How Many Solar Panels are Needed to Run an Air Conditioner or Heat Pump?

Written-by

Janet Richardson

Reviewed-by

Richard Burdett-Gardiner

Updated on

Sep 29, 2024

How Many Solar Panels are Needed to Run an Air Conditioner or Heat Pump?

Well, that’s a huge question, but we’ll do our best. Before we crunch the numbers let’s talk about why there’s no simple answer. The most obvious reason is the vast range of solar PV systems, heat pumps, and air conditioners. Then, we must factor in that two identical systems in two different locations will have varying results. In fact, there are so many variables that can affect the outcome it’s almost impossible to get an exact answer. Yep, everything from where you're located in the UK to the size of your garden can alter the numbers, but since we don’t deal in impossible. We’ll do our best to work out if it's worth getting a solar air conditioner or solar powered heat pump.

Firstly, we need to tackle the elephant in the room. As we all know, solar photovoltaic panels generate electricity from sunlight. In the summer, with longer brighter days they will generate a lot more energy than in the winter. On average a 4kW solar PV system will generate about 9-11 kWh per day, but if we split this up over summer and winter, the same system will produce approx. 24 kWh per day in the middle of summer, most likely more than you will need, and only 5-8 kWh in the winter, most likely less than you need. 

24kW is much more than you need to run most air con systems for cooling your home or office in the summer, so that's pretty simple to work out and a great use of solar power. This said, a heat pump for space heating will be used in the winter when the days are shorter and darker, and your solar panels aren't doing as much. A solar PV system generating 5-8 kWh per day in the winter, for a property with all the usual electrical demands plus a heat pump, isn't going to go very far. But we'll get to that. 

So, solar panels can subsidise your electricity demand in the winter, and go some way towards covering the demand of a heat pump system, but they won't cover the usage of a heat pump unless you have an extremely large system, and that just wouldn't be cost effective. 

Solar powered air conditioning, great solution. Solar powered heat pump, not so clear cut.. 

The basics

Before we get to the figures, let’s discuss the equipment we’re studying. 

What are solar PV panels?

Solar panels are, in domestic terms, consumer devices designed to generate power from the sun. There are two distinct variants of solar panels, solar thermal and photovoltaic cells. Photovoltaic or PV cells work in a different way to solar thermal panels, which instead harness the power of the sun to heat water. Solar PV panels, generate electricity. This energy can power the appliances in your home. From charging your phone to running the spin cycles of your washing machine, there isn’t much that they can’t cope with. Of course, the more panels you have the more power you can generate, and this is another variable we’ll discuss.  Another factor we’ll cover is the simple fact that solar panels need daylight to work. Therefore, in the hot summer months, your panels will produce more power than they will in the shorter days of winter.

Solar storage or solar batteries

As discussed, solar cells capture and convert radiation from the sun into electrical energy. So, if you want to power anything at night, you’ll need something to store that power.  Assuming your panels generate surplus electricity during the day, one option is adding solar storage or batteries.  As you’d imagine these devices work like traditional batteries. During the day any excess energy produced by your array is redirected to the storage cells and saved for later use.

What are heat pumps?

This technology uses the laws of thermodynamics to extract heat, or cold, from an external source. Depending on your situation this source may be the outside air, the ground below your garden, or a nearby body of water like a canal or a pond.

What is air conditioning?

As mentioned above, because heat pumps extract and supply, some provide heating and cooling, so heat pumps can also be air conditioners. They work by using a refrigeration cycle which transfers heat from the indoor air to the outdoor air.
Most heat pumps that are used for heating in the UK, don't do cooling as well. In fact, air-to-air heat pumps that offer heating and cooling, aren't applicable for the government's Boiler Upgrade Scheme (BUS). Conventional air to water, or ground to water heat pumps are designed to be used with a central heating system, radiators or underfloor heating loops. For the sake of this article, we’ll consider heat pumps and air conditioners to be two different technologies. 

Are heat pumps also considered a renewable energy?

