Home Backup Power: Generator vs. Battery

In recent years, homeowners have become more concerned with backup power solutions. Severe weather events like Hurricane Harvey, Irma, and Maria have magnified the need for backup power. The two most common home backup power technologies are generators and batteries. These piece will explore the pros and cons of each of these backup technologies.

Before we dive into which technology is best for your home, let’s discuss your current energy usage. The average daily electricity consumption of an American household is around 30 kilowatt-hours (kWh), but ranges from about 16 kWh to 40 kWh. Utility rates, temperature, lifestyle, and environmental conscientiousness are some of the key factors that account for the variance in electricity consumption throughout the country.

Additionally, consumption is usually not evenly distributed throughout the day. Home electricity consumption typically peaks in the morning when people wake up, cook breakfast, and run the coffee machine. Electricity consumption peaks again in the evening when Americans get home from work, turn on their lights, cook dinner, and watch TV. It is important to understand when you use electricity so that you can reduce your consumption during a blackout. Why should you reduce consumption during an outage? Both of these technologies by themselves are more expensive than your utility and their use should be limited if possible. Therefore, during a power outage, your backup power system should be able to provide slightly less energy than you use on an average day.

Your Backup Power Options 

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There are two types of backup power systems most popular with today’s homeowners: batteries and generators. Batteries are usually mounted behind your home’s electrical meter or indoors in the garage. They can be charged from any source of electricity (including solar!). For most homeowners, that means that you charge your batteries with electricity supplied from the grid. However, homeowners with solar panels can also charge their batteries using energy from their solar panels. (These homeowners can also charge their batteries with electricity from the grid.) Generators, on the other hand, are connected to your home’s main gas line (or to a dedicated tank, depending on availability and preference), and burn various types of fuel (often natural gas or gasoline) to generate electricity.

Choosing the Right Option

Both have advantages and disadvantages, so choosing between the two is not always an easy task. How do you make the decision? What are the main criteria involved?

Let’s start with the basics: how long do you expect an outage to last?

In most urban and suburban areas, power outages rarely – and only under catastrophic circumstances, such as natural disasters – last for more than a few hours. 7-10 kWh can cover the power requirements of an average home for one evening. If you are conscious of the power outage, you can also reduce consumption as the utility works to get the grid back up. Both generators and batteries can supply the 7-10 kWh needed for a short power outage so the choice boils down to economics and environmental impact. A generator costs between $1,500 and $5,000 depending on brand and quality. You can expect to pay an extra $500 to $1,000 for installation. Batteries that can store 7-10 kWh can cost $3,000 to $5,000, but these systems also require an AC/DC power inverter (typically around $2,000) and professional installation (around $1,000). In total, you can expect to pay more upfront for a battery system, but you won’t have to pay for fuel like you would for a generator. Additionally, there are environmental impacts to consider. Batteries, especially when storing power from solar panels, are more environmentally friendly than fossil fuel generators.

If you want to prepare for longer outages or want to go completely off the grid, there are other factors to consider. For example, over a period of four days, most US households use about 120 kWh. In order to store that much energy with battery technology, you would have to purchase several batteries, which is likely to be prohibitively expensive. Generators, on the other hand, have the same upfront cost whether you wish to generate power for a few hours or a few weeks. You still have to pay for the cost of fuel, but running a generator for a four day long outage is significantly cheaper than buying batteries that can store enough energy to power your home for that same period of time. That said, if a major storm occurs (like Harvey or Maria), obtaining fuel is often an issue.

There are two main types of generators: portable and standby. Portable generators can vary in size. A smaller one can power a refrigerator and electronic devices while a larger one can run most appliances and air conditioning. Portable generators need manual operation. Most of them are powered by gasoline. Standby generators can handle a bigger load, and operate automatically. They are installed outdoors and are quieter than portable ones. They last longer than portable generators, and can be hooked up to natural gas or propane lines. That can be helpful during a major storm when gasoline supplies are low.

A generator will continue to provide energy as long as it has fuel to run on. However, running a generator for two weeks – while certainly possible – is expensive, loud, and polluting. For instance, with a Diesel generator, you can get about 7-10 kWh per gallon of fuel, which means you would need 3.5-4 gallons per day. The cost of fuel is not the only thing you need to consider; if you use a fuel like gasoline, you need to think about storing it safely. You could also run your generator on natural gas and connect to the main gas line. However, in the event of a natural disaster, a gas outage is often just as likely as an electricity outage. In fact, these shortcomings – high fuel cost and potential safety hazards — are what historically causes some homeowners to consider solar power as an alternative source of power when the grid goes down. Paired with the latest battery system, solar panels can provide a reliable source of energy during an outage.

Home batteries can be installed outdoors or indoors. They require low maintenance, are quiet, and are environmentally friendly. Lithium-ion home batteries have a small carbon footprint and a long life cycle, and can be connected to the cloud. They store energy rather than generate it. A grid-tied solar PV system with battery backup can respond quicker to a power outage than an auto-start generator can and there is no fuel cost. However, if an outage occurs during a winter storm, sunless days can deplete the battery. A large load will require more batteries and inverter capacity, which can increase the system’s cost. The average lifespan of a battery is about 10 years.

How would a “Solar + Battery” backup power system work? Solar panels would generate power during daylight hours, and batteries would store that solar energy for use at night. Solar + Battery backup power systems can provide energy for extended power outages and can even be used to go completely off the grid. Additionally, you can use the solar panels to generate free power when there isn’t an outage, which can save you thousands of dollars on your electric bill. There are even financing options available for solar with zero upfront costs for those who qualify. (You can check out our free solar calculator to see how much you could save with solar.)

Presently, it is early adopters who are opting for batteries to back up solar power. It is a relatively new technology with a higher cost. A study by Enphase on 550 solar and prospective solar homeowners in key solar states found homeowners prefer generators rather than lithium-ion battery systems. There are two reasons why: cost and maintaining power. About 80 percent of the homeowners surveyed by Enphase considering backup power were open to buying a generator. Less than 20 percent of them were considering buying batteries.

As battery costs decrease, they will likely become a more affordable/viable option for storage and backup. Energy storage costs may decrease by up to 70 percent in the next 15 years, a 2016 report found. The report found that “, Solar storage will become more competitive as new battery technology drives prices down.”

How long you want to have power during an outage is the most important question homeowners have to answer when deciding on backup sources of power. However, there are a lot of other variables to take into account including generator maintenance, safety, fuel storage or gas line connection, environmental impacts, and sun exposure. These factors, as well as those mentioned above, can vary significantly by region. We suggest speaking with a local service provider specializing in home backup power. These professionals can lend expertise and help you make the best decision for your family and your home.