Mālama Solar

EnergyHow many solar batteries does my home need?

How many solar batteries does my home need?

This is a common question for people looking into solar power. As we all know, solar panels only produce energy while the sun is shining, so in order to have more reliable energy, your system needs batteries to cover the times when the sun isn’t shining. Do you need batteries? Should you buy a Tesla Powerwall? How long do they last?

The good news is that when you work with us here at Mālama Solar, you don’t need to wonder or guess—we’ve done hundreds of installs and know exactly how to size your system. Here’s how we do it:

It depends.

That’s not a complete answer but it’s accurate. So much depends on the size of your home, the amount of energy you use, and the layout of your roof even. What we’re looking for is a system that is efficient in producing the right amount of energy, and when it comes to batteries, we’ll install the amount of storage to get you through the average night.

We’re a solar company based in Hawaii, so our customers who are Hawaii residents don’t have to worry about extreme weather events that could impact battery performance—for the most part, our weather is predictable and stays within a pretty comfortable temperature range.

Are you still on the grid?

Probably. At least where we do business, the majority of Hawaii solar customers are still connected to the grid. That’s true in most places, not just Hawaii. That means when you use more electricity than your panels can produce or use up what’s stored in your batteries, your home will draw what it needs to make up the difference.

In this case, your home will normally need 1-2 (but in rare cases more than 2) standard batteries to cover your electricity needs when the sun isn’t shining. We install the latest Tesla Powerwall batteries and Generac batteries with our systems, and both have pretty comparable capacities and performance. A Tesla Powerwall battery has a capacity of 13.5 kilowatt hours and a Generac PWRcell battery has a capacity of up to 18kWh. That’s roughly the amount an average Hawaii resident uses in one day.

Are you off the grid?

If you’re in the minority who are truly looking to be completely off the grid, your needs are different—not only for your solar panels but for your batteries as well, because once you use up your storage, your lights go out. Off-the-grid solar users will usually want a greater number of batteries in that case to cover any potential longer stretches of bad weather or emergencies that might arise.

Based on average use, an off-the-grid home will need more batteries to cover those rare scenarios. If you’re truly off the grid, you’ll likely also be looking for ways to conserve energy and limit your use, especially if you see a stretch of cloudy weather coming your way. At that point, it’s up to you—how long do you want to be able to go? It’ll add up, but you’ll be truly self-sufficient. But again, most people are not in this scenario, especially in Hawaii where many permits require connection to the public utility.

How much electricity does your system produce?

When we quote out your system, we look at the amount of electricity you use in a day and your average usage over a full year. In general, we size our customers’ PV systems to cover your average usage, not peak usage. But that doesn’t mean your solar panels only produce what you can use while the sun is out—they’re designed to produce plenty for your full day’s use plus a full battery charge to cover what you’ll need overnight. You don’t want to overdo it, either—if you get four batteries installed but your system can only charge three during the day, that extra battery is unfortunately just wasted money. You want your battery bank and capacity to match the output of your solar panels as closely as possible.

Let us do the calculations.

We’ve got lots of experience sizing PV systems and batteries for Hawaii residents. We’re based in the Honolulu area and also have local crews on the Big Island, and we’re always ready for a chat about your solar needs. Give us a call or text to learn more about going solar!