Solar panels produce power only when the sun is shining. So if solar panels generate energy only during sunny days, how can you use solar energy at night or on cloudy days when the sun isn’t shining? This is where energy storage comes in handy! In this post, we will be looking at how can solar energy be stored.
We will start by discussing what is energy storage. Next, we’ll look at how solar energy storage works, including its advantages. Then we’ll wrap up by outlining the best methods to store solar energy on commercial and residential levels.
Wind turbines produce power only when the wind blows. Hydraulic turbines produce power only when there is flowing water to turn the turbine! And solar panels produce energy when the sun is shining.
But there is a problem!
What happens when the sun stops shining or the wind stops blowing?
We have to turn back to burning fossil fuels for energy.
So how can we manage our lives on renewable energy which is so variable and weather dependant?
Besides this, energy supply and demand must be equal at any given moment. However, peak energy demand tends to come during the summer afternoons and evenings, coinciding with falling solar power generation . This causes the supply and demand issue.
In fact, solar panels generate more than enough electrical energy while the sun is shining to meet our energy demands for days, weeks, months, seasons, and even years, thanks to new methods of storing energy.
Energy Storage refers to technologies that capture electrical energy and then store it as another form of energy (chemical, thermal, mechanical), and then release it for use when it is needed.
“Related Article: Solar energy can power many products. When paired with solar storage technologies it ensures that these products run seamlessly!”
US Energy Storage Market
How big is the energy storage market? It currently makes up about 2% of U.S. generation capacity but it is expected to grow significantly. A report from Wood Mackenzie and the U.S. Energy Storage Association found that the market for U.S. battery storage will grow sixfold, to a total of nearly 7.5 GW, by 2025 and will create a $7 billion/year market by 2025. 
How Energy Storage Works
A common example of energy storage is a lithium-ion battery – the same batteries that power your phone or power bank. They use reversible chemical reactions to store electricity. Allowing them to absorb power and discharge it later.
One other thing to note is that storage and retrieval of energy aren’t 100% efficient.
Some amount of energy is always lost in the process. But still, energy storage provides you the flexibility to use energy whenever you want to.
Two important concepts used with energy storage technologies are:
- Energy Capacity
- Power Capacity
The energy capacity of an energy storage technology refers to the total amount of energy that can be stored. It’s usually measured in kilowatt-hours (kWh) or megawatt-hours (MWh).
The power capacity of an energy storage technology refers to the amount of energy that can be released at a given time. It’s usually measured in kilowatts (KW) or megawatts (MW).
Depending on the application, different combinations of energy and power capacities of storage can be used.
What Are the Advantages of Storing Solar Energy?
As explained above, the output of renewable energy technologies is not stable. The energy has to be used at the moment it’s produced. Also, solar energy isn’t always produced at the time energy is needed the most.
These and other issues mentioned above make solar energy storage essential and greatly expands the uses of solar energy.
In fact, by storing renewable energy we overcome many challenges. Here are some of the most notable advantages of storing solar energy:
- Balances demand & supply of energy. The output of renewable energy technologies such as wind and solar is variable. Storage solutions have a great potential for smoothing out the electricity supply from these sources, ensuring that generation matches demand at all times. For example, when solar panels pump out more energy than is needed, a surplus amount of energy can be stored and used when needed. Thus balancing the supply and demand of energy.
- Ensures the consistent flow of energy. When there are passing clouds, for example, the output of a solar panel will result in decreased generation of energy. This results in an inconsistent flow of energy. Storage solutions can help make the flow of energy consistent during brief disruptions
- Can act as backup power when there is a power outage. If you’re using an off-grid solar PV system (stand-alone power system), then you can use the stored solar power when there is a power outage or blackout. However, this is not the case with on-grid solar PV systems (grid-tied solar systems).
- Helps you reduce energy costs. Switching to energy storage allows you to divert your peak demand away from the power grid during high-demand periods because energy prices are higher during these times.
