Off-grid solar batteries: A guide to energy self-reliance
We’ve all fantasized about leaving it all behind and living off the land, trading in a cubicle for a simple life in the country. One way to power that dream is with off-grid solar batteries.
Off-grid systems can power electrical devices in areas the power lines don’t reach, allowing people to enjoy modern conveniences in the most remote environments.
Solar panels are often the first choice for off-grid systems. They harness energy from the sun, a readily available power source, to energize everyday electronics.
The sun isn’t always out, obviously, so you’ll need some kind of backup energy source to keep your lights on. But what kind of off-grid solar batteries will you need? And how many should you install?
Like many aspects of solar installation, there are a lot of factors to consider when designing an off-grid system. In this blog, we’ll lay out just a few of those variables. But we won’t provide hard and fast rules or calculators to determine how many batteries you’ll need, as each individual situation will invite its own changes.
If you’re thinking about going off-grid, don’t hesitate to give our experts a call. We’ll be able to design the best system for you.
Now let’s get down to business.
Using off-grid solar batteries takes some planning. You’ll need to think about your home or cabin’s energy usage in order to design a properly sized system.
So first things first, how much energy do you typically use? Does that energy use change with the weather? Are there devices that you could survive without?
For reference, the average Minnesota home uses 759 kilowatt-hours (kWh) of electrical energy per month, or 25 kWh per day, according to the U.S. Energy Information Administration. Batteries are often rated in amp-hours, or the amount of current they can supply over time, as well as voltage.
A 12-volt, 200-Ah battery could theoretically provide 2.4 kWh of electricity (12 x 200 = 2,400), not accounting for any inefficiencies that come with electrical systems. Remember, an average home may use 10 times that much in a day, so that battery only provides enough energy to power a typical Minnesota home for about two hours.
As you can see, it takes a lot of energy to power an entire house. That’s why it’s more common to see off-grid systems in RVs and small cabins. Another option would be to use an off-grid system to power only critical loads in your house, such as heating equipment.
At the end of the day, the less energy you use, the smaller and more affordable your off-grid system will be.
Depth of discharge
Batteries come in all shapes and sizes, but they all turn chemical energy into electricity. Solar systems have commonly used lead acid batteries, but technological advancements have meant greater adoption of lithium-ion batteries.
Solar Power World has a helpful guide of different types of batteries used in renewable energy systems.
One of the biggest differences among battery types is their “depth of discharge.” That refers to how much you’re supposed to drain the battery.
For example, if you routinely discharge a lead-acid battery below 50%, you’ll end up shortening its useful life. Lithium-ion batteries can sustain greater levels of discharge.
Though lithium ion batteries are more expensive, you’ll need fewer of them. That’ll save you space in your garage, basement or wherever you place the system.
You’ll also have to consider how often you’ll need to replace your batteries. Your solar panels could last two decades or more, so you’d want your batteries to be around to absorb that energy.
Many factors will affect your battery’s shelf life, including depth of discharge, battery type and even temperature.
This lithium iron phosphate battery is rated to last 2,000 cycles with a 100% discharge. But one battery costs north of $1,000.
Meanwhile, discharging this cheaper lead acid battery completely will net you about 300-400 cycles before its capacity dips to 60%. Alternatively, you could discharge the lead acid battery less and use only about 30% of its capacity, extending its life. But you would need more batteries to maintain your energy output.
Powering your devices
As EnergySage lays out, battery power ratings determine how many devices you can power at one time.
Appliances and electronics have some kind of power rating to show how many watts they require to run. Using a 1,000-watt microwave and an 800-watt coffee maker at the same time will require 1,800 watts.
Knowing how many and which types of loads you’ll be powering at the same time in your setup will help tell you how many off-grid solar batteries you’ll need.
Also, batteries may have some kind of peak output rating. The Enphase battery has a higher peak power rating than its continuous rating. But it is only meant to maintain that peak power output for 10 seconds. That can be helpful for loads that have a motor, which require a lot of power when first starting up.
Days of autonomy
Another factor to consider: How long will the batteries need to power the home without being recharged?
This is referred to as “days of autonomy.” Given that solar panels don’t work as well on cloudy days, or in seasons when the sun is low, you’ll have to think about how long you’ll want your batteries to last.
During the middle of summer, the Duluth area sees plenty of sunshine to keep batteries charged. But that changes by December, when we see less than a third of the solar radiation on a given day.
If you’re planning to use your off-grid system in the depths of winter, you need to plan for the worst of scenarios. But designing your system with more days of autonomy will mean more batteries and more costs.
This is only scratching the surface of everything you’ll need to consider when thinking about designing an off-grid solar system. But hopefully you have a better idea of what to expect.
Thankfully, the experts at Wolf Track Energy have plenty of experience with off-grid systems and can design a system that meets your needs and budget. Contact us below to learn more.
Read more from Northland’s solar energy experts:
- REAP grants for solar: How to get financing for your system
- Net metering in Minnesota: What to know
- “How many solar panels do I need?” Find out here
- Solar panel warranty: How to protect your investment
- Getting solar quotes? Here’s how to read your proposal