever grid operators need it, including after the sun has set. In this way, storage acts as an insurance policy for sunshine.
  2. “Firming” solar generation – Short-term storage can ensure that quick changes in generation don’t greatly affect the output of a solar power plant. For example, a small battery can be used to ride through a brief generation disruption from a passing cloud, helping the grid maintain a “firm” electrical supply that is reliable and consistent.
  3. Providing resilience – Solar and storage can provide backup power during an electrical disruption. They can keep critical facilities operating to ensure continuous essential services, like communications. Solar and storage can also be used for microgrids and smaller-scale applications, like mobile or portable power units.

Types of Energy Storage

The most common type of energy storage in the power grid is pumped hydropower. But the storage technologies most frequently coupled with solar power plants are electrochemical storage (batteries) with PV plants and thermal storage (fluids) with CSP plants. Other types of storage, such as compressed air storage and flywheels, may have different characteristics, such as very fast discharge or very large capacity, that make them attractive to grid operators. More information on other types of storage is below. 

Pumped-Storage Hydropower

Pumped-storage hydropower is an energy storage technology based on water. Electrical energy is used to pump water uphill into a reservoir when energy demand is low. Later, the water can be allowed to flow back downhill and turn a turbine to generate electricity when demand is high. Pumped hydro is a well-tested and mature storage technology that has been used in the United States since 1929. However, it requires suitable landscapes and reservoirs, which may be natural lakes or man-made by constructing dams, requiring lengthy regulatory permits, long implementation times, and large initial capital. Other than energy arbitrage, pumped hydro’s value of services to integrate variable renewables are not fully realized, which can make the financial payback period long. These are some of the reasons pumped hydro has not been built recently, even though interest is evident from requests to the Federal Energy Regulatory Commission for preliminary permits and licenses.

Electrochemical Storage

Many of us are familiar with electrochemical batteries, like those found in laptops and mobile phones. When electricity is fed into a battery, it causes a chemical reaction, and energy is stored. When a battery is discharged, that chemical reaction is reversed, which creates voltage between two electrical contacts, causing current to flow out of the battery. The most common chemistry for battery cells is lithium-ion, but other common options include lead-acid, sodium, and nickel-based batteries.

Thermal Energy Storage

Thermal energy storage is a family of technologies in which a fluid, such as water or molten salt, or other material is used to store heat. This thermal storage material is then stored in an insulated tank until the energy is needed. The energy may be used directly for heating and cooling, or it can be used to generate electricity. In thermal energy storage systems intended for electricity, the heat is used to boil water. The resulting steam drives a turbine and produces electrical power using the same equipment that is used in conventional electricity generating stations. Thermal energy storage is useful in CSP plants, which focus sunlight onto a receiver to heat a working fluid. Supercritical carbon dioxide is being explored as a working fluid that could take advantage of higher temperatures and reduce the size of generating plants.

Flywheel Storage

A flywheel is a heavy wheel attached to a rotating shaft. Expending energy can make the wheel turn faster. This energy can be extracted by attaching the wheel to an electrical generator, which uses electromagnetism to slow the wheel down and produce electricity. Although flywheels can quickly provide power, they can’t store a lot of energy.

Compressed Air Storage

Compressed air storage systems consist of large vessels, like tanks, or natural formations, like caves. A compressor system pumps the vessels full of pressurized air. Then the air can be released and used to drive a turbine that produces electricity. Existing compressed air energy storage systems often use the released air as part of a natural gas power cycle to produce electricity.

Solar Fuels

Solar power can be used to create new fuels that can be combusted (burned) or consumed to provide energy, effectively storing the solar energy in the chemical bonds. Among the possible fuels researchers are examining are hydrogen, produced by separating it from the oxygen in water, and methane, produced by combining hydrogen and carbon dioxide. Methane is the main component of natural gas, which is commonly used to produce electricity or heat homes.

Virtual Storage

Energy can also be stored by changing how we use the devices we already have. For example, by heating or cooling a building before an anticipated peak of electrical demand, the building can “store” that thermal energy so it doesn’t need to consume electricity later in the day. The building itself is acting as a thermos by storing cool or warm air. A similar process can be applied to water heaters to spread demand out over the day. 

Ultimately, residential and commercial solar customers, and utilities and large-scale solar operators alike, can benefit from solar-plus-storage systems. As research continues and the costs of solar energy and storage come down, solar and storage solutions will become more accessible to all Americans.

Additional Information

Learn more about solar office’s systems integration program. 

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Where does solar energy get stored?

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