What Size Solar System Do I Need To Go Off-Grid?

How Do I Calculate What Size Solar System I Need?

Solar panels are becoming more and more popular, but many people don’t know what size solar system they need to go off-grid. So, here’s a guide to help you figure out the size of solar system you will need.

First, let’s do a rough calculation of how much electricity you’ll be using on a daily basis.

When calculating how much electricity you need from an off-grid solar system, you want to look at kWh (kilowatt-hour).

A kWh is a way to measure the amount of electricity used in 1 hour. And, to figure out what size solar system you need, you need to know how many kWh of energy you typically use in 1 day (on average).

Knowing your daily energy requirements is important when deciding what kind of solar power system is right for you. If you only use a small amount of electricity each day (like me), a few portable power stations (Amazon) with a few solar panels may be a better and easier option than a bigger, classic off-grid solar PV system.

Let’s start calculating…

Daily Energy Needs

If you don’t have an energy monitoring system, then you can look at your electric bill. Just look at the kWh (kilowatt-hours) used each month to see how much electricity you use on average and divide that number by how many days are in the month to see how many kWh you roughly use on a daily basis.

Another way to calculate your energy needs is by creating a list of all the appliances you use everyday (like the fridge, stove, TV). Now, write down how many watts each appliance uses*. Then figure out how many hours each appliance is used during the course of a day.

Once you finish your list of appliances (with watts and hours used), you then want to multiply the watts and the hours for each appliance to get watt-hours.

Here’s an example:

Fridge

350 watts x 24 hours = 8,400 Wh (watt-hours)

Microwave

1000 watts x 0.4 hours = 400 Wh

TV

100 watts x 2 hours = 200 Wh

10 LED Light Bulbs

70 watts x 5 hours = 350 Wh

Desktop Computer

150 watts x 4 hours = 600 Wh

This totals 9,950 Wh.

Then, take the total of those watt-hours and divide them by 1000 to get kilowatt-hours (kWh). For example, 9,950 Wh ÷ 1000 = 9.95 kWh (or just use this watt-hour to kilowatt-hour conversion calculator on google.com)

How Big Should My Off-Grid Solar System Be?

We’re going to pretend that you only need roughly 10 kWh of electricity per day.

So you would think that if you and your family use about 10 kWh per day, something like a 14 kWh solar system would have more than enough power for your family! Right?

Nope! Not so fast…

There are other things to consider when sizing a solar power system. Keep reading!

Off-Grid Backup Power Required

Even though you might think that you only need a solar system that can supply you with around 10 kWh every single day, you also want to have enough backup power for when there are cloudy, rainy, or snowy days.

When it’s not sunny outside, your solar system is not going to optimally charge your batteries. So, typically you want 3 to 5 days of power stored in your batteries for those gloomy days.

If you live in the United States where you can sometimes get up to 3 days of rain, you would multiply your energy needs (in this case, 10 kWh) by 3. If you live in a cold climate, let’s say in Northern Canada, then you might want to multiply your energy needs by 5. If you live someplace where there’s a lot of sun, like Las Vegas, you can probably multiply your energy needs by 2.

So let’s say we decide that 3 days of backup power is good for us. So, we multiply 10 kWh by 3 to get 30 kWh.

So, 30 kWh should roughly be the total size of your solar system, right?

Not so fast!

You also have to figure out what kind of battery (lithium or lead-acid) your system is using.

Lithium vs Lead-Acid Batteries

When shopping for a solar power system, you’ll often see options to buy lithium batteries (lithium-ion or LifePo4 batteries) and lead-acid batteries (usually AGM batteries).

Let’s say that we need a solar system that provides us with 30 kWh of power. 30 kWh is the size of our battery bank, which is just a term we use for a collection of batteries that work together.

If you have a 30 kWh lithium battery bank, you’ll be able to use 30 kWh from those batteries.

However, if you have a 30 kWh lead-acid battery bank, you’ll only be able to use half of that power (15 kWh) because it’s recommended that you only discharge a lead-acid battery down to 50%. If you discharge a lead-acid battery more than half, you can damage the battery.

So if you have a solar system that uses lead-acid batteries, and you need 30 kWh of power, you’ll have to get double the amount of batteries! So, you’ll need a 60 kWh lead-acid battery bank to get the same amount of usable power as the 30 kWh lithium battery bank. (This is one of the reasons I always recommend solar systems with lithium batteries.)

To learn more about the differences in these solar batteries, check out my post: AGM vs Lithium Batteries for Solar

Solar Power Systems & Limitations

All solar power systems have limitations in the amount of electricity that can come out of the system at once.

Here are 2 terms you want to know when trying to figure out how big your solar system should be; continuous power and peak power.

To learn the difference between continuous and peak power, let’s pretend we’re looking at buying a small solar system that provides 3600 watts total with a surge of 7200 watts.

Continuous Power

Continuous power is the amount of power that the solar power system can supply continuously (long-term). In this case, our solar system can provide 3600 watts long-term.

Now, let’s say we want to be able to run a fridge, TV, lights, a desktop computer, and a dryer all at the same time.

Fridge = 350 watts

Microwave = 1000 watts

TV = 100 watts

10 LED light bulbs = 70 watts

Dryer = 3000 watts

Desktop Computer = 150 watts

This totals 4670 watts, so your 3600-watt solar system won’t be able to handle all of those appliances running all at once.

