off grid with solar

Going off-grid with solar: what does it mean and how much will it cost? (Part 2)

This is Part 2 of a two-part series that explores the economics of going completely off-grid with solar. Part 1 focuses on what it actually means to go “off-grid” and how to start thinking about calculating the costs for cutting the cord with your utility. Part 2 discusses two real-world examples of sizing an off-grid solar energy system, along with the feasibility of going through with an off-grid solution. Check out Part 1 here.

The notion of living off-the-grid is becoming increasingly popular. Given the rising cost of electricity throughout the country, it’s hard to not at least consider cutting the cord every time a utility bill comes through the mail. But what does it really mean to go “off-grid”? For such a simple concept, the logistics of going off-grid are in fact rather complicated and very costly. 

What does it mean to go “off-grid”?

Taking your home off-grid from an electricity perspective means completely removing any connection to the larger electric grid, which powers the large majority of homes, buildings and businesses throughout the country. This means that to go off-grid, you’ll need to meet all of your household needs with electricity produced on-site. 

Importantly, installing solar panels on your roof does not mean that you’ve gone off the grid. Most solar energy systems are not designed to consistently generate enough electricity to be a home’s only power source, which is why the vast majority of solar homeowners maintain a connection with their utility company. 

In these cases, a policy called net metering allows you to put the electricity produced by your solar panels back onto the electric grid when you aren’t using it, and to then pull from the grid when your solar panels aren’t producing, at night or when the weather is less than ideal. At the end of the month or year, you’re billed by your electric utility on the net of production from your solar panels and the electricity you used from the grid, hence the term net-metering. 

In an off-grid solar energy system, you don’t have access to the larger electric grid when you need it, either at night when your solar panels aren’t producing or in the event of a prolonged period of cloudy weather. Instead, you need to create your own personal “grid”, installing on-site battery storage to store the output from your solar panels for use at a later point in time. 





Don



Two examples of off-grid solutions

Instead of looking at averages across the whole U.S. and making several uniform assumptions, as we did in Part 1 of this series, let’s look at what it would take to go off-grid in two real, specific places: Massachusetts and Arizona, two states where solar energy has seen significant growth and support over the last decade.

Example: going off-grid in Massachusetts

In order to go off-grid successfully in Massachusetts, you’ll need to plan for the cold, snowy winter months that typically might have days with only 3 sun hours each. For this example, we’ll assume a residential home using 750 kWh of electricity per winter month, which comes out to 25 kWh of electricity per winter day.

Fewer sun hours in a winter day means you’ll need to install a much larger storage system and solar array to harness enough electricity for your property. What’s more, extended periods of cloudy weather and snow reduce sun hours further. To be safe, let’s say you want to install an off-grid solar energy system with storage that will be able to run your home on solar electricity for one week

How does the math on an off-grid system in Massachusetts pan out? 7 days of electricity use in the winter adds up to 175 kWh (25 kWh/day x 7 days). Using Tesla Powerwall batteries with 95% depth-of-discharge, that means you’ll need a storage system with a total capacity of about 184 kWh, which comes out to 14 individual Tesla Powerwall batteries. Even if you allow for the small amounts of sunlight that will get through to your solar panels during cloudy and snowy days, you’re still looking at potentially 10 or more batteries.

Once you’ve sized your battery storage setup, you can calculate the panel array size needed to keep it full. Assuming you want to be able to charge 184 kWh worth of battery storage in a week, you’ll need to install an 8.8 kW system (8.8 kW x 3 sun hours gets you 26.3 kWh of electricity per day, and multiplied out over a full week, that adds up to about 184 kWh of solar electricity).

Example: going off-grid in Arizona

In order to go off-grid successfully in Arizona, you’ll need to plan for the hot summer months when you’ll be running your AC at full blast. Unlike winter in Massachusetts, there is plenty of sun to go around, so we’ll assume 7.5 sun hours each day during the summer months in Arizona. We’ll also assume a residential home using 1050 kWh of electricity per month, which comes out to 35 kWh of electricity per summer day.

More sun hours per day means you won’t need to install a much larger solar panel system than usual, but a high electricity load leads to an increased need for storage. And to be safe in the case of cloudy weather, let’s say you want to install an off-grid solar energy system with storage that will be able to run your home on solar electricity for three days.

How does the math on an off-grid system in Arizona pan out? 3 days of electricity use in the summer adds up to 105 kWh (35 kWh/day x 3 days). Using Tesla Powerwall batteries with 95% depth-of-discharge, that means you’ll need a storage system with a total capacity of about 111 kWh, which comes out to a little less than 8 individual Tesla Powerwall batteries.

Once you’ve sized your battery storage setup, you can calculate the panel array size needed to keep it full. Assuming you want to be able to charge 111 kWh worth of battery storage in 3 days, you’ll need to install a 4.9 kW system (4.9 kW x 7.5 sun hours gets you about 37 kWh of electricity per day, and multiplied out over a full week, that adds up to about approximately 111 kWh of solar electricity).

Reduce the cost of going off-grid with energy efficiency

If you’re determined to go off-grid and don’t want to break the bank in doing so, taking appropriate energy efficiency measures around your home to reduce your electricity load is a necessity. In the examples above we assumed standard home setups and standard energy use habits, but by using efficient appliances, properly insulating your home, and shifting your habits to use less energy, you can reduce your electricity load in any type of weather, sometimes dramatically. It’s important to keep in mind that making energy efficient decisions is a way to cut down on the amount of electricity you use, and possibly make going off-grid more affordable.

Bottom line: off-grid is possible, but it might cost more than you think

Going off-grid isn’t cheap. And considering the cost of going solar and staying connected to the grid averages under $18,000 in 2019, it’s hard to justify the extra cost of going off-grid.

For property owners with unusually low electricity loads, an off-grid solar solution might be practical. However, for the vast majority of solar shoppers, going off the grid with solar is a much more involved and expensive process than you might initially think. Costs, physical space constraints, and energy-hungry habits all contribute to make going off the grid a daunting proposition. 

Staying connected to the grid provides the benefit of backup power whenever you need it. Instead of installing 8 extra home batteries to protect against the edge case of an extended period with low solar energy production, you can simply rely on the grid to provide electricity. Of course, that means you’ll need to pay a utility electricity bill. But installing solar panels can reduce your average bill significantly, especially when you consider the added financial advantages of net metering credits.

Going off-grid is entirely possible, and it’s even possible to do it while keeping modern conveniences. But it’s rarely as simple or cost-effective as installing solar panels and staying connected to the grid.





Don




This post originally appeared in Mother Earth News.

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