Heat Pumps and solar

Monday, September 13, 2021
Veli Markovic

It’s cold here!

How does a heat pump stack up against a solar hot water system with natural gas augmentation? 

How big a heat pump do you actually need? Do they work well in cold conditions? All will be revealed!  

What is a heat pump?

  • A heat pump is a standalone, two-component appliance
  • Uses refrigeration technology and electricity 
  • Provide heating,cooling, hot water 


What are the main components?

A heat pump has two components:

  • A condenser unit that most often sits outside of a home that produces the heating or cooling, and 
  • An indoor unit that typically sits on a wall and passes hot or cool air into the home; a reverse cycle air conditioner 
  • Hot water heat pumps have a water storage component

How does a heat pump work? Getting warmer and cooler!

  • It extracts heat from the air outside of your home
  • Then transfers it to a refrigeration coolant
  • The coolant is then compressed
  • This increases the temperature significantly
  • The coolant is then moved to the indoor unit of the heat pump
  • It passes air over the hot coolant
  • This increases its temperature to accommodate the thermostatic call for heat inside the home

In cooling mode the process is reversed, transferring heat out of your home and returning cool air to the inside.

The refrigerant has an evaporation or boiling point of < 0. Temperatures that feel very cold to us still makes the refrigerant “boil” because air that has been drawn in is far warmer than the refrigerant, and this turns the refrigerant from a liquid into a gas inside the heat pump’s piping.

A compressor pumps the now gaseous refrigerant through a small valve, creating heat  and a heat exchanger transfers the heat from the heated refrigerant gas pipes to a tank where water is stored.

The temperature of the refrigerant has now dropped dramatically as the heat has been drawn away, so it returns to a liquid state and the heat pump cycle begins again.

All three systems work the same way

A hot water heat pump: 

  • Concentrates ambient heat from the surrounding air, 
  • Then send (“pump”) that heat into the water in their storage tank
  • This heat is maintained due to the insulative nature of the tank

Concentrating existing heat 

Since this process merely concentrates existing heat instead of having to create more, heat pumps reduce annual hot water energy requirements by:

  • 50-80% compared to electric-resistive home systems.

Thus, they are considered renewable systems and are eligible for STC rebates ( Australia).

Are Heat Pumps More Environmentally Friendly?

Yes – 70% more than traditional electric storage systems. Heat pumps decrease more than just your electricity bills and if you switch to a heat pump from a traditional electric system, the pump can lower your hot water heating carbon footprint by 70%.

Suitable conditions for heat-pumps

A heat-pump water heater might be worth considering if a solar hot water system is not suitable for your household. For example when:

  • There is a lack of roof space for solar panels
  • Your house is oriented poorly for solar panels
  • Electricity is your main fuel choice.

The amount of heat transferred to the water in the storage tank depends on the surrounding air temperature.

Heat-pump water heaters are therefore generally better suited to warmer climates and are not well suited to cool climates – especially where frosts occur regularly.

In cooler climates, the compressor will run for longer periods, which can result in greater energy consumption and a shorter life expectancy for the pump.

What are the benefits of a heat pump when used with solar electricity?

  • Your heat pump is powered by electricity
  • When you pair solar panels for electricity with heat pumps for heat 
  • You are heating your home for less cost

Integrated or a Split Heat Pump System?

What size heat pump do I need?

  • Count the number of people in your household
  • Assume that each person will use around 50 litres of hot water per day.
  • Require that your hot water tank keeps 1.5 days’ capacity at all times.
  • Multiply the number of people by 75

What are the benefits of having a heat pump?

Massive savings in hot water related expenses over the long term.

A heat pump produces between 3 – 5 times the amount of renewable energy than electricity required to power the unit and it’s an environmentally friendly hot water option given the reduction in greenhouse gas emissions through less energy requirements.

A  heat pump is effective even in fairly low temperatures. In extreme cold, an electric assist is activated to ensure the water stays at the desired temperature.

No roof space or panels needed!

Ease of installation as a solar heat pump uses the same connections as an electric hot water system.

Government incentives

There are incentives available to Victorians ( Australia) replacing an existing hot water system with a heat-pump water heater:

  • Small-scale Technology Certificates (STCs)
  • Victorian Energy Efficiency Certificates (VEECs), also known as the Energy Saver Incentive.
  • Solar hot water rebate


Heat pumps extract air from the environment, compress it and then release the energy and hot water heat pumps are quite efficient when compared to purely resistive electric loads. Hot water heat pumps attract government rebates and when combined with solar make a formidable combination.

If you’d like to see more of what Greenwood Solutions get up to in the real world of renewable energy, solar, battery storage and grid protection check out the following pages:





About the author

Veli Markovic

CEC Designer
Veli has nearly two decades of experience in the renewable industry. He is passionate about providing people with valuable education and is highly regarded throughout the industry as an educator and operator.
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