Storage

Solar Battery Guide: Benefits, Features, and Cost

Palmetto
A solar battery mounted to the wall of a solar powered home to provide energy storage.
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Generating clean, green energy for your home using solar panels helps you save money, use less fossil fuel, and reduce your environmental impact. Whether you're thinking about installing a new solar power system, or you’ve already gone solar, battery energy storage can help you leverage the full potential of your solar panels. By storing the excess energy your solar panels produce, solar-plus-storage provides a reliable, low-cost power backup option so when the sun goes down, the clouds roll in, or the lights go off in your community, you always have power on hand and savings in store.

In this article, we’ll look at how solar batteries work, and then dive into solar battery cost and what you can expect to pay, solar battery benefits and why you should consider adding storage to your solar power system design, solar battery features and what to compare when looking at different solar battery options, and solar battery types so you know the advantages and disadvantages of each solar battery material. Our goal is to help you decide what the best solar storage options are for your home.

How Does A Solar Battery Work?

Consider your home's energy needs on a typical day: Usually, a home requires more energy in the morning when people are getting ready, and at night when more appliances and electronics are in use. During the day when people are away from their home, power demands go down, but these are actually the most productive hours of the day for your solar power system, when it is generating the most electricity. Therefore, the ratio of energy production to energy consumption is highest during the day, meaning there is excess power being generated.

If you don't have an energy storage solution, that excess power is being fed back to the grid, and you might get some credit for it if your utility supports net metering. Alternatively, you can add a solar battery to your solar power system, and store this surplus renewable energy to use when needed to power your home. Solar batteries work by storing the excess energy produced by your solar panels, and then feeding that excess energy back into your system when needed. Solar batteries can either store excess energy as DC electricity that’s produced by your solar panels, or they can store AC electricity that’s already been converted by your inverter.

Can you go "off-grid" with a solar battery?

The short answer is that even with solar battery storage, going completely "off-grid" is usually not worth the extra cost and complexity. Staying connected to your utility gives you more options for where to get electricity, and you can install a much smaller solar power system that will cost a lot less, and still save almost as much money as you would with a much larger system, where most of that excess capacity goes unused most of the time.

To go completely off-grid, you need enough solar battery storage to last for multiple days of typical usage, and you need enough solar panels to both power your home, and keep those solar batteries charged at all times. It might be possible during the summer months when there’s plenty of power being generated, but when winter rolls around and your solar panels have fewer hours of sunlight to generate electricity with, it’s going to be difficult to generate the excess electricity you’d need to keep enough in reserve. No one wants to stress over how much electricity you have stored up, and whether or not it can last through multiple days of storms and cloudy weather!

By staying connected to the grid, you’ll always have a backup source of electricity when needed, and you can use your solar power when it’s available to power your home, without stressing about what happens when production is lower than average. Adding a solar battery while staying connected to the grid gives you even more control over your electricity, and helps use the full capacity of your solar panels without letting any excess electricity go to waste.

What are the benefits of adding a solar battery to your solar power system?

There are a variety of solar battery benefits that homeowners consider when deciding to integrate energy storage into their solar power system design:

  • Energy Independence - Perhaps the ultimate reason for why you might want a solar battery installation. Solar energy storage technology enables you to have more control over where your energy comes from, how it gets used, and what you can do with it.
  • Increase Your Savings - By drawing power from your solar battery, you can still use the more affordable electricity that your solar panels produce, even at night or during a storm. If you live in an area where electricity prices depend on time-of-use metering, you can save even more by drawing power from your solar battery when the utility companies charge higher rates during the night or peak hours.
  • Better For The Environment - By increasing the energy-producing potential of your solar PV system, you can reduce your fossil fuel usage even more, reducing your environmental carbon footprint, and supporting technologies that will help continue the international drive towards a better climate future.

Electricity During Storms, Severe Weather, and Other Power Outages

The grid power supply can be affected by seasonal storms and other severe weather conditions that lead to power outages, sometimes extending for hours or even days. A good example is the huge winter storm that hit Texas in mid-February 2021, causing power outages for at least 4.5 million customers. To add insult to injury, some Texans were even stuck with huge utility bills as some electricity rates skyrocketed more than 7,000% in a matter of days.

