Learn how to size your solar system

A step-by-step resource to help applicants size SOMAH solar photovoltaic (PV) systems and identify additional opportunities for low-cost energy savings and load reduction.


The Solar Sizing Tool

The Solar Sizing Tool (SST) is a quick and easy-to-use spreadsheet tool designed to help identify ideal sizing for a PV solar system and associated common area and tenant VNEM allocations. This is based on a property’s historical electricity consumption, energy efficiency opportunities, and electric load addition opportunities, such as electrification equipment and EV charging.

On average, the SST can be completed within 30 minutes. The tool requires the user to enter property-specific energy use equipment into a data entry form. Once property data is entered, the SST will automatically identify no-cost energy efficiency measures provided by Energy Savings Assistance programs offered by utilities. This will factor into the maximum size of the PV system for the property. The SST also identifies electric load addition opportunities, such as electrification of gas or propane equipment, or installation of EV chargers, which will allow for a larger PV system to be eligible for SOMAH rebates. Additional incentives and system size increase after the Energy Efficiency Compliance Milestone is allowed so long as additional load justification is provided to, and approved by, the SOMAH Program Administrator.

When to use the Solar Sizing Tool

The SST must be submitted via PowerClerk at the Energy Efficiency Compliance (EEC) Milestone of the application process, and must be completed by a qualified energy auditor. The SST must be submitted within 60 days of the reservation request approval notice.

The EEC Milestone also requires the applicant to document energy efficiency compliance, by submitting a completed whole building energy audit, or by submitting documentation showing proof of current or historic enrollment in a whole building energy efficiency program, recent construction under Title 24, or recent compliance with a TCAC rehabilitation. Upon submission, the applicant will need to submit a signed copy of the SST results.

The SOMAH PA will review the submitted SST and accompanying documentation to confirm accuracy and will conduct site visits on a sampling basis to verify accuracy.

Download the Solar Sizing Tool (.xlsm)


Example energy-saving opportunities

Energy efficiency measures

  • Roof insulation
  • Water heaters
  • Space heating and cooling
  • Refrigerators
  • Pool pumps
  • Common area lighting

Load addition measures

  • Apartment and central electric heat pump water heating
  • Apartment electric heat pump space heating
  • Electric cooking
  • Electric drying
  • High performance ventilation
  • Electric heat pump pool heating
  • Electric vehicle charging