Pairing Grid-Tied PV Power with a Minisplit Heat Pump

Intermediate

Inside this Article

Once upon a time, powering resistance electric heating appliances with a PV system was considered a no-no. Today, the high efficiency of minisplit heat pumps and the decreasing cost of PV modules is making solar-electric space heating a viable solution.
Make sure your home heating strategy can meet your needs­—only then can you determine how large of a PV system will be needed to offset your heating load. Online Manual J calculators can help provide a more precise estimate.
Other than direct-gain passive solar heating, an MSHP may be the easiest way to use solar energy for efficient space heating—and it’s definitely easier to retrofit than passive solar strategies.
Modern technology allows minisplits to be programmed to operate in step with PV production, either through simple scheduling or based on actual PV output data.
When used in high-efficiency homes and moderate climates, MSHPs may be able to provide the majority of a home’s heating demand. In many applications, however, the use of backup heat is necessary.

An advantage of minisplit heat pumps (MSHPs) is they are an efficient electricity-based heating and cooling appliance. Paired with a net-metered, grid-tied PV system, solar electricity can then be used to offset a home’s heating and cooling demands. Heat pumps use electricity to move heat, either by expelling it from inside the house during the summer or by extracting heat from outdoor air and moving it inside during the heating season. By using electricity to move heat instead of generate it, an MSHP offers an efficient method of using electricity to condition a building. In many climates, an MSHP is two to four times as efficient as electric resistance heat.

MSHPs can use solar electricity directly to provide high-efficiency cooling or heating. When the output of the PV system exceeds the electrical demand of the home, net-metered systems export the excess to the grid. In many locations, the local utility provides credits for this exported electricity.

In climates with high cooling loads, MSHPs provide a much quieter and evenly distributed cooling option than traditional window-unit air conditioners. In many cases, the electrical consumption of an MSHP is half that of an efficient window unit. Since PV generation and cooling demand often coincide, solar electricity and cooling via an MSHP can be a good match. In these applications, a significant portion of the electricity generated by the PV system can be directly consumed by the MSHP.

In the winter, when PV generation is lower, homeowners can draw upon net-metering credits to offset electrical consumption, including the draw of an MSHP. This article explores leveraging a net-metered PV system along with an MSHP to move a home toward net-zero energy use, and includes methods for sizing a PV array to accommodate an MSHP’s load.

Estimating MSHP Electricity Consumption

The most challenging part of sizing a PV system for an MSHP is to determine how much electrical energy the heat pump will consume. For new construction, heating professionals typically use a Manual J calculation to estimate the heating demands for individual rooms and for the whole home. Heating demand depends upon the building envelope’s thermal efficiency and surface area, the local climate, and the indoor temperature required to keep occupants comfortable.

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