Off-grid Living: How many Solar Panels and Batteries do you need to run your home?

 

So you’re looking to go off the grid, or maybe just build a backup power system to ensure you can survive a long-term grid-down situation e.g.: The recent strike by several Electricity Distribution Companies in Nigeria. If you’re like most people who email us, you probably have a number of questions on how to do it, how much it costs, and what you will need to be successful.

• How many solar panels will you need to power your home?
• How many batteries will it take to keep your home running?
• What can you realistically power with an off-grid solar setup?

Going through thousands of articles and forums, and after talking to hundreds of experts; one thing that never fails is, the topic of solar can be downright confusing. We will not over complicate this article or bog you down with theoretical examples and difficult mathematical equations. We are going to look at baseline figures on how much power you consume, how many batteries you need to power your home, and how many solar panels you need to maintain those batteries to guarantee you have the power you need when you need it.

 

Determining your power needs: How much power does your home consume?

The first step in determining how many solar panels and batteries you need to power your home is finding out how much power your home is actually using. There is a mathematical way to determine this, and it is called a Power Audit.

Estimating your Power Consumption

The first way looks at the manufacturer’s guidelines to determine the power draw. The wattage of an appliance can usually be found on a label attached to the power cord. It’s listed in either amps or watts; you want to know the watts — don’t worry if it doesn’t tell you there is a simple formula for figuring it out. Volts x Amps = Watts. For simplicity sake, the average household wiring is 120 volts; chances are, your appliances and anything you plug into the wall runs at 120 volts. Trust us on this one. So let’s say the tag on your appliance says it draws three amps; you simply multiply 120 x 3 giving you 360 Watts! Now you know how many watts that appliance uses per hour. (Side note, some appliances have a startup draw which can be higher, but for now, we are keeping things simple. We will worry about that later.)

Next, we need to figure out our average daily use:

So we take the 360 watts and multiply that by the hours a day we run that specific device and come
up with a daily wattage figure.  So, if we run that device 3 hours a day, we will need 1080 watts a day.

In the case of something like a refrigerator which may draw 400 watts an hour, we need to multiply the number by 24 hours coming up with 9,600 watts a day. Our experts here at Sygnite can carry out a free power audit of your facility to accurately determine how much power is consumed in your home, office or facility.

Battery Bank Size: How many batteries do you need to run your off-grid system?

Now that we have our numbers, we can start figuring out what we really need and how much our off-grid system is going to cost us. Ok, so we hope we don’t lose you here; but when we are looking at batteries, we need to calculate what we need in AMP hours (AH) – this is how batteries are rated.

Amp Hour (AH) gives you a measurement of battery capacity.  In other words, it tells you how much energy can be stored by the battery. To come up with the number, we are going to divide the total battery capacity required by the voltage of the battery. So in the case of a 12-volt deep cycle battery, we are going to divide our 9,600 number (watts a day for the refrigerator) by 12 (volts) which tells us we need 800 amp-hours.

So assuming we found some deep-cycle batteries rated at 200 amp hours, we would need four batteries for our system.

Solar Panels: How many Solar Panels do you need to run an off-grid system?

Ok, we hope we didn’t lose you there; but don’t worry, we are almost home. Now we can estimate how many solar panels you need to maintain your system.
Let’s say you have a 100-watt panel. You want to take that number and multiply it by the number of direct sunlight hours you have in a day. So let’s say you average about 6 hours of direct sun a day, that one panel can produce 600 watts a day.

Panel watts x hours of sun = Daily Output

Next, take your daily wattage needs, in the case above 9600, and divide it by the daily panel output.

Daily Need divided by Daily Output = Number of Panels

So in the case above, to achieve my 9600 watts a day, you would need sixteen 100 watt panels. Now, of course, this will depend on the wattage of your panels, but you should be getting a better idea of what you need to power your setup. For the 9600-watt system, I would need sixteen 100-watt panels and four 200-AH batteries.

 

NB: Remember these are baseline figures to help with your estimation; in the real world, these are only numbers and just like all areas of preparedness you need to compensate for failure points. It’s better to go a little bigger and overcompensate because when it comes to off-grid power there are hundreds of factors that we can’t account for that are going to pop up at some point down the road. If a ten-day storm comes through and you
lose the sun, you need to have a backup plan!