How Many Solar Panels to Run Heat Pump?

Can Solar Panels Power a Heat Pump?

In an effort to reduce the use of fossil fuels and conserve the environment, many homeowners are choosing to replace their heating equipment with heat pump models.

Heat pumps are characterized by extracting heat from the air, ground, or water and transferring it to the house to warm it in the winter. Unlike boilers that use gas to generate heat, heat pumps use electricity only and are more energy efficient.

If the cost of electricity in your area is less expensive relatively to your gas costs, it use to be great value to put in a heat pump to heat your house with electricity instead of using gas.

However, if you are going to rely on network electricity to run it, there is still the fact that it consumes more electricity than any other home appliance.

Fortunately, just as residential solar panels can power any home appliance, they can also power a heat pump in a more sustainable way.

So if you are interested in the idea of running your heat pump on solar energy but you have no idea how many solar panels you will need, Don't worry. In this article, we are going to show how to size a solar system to cover a heat pump's power consumption.

How Much Electricity Does Heat Pump Use?

In order to accurately estimate the number of solar panels that you need to operate the heat pump, the first step that must be taken is to find out how much electricity a heat pump uses.

On average, a heat pump generally uses between 4 and 20 amps and 230 volts.

In cooling mode, the heat pump will use anywhere from 0.54 kW to 4.27 kW per hour, depending on unit size (in British Thermal Units, or BTUs), and Seasonal Energy Efficiency Rating (SEER).

You can use the following equation to get the average energy use of a heat pump in cooling mode:

The average energy use in cooling mode (kW) = BTU / SEER

In heating mode, the heat pump will use anywhere from 1 kW to 7.5 kW per hour, depending on unit size (in British Thermal Units, or BTUs), and the Seasonal Heating Performance Factor (HSPF).

You can use the following equation to get the average energy use of a heat pump in heating mode:

The average energy use in heating mode (kW) = BTU / HSPF

You can find the SEER, HSPF, and BTU ratings for your heat pump on the heat pump specification label.

Starting current!

The current we mentioned above relates only to the running power, since the heat pump has the same principle as refrigerators runs in cycles. It needs a larger starting current (or startup power requirement), usually two to three times greater than the operating current.

In this case, the use of a heat pump soft start device becomes “essential”, especially if you want to run a large unit with a home solar energy system.

The device allows the heat pump to start using up to 70% less power than normal.

What Is The Average Heat Pump Electricity Usage Per Year?

By choosing the appropriate heat pump for the size of the house, the required heating or cooling needs, and properly set. It is normal for the unit to run at a rate of two cycles per hour, and each cycle takes between 15 and 20 minutes.

We can estimate 2 cycles per hour and 15 minutes per cycle.

2 cycles × 15 minutes = 0.5 hour

0.5h × 16 hours a day = 8 hours a day

8h × 30 days a month = 240 hours a month

240h × 6 months = 1440 hours a 6 months

This means a heat pump runs 240 hours a month on average.

How much electricity do heat pumps use in cooling mode?

Let's use an average 3 ton (36,000 BTU), 16 SEER-rated heat pump.

Heat Pump Size
Wattage
Length of Time Powered
Electricity Used
3 tons (36,000 BTU)
2.25 kW 1 hour 2.25 kWh
1 day 18 kWh
1 month 540 kWh

The electricity consumption for your heat pump during the warm months will be about 540 kWh per month.

How much electricity do heat pumps use in heating mode?

Let’s look at the same 3-ton (36,000BTU/h) heat pump with a HSPF of 9.

Heat Pump Size
Wattage
Length of Time Powered
Electricity Used
3 tons (36,000 BTU)
4 kW1 hour4 kWh
1 day32 kWh
1 month960 kWh

The electricity consumption for your heat pump during the warm months will be about 960 kWh per month.

The Average Heat Pump Electricity Usage Per Year

In summary, to heat an entire home in the colder months with an average 3 ton / 16 SEER / 9 HSPF heat pump, you need 5,760 kWh of energy. While cooling it in the warm months requires 3,240 kWh of energy. in total, your heat pump's energy usage per year would be about 9,000 kWh.

These numbers are consistent with a report by the U.S. Department of Energy (DOE).

The energy you need for heating is greater than the energy you need for cooling. This is because the HSPF is always less than the SEER.