When running the 3000-watt dryer, you’ll only have 600 watts left to run other appliances. So, if you don’t want to get a bigger solar system, you might have to run the dryer early in the morning or late at night when everyone’s sleeping. Or you could get a fuel-powered generator (Amazon) for those times you want to run the dryer during the day.

Peak/Surge Power

Peak power (sometimes called surge power) is the maximum power that the solar system can sustain for a very short period of time (something like 10 or 20 seconds) when starting an appliance.

In the example above, we were looking at a solar system that provides 3600 watts total with a surge of 7200 watts. This means that you can continuously use up to 3600 watts to power your appliances but your solar system might also be able to handle up to 7200 watts for a few seconds.

Understanding peak power is important when sizing a solar system that needs to handle large amounts of power quickly, such as motors and HVAC systems. Appliances like an HVAC have a big spike in power usage when the motor starts. (For example, an HVAC unit could have a surge wattage of 3950 watts and a continuous running wattage of 3250 watts.)

It’s also important to understand peak power because surges in power can cause damage to electronic equipment (it could overheat or even catch fire).

If you have a professional installing your solar system, they might recommend a “soft start” for appliances with big spikes in power usage.

Sizing Your Solar System: Wh vs W (Watt-hours vs Watts)

When you’re shopping for a solar power system, it can be confusing to understand what all of the different terms mean. So let’s recap what a Wh (watt-hour) and a W (watt) is.

Watt-hour (Wh) or Kilowatt-hour (kWh) are measures of how much energy your battery bank can hold.

Let’s say you have a 100W (100 watts) TV, and you have the Ecoflow River Pro (Amazon). The River Pro’s wattage is 720 Wh (watt-hours). You can use the watt-hours to figure out how long you can power the 100W TV.

720 watt-hours ÷ 100 watts = 7.2 hours

So you can see that the Ecoflow River Pro will be able to power a 100-watt TV for approximately 7.2 hours.

Watts (W) or Kilowatts are telling you how much energy your solar system can generate at any given time.

Let’s say you have the Ecoflow River Pro and it has an output wattage of 600W (600 watts). That means that you can only plug in appliances/devices that use less than 600 watts. For example, you couldn’t plug in a 1000-watt microwave.

But, you could have 6 TVs (100 watts each x 6 = 600 watts) powered by the River Pro at the same time. But you couldn’t have 7 TVs powered by the River Pro all at once because 700 watts is more than the Riverpro’s maximum wattage of 600W.

It’s important to remember that W (watt) and Wh (watt-hour) are not interchangeable – a watt is not equal to a watt-hour.

How Many Panels Do You Need for off the Grid?

If you need a 30 kWh solar power system, then chances are that you’ll need a professional installer. They’ll be able to guide you in how many solar panels you’ll need.

Just remember that you really want to buy as many solar panels as your solar power system and budget will allow.

Solar panels are cheaper than batteries, and it makes sense to spend a little more money to buy solar panels that can produce more energy than you need at any given time.

But what if you want to buy a solar power kit (Amazon) or a portable power station? How many solar panel watts should you get?

Portable power stations are easy. They will tell you exactly how many solar panels (and how many watts) you can plug into them.

For example, let’s look at a few Ecoflow portable power stations*:

Ecoflow River Mini = 100W from a solar panel (maximum)

Ecoflow River Max = 200W from a solar panel (maximum)

Ecoflow Delta Max = 800W from solar panels (maximum)

Ecoflow Delta Pro (3.6 kWh – Amazon) = 1600W from solar panels (maximum)

So when designing a solar system, always start with how many watt-hours (or kilowatt-hours) you need from a solar kit or portable power station. Then, just add the recommended maximum amount of solar panels (I really like Renogy solar panels – Amazon).

Conclusion: What Size Solar System Do I Need?

A big solar power system might not be for everyone.

For example, if you only need to power small appliances and charge devices like a phone or laptop, portable power stations (Amazon) may be sufficient. And portable power stations are plug-and-play, so there’s no learning curve. Just take it out of the box and use it right away!

My wife and I have been living off-grid for awhile now and we solely live on our Ecoflow portable power stations (Amazon) and Renogy solar panels (Amazon). We have the River Mini, the River, the River Max, The River Pro with an extra battery, and an Ecoflo Delta Pro to run our entire off-grid home (my wife and I also work full-time from our home office).

However, we are very aware of how much energy we use and we downsized our fridge to a 58-quart Alpicool CF55 Portable Refrigerator/Freezer (Amazon) and got a gas-powered generator (Amazon) to run our washing machine and dryer.

And if you are looking for a small to mid-sized, DIY solar power system, there are plenty of solar power kits online. Solar power kits are a great way to learn how to build your own small to medium-sized solar system. (I’m a huge fan of Renogy’s solar kits – Amazon).

Nevertheless, if you want to live completely off-grid and you need a system to run your entire home or cottage (especially if you have kids or you use a lot of electricity), then you really should think of investing in a bigger solar power system installed by professionals.

It is also advised that you include an alternative gas, diesel, or propane generator (Amazon) to your setup so that there’s an uninterruptible power supply.

What size off-grid solar system do you need?

There is no definitive answer to this question, as it depends on a variety of factors, including the size of your home and how much energy you use. Generally speaking, though, you will need a solar system that can produce at least 3-5 times the amount of energy you use each day. So if you use 1,000 kWh of energy per month, you will need a solar system that can produce 3,000-5,000 kWh of energy each month.

Yame Smith, OffGridPower101.com