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One of the most common questions fielded about solar power is how many batteries you’ll need to power a whole house.
It’s not surprising that living off-grid on purely green, renewable energy is the ultimate goal of investing in solar.
Sure, some may go in with smaller eco-missions, perhaps just to power a single appliance or to keep the lights in their home or RV, but complete energy independence is an enticing prospect for solar enthusiasts.
Perhaps the most asked version of this question is how many solar panels does it take to power a house?
But if you really want to go off-grid, an equally important question is how many solar batteries are needed to power a house? Let’s find out!
Figuring Out How Many Solar Batteries You Need
Obviously, it’s impossible for me to give you a concise answer here, as I lack all the relevant information to figure out how many batteries you’d need to power your home.
However, I am going to talk you through all the things you’ll need to consider to figure it out for yourself.
Solar Battery Count Considerations
The Golden Rule
If you’re looking to power your home with 100% solar power from January to January, the golden rule is to plan your system to be fully operational during your solar panel system’s least productive point in the year.
For example, if you live somewhere that gets quite sunny in the summer, but terribly overcast and snowy in the winter, you’ll need to plan your solar battery storage system around the cold months, otherwise, you’ll be short of energy when they come around.
Location & Climate (If You Live Somewhere Gloomy)
Following on from my last point, as you’ll be harvesting 100% of your energy from the sun, the climate of the area in which you live is of crucial importance.
Let’s say, for example, that you live in Massachusetts, a state that gets fairly brutal winters; there’s a good chance you’re only going to get maybe 3 hours of direct sun a day.
Typically, a wintering household will use roughly 750 kWh per month, which equates to 25 kWh hours of power per day, and to cover this stretch of the year, you’d need quite a significant panel array and storage system.
Now let's say that to ensure that you’re never left in the dark, you want to develop a solar setup that, when at full capacity, can power your home for a week of no sun whatsoever.
Using a 750 kWh a month estimation, we can state that you’ll need 175 kWh of stored energy to hold you over for a week, but what does that mean in terms of batteries?
Well, let’s say for the sake of example you’re absolutely loaded and can afford to outfit your system out with numerous Tesla Powerwall batteries rated for 13.5 kWh a pop.
Taking into account their 95% depth of discharge, you’re probably looking at about 14 batteries.
Even if we forget the survival for a week thing, and you’re just looking for enough batteries to get you by during low sunlight days, you’re still going to need about 10 Powerwall batteries, which is a serious investment.
As it’s unlikely you’re made of money, you’ll probably be looking to bring in a slightly more affordable selection of batteries, but that 13.5 kWh Powerwall performance is difficult to find across the general market.
Your best bet is probably something like this Ampere Time monster; however, even this sizable battery is capped at 400 Ah, which translates to roughly 4.2 kWh, meaning you’d need slightly over 40 of them to survive a week of no direct sun whatsoever.
Location & Climate (If You Live Somewhere Sunny)
Okay, so the battery budget for Massachusetts residents is looking pretty steep, but what about if you lived somewhere that got lots of sun year-round, like Arizona?
Well, needless to say, an Arizona resident wouldn’t have to build such a gargantuan system, but there will be certain things to factor in, such as the drain of powerful AC systems to keep them cool during those absolute scorchers.
Arizona likely gets roughly 7.5 hours of good sun per day during the summer, and we’ll estimate that the average home uses about 1050 kWh of energy per month, amounting to 35 kWh of power used each summer day.
As you will almost never go without sun for a week in this part of the country, let’s say that you want to be covered for just 3 days.
You’d need a battery bank with 105 kWh of storage, equating to slightly fewer than 8 Tesla Powerwalls.
Using our more attainable 400 Ah Ampere Time unit, you’re looking at something more to the tune of 25 batteries, which is still mighty expensive.
Thankfully, if you live in Arizona, you can skimp a little on the panel array, which brings me to my next point.
Solar Panel Count
If you live in an area that gets a lot of overcast days and very gloomy winters, it’s essential that your solar panel network grows in tandem with your power bank.
It’s no use having the capacity to store a lot of power if you’re not pulling it in.
In sunnier climates, you will still need a sizable storage bank to power your home, but your solar panels will be drawing a lot of energy, so you won’t need as many of them.
If you’re looking for a more specific estimate of how many solar batteries you’ll need to power your home, there’s only one way to do it… lots and lots of math.
Well, not that much I suppose.
If you have a few electricity bills handy, you can use those to get a general breakdown of your energy usage per month, but it’s best to tally up all your appliances and electrical systems individually to get a precise power consumption total.
You can do this manually if you like, but there's a pretty great power consumption calculator on the US Department of Energy website.
Once you know your average kWh usage per year, you can simply divide that by 12 to get your monthly power consumption or divide it by 52 to get your weekly consumption.
Once you have these figures, it’s just a matter of choosing a solar battery and buying multiples until you reach your target figure.
To hold you over during those long periods when the sky’s looking grim and the sun can’t nose its way through, you’ll need anywhere between 10 and 40 solar batteries depending on the efficiency and capacity of the batteries.
Setting yourself up to be completely off-grid using solar power exclusively is a pricey endeavor, one that may not completely pay off in the long run, depending on the climate of your area of residence.
But it’s not purely a financial matter.
Going solar is about doing what you can to ease the environmental burden on our shared home, and if it does start paying dividends in the end, well… that’s just a lovely little bonus!