Solar Battery vs Generator for Grid Resiliency

It is safe to say that climate change is already impacting modern society’s ability and methods for meeting basic human needs for clean water, nutritious food, secure housing, and reliable electricity.  The last 5 years have been the hottest ever recorded. ​100-year floods, devastating wildfires, and severe drought are rampant and become increasingly normalized. ​

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Larger and more frequent hurricanes leave countries and states in a constant rebuilding cycle. Even large power companies aren’t immune to these devastating impacts of severe weather. In October, California’s largest electric utility threatened to cut the power supply of 500,000 customers for as many as five days over wildfire threats.

Nearly 75% of Americans say that climate change is “personally important” to them. That means that many Americans have started to think about and prepare for extreme weather events with the capability of knocking out power for days or weeks at a time. What’s the best way to secure your home and your quality of life in a grid-outage situation that is both environmentally friendly, affordable, secure, and reliable? We here explore the best long-term solution to building resilience in your home and business.
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There are two commercially available and affordable options for most Americans to keep the lights on when the grid goes down: natural gas/propane generators or solar energy coupled with battery energy storage. Both generators and Solar + Battery allow homeowners to experience uninterrupted power supply through the use of an automatic transfer switch which makes your home’s electrical circuits their own island, separate from the rest of the grid and allows you to consume the energy being generated on-site.

Natural Gas or Propane Generators

Name-brand residential generators can cost anywhere from $8,000 to $12,000 after installation. Like any fossil-fuel-powered combustion engine, generators need to be exercised and will generally run automatically about once a week for 10 minutes to keep the moving parts lubricated. These motors also require regular service, with annual maintenance costs of around $400. Even the best commercially available residential back-up generators typically have warranties lasting no longer than five years. Considering the long term maintenance costs of generators, the total cost of ownership over a ten year period is roughly $12,000-$16,000 excluding the cost of propane or natural gas fuel used to run the system.

In areas without access to natural gas service, propane tanks can cost well over $1,000. Propane costs, on average, between $2.00-$2.50 a gallon. A generator sized to provide back-up power to an average 1500-2000 sq ft home will consume between 2-4 gallons of propane an hour. That means for a 24-hour grid-outage, the fuel costs for a propane generator system can cost $120. 

The fuel costs for fossil-fuel run generators are considerably lower in areas where natural gas service is available.  A generator sized to provide back-up power to an average 1500-2000 sq ft home will consume between 150 to 300 cubic feet of natural gas per hour (or 1.5 – 3 Therms). In the State of Georgia, the rough average cost of a therm in 2019 is about $1 meaning that running your home on a natural gas generator during a 24-hour grid outage can cost around $75 dollars. 
Over the course of ten years, assuming an average of 5 days of grid outage each year, the total cost of owning a fossil-fueled powered generator can range from $15,750 to $23,000. But remember, a back-up generator’s only purpose is to provide electricity when the grid is down, however often that may be. This makes it very difficult- if not impossible- to quantify any ‘return-on-investment’.

Solar + Battery Storage

Solar Energy plus Battery Energy Storage, on the other hand, is an investment opportunity to become grid resilient and own your own power production that works to create a return on your initial investment from day one. In addition to providing immediate back-up power to your home in the event of a grid-outage, energy storage can also help your home to maximize the value of the clean solar energy produced in the home and in variable rates offered to you by your utility company. 

During sunny days, a solar battery system will capture and store any surplus solar energy being produced on your roof but not immediately consumed in the home. That power remains available until demand in the house again exceeds the energy produced by the solar energy system. As the sun goes down and your solar energy system stops producing, the home battery system will discharge and power the demand in the home. This process of maximizing the amount of solar energy that you consume in your home can help ensure that you receive the greatest value for every kWh your solar energy system produces.

Over time, regular operations of the battery will allow you to use less and sometimes eliminate your night time consumption. In what is called ‘backup mode’, the battery will charge and stay charged until power is lost, it is then at that point that the battery will discharge and provide power to the home. 

The amount of energy discharged from the battery and where it is discharged can be catered to the homeowner’s preferences. For example, if a homeowner wishes to only run the ‘essentials’ during an outage the battery will keep the set essentials powered while reserving power from the rest of the home. Some batteries can even gather weather data from the internet and presumptuously charge in preparation for a potential outage.

In the Georgia market, two Tesla Powerwalls (27kWh of battery capacity) will cost roughly twenty-three thousand dollars (including installation) and is often adequate to provide whole-home backup for the average Georgia home. This means when the power goes out, your entire home will be powered without having to choose which appliances get power and which do not. 

Modern battery storage systems require virtually zero maintenance and when paired with a solar energy system is also eligible for federal tax credits. In 2020, the Federal Residential Clean Energy Tax Credit for solar + storage systems will be 26% making the after-credit cost of your two Tesla Powerwall batteries just seventeen thousand dollars.

The industry-standard warranty for any lithium energy storage system doubles that of even the best residential generators at 10 years, guaranteeing 70% of the battery’s original capacity is available after that same amount of time.
Solar + Storage creates the opportunity for homeowners to essentially become their own power plant with a strong return on investment. The typical return on investment for owning a solar energy system in Georgia can range from 6-12 years generated when the sun is shining and the grid operating, however, only when the system is paired with a battery or generator does it provide power when the grid is out.

Generators are reliable if you have a fuel source but are used very infrequently, burn fossil fuel, are accompanied by high maintenance costs and have zero return on investment. Adding solar with a battery can do more than make you grid resilient during outages but it will also reduce your demand for energy from the grid and thus save you money on your utility costs.

Unlike generators, a battery will be charged and discharged every day working to help you save instead of sitting idle awaiting power outages. When considering the functionality and overall cost of ownership of solar alone vs solar with storage, a solar energy system paired with a battery is the wiser investment overall and does more than simply providing you backup power during an outage, it brings intelligent energy consumption to the next level.

When you’re ready to take control of your home’s energy with solar + storage, give us a call at 770-485-7438 and let us show you all the power the sun can bring to your home!

**Costs fluctuate based on labor prices and region

   Written by Matthew Johnson,
​   CSUSA Solar Consultant