How Many Batteries Do You Need To Go Off Grid?

Are you ready to go off the grid and power your home with sunshine? Great! But before you start installing solar panels, you’ll need to know how many batteries you need to store all that clean, renewable energy. It’s not as complicated as it sounds – just follow these simple steps, and you’ll be on your way to energy independence!

Factors to Consider While Sizing Your Battery

Here’s how to calculate the number of batteries you need for an off-grid solar system:

  1. First, you need to know how much electricity you use daily. This is like filling up a bucket with water. The bigger the bucket, the more water (or electricity) it can hold.
  2. Next, you need to decide how long you want to be able to use electricity without the sun shining. This is like sizing your swimming pool. If it’s too small you won’t fit in. But if it’s too big, then it will be too expensive.
  3. To figure out how many batteries you need, you need to multiply the amount of electricity you use every day (buckets of water) by the number of days you want to be able to use electricity without the sun shining (pool size). This is like filling up the pool with buckets of water. The bigger the pool, the more water (or electricity) it can hold.

Example of Sizing Your Off-Grid Solar Battery

For example, let’s say you use 10 kWh of electricity every day, and you want to be able to use electricity for three days without the sun shining. You need a battery that can hold:

10 kWh  x 3 days = 30 kWh of electricity.

Now you are thinking, how do I estimate my power needs?

Good question!

You need to estimate the worst-case scenario. This will most likely be winter when we use more heating and lights than usual. It can also be summer when your AC is working all day.

You can use a kill-A-watt meter to look at your daily consumption of several devices. You can look at the daily kWh of the particular device. This can be useful for a fridge where the load is not constant.

Kill-A-Watt meter from Amazon

Here are some basic appliances which almost every household uses:

Appliance Power
AC unit 1200W (when the compressor is on)
LED Light 5W
TV 50W
Computer with monitor 80W
LED Lights 5W/piece
Dishwasher 1500W per cycle

Solar Battery Calculator

In this calculator, you can fill in your loads, and it will calculate the battery size and the amount of solar power you need.

sizing your battery
W
W
W
W
W
h
h
h
h
h
Wh
Wh
Wh
Wh
Wh
Wh

Days of Autonomy

This is as a backup if the sun doesn't shine. I recommend having at least three days worth of energy stored in your batteries. We will size the battery bank according to these amount of days.

Days

Battery Size

Here you can see the calculated battery sizes according to the values you entered. You will see that you need more capacity if you choose for lead-acid. This is because you can only use 50% of a lead-acid battery without damaging it. Further, the efficiency of a lead-acid battery is 80%. For lithium we can use 80% of it's capacity and it has an efficiency of 99%.

Ah
Ah
Wh
Wh

Required Solar Panels to Charge the Battery

In this section, we calculate the total power of solar panels you need to charge the battery in one sunny day. The number of sun hours per day can be seen on this website. For the USA, this can be from 3-6 hours. It depends on the season and latitude. Choose the lowest number if you want to use your battery all year-round.

Hours/day
Watts
Watts

Send Report to Email

You can send this report to your email by filling in your email address and clicking the 'send pdf to email' button. You will receive the PDF in your inbox. Make sure to check your spam folder too.

* I do not store or use your email for further communication. It is only to receive the PDF.

What Battery Should You Buy?

I recommend using server rack lithium batteries (LiFePO4). They are stackable. So if you need more storage, you can easily add more later.

Every battery is 48V and 5kWh. Here you can see an image of such a stacked battery.

4 lithium batteries for a total capacity of 20kWh

Recharging The Battery

Solar panel array to charge the battery

You should size your solar array so that the battery will be charged in one day of sun. Most of the time, the amount of sun hours is 3-4 hours. To charge a 30kW battery in three hours of sun, you need:

30,000Wh/3 hours= 10,000W

You need a 10kw solar array to recharge the battery in one day.

Generator backup

On a cloudy few days, you still need to be able to recharge the batteries. That’s where a generator comes in. A generator creates a good balance between the cost of batteries and available backup power.

You need a charger for this. I use the Victron Multiplus II 3kVA to recharge my home battery when it’s depleted. The Multiplus II is an inverter/charger that takes energy from the battery and turns it into AC. It can also take power from a generator and charge the battery. It can also charge the battery from the socket at your home. Keep in mind the charging current of the inverter/charger. This should not exceed the rated charging current of the generator.

Conclusion

There you go.

Using the calculator, you now should know how many batteries you need to go off-grid.

If you have additional questions, leave a comment below to other people are helped too.

Leave a Comment