Storing Solar Energy – How Solar Batteries Work
Solar panel systems have become one of the fastest-growing sources of energy in the United States. According to the Solar Energy Industries Association, the solar market doubled in size in 2016. The popularity of solar power has led to the rise of another renewable technology: solar batteries that can store extra solar power for later use. Companies like Tesla & LG are developing batteries that can be installed with solar panels to create “solar-plus-storage” systems for your home.
The typical solar energy system includes solar panels, an inverter, equipment to mount the panels on your roof, and a performance monitoring system that tracks electricity production. The solar panels collect energy from the sun and turn it into electricity, which is passed through the inverter and converted into a form that you can use to power your home.
Most of the residential solar energy systems are connected to the electricity grid (or “grid-tied”). When your panels are producing more electricity than your home needs, the excess is fed back into the power grid. Conversely, when your home needs more electricity than your solar panels are producing, you can draw power from the electric grid. In most cases, you receive a credit on your utility bill for the electricity you send back to the grid. Later, when you are using more electricity than your solar panels have generated, you can use those credits instead of having to pay more to your utility. This process is known as net metering.
- Solar batteries work by converting the DC energy being produced by your solar panels and storing it as AC power for later use. In some cases, solar batteries have their own inverter and offer integrated energy conversion. The higher your battery’s capacity, the larger the solar system it can charge.
- When you install a solar battery as part of your solar panel system, you can store excess solar electricity at your home instead of sending it back to the grid. If your solar panels are producing more electricity than you need, the excess energy goes towards charging the battery. Later, when your solar panels aren’t producing electricity, you can draw down the energy you stored earlier in your battery for night use.
- You’ll only send electricity back to the grid when your battery is fully charged, and you’ll only draw electricity from the grid when your battery is depleted.
What this means in practical terms is that homes with solar-plus-storage can store excess solar power onsite for use later when the sun isn’t shining. As a bonus, since solar batteries store energy at your home, they also offer short-term backup power if there’s a power outage in your area.
How to compare your solar storage options
As you consider your solar-plus-storage options, you’ll come across a lot of complicated product specifications. The most important ones to use during your evaluation are the battery’s capacity & power ratings, depth of discharge (DoD), round-trip efficiency, warranty, and manufacturer.
- Capacity & power
Capacity is the total amount of electricity that a solar battery can store, measured in kilowatt-hours (kWh). Most home solar batteries are designed to be “stackable,” which means that you can include multiple batteries with your solar-plus-storage system to get extra capacity. While capacity tells you how big your battery is, it doesn’t tell you how much electricity a battery can provide at a given moment. To get the full picture, you also need to consider the battery’s power rating. In the context of solar batteries, a power rating is the amount of electricity that a battery can deliver at one time. It is measured in kilowatts (kW).
A battery with a high capacity and a low power rating would deliver a low amount of electricity (enough to run a few crucial appliances) for a long time. A battery with low capacity and a high-power rating could run your entire home, but only for a few hours.
- Depth of discharge (DoD)
Most solar batteries need to retain some charge at all times due to their chemical composition. If you use 100 percent of a battery’s charge, its useful life will be significantly shortened.
The depth of discharge (DoD) of a battery refers to the amount of a battery’s capacity that has been used. Most manufacturers will specify a maximum DoD for optimal performance. For example, if a 10 kWh battery has a DoD of 90 percent, you shouldn’t use more than 9 kWh of the battery before recharging it. A higher DoD means you will be able to utilize more of your battery’s capacity.
- Round-trip efficiency
A battery’s round-trip efficiency represents the amount of energy that can be used as a percentage of the amount of energy that it took to store it. For example, if you feed five kWh of electricity into your battery and can only get four kWh of useful electricity back, the battery has 80 percent round-trip efficiency (4 kWh / 5 kWh = 80%).
A higher round-trip efficiency means you will get more economic value out of your battery.
- Battery life & warranty
For most uses of home energy storage, your battery will “cycle” (charge and drain) daily. The battery’s ability to hold a charge will gradually decrease the more you use it. In this way, solar batteries are like the battery in your cell phone –as your phone gets older you’ll start to notice that the battery isn’t holding as much of a charge as it did when it was new.
