Use the Federal Energy Management Program solar hot water system calculator to estimate what size of solar hot water system will work best for your federal facility and how much it will cost. 

The Energy Independence and Security Act (EISA) of 2007 Section 523 requires new federal buildings and major renovations to meet 30% of hot water demand using solar hot water equipment if it is life cycle cost effective. This tool can help agencies meet that goal. 

Download the spreadsheet and follow the steps in the instructions to calculate your agency’s approximate solar hot water system size and cost. Note that calculator results do not include available incentives or rebates.

 

Calculator Options

The optimal system size is often larger (providing 60–90% of the load) depending on the solar resource, so this calculator is offered with two options.

Scenario 1: Determine the system size based on the solar resource and the cost-effectiveness of that size.

Scenario 2: Calculate cost effectiveness of a solar water heater to meet the required 30%, or another specified percentage, of the water heating load. 

The spreadsheet calculator includes tabs to help with solar resource data and reasonable assumptions for the cost of a solar water heater of different size ranges.