We’ll get this out of the way now as it may well be the reason you’re considering powering your heat pumps via solar. The technical answer is not really, but there’s more to it than that. Heat pumps need electricity to work, but they don’t use this power to generate heat. Instead, the electricity powers pumps that either move a refrigerant around which is converted into heat for your home or office. Because the power needed to run a heat pump is less than the equivalent amount to heat your home, some folks do consider them a renewable energy source. In short, they are so efficient that heat pumps are eligible for grants and incentives reserved for true renewable energies. Of course, if you can source the electricity they need from another renewable source, solar panels we’re looking at you, then it’s a no brainer. 

About Solar Power Usage

When solar panels are discussed, we usually refer to the power that is produced by them in at least one of the following ways:

• Watts (w)
• Kilowatts (kw)
• Kilowatts per hour (kwh)

Solar panels work by absorbing the light produced by the sun and converting it into electricity. As a result of this, it makes sense that the more surface area that a solar array covers, the more sun it can absorb. Therefore, the more electricity can be created. You should expect the average solar panel system to produce between 9 and 11 kWh per sq. ft. each year.

The average household uses approx. 2700 kWh PA, and a 4kw system will generate a comfortable 3,400 kWh of electricity each year. This doesn't mean that a 4kW system on its own will cover all your energy demand because unfortunately, it's unlikely the solar panels will generate all the electricity for each hour you need it through the year. They will produce too much in the summer and not enough in the winter. The good news is that any excess electricity can be stored in a battery for use on demand, or sent back to the grid in return for the Smart Export Guarantee (SEG). 

A 4kW solar PV system is likely to take up around 220 sq. ft. or 20.4 m2 of roof space. This may seem like a lot, but it isn’t as bad as it sounds. To place it in different measurements, you may need a roof area of 6m x 4m. This will fit on most of the rooftops in the UK. Each of the solar panels that make up this array will be around 17 sq. ft. or 1.6m2, and will have an optimal output of around 345w.

The total output of the solar panels that have been installed on your roof will also depend on several other factors. These include:

• The size of the system that has been installed
• The efficiency of the system (the output of the panels in watts)
• The orientation of the roof
• The pitch of the roof
• Any shading that may effect the panels
• Climate conditions
• Cleanliness 

If you want to get the most out of your panels, you should have them facing south at an angle of 32 degrees and keep them clear of dirt and detritus. This will leave them in their most efficient state for energy production.

How much Power does your Heat Pump / Air Con Unit need?

Air conditioning units

Before we can answer the big question, we need to know how hungry these machines are. A standard air con unit might be rated at 1.3kW. This means the unit needs 1.3 kilowatts of power to function because unlike heat pumps that have a high coefficient of performance (COP), air conditioning units run on a 1 to 1 basis. Basically, you get out, what you put in. 

So, the average air conditioner uses 1.3kw of power, and the average solar panel system ranges from 2kw to 4kw. So, if you decide to power an air conditioner with a 2kW solar PV system, it is going to use up the majority of your solar energy.

Some air conditioners will even use as much as 2.5 kW, meaning that the minimum power of your solar panel system would need to be 3kW just to power the air conditioning. Putting this into a little more perspective, if you had a 2kW solar PV system and were running a 1.3 kW air conditioner, the solar panel system would provide you with 5-7 units of power for the day in the summer. This would be consumed by the air conditioner in a mere four or five hours.

Heat pumps

Heat pumps systems are high demand appliances that require a lot of energy to keep running. The average three bedroom property in the UK will require a heat pump with a capacity of between 8-12 kW. 

Solar Powered Air Conditioner Considerations

Local sunlight hours
Even in the UK, the difference between how many sunlight hours you see will change depending on where in the country you live. Last year, for example, Eastbourne saw an entire hour of sunlight more per day than Durham. More sun means more power and you have a better chance of powering your heat pump via solar in you live on the south coast than any where else in the UK.  

Orientation of your solar array
Again, solar panels need sunlight. Unless your roof faces south, or at least east to west through south, you can forget using solar panels to power a heat pump or air conditioning unit. Some orientations are more effective than others, but the longer your array spends in direct sunlight the more power it can generate.