Your solar battery will have a warranty that guarantees a certain number of cycles and/or years of useful life. Because battery performance naturally degrades over time, most manufacturers will also guarantee that the battery keeps a certain amount of its capacity over the course of the warranty. How long your solar battery lasts depends on the brand of battery you buy and how much capacity it will lose over time.
Many different types of organizations are developing and manufacturing solar battery products, from automotive companies to tech startups. While a major automotive company entering the energy storage market likely has a longer history of product manufacturing, they may not offer the most revolutionary technology. By contrast, a tech startup might have a brand-new high-performing technology, but less of a track record to prove the battery’s long-term functionality.
Whether you choose a battery manufactured by a cutting-edge startup or a manufacturer with a long history depends on your priorities. Evaluating the warranties associated with each product can give you additional guidance as you make your decision.
Solar battery lifespan
The general range for a solar battery’s useful lifespan is between 5 and 15 years. If you install a solar battery today, you will likely need to replace it at least once to match the 25 to 30-year lifespan of your PV system. However, just as the lifespan of solar panels has increased significantly in the past decade, it is expected that solar batteries will follow suit as the market for energy storage solutions grows.
Proper maintenance can also have a significant effect on your solar battery’s lifespan. Solar batteries are significantly impacted by temperature, so protecting your battery from freezing or sweltering temperatures can increase its useful life. Quality maintenance efforts can also impact how long your solar battery will last.
What are the best type of batteries for solar?
Batteries used in home energy storage typically are made with one of three chemical compositions: lead acid, lithium ion, and saltwater. In most cases, lithium ion batteries are the best option for a solar panel system, though other battery types can be more affordable.
- Lead acid
Lead acid batteries are a tested technology that has been used in off-grid energy systems for decades. While they have a relatively short life and lower DoD than other battery types, they are also one of the least expensive options currently on the market in the home energy storage sector. For homeowners who want to go off the grid and need to install lots of energy storage, lead acid can be a good option.
- Lithium ion
Most of new home energy storage technologies use some form of lithium ion chemical composition. Lithium ion batteries are lighter and more compact than lead acid batteries. They also have a higher DoD and longer lifespan when compared to lead acid batteries. However, lithium ion batteries are more expensive than their lead acid counterparts.
A newcomer in the home energy storage industry is the saltwater battery. Unlike other home energy storage options, saltwater batteries don’t contain heavy metals, relying instead on saltwater electrolytes. While batteries that use heavy metals, including lead acid and lithium ion batteries, need to be disposed of with special processes, a saltwater battery can be easily recycled. However, as a new technology, saltwater batteries are relatively untested.
About Green Brilliance
GreenBrilliance is established with the mission to provide solar energy solutions in the DC, MD & VA areas. GreenBrilliance is a vertically integrated; end-to-end Solar Energy Services Company headquartered in the DC metro area delivering turnkey solar EPC solutions to homes, businesses & utility large scale projects at very competitive prices.
As a top-quality EPC provider, we have in-house engineering & design teams, our vertical integration across the value-chain enables us to achieve operational efficiencies leading to cost & time savings for our customers & ensures delivery of superior products at an unmatched value. At GreenBrilliance we realize & appreciate the significance of our role in educating & delivering PV systems to our customers. “An educated customer is the best customer.” We believe in excellent customer service both pre-&-post installation.
Green Brilliance has worked on & excelled in several battery storage related projects in the residential as well as commercial sector. We have worked with various manufacturers such as Sonnen, SolarEdge, LG & Tesla. We are also the officially licensed & certified installers of LG & Sonnen batteries.
GreenBrilliance recently ranked 33rd in the top hundred installers in the world by the list published by the renowned ‘Solar World Online’ with a fantastic portfolio including the prestigious “Ronald Reagan International Airport” in Washington DC.
Core Capabilities & Services:
- Solar Consultation
- PV Design & Engineering
- Permits & Utility Interconnection
- Operations & Maintenance
Our Expertise :
- Design & engineering
- Grid-tied Distributed Solar Systems
- Off-Grid/Micro Grid Systems
- Commercial/Utility Scale Systems
- Solar Storage Systems
Compiled By : Nishanth Mahankali – Solar Design Engineer – GreenBrilliance LLC