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Estimate Solar Production and Energy Requirements

NREL's PV Watts System

Estimate your solar energy potential with NRELs PV Watts system. The National Renewable Energy Lab has developed a tool to estimate the monthly and annual solar production at a specific site. This link is for Traverse City.


  • Input the system size in DC watts
  • Change the tilt angle to either the optimum (33 degrees) or your roof slope.
  • Change the azimuth to the direction that your system will be facing. 180 South is optimum.
  • Change the Cost of Electricity to your current retail rate (11 cents for Cherryland and TCLP, 15 cents for Consumers)

Estimate Your Requirements

You need to determine how many kilowatt hours of energy you use in a year to properly size a solar array.


Log into your account and go to:

  • "View Billing History"
  • "Billing History"
  • "View Usage"

You should get a two year history of monthly usage.

Use this to determine your average annual usage.

Multiply your annual requirement / usage by 0.9 (90%) to determine the DC size of your system.

Example: If you use 10,000 kwh per year, you will need an 9,000 watt (9 kw DC) system to provide all your electrical needs.

Consumers Energy

Your monthly printed bill shows historical energy usage.

Be aware that Consumers has an "Energy over 600 kwh" program that raises the energy charge in June-Sept by 5 cents per kwh when your monthly usage exceeds 600 kwh. Look at the bottom of this page for more details. The rate page is D-9.00

This premium needs to be used when calculating system payback.

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