78% of US adults are concerned about rising home energy costs. That’s from a 2024 CNET survey. There’s never been a better incentive to go solar.
But how can you make the most of your investment? How do you get the most energy from your system? Let’s look at an often-forgotten but vital solar system component: the battery.
When solar was first taking off, energy storage technology lagged behind.
So, people who wanted an off-grid solar system with in-home energy storage relied on lead-acid batteries. These are the heavy batteries used by combustion cars. In fact, I once saw a solar-powered mobile home use around six lead-acid car batteries for energy storage.
Lead-acid batteries are not as efficient or long-lasting as the new lithium-ion batteries. Lithium-ion batteries are lighter, more reliable, smaller, and can hold more energy for longer. These are the types of batteries you have in your phone, tablet, and computer. It’s also what electric cars use.
Battery priorities: What would you do with a battery?
Innovations in energy storage have quite literally fuelled the nomad and off-grid movements. With batteries, you can live a completely energy-independent lifestyle and not worry about outages. Even during long, overcast periods, off-grid solar power systems provide consistent power for days.
So, if you lived in a rural area and couldn’t rely on your power company, you could cut them off! But what about homeowners in suburban or urban areas? What about the average homeowner looking to go solar?
Until recently, batteries weren’t practical for most homes.
Until recently, most homeowners who went solar relied on a grid-tied system. In this system, your neighborhood’s electrical grid acts as your battery. At peak sunlight hours, your solar panels produce more electricity than you need. So that excess energy goes to the grid— to your neighbors. The utility-scale power plant powering your city could then produce less.
At night, when your solar panels aren’t producing electricity, but you still need the lights on, you draw power from the grid. This balances out through a program utility companies run called net metering.
But what about power outages?
You’re probably thinking that batteries would be great for power outages. They could act like a backup generator but without the fumes or pollution.
But until recently, you couldn’t do that. Grid-tied solar power systems automatically shut off during outages as a safety precaution. Being grid-tied is a two-way street. If you can get power, you can give it. So, if your solar power system is turned on during a power outage, it will send power to a damaged grid. That could harm the electricians trying to repair the grid.
Today, grid-tied systems can use battery backups thanks to recent innovations.
Green energy innovated grid-tied systems into what are called hybrid solar systems. But most people just call this setup a grid-tied solar system with battery backup.
Here’s a simplified overview of a grid-tied system:
- Solar panels produce DC electricity.
- That DC electricity goes to an inverter.
- The inverter converts DC power into AC, which your home can use.
- The inverter sends surplus energy to the grid.
Here’s an overview of a hybrid solar system:
- Solar panels produce DC electricity.
- That DC power goes to a charge controller, which regulates the energy flowing between all the different components.
- That charge controller sends the amount of energy you’re consuming to a hybrid inverter and surplus energy to your battery.
- This hybrid inverter can manage both grid-tied functions and the battery backup. If your system is still producing excess energy when your battery is full, it sends it to the grid.
During a power outage, your hybrid solar system automatically disconnects you from the grid. So you can use your solar panels and battery to power your home.
How do these batteries actually work?
Let’s take a closer look inside a lithium-ion battery. Within each lithium-ion cell are two electrodes separated by an electrolyte solution. That’s a lot of technical jargon. Electrodes are metal terminals that can conduct electrical currents through nonmetal materials. In this case, these electrodes need to conduct an electric current through lithium compounds. Doing so creates lithium-ions, lithium atoms that are electrically charged. An electrolyte is a material that can conduct ions but not electrons. See where this is going?
When you charge a lithium-ion battery, you’re sending electricity through electrodes. The electricity positively charges lithium atoms into ions so that they can pass through the electrolyte. These ions move from the cathode (the positively charged electrode) to the anode (the negative electrode). Those ions become trapped in the anode, thus storing electricity as chemical energy.
