California Air Resources Board

This website highlights existing zero emissions backup power options that could be used to power a residential home during an electrical grid outage. Generators burning fossil fuels have historically been used for residential backup power. These generators produce a lot of emissions, including poisonous CO, are loud, and require frequent maintenance. In the last few years, alternative backup power options that eliminate these disadvantages have become available for residential use. The alternative technologies produce zero emissions and are powered by batteries, batteries plus solar panels, or fuel cells.  

Please explore the tool below for more information about alternative backup power options. The following links provide detailed information about Using This Tool , and Assumptions used for development .

Disclaimer: This tool is designed to provide information to a general audience on what backup options might be a good fit for different situations. However, appliance power and energy demands vary greatly and this tool should be used for general guidance only. For a complete list of similar tools, checkout CARB's Technology Clearinghouse tools including information on commercial emergency backup power options. 

Using This Tool

The tool guides you to available technology options that fit your needs based on: 

What do you intend to use the backup power for? Details for each set of assumptions can be found in the tool assumptions section below.  

• Basic Communication is the lowest energy use category that includes basic communications such as charging phones and tablets, powering laptops, internet routers, and very limited lighting. 
• Critical Loads includes all the items in the basic communication category plus additional appliances such as a refrigerator, a medical device, and a box fan. 
• Critical Loads + AC + Pump includes everything above plus a portable window-type AC and a well water pump. 
• Whole Home is the highest energy use category. Energy use varies from home to home, we recommend professional assistance when sizing a whole home backup system.  

Are you looking for portable or integrated options? 

Portable backup power options can generally be moved from place to place and require devices to be plugged into it. Integrated backup options are built into a home's electric circuits and allow devices to be powered automatically whenever the power grid goes out. 

How many days of backup power are you interested in? 

Many power outages only last a few hours, however there are backup options that can supply power for multiple days. Battery backup systems used for longer timeframes can often greatly benefit from integrated solar panels that will recharge the batteries and reduce the cost of energy storage.  

What is your price range? 

There is a broad range of prices for these technologies, based on the features of each. The slider at the bottom of the tool can be used to narrow down available technology by price.  

Assumptions

Conventional generators and fuel cells can be sized based on power demand and runtime is not a concern since they can be refueled quickly. Battery backup technology must be sized based on power demand as well as total energy storage to ensure sufficient runtime. Adding solar panels to a battery backup systems increases the amount of time it can run, but has no effect peak power since this is limited by the AC power inverter, not the battery pack power.  

Sizing based on power – It is assumed that all backup system that produce less than 1.5kW can only be used for the basic communication use category. Similarly, the critical loads use case only includes systems that can produce at least 2kW. Finally, some appliances have startup loads that are much larger than their operating power demands which may need to be considered when sizing backup power equipment. 

Runtime - Total energy used by appliances is the product of the device average power demand and the hours of operation. Power is measured in kilowatts (kW) or watts (W) and time is measured in hours(h). Battery storage is measured in kilowatt-hours(kWh = kW*h). Runtime, in hours, can be calculated by taking the battery capacity (kWh) divided by the power (kW). The 0-1 day runtime use case includes all battery backup systems that can provide sufficient power, but they may have very short runtimes. 

The runtimes and use provided in this tool are based on manufacturer specifications and generic assumptions and are not intended to be used to determine household power demand. More home-specific calculations can be done by measuring your appliance loads using a meter or by using power estimation tools provided by government and manufacturer websites, including the Department of Energy’s electricity use calculators.  

Solar can add additional runtime by producing power to recharge the batteries when the sun is shining. The amount of energy a solar panel of a given size can produce is dependent on how much sunlight hits it. This can be affected by the weather, time of year, angle of the panel, and any obstacles that shade the panel. The assumed sunlight factors can be found in the Solar Capacity Cost Adjustment Assumptions section below. . 

The following assumptions were used in this tool: 

The California Energy Commission and the California Public Utilities Commission have jointly developed a number of calculators to help residents determine their individual solar system costs and benefits.  

The assumptions used in this tool for solar are as follows: 

• Size of solar is based on the maximum capacity of the battery model multiplied by the sizing factor. A sizing factor of one (1) would fully charge the battery every day resulting in continuous runtime. For this tool a sizing factor of 0.5 was used.   

• Maximum solar size factor is implemented to cap panel size estimates for very small battery systems sizes. 

• Average dollar per watt of solar system is based on the average cost of panels across the manufacturers listed. 

• The average amount of sunlight available for the solar panels was estimated to be 4 hours per day using the following tool: https://pvwatts.nrel.gov/pvwatts.php 

  • Example calculations: For a battery capacity of 1kWh, the solar is sized to provide 0.5kWh from 4 hours of sunlight resulting in a solar array size of 125W at a cost of $2.58/W.

Although some portable models can be integrated, these devices are only listed once in the data. The criteria to determine if a device was portable or integrated are as follows: 

Portable: 

• Designed to be movable, e.g., has wheels or handles 

• Appliances are powered through manual connection to receptacles on the unit 

Integrated: 

• Does not meet portable criteria 

• Wired through transfer switch 

For more information, please email us at: TechnologyClearinghouse@arb.ca.gov 

For assistance with web accessibility, please email: webaccessibility@arb.ca.gov.