Depending on the size and efficiency of the heat pump unit, the table below lists the average power requirements for 1-6 ton 14-22 SEER and 8-12 HSPF heat pumps:

Heat pump size 8 HSPF 9 HSPF 10 HSPF11 HSPF12 HSPF
1 ton  3,394 kWh 2,918 kWh 2,626 kWh 2,387 kWh2,188 kWh
2 tons  6,566 kWh 5,836 kWh5,253 kWh
4,775 kWh4,377 kWh
3 tons  9,849 kWh8,755 kWh7,879 kWh 7,163 kWh
6,566 kWh
4 tons13,132 kWh
11,673 kWh
10,506 kWh
9,551 kWh
8,755 kWh
5 tons 16,416 kWh14,592 kWh 13,132 kWh
11,939 kWh
10,944 kWh

How Much Energy Does A Solar Panel Produce?

After addressing the question of how much electricity a heat pump uses in detail, the next step is to determine how much energy do solar panels produce.

Using the solar panel wattage, and the number of peak sun hours per day for your area, you can measure how much electricity a solar panels will produce by using this formula:

Solar panel output x Average Peak sun hours = Daily kWh per day

  • The wattage output rating of residential solar panels varies between 250 and 450 watts per hour.

  • Not all regions of the US get the same amount of sunlight, so the number of peak sun hours varies depending on the location. The southwest is the sunniest region of the country.

The majority of the US get 3 to 5 peak hours of sun per day.

For example, in the winter months we’ll use an average of 3 hours, this means that the average 400W solar panel output of electricity per day is 400 x 3 = 1.2 kWh

while in the summer months we can use 5 hours, this means that the average 400W solar panel output of electricity per day is 400 x 5 = 2 kWh.

Can solar panels power a heat pump?

To heat your home with a solar panel heat pump, the solar panels must absorb enough energy from the sun. Usually, you will use the heating mode in the winter months when there are fewer peak sun hours than in the summer! This means that the energy available from the sun in the winter will be less.

Let's take a look at the difference between the amount of energy that solar panels will produce in the winter and summer months. Accordingly, we determine how many solar panels are needed to run heat pump.

In a temperate state like North Carolina, Jacksonville gets an average of 4.6 peak sun hours per day. This value also represents the average peak sun hour per day in the US.

Month
Peak sun hours per dayPeak sun hours per monthSolar panel output per day (400W)
January 4.21321.7 kWh
February4.41241.8 kWh
March4.91531.9 kWh
April5.51662.2 kWh
May5.31652.1 kWh
June4.81451.9 kWh
July4.61441.8 kWh
August4.21311.7 kWh
September 4.21261.7 kWh
October4.81491.9 kWh
November4.61381.8 kWh
December 41231.6 kWh

We used the Global Solar Atlas to find the peak sun hours per day (irradiance) in Jacksonville, North Carolina.

In the summer months, the output of the solar panel in six months of summer is 347 kWh, while in the winter it is only 324 kWh.

The average 400W solar panel output per year is 671 kWh.

→ To make the heat pump completely independent of the network using a battery bank, it is preferable to calculate the number of panels using:

  • The heat pump energy requirement for heating mode = 5,760 kWh.
  • Solar panel output (400 watts) in 6 months of winter = 324 kWh.

Number of 400 watt solar panels required = 5,760 / 324 = 18 solar panels.

→ If your area supports net metering, then you don't have to worry about the low power available from the sun in the winter months. In this case, there is no need to complicate the calculations. You can calculate the number of panels using:
  • The heat pump energy requirements per year = 9000 kWh.
  • Solar panel production (400 watts) per year = 671 kWh.
Number of 400 watt solar panels required = 9,000 / 671 = 14 solar panels.

Thus, in the case of an grid-tie solar system, you’ll need 5.6 kW of solar panels (18 panels x 400W).

In the case of an existing off-grid solar system, you’ll need 7.2 kW of solar panels (18 panels x 400W) to meet the demand in winter.

Related articles: 

Summary – How Many Solar Panels to Run Heat Pump

Depending on the size and efficiency of the heat pump unit, the table below lists the number of solar panels required to runs the 1-6 ton 14-22 SEER and 8-12 HSPF solar heat pumps:

Heat pump size8 HSPF9 HSPF10 HSPF11 HSPF12 HSPF
1 ton 5 panels
5 panels
4 panels
4 panels
4 panels
2 tons 10 panels
9 panels
8 panels
8 panels
7 panels
3 tons 14 panels
14 panels
12 panels
11 panels
10 panels
4 tons20 panels18 panels
16 panels
15 panels
13 panels
5 tons 25 panels22 panels
20 panels
18 panels
17 panels

Note: In the case of an off-grid solar system, it is necessary to add more solar panels to meet the demand in the winter season (between two to four panels).

For example, you will need 9 panels for an off-grid solar system and 5 panels for a grid-tied solar system to operate a 1 ton 8 HSPF heat pump.

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