When you want energy from your battery, you “flip a switch”— you complete a circuit. The electrons of the lithium atoms in the anode flow through the external circuit. This creates electricity for your A/C, heater, lights, TV, phone charger, microwave— your whole house. Those electrons end up back at the cathode, which attracts the lithium ions back through the electrolyte.
The top two considerations when shopping for a solar battery are price and capacity.
Now that you understand the science behind lithium-ion batteries, you’ll better understand Lifespan and Capacity. So, let’s learn how to shop and maintain solar batteries.
Capacity is measured in Kilowatt-Hours, and its range can vary widely.
We’ve seen everything from 3 kWh batteries to 20 kWh power walls. For context, the average home in the Virginia Beach area consumes around 1.51 kWh per hour.
So, if you’re looking for a battery backup to cover you during power outages, ask yourself, how long was your last outage? Most people opt for a 10 to 13 kWh battery.
Similarly, prices can also range wildly.
We’ve seen small batteries for $3,000 and robust home backup systems for $15,000. Commercial battery backup systems can cost as much as $25,000 or higher.
However, if you’re looking for a decent-sized battery for your residential solar power system, expect to spend around $10,000. That is a hefty price, but quality batteries are worth the price. Solar is already a steep investment, but that battery price is eligible for the 30% federal solar tax credit.
How to maintain your solar battery.
As with all electrical equipment, a solar battery will gradually degrade with time. Its capacity will decrease over its lifespan in a process called capacity fade. Your battery’s current capacity is called its State of Health (SOH), and it decreases by around 1-4% annually.
Battery warranties are very similar to solar performance warranties for this reason. These warranties reflect the battery’s future capacity. They generally say something along the lines of, “Your battery will still function at 60% – 80% of its original capacity after 10 years.”
For example, you might have a 10 kWh battery with 70% SOH after 10 years, resulting in 7 kWh of usable capacity.
So, how can you keep your battery healthy for years to come? Some things like temperature and weather are outside of your control. But the biggest factor in your control is the Depth of Discharge (DoD).
Depth of Discharge is the percentage of capacity that can be used before stressing out the internal components. In essence, you can’t use 100% of the battery’s stored energy without damaging it. You always need some fuel in the fuel tank. If you’ve ever let your phone battery drop to 0%, then you have experienced the depth of discharge problem.
Lead-acid batteries have DoDs of around 50-80%. That’s fine for cars but leaves a lot on the table as part of a solar-energy system. Luckily, Lithium-ion batteries have DoDs of 80-95%. If you have a brand new 10 kWh Battery, you can discharge it to use 9.5 kWh of electricity. For a 10-year-old battery with 70% SOH, you have 6.65 kWh of usable power.
We have a partnership with Tesla as a Certified Tesla Power Wall Installer.
And we’re proud of it! As your local Solar Company in Virginia Beach, we know Tesla Powerwalls are popular choices for homeowners. And for good reasons.
Many people like the fact that they can easily integrate an EV charger into their Powerwall. They like the high capacity of 13.5 kWh. However, we like the fact that you can effortlessly expand your Powerwall with up to 4 battery units. So, 10-15 years down the line, when the SOH of your original battery has decreased, you can easily add another one.
So, is a battery backup right for YOU?
You can have energy independence and emergency power, but it will cost you a few thousand dollars. Solar is already a steep investment. Depending on how you’re financing your solar project, a battery backup might be a worthwhile addition.
But is it right for you?
Some areas in coastal Virginia are prone to storms and experience more frequent outages. Some rural areas are adapting to their aging power infrastructure. Someone with an electric car might appreciate the extra capacity.
One good thing about battery backups is that they can be added to existing solar systems.
You don’t have to buy a battery backup right away. You can install a grid-tied system now and easily add a battery later.
As one of the best Solar companies in Virginia, we offer battery backups as optional upgrades for both residential and commercial systems.
So, is a battery backup right for you right now?
To answer that, we recommend a solar site assessment. We can come out to your home on your schedule and discuss your needs.