The type of panels in your system
In the UK there are three main types of solar panel, excluding thermal panels, monocrystalline. polycrystalline, and thin film solar cells.  In terms of efficiency, monocrystalline panels offer the biggest bang for buck with a rating of up to 24%. Next best is polycrystalline cells with an average efficiency of around 17%. Pulling up the rear we have thin film cells with an efficiency hovering around 8%.  As you can guess, powering a heat pump system would take less monocrystalline cells than polycrystalline cells, which in turn would take up less space than an equivalent array of thin film cells.  However, because of their cost if you have the space, it may be cheaper to opt for more less-efficient panels than to install less high-end, big-ticket cells.    

Special upgrades for your array
If you can afford them, there are a few aftermarket accessories that can help increase the power output of your solar panels. These includes mechanical solar trackers that physically track the sun and rotate your cells to keep them in direct sunlight. These are only applicable to ground mounted arrays.
A solar diverter can send any excess electricity not used at the point of generation to heat water in your hot water cylinder.  
Another device designed to improve the efficiency of your solar system are micro invertors. These clever gizmos allow your panels to reroute their circuits if they encounter obstructions like debris or shadows.
Solar storage solutions, solar batteries, can store the electricity generated by your panels for use on demand. They can also be used to take power from the grid at off-peak times for use during peak times.   

How well maintained your system is 
Looking after your system plays a big part in its efficiency and in solar terms efficiency is everything. Keeping your array clean and free from shadows and obstructions can make all the difference. In a perfect world, you should service your system at least once a year, but there’s no harm in doing it more often. You should always keep an eye on the panels themselves.  

What can you do to Improve the Returns?

There are ways to improve the return on your investment and efficiency of a combined solar PV and heat pump system. Let’s discuss them one by one: 

Insulation
Heat pumps work best in homes with good insulation. If your home losses heat through windows or other weaker spots in your house, then your heat pump will have to work harder and therefore draw more power. These days it’s possible to hire devices like thermal imaging cameras to look for cold spots where heat can seep out of your home. Covering these gaps and upgrading your overall insulation can make a big difference in the amount of power your heat pump uses.

Energy efficient appliances
With advancements in technology in the consumer electronics market today it’s possible to make big savings on the power you use. You can even cut your energy consumption by 20 to 30% just by replacing some of your appliances. Of course, swapping out old bulbs for more modern energy saving LED bulbs can also make a difference and every watt you can save means more power for your heating system.

Changing your lifestyle habits 
It’s possible to reduce the overall amount of energy you use by changing how and when you use the appliances in your home. Even little changes like waiting for a full load and using the washing machine less can make a difference. It’s also a good idea to clean vents on devices like Fridges and to make sure you use these devices at full capacity. Well maintained appliances are more efficient, so anything you can do to reduce the amount of energy you consume will help. Another simple way to save energy is to change you own habits. Swapping out nighttime heating for a blanket, even an electric one, can lower your power usage a lot. 

Keep an eye on tariffs and deals
Some energy providers offer special deals for those using renewable energies. These can often include associated technologies like heat pumps. In addition, some providers offer incentives like Saver Sessions. During a session you can reduce your bill by using less power, or fixed fee hours where you can use all the power you want for a flat fee. By choosing your supplier with care, you can find the extra energy or funds needed to switch to a solar PV, and air conditioning or heat pump system.

So, can a Solar PV System Run an Air Con or Heat Pump in the UK? 

The Average solar panel system can effectively power an air con unit in the UK. Your solar panels will be generating peak output when the days are warm and long, and you require cooling for your property. However, the efficiency and feasibility depend on several factors, including the size of the solar array, the conditioning unit's energy consumption, and weather conditions.

In winter, when solar output is significantly lower, solar panels alone are highly unlikely to meet a heat pump's energy demands. While solar panels can contribute to powering a heat pump, especially with a properly sized system, it will still be necessary to take power from the grid to cover the requirement of a heat pump system year-round. Solar panels will bring down the running the costs of a heat pump year-round, but the average solar PV system won't cover the demand completely, and it wouldn't make sense from an economical perspective, to install a system that could. You would generate far too much electricity in the summer and significantly increase the payback period. 

Want to Know More?

Have you found yourself interested in solar panels? If you want to contact a local installation company, browse our online directory of approved installation companies. Or simply give us a ring using the number at the top of this page and have a chat.