Explaining the terminology: off-grid, net-zero energy, and battery backup

We get a lot of questions about going “off-grid,” making a home “net-zero energy,” and what “battery backup” is, and there seems to be some confusion about these options. Here we will address the differences between these three terms as well as discuss some of the pros and cons of each.

Here are the simplest ways to explain the three terms:

• “Net zero” means a home that has a solar array that is sized to produce enough energy to offset 100% of the total electricity consumption in the home annually, but that home is utility connected and regularly uses the utility grid at night or during bad weather to power the home.
• “Battery backup” means having a home battery system (typically paired with a solar array) that provides a secondary power source for the home if the utility grid goes down (i.e., a blackout).
• “Off-grid” means there is no connection to your electric utility, and your solar and battery system are the primary source of electricity in the home.

Let’s go a little further into each definition:

NET ZERO

It’s much more common for a home to be net-zero energy than to be fully off grid. Net zero homes are designed to produce at least as much energy as they use in a year but are still connected to the grid so they can access traditional power sources as needed. In the case of solar, the energy production occurs during the day but doesn’t come at night or during cloudy weather, so the grid provides electricity when the house’s solar isn’t producing enough. Overall, the daily solar production adds up throughout the year to be enough to offset 100% of the total energy consumption in the home on an annual basis. This is why we call it net zero energy.

Regardless of how efficient a home is and how little the homeowner requires outside resources, by definition, grid-connected homes can’t be considered off-grid. Additionally, while net-zero homes may be energy efficient, they don’t have to be, as long as enough energy is produced to meet the home’s yearly needs. One other important note: net-zero energy does not refer to battery backup systems as a home does not require a battery backup to be net-zero energy.

The pros of maintaining a grid connection include lower costs on the front end, with less equipment needed to produce and store power than the full off-grid option. Additionally, net metering – at least in states where the policy hasn’t been severely reduced or eliminated by utility-friendly legislatures – can provide a nice financial benefit for homeowners who send energy back to the grid from their solar energy systems.

On the negative side, as most of us learned during Hurricane Ian (or already knew from previous storms), the grid is not 100% reliable. When the grid goes down, solar energy systems shut down to prevent energy from back-feeding and to keep utility workers safe. This is where battery backup can help.

BATTERY BACKUP

A battery backup system comprises batteries, battery management systems (BMS), and battery inverters (again, usually paired with a solar array) that provide a secondary source of power to the home in the event that the primary power source (the utility grid) goes down. As we will see later, a battery backup as a secondary power source is a key distinction because it allows the backup to be sized much smaller than would be required if it were the primary source of power for the home. Because it will only be used in a blackout, the homeowner can decide which devices in the home will be powered while the grid is down. Things like refrigerators, lights and fans are usually first on the list of electrical loads to “protect” with the battery backup, while larger loads – such as ovens, clothes dryers and even air conditioning – can also be protected with larger battery backups. With a battery backup, during a blackout event, the homeowner will need to manage their available battery resource to ensure the batteries are not drained down.

However, even a large battery backup is relatively small compared to a true off-grid system, with batteries and solar being designed to provide from a few hours to a few days of runtime before a recharge from the solar will be needed (before the battery runs down completely).

The biggest benefit of a battery backup system is – first and foremost – the peace of mind of knowing that key appliances will continue to work seamlessly should the grid go down. Users will enjoy much greater energy independence, with the ability to manage power loads (even remotely). Batteries are also quiet and odorless, and Lithium-Ion batteries require zero maintenance, unlike gas-powered generators, which require monthly starting and testing, and regular oil changes and other maintenance.

On the negative side, batteries aren’t cheap – they require higher upfront costs than just a solar energy system alone. A well-designed battery system will be able to provide all the backup power one needs, but the cost is significant. A solar + battery system is also electrically more complex, requiring expert design and installation. The electrical code and complexity of these systems require an installer to have expert knowledge and skill. Sadly, we’ve had to rescue a number of clients whose battery systems were installed incorrectly, causing serious electrical problems in the home.

OFF GRID

A home that is fully off-grid is one that is autonomous and self-sufficient, not connected to public utilities, and can meet its natural resources requirements through alternate sources (such as solar energy plus home batteries, rainwater catchment systems, greywater recycling systems, autonomous septic tanks/composting toilets, etc.).

For our discussion, we will focus on the electrical side of the “off grid” question. In this case, those who are planning to go off grid must ensure their full electrical needs can be met, not just for backup situations but also for everyday life. There is a large difference between powering a few appliances for a couple of hours after a storm and powering a whole home during a large dinner party, after three weeks of bad weather in hot and steamy August. The off-grid system must manage that in August as well as in cold and rainy December. Per the electrical code, fully off-grid systems must be designed for what is essentially the worst-case energy scenario, meaning full electrical load (everything in the house turned on) for an extended duration, which means they must be significantly larger than even the largest battery backup system might be.

Because of this, true off-grid systems are exceedingly rare in areas where utility power is available.

The biggest benefit of being off-grid is, first and foremost, complete energy independence. You will never be subject to continuous, burdensome utility rate increases. The option to go off-grid is also a literal lifeline for remote and/or underdeveloped communities.

The obvious negative of going off-grid is that there will be no back-up system should the system fail. Also, going off-grid will require a much larger front-end investment than a battery backup system would require. Finally, significant lifestyle changes may also be necessary to go off-grid successfully, depending on budget and other factors (like the solar resource at the site).

So there you have it – our breakdown of “net zero,” “battery backup” and “off-grid.” Please reach out to us if you have any inquiries about whether any of these options might be a good fit for your home!