- Provides energy on-demand. Not everyone needs electrical energy during the day. By storing solar PV energy, you can use it whenever required. For example, if you’re living in a remote area, where the electrical grid only provides power during the day, you can store solar PV energy and use it during the night. Moreover, solar energy storage can help you have enough power during the winter season.
- It can provide energy during emergencies. Solar energy storage can help increase power system resiliency. Solar-plus storage (charging batteries using solar energy) can help reduce stress on the grid during extreme heat events or natural disasters. They continue to provide power reliably, even if backup generators fail as they did after Hurricane Sandy .
- Ensures power stability. Another advantage of solar energy storage is that islands and microgrids that are cut off from the main electrical grid system, rely on energy storage to guarantee power stability and efficiency.
Now you know why it’s essential to store solar energy. Let’s look at the methods and technologies that help store solar energy efficiently.
Solar Energy Storage Technologies
In terms of storage duration, solar energy storage technologies have two kinds: short-term storage and longer-term storage.
Short-term Vs Long-term Solar Energy Store
Depending on the purpose of energy storage, one or both of these technologies may be used together.
As the names imply, short-term storages provide support that lasts for some minutes, for example, it will ensure a solar plant operates smoothly during output fluctuations due to passing clouds.
These kinds of storage systems are used with the electric grid to provide relief during peak demand hours, facilitate the integration of renewable energy sources, and ensure grid reliability.
On the other hand, longer-term storage will provide energy supply for hours, days, and even weeks, when solar energy production is low or during a major weather event.
Methods Solar Energy Can Be Stored
Solar energy storage technologies fall under these three general categories:
- Thermal Energy Storage
- Battery Storage (Battery Bank)
- Mechanical Storage
Let’s briefly explore each of these categories.
#1 What is Thermal Energy Storage?
Thermal storage technology uses special fluids such as molten salt to absorb and retain the heat energy of the sun. The heated molten salt stores the heat energy at a temperature of over 1000 Fahrenheit degrees in a contained system of pipes and insulated storage tanks. It’s then used to make steam to power a generator and produce electricity.
The power plants that use thermal storage are called Concentrating Solar Plants (CSP). CSPs are currently operating or proposed in different countries. China’s Molten Salt Fresnel CSP Plant is one such example.
#2 What is Battery or Battery Bank Storage?
Solar PV can be stored in lead-acid batteries or lithium-ion batteries, with lead-acid batteries being the slightly cheaper option. These batteries use reversible chemical reactions to store electrical energy.
In this method, a solar battery or a battery bank (depending on storage capacity) is constructed by connecting batteries together. The battery bank is then used to store the electrical energy produced by solar panels. Once the battery bank is charged, you can use the stored solar energy on-demand. Similar to how you charge a power bank using a solar panel.
With the growing electric vehicle industry, advancements in EV battery technologies are expected to continue. Battery prices will likely decline because of this increased demand for EV batteries and technological improvements.
Tesla Powerwall Battery
An example of a lithium-based battery storage system is the Tesla Powerwall. It’s a fully integrated AC battery system for residential use that enables you to use the sun’s stored energy during the day or night. The rechargeable lithium-ion battery pack also can be used to store excess energy. Moreover, the system can disconnect itself from the grid to act as a battery backup system in case of an outage.
The first Powerwall introduced in April 2015 produced a 6.4kWh capacity but has since been updated with the current Powerwall 2 / Powewall+ versions.
#3 What is Mechanical Storage?
One other way to generate electricity is to take advantage of the potential energy of things like water in hydroelectric power. Mechanical storage of solar energy uses a similar concept; it converts excess electrical energy into mechanical power and then back into electricity for later use.
