How to Size a Generator For Your Home

I’m trying to learn about home generator systems for an off the grid cabin, How many watts do I need from a generator? How to Size a Generator for an Off Grid Power System.

Home Generator for Backup or Off Grid Power
Electrical Question: I’m trying to learn about home generator systems for an off the grid cabin.

How many watts do I need from a generator?

The cabin is small 24 x 36.

• I need power for the following:
  • Lights.
  • Refrigerator.
  • A computer.
  • Television.
  • Fan, etc.

I also plan to use tankless Hot water heater from LP as well as gas stove for cooking.

• I just need some direction with a generator and whatever else is need to set it up, such as:
  1. Transfer Switch
  2. Electrical panel
  3. Stuff like that.

This electrical question came from: Jace, a Homeowner from Denver, Colorado.
See more about Home Wiring for Colorado

Dave’s Reply:
Thanks for your electrical question Jace.

Application: Off Grid Generator Project.
Skill Level: Intermediate to  Advanced – Best performed by a Licensed Electrical Contractor.
Tools Required Electricians pouch of hand tools and the various power tools necessary for installing the generator and transfer switch.
Estimated Time Depends on the type and size of the generator and transfer switch and the available access to the project area.
Precaution Any existing electrical wiring within the immediate area that may interfere with the installation of the transfer switch may need to be relocated if necessary.
Important Installing a generator and transfer switch must be well thought out and performed with a permit with all work being inspected.

How to Size a Generator for an Off Grid Power System

NOTE: The size of the generator will depend on the electrical devices that will be connected to the generator system.

• Generator Sizing Basics: Properly sizing a generator for your home starts with making a list which contains the following electrical load information:
  1. The voltage
  2. The amperage or watts
  3. The duration or how many hours each item will be running
  4. How many of these items or circuits will be on at the same time

The electrical load information is vital for selecting the right size and type home generator to ensure the performance of the generator will be sufficient for the electrical loads that will be required.

Generator Transfer Switch and Circuit Panel

The amperage rating of the transfer switch, and circuit capacity of the electrical distribution panel is based upon the connected load as described above.

• Generator Transfer Switch: Even with an off grid system, there may be one or more sources of electricity which will be connected to the system. The additional power sources will need to be identified for proper system integration.
• Charge Controller and Voltage Regulator: Power sources such as solar panels and windmill power are typically connected to the charge controller, therefore the controller must be sized and configured for the power that will be produced and connected to the system.
• Inverter and Electrical Circuit Distribution Panel: Before the power can be used by the home for 120volt ac devices the power being produced must be conditioned and converted by an inverter. The inverter supplies power to the electrical circuit distribution panel, which supplies power to the home.
• NOTE: Many off grid system components are being produced where several functions are integrated together making it much easier to build and configure, such as integrated charging controllers and inverter systems.

More about Home Generators

The resources below will lead you to more expanded information that will help you with all the key factors to consider along with free information you can use to help you select the right generator to purchase for your home.

Home Generators

Home Generators
This series covers a wide variety of topics all about home generators including sizing, selecting, connecting and safely operating this all important addition to your home.

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House Wiring Circuits and Circuit Breakers
This article looks at common 120 volt and 240 volt house wiring circuits and the circuit breakers that are installed identifying the types and amperage sizes used in most homes.

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Basic Home Wiring Diagrams

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