Another example of severe weather leading to large-scale power outages was the massive 2019 wildfires in California. More than 2 million customers were left without power after the utilities turned off the grid to prevent high winds from knocking down power lines and starting even more wildfires.

Having solar battery storage added to your solar power system can save you the stress of having to experience similar occurrences in the future, as you can use the power that’s stored in your battery, even if the rest of the grid is experiencing a blackout. With climate change causing more severe weather and larger and even more destructive storms, it’s a safe bet that large-scale blackouts will continue to be an issue in the coming years.

How much energy can be stored in a solar battery?

The energy that a solar battery can store is measured in kilowatt-hours (kWh), and different manufacturers produce batteries that can hold varying amounts of power. For example, the Sonnen Eco is available in capacities that range from 5 kWh all the way up to 20 kWh in a single battery.

In addition, most solar batteries can be linked together or installed in an interconnected design to offer a larger combined storage capacity if your needs are higher than what a single battery can provide.

How do solar batteries fit into the larger electric grid?

At peak hours of the morning and evening, demand on the electric grid increases drastically, as more people are at home using more electricity. (This change in demand is called the “duck curve”.) The increased demand causes utilities to scale up their electricity generation at power plants, and the sudden rise in demand at certain hours of the day may cause disruptions, and there are risks of oversupply.

Basically, utilities have to be prepared for peak demand, and a lot of their electricity generation potential goes unused when demand is lower. Building this excess electricity generation capacity is expensive, and leads to higher utility rates as a result.

Adding solar batteries to home solar PV systems can help flatten the demand curve, so the grid can be designed for more typical usage and doesn't need to be built for surges and spikes. During the day when demand is lower, solar panels can charge solar batteries, and then when demand increases, solar batteries can help supply the extra power that’s needed, so it doesn’t have to be generated by the utilities. Therefore, solar battery storage plays a crucial role in streamlining grid power production and distribution, and can better align utility capacity with normalized demand.

How much does it cost to add a solar battery to your home?

Your solar battery cost depends on a variety of factors, including power rating, depth of discharge capability, round-trip efficiency, and the warranty that's provided, but the biggest factor is the capacity of the battery. Typically the bigger the solar battery, the higher the cost.

A good rule-of-thumb for solar battery cost is that the cost per kilowatt-hour ranges from $400 to $750. Therefore, a typical home solar battery is going to cost between $10,000 and $20,000, including installation costs.

If you need multiple batteries, the cost for the entire battery backup system might be higher, but Palmetto can make a recommendation for how many batteries you would need, based on your home’s typical energy use, and provide you with various options for how much solar battery storage you might want to include in your overall system design. If you’re looking for an answer to, “How much is a solar backup battery?” then that’s a good place to start.

How Net Metering Credits Affect Solar Battery Economics

Net metering is when the utility gives you credit for excess electricity that your solar power system generates and feeds back into the grid. Net metering basically turns the power grid into your home’s backup battery, although the economics of net metering compared to battery storage are going to be different, unless you receive the same credit from the grid when providing electricity as you pay when receiving electricity. (This is called 'true net metering', and is not offered by many utilities).

Utilities generate electricity at a very large scale, so they can generate it for much less than they charge for it. As a result, even when a utility gives net metering credit for electricity they receive from a homeowner, they want to credit the homeowner the same rate that they can generate it for themselves.

For example, a utility might charge $0.12 per kWh for the power drawn from the grid, but only give credits worth $0.05 per kWh when you feed the grid. This means that if you get credit for electricity that you add to the grid, but then you have to buy it back later at a higher cost, you end up paying $0.07 more for the same electricity that you could have saved into a solar battery system when you generated it. Therefore, it's often more economical in the long run to add solar battery storage to your home instead of using net metering credits, because you can capture the full value of any excess electricity that your system generates.

