In SAM, residential and commercial projects buy and sell electricity at retail rates. They may be financed with a loan. These projects recover investment costs by selling electricity at rates established by an electricity service provider. SAM calculates metrics for these projects at the project level, assuming that a single entity develops, owns, and operates the project.
For residential and commercial projects, SAM calculates the project's levelized cost of energy, which represents the cost of installing and operating the system, including debt and tax costs, and accounting for incentives. The model also calculates the net present value of the after tax cash flow, and a payback period representing the number of years required for the cumulative after tax cash flow to cover the initial equity investment in the project.
Commercial projects may qualify for tax deductions under the Modified Accelerated Depreciation Schedule (MACRS) described in the United States tax code. SAM provides options for specifying custom depreciation schedules in addition to the MACRS mid-quarter and half-year schedules on the Depreciation page.
Residential and commercial projects are typically smaller than 500 kW, although SAM does not restrict system sizes, so it is possible to model any size system using either the residential or commercial financial model.
SAM's Electricity Rates page provides a range of options for specifying the retail electricity rate structure for a project. The rate structure may include any of the following:
- Flat buy and sell rates (with or without net metering)
- Time-of-use energy charges
- Monthly demand charges (either fixed or time-of-use)
- Tiered rates
- Fixed monthly charges
For projects with demand charges and tiered rates, SAM requires electric load data, which is specified on the Electric Load page.
Electricity Bill Calculator, September 2021
This webinar describes SAM's electricity bill calculator for SAM 2020.11.29 and later, including a description and demonstration of net metering, net billing, and buy all/sell all metering options, and a new "Billing Demand" feature for Fall 2021. It follows up on the 2017 webinar below that puts the bill calculations in the context of the Residential/Commercial financial model with discussion of load data, the electricity bill's effect on the project cash flow, etc.
- Presentation slides (PDF 542 KB)
Electricity Rates and Bill Savings for Residential and Commercial Projects Webinar, Jun 2017
This webinar is a walk-through of the inputs and results associated with electricity bill calculations for SAM's residential, commercial, and third party financial models. It covers weather and load data, electricity rate inputs, electricity bill savings, impact of bill savings on project cash flow.
Short How-to Video on Importing Load Data
These sample spreadsheets are intended to help you understand how SAM's Residential and Commercial financial models calculate financial metrics such as net present value (NPV), levelized cost of energy (LCOE), and payback period.
The following Excel files were generated in SAM 2020.2.29 by clicking Send to Excel with equations from the Cash Flow tab on the Results page for the default PV - Residential and PV - Commercial cases. They replicate SAM's calculations with Excel formulas using inputs from the SAM files. You can generate similar workbooks yourself from the Windows version SAM, or use these sample workbooks if you are using the Mac or Linux version of SAM, or not using SAM at all.