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.

Comments (7)

Christoph Dietzfelbinger's picture

How well do those things work in a northern climate? I live with a 9.6 kW net metering systems at 55 degrees latitude. Can I heat small rooms or a bathroom that way in the winter when it gets to -25 C?

Jim Rice's picture

Can this be powered from 14-cr235 batteries charged by 5kw pv array

Michael Welch's picture
Possibly, but you'd have to figure out how much energy the MSHP will use for your particular needs and location, then add that in with whatever else your PV system is powering.

One thing, with 14 6 V batteries, it sounds like you have a 12 V nominal system with 7 strings of batteries in parallel. Having that many strings will definitely impact the longevity of your batteries. We usually recommend a maximum of 3 parallel strings in a battery bank, and that means using higher capacity batteries to achieve the same amp-hours of storage.
Jim Rice's picture

Michael thanks for your super quick response! I'm trying to educate myself on PV & Electricity. Yes I have a small cabin (600 ft2) with all Led lights (6 - 6w bulbs & 2 - 45w outdoor lights I need to replace). I have a energy hog window unit & want to replace with MSHP. We have incredibly humid weather in mainly Jul, Aug & Sep - You're in the "garden spot" for weather! I used to live in Santa Cruz many moons ago & traveled to Redding & over to your "neck of the woods" often. Thanks, Jim (ke4lxk)

Michael Welch's picture
Hi Jim. Yeah, pretty mild around here. If your cabin is well insulated, and assuming there are not any huge loads and that you have good sun exposure, your 5 kw PV system should be able to handle an MSHP just fine -- maybe even in the winter. Your battery will likely eventually be your biggest problem.
Jim Rice's picture

Michael, thanks I have a Jotul wood stove for heat. What kind of batteries would you recommend & how many? Yes, winters are relatively mild. Thanks!

Michael Welch's picture
You really need to figure out your total loads for summer and winter before you can size your system. Here are some good articles to help you with this. https://www.homepower.com/search/content/load%20analysis
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