How Time-of-Use Metering Credits Affect Solar Battery Economics

Time-of-Use (TOU) rates refer to electricity rates that vary depending on the time of day that the electricity gets used. Usually, rates are highest during peak hours (mornings and afternoons/evenings) and lowest during the day when solar panels are producing the most electricity. Therefore, if you live in an area with TOU rates, you can leverage your solar battery benefits by storing the additional solar energy generated when the rates are low, and using it during peak hours when rates are high, instead of paying for grid power.

How Demand Charges Affect Solar Battery Economics

Demand charges are when the electricity rate your utility changes depends on how much electricity you use. The more you use, the higher the rate. The rates may also depend on the amount of electricity you use during peak hours when power demand is higher. This policy is meant to encourage homeowners to reduce their total electricity usage.

If you have solar power and can store excess energy in a solar battery, you can significantly decrease the amount of energy you use from the grid, so you’ll pay even less for electricity from utilities with demand charges, because your total electricity usage will be much less.

Are tax credits offered for the purchase of a solar battery?

There’s no single answer to the question, “Are there tax credits available for solar batteries?” because it depends on where you live, and how your solar power system is designed.

While installing a solar panel battery, you might qualify for various financial incentives from federal and state governments. For example, as long as the batteries you install are charged by solar (and not by the grid), they are eligible for the solar investment tax credit, which saves you 26% off the total cost of installation. Tax credits are directly applied to your tax bill, making it a smart way to save while acquiring an effective way to store solar energy.

In addition, some states like California have rebates specifically for batteries for solar panels that can significantly reduce the cost of acquiring them, through incentives like the Self-Generation Incentive Program (SGIP). Other states like Maryland have also passed an income tax credit for energy storage systems in recent years.

Solar Battery Features To Consider When Comparing Storage Options

There’s no easy answer to the question, “What is the best battery for solar storage?” because each battery has pros and cons that you should compare. Before you decide which solar battery option is right for you, you'll want to consider the four key solar battery features: Capacity and Power, Depth of Discharge, Round-Trip Efficiency, and Warranty.

1. Capacity and Power

Comparing solar battery power and capacity is usually the first step in determining which solar battery is the best match for your family’s needs.

Solar battery capacity is the amount of power a battery can store, measured in kilowatt-hours, or kWh. Solar battery capacity determines how long you can power your home with the energy stored in the battery. (Keep in mind that most home solar batteries can be “stacked” to include multiple batteries in a single installation, so you can increase their overall storage capacity.)

Solar battery power rating is what tells you how much power the battery can deliver all at once, measured in kilowatts. Having a battery with a large capacity is great, but you also need to know how much of that capacity you can access at any one time. The higher the power rating, the more devices you can power at the same time.

A battery with a low capacity and a high power rating means the battery is capable of powering many appliances at once, but for a short period of time. In contrast, a battery with a high capacity and a low power rating can only power a few electronic appliances at once, but it can do so for an extended amount of time.

Power and capacity isn’t an either/or comparison, and a good battery can offer both a large capacity and a high power rating, so you’ll want to just keep an eye on both features and find the right combination for your family’s needs.

2. Depth of Discharge (DoD)

Depth of Discharge is the maximum percentage of a battery’s capacity that can safely be used without the need for a recharge. Draining a battery completely can actually damage the battery, so the Depth of Discharge helps you understand how much of a battery’s total capacity can actually be used.

For example, a battery with a 10 kWh capacity and 90% depth of discharge rating tells you that you shouldn't use more than 9 kWh (90% of 10 kWh) before recharging to avoid damaging the battery and shortening its lifespan. The higher the Dept of Discharge, the more of your battery you can actually use on a day-to-day basis.

3. Round-Trip Efficiency

When a battery stores or distributes electricity, some energy turns into heat during transmission, and some is needed to run the technology inside of the battery itself, so it's not possible to draw back the same amount of energy that you feed into a solar battery. Therefore, round-trip efficiency measures the percentage of energy you can get back from a battery, compared to what the solar panels feed into the battery. For example, if you feed 10 kWh into your battery, but you can only get 8 kWh back, the battery has an 80% round-trip efficiency.

