Solar PV and Water Heating
Photovoltaics (PV) and solar water heating systems are items we encounter occasionally in our residential work. A PV system harnesses the power of the sun to convert sunlight to electricity. A solar water heating system uses solar energy to heat water for domestic use, and the solar contribution is calculated as a fraction of the total hot water used in a typical year. Neither PV nor solar water heating is a mandatory requirement in a new home, an addition or an alteration project.
Through the performance modeling method, a new home can receive compliance credit for installing solar PV and/or solar water heating. An addition or alteration project can receive compliance credit for solar water heating if there is an alteration to the current water heater, but there is no addition or alteration credit for PV.
New PV Systems for New Homes
The amount of performance modeling credit the energy code allows for a PV system is based on the home’s climate zone and the system’s rated power output. The credit earned is meant to be a tradeoff equivalent to a high performance wall or attic. This is why a PV system in a mild climate zone will not provide as much credit as the same system would in a hot climate zone. For any compliance credit, the PV system for a single-family residence must have a rated power output of at least 2 KW. Only in hot climate zones, such climate zone 12, will increasing PV output above 2 KW also increase compliance credit. This corresponds to more high performance building requirements in hot areas. The PV system must be on the structure of the home or on an attached garage or overhang. This type of performance credit is still not something we see a lot of in our office, but it has been a nice credit for some projects with many compliance obstacles.
PV Summary:
- Energy compliance credit only for a new home
- Must be at least a 2 KW system • Must be a new system
- Must be attached to the home
New PV Systems for Existing Homes
A PV system may be added as part of an addition or alteration project, but Title 24 will not provide the project any compliance credit. This is because the requirements for additions or alterations are not as stringent as those for new homes. While an owner may have many good reasons to add a PV system, the system will not give any Title 24 energy compliance credit or allow an owner to install electric resistance space or water heating equipment.
Solar Ready Requirements for Subdivisions of 10 Homes or more
New subdivisions with 10 or more dwelling units must meet mandatory “solar ready” requirements to allow future solar installations. Solar ready homes are built with a designated solar zone on the roof or overhang and an electrical service panel capable of accommodating PV and solar water heating systems. The solar zone must be free of shade, penetrations, and obstructions, and be oriented for optimal solar access. There are exceptions to this requirement, but it would be best to consult with us to review these together.
Solar Water Heating
A solar hot water system can be a performance compliance credit when installed as part of a new or altered domestic hot water system. Typically, the solar system designer provides the solar fraction for the system which we can use in our energy analysis. The solar fraction represents the percentage of total annual domestic hot water use that will be generated from the solar water heating system. This percent tends to be a small number (under 40%). If a project is very early on in design, this percent may not be calculated yet. In that case we will use a small number, say 5% to 10%, to receive modeling credit. As is the case with all things in the CF1R, you can always do better than the report says. Solar water heating is currently not common for single-family residences.
