In the last PV 101 Installment we discussed the basic principles of photovoltaics (PV) and modules.  When designing an optimal solar electric system for grid-tie or off-grid, the first step is determining daily average electricity usage or loads.  This article will review the basics, as well as important considerations when calculating your electrical loads…


First Things First: Use Energy Efficiently!
Gadgets and appliances that use electrical power are defined as “loads”. Loads are the primary factor with the cost and size of a solar electric photovoltaic system. By minimizing and conserving energy in a household, you can reduce the overall cost of your PV system. By load shifting (a method of supplying energy from non-electric sources) and increasing your energy efficiency, you will directly effect the need for additional electric power. Keep in mind that living without unnecessary items and avoiding/reducing use of inefficient appliances will go a long way to a using your energy efficiently.

The Basics of Electric Load Evaluation
If your home is connected to the utility grid, your energy usage has already been calculated for you in kilowatt-hours per month on your electric bill. If not, or if you are building a home and would like a renewable energy system to power it, you may be asked to complete a load evaluation form analysis.  In order to size a photovoltaic system, you must be able to calculate the average daily electrical energy consumption in watt-hours as well as the total connected watts.

Considerations for Calculating Load Estimates
There exists different variables when calculating a load evaluation analysis.  Some important details to consider are:

  1. Always use the correct load estimate numbers
  2. Don’t forget the phantom loads (loads that draw power when devices are turned off)
  3. The refrigerator is one of the single largest energy loads in a home (try an energy efficient model)
  4. Some equipment/appliances cycle on and off (“Duty Cycle”)
  5. Examine all opportunities for energy conservation and load shifting
  6. Future loads may change
  7. Refer to manufacturer’s numbers, not just generalized sources

How To Calculate Electrical Loads
Here are the steps to calculating the average daily electrical energy use in watt-hours:

  1. List all your electrical appliances, by room.
  2. Check if they are AC or DC
  3. List the quantity
  4. List each individual wattage
  5. List how many hours per day and days per week each item is used

It should look similar to this:


Load Evaluation Worksheet

Load Evaluation Worksheet

By using this formula, homeowners can estimate their electrical load themselves, and provide their installer with the most accurate information to design an optimal pv system.

Are you ready for a grid-tie or off-grid residential system estimate?  Call PPC Solar at 877-736-5896 or email us today.

For more basic solar information, stay tuned for the next PV 101 blog installment – Batteries For Energy Storage!



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