4. Warranty

The warranty terms help you determine how long you can expect a solar battery to last. Think about your cell phone — have you noticed that as it gets older, it just doesn’t hold the same charge as it did when it was new? Solar batteries are just like the battery in your cell phone, only much bigger.

Warranty terms specify the number of cycles (one cycle = one charge and discharge) that the battery should last, as well as the capacity it should retain, before the warranty expires. As the battery's cycles increase, its ability to retain a charge decreases. For example, you might get a 10 year, 5,000 cycle, 70% capacity warranty, which means that if the battery is less than 10 years old and has had less than 5,000 cycles, it should have at least 70% of its original capacity remaining.

The warranty that comes with a battery impacts the price of that battery. Typically, more expensive batteries are going to include longer or better warranty terms, and that warranty can prevent you from dealing with issues down the road as your battery gets older.

What is the battery life of a home solar battery?

The features of the battery you choose will determine how long your solar batteries last, and what the battery life is expected to be. For instance, how quickly the capacity rating of the battery decreases determines how long it can be used before needing a replacement. The typical home solar battery has a battery life between 5 and 15 years before the performance of the battery is reduced enough that it will need to be replaced.

What is the lifespan of a home solar battery?

Generally, the solar battery lifespan you can expect is between 5 and 15 years. As with most batteries, a solar battery’s lifespan can be increased with proper maintenance, such as making sure that it operates at specified temperatures, doesn’t discharge beyond its Depth of Discharge limit, and maintains a proper charge level when not in use.

What materials are home solar batteries made from?

Most people who want to know, “What are the different types of solar batteries?” are looking to compare the different battery materials. Solar batteries can be manufactured from lithium-ion, lead-acid, and even saltwater. Each material has different characteristics, with advantages and disadvantages.

Lithium-Ion

Home solar batteries made with lithium-ion are made with the same chemical composition used to create mobile phone, laptop, and electric vehicle batteries. Lithium-ion solar batteries like Tesla Powerwall and sonnenCore are popular for their compact design, higher Depth of Discharge rating, and extended lifespan compared to lead-acid batteries. Because of these benefits, lithium-ion batteries are typically more expensive than other solar battery types, but this initial investment can pay off over time.

Lead-Acid

Lead-acid batteries are similar to the battery type found in most gas-powered vehicles, and have been used for decades as solar storage options, though they are now typically used in more DIY storage solutions. Lead-acid batteries are significantly cheaper than other solar battery types, but they have a shorter lifespan and lower Depth of Discharge rating. Lead-acid batteries also have less capacity than lithium-ion batteries, so multiple batteries are usually connected together into a solar battery bank to provide enough storage, making the installation more complicated.

Saltwater

Saltwater batteries are relatively new to the energy storage market, and as the name implies, they use saltwater as the electrode to store energy. The key benefit of a saltwater battery is that they don't use heavy metals (lead and lithium) that require a careful disposal process once the battery is no longer being used to store electricity. Saltwater batteries can be recycled, which makes them more eco-friendly. However, saltwater storage is still a new and unproven technology, and no company is currently selling saltwater battery technology at a large scale for home use.

Where can I get the best solar battery?

Palmetto has been helping thousands of homeowners across the US access clean solar energy for more than a decade. Our end-to-end solutions promise results that you can track, and savings you can count on. With many years of experience designing solar power systems that include battery storage to maximize your savings, we have the knowledge needed to precisely determine which battery option will work best for you.

If you're considering adding solar battery storage to your home, visit the Free Solar Savings Estimator which will automatically forecast your future savings if you decide to go solar — based on your current utility bill, the specific programs and incentives that are in your area, and other factors. We even take into account variables like the Solar Investment Tax Credit, and how much that tax credit can save you if you add solar storage to your overall home solar plan. Getting your free estimate is the easiest way to compare solar storage options, and get the best solar batteries for your home, so we look forward to helping you get started on a journey towards energy independence.

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