Some technologies that use the mechanical storage concept include:
- Pumped hydro: Pumped hydroelectric storage allows you to store energy by storing excess generation for later use. Many hydropower facilities have two reservoirs at different elevations. When supply exceeds demand, water is pumped into the upper reservoir (using this excess electricity) thus storing water for later use. The water is discharged from the upper reservoir by flowing downhill through turbines to produce electricity when needed.
- Compressed Air: Compressed air is pumped into large vessels such as a tank or underground formation. The energy stored in this compressed air is later released to generate power.
- Flywheel: A flywheel is a heavy wheel attached to a rotating shaft. During off-peak demand periods, this technique uses surplus energy to turn a flywheel and store energy. Later, the power is produced from the flywheel to meet demands.
Some of the methods discussed above are only suitable for commercial applications. While others are suitable for residential applications. Let’s explore these methods on both commercial and residential levels.
Commercial Solar Energy Storage
Pairing commercial energy storage solutions with renewable sources such as solar or wind allow businesses to maximize the use of these intermittent sources by storing excess energy when it is produced and using it when needed.
According to the estimates of US DOE, outages are costing American businesses $150 billion annually . This is a huge amount of money lost!
Investing in solar energy storage technologies can help avoid these losses.
Thermal and Mechanical Energy Storage Systems
Thermal and mechanical energy storage systems cost a lot. But, the benefits of these storage options far outweigh the costs.
For example, solar energy storage solutions can help utilities keep up with peak energy demand thus reducing energy costs. Additionally, it can help provide critical backup.
Since utility companies and businesses have bigger budgets than individual households, mechanical and thermal storage are viable options.
Battery Storage Systems
Battery storage systems, on the other hand, can be used for both commercial and residential applications. For example, Tesla – an electric vehicle and clean energy company, provides commercial battery storage systems that offer greater control, efficiency, and reliability across the electric grid.
Tesla’s Powerpack is a scalable energy storage system, intended for utility companies and businesses. It contains 16 individual battery pods, each with an isolated DC-DC converter. The Powerpack has up to 232 kWh (AC) energy capacity and up to 130 kW (AC) power capacity .
Frequently Asked Questions
How much solar energy can be stored in a Tesla Powerwall Battery?
The current Powerwall 2 and Plus version battery can store up to 13.5 kWh of solar energy (12.2+10%). 12.2 kWh of energy – enough to power your refrigerator and other small electronics for an entire day or when the lights go out! It also has 10% more reserve capacity so you never have to worry about running low on electricity during peak times like morning or evening hours. 
How much storage do I need?
Every home’s energy needs are unique. The same way you would size your solar panel energy system to meet energy requirements; battery storage capacity should also be matched with your energy requirement. It also takes into account the duration of time you need your battery storage to provide you with power.
How much does a battery storage installation cost?
The installation costs of battery storage depend on the type and size of your home’s energy storage system. The costs of installation depend on the amount of electrical work required to backup your critical loads, labor costs, and required electrical materials such as wires, switches, and panels.
Energy storage can help you reduce your reliance on the grid by storing your solar energy for later use when the sun isn’t shining. Using a solar energy storage system in your home has many benefits including, lowering your carbon footprint, keeping you connected during power outages, and also help you save money.
Thermal and mechanical storage solutions are too expensive for the average homeowner. Therefore a cost-effective way to store solar energy in your home is to use battery storage. When it comes to battery storage systems, there are many options available to homeowners, lithium-ion, lead-acid, sodium, and nickel-based rechargeable batteries – to name a few.
Lithium-ion rechargeable batteries are lightweight, have a high energy density, and are suited for a range of needs. A lithium-ion battery is a preferred choice for solar energy storage systems. In terms of costs, they are relatively cheap.
 Peak energy demand tends to come during the summer afternoons and evenings.
 Backup generators failed after Hurricane Sandy.
 Energy storage in the United States is anticipated to reach almost 7.5 GW each year by 2025.
 Outages are costing American businesses $150 billion annually.
 Tesla Powerpack
 Tesla Powerwall