If you’ve got solar panels already, adding batteries can increase your savings and independence. Here’s what you need to know.
Solar panels are a great way to capture free, clean energy from the sun for yourself or to feed it into the grid for more savings on your utility bill, but it’s attaching a battery bank that gives you real energy independence.
Without solar batteries, even a house covered in photovoltaic panels will leave homeowners literally powerless when the grid goes down.
How solar batteries work
The simplest way to think of batteries is to imagine that the electricity in your house flows through wires in much the same way as water through plumbing. Batteries fill the role of a storage tank, making electricity readily available when it’s needed, just as indoor pressure tanks and water heaters do with water. When batteries are tapped for energy, their reserve of stored electricity is depleted, but in a properly wired system they can be automatically replenished by “catching” any excess electricity flowing through the system from sources like solar panels or the grid.
Depending on your goals for installing batteries, your system might look a bit different.
1.Connect just to solar panels: Batteries connected only to solar panels will fill when the sun shines and discharge when you use electricity and the sun is down or behind clouds. It’s one option if you are off-grid and away from electrical utilities.
2.Connect to solar panels and to the grid: If you have a solar inverter that can temporarily disconnect you from the grid, you have what’s known as a hybrid solar system. In such a system, you can charge your battery with your solar panels or the grid and use the energy stored there in your home or send it back to the grid and save some money via rate arbitrage (if you have time of use rates). A hybrid system can also keep your house powered during a power outage.
3.Connect just to the grid: While we wouldn’t call them solar batteries, you can install batteries without solar panels at all. They would charge from the grid and would be useful for back up power or for enrolling in a virtual power plant.
Different types of solar batteries
There are several kinds of batteries used in battery backup systems, including lithium-ion and lead-acid batteries. Here’s a quick overview.
Lithium-ion batteries
There are multiple lithium chemistries on the market, including nickel-manganese-cobalt, lithium polymer and lithium iron phosphate. The latest lithium technology comes with less danger of fire than older headlines might lead you to believe. They’re capable of a deeper discharge than lead acid batteries (you can use up to 90% of a charge per cycle without inflicting much damage) and are much easier to maintain with a longer lifespan. They’re also significantly more expensive and sensitive to temperature. Increasingly, though, they are becoming standard in residential solar applications.
Lead-acid batteries
The basics of this technology are essentially unchanged for over a century. They remain inexpensive and widely available. For solar systems, it’s popular to use somewhat more expensive sealed batteries that require less maintenance and eliminate the risk of dealing with a potential acid spill and hydrogen off-gassing. For a while, sealed lead acid seemed to be the future of solar batteries.
However, all lead acid batteries require more careful monitoring of charge levels compared with lithium-ion and can’t compete in terms of efficiency, energy and lifespan but are a good and plentiful budget alternative.
Flow batteries
Flow batteries (or redox flow batteries) are less common in home systems since they’re mainly designed for commercial use. However, the technology appears promising, and it could become more widely used in residential battery backup systems in the near future.
Nickel-cadmium batteries
Nickel-cadmium batteries have a high energy density with double the energy of a lead-acid battery. Nickel-cadmium batteries are very durable, expensive and work well in extreme temperatures making them a good choice for large-scale commercial and industrial projects. Cadmium is toxic, however, and generally not appropriate for residential use
How to set up a battery backup system
It’s best to use a certified solar installer or electrician to install your solar batteries and connect them to your solar array, your home, the grid and an EV charger, if you desire. You should expect to spend a few thousand dollars for the labor involved, and there may be additional components like inverters, charge controllers and EV charge stations that can also add hundreds or thousands of dollars in expense.
If you have confidence in your DIY skills and experience with electricity, it is possible to install batteries yourself. Just be sure to check with local regulations, building codes and equipment warranties.
If you go the DIY route, make sure all batteries are the same age (ideally new). Don’t mix new batteries with older ones to help make sure they take a charge evenly.