This is because they pull a constant current, so once you know an appliance power rating in watts, you can match that with solar panel output.
Some appliances, like fridges, freezers and air conditioners, are not so straight-forward, as they contain compressors with motors. This means that the power they draw varies and needs to be averaged out.
How Many Solar Panels To Run Air Conditioner?
An air conditioner would need 1200 watts of solar panels for each Ton of cooling capacity, assuming irradiance of 4 Peak-sun-hours/day. A 100Ah battery (such as this one by Renogy) is recommended per Ton for each hour anticipated running time. This will allow running when irradiance is low and also provide a reservoir to supply motor surge current.
These are the things we need to know before building a solar system to run an air conditioner:
- Why air conditioners are rated in tons
- AC power rating (kW)
- What is surge current and power factor?
- How long will the air conditioner be running?
- Are batteries needed to run your air conditioner?
- What type of batteries are best suited for solar energy storage?
- How much energy do solar panels generate?
- Solar panel sizes you’re going to use
- Inverter sizing (and why you need one)
Video – How many solar panels are needed to run AC on an RV?
Solar powered air conditioning is a really good thing to have, specially in countries with hot humid conditions and plenty of sun!
Solar AC makes a great DIY project, but we need to explore AC electrical and cooling characteristics before answering the question ‘how many solar panels do I need to run an air conditioner unit?’
Can you run air conditioner off solar panels?
When talking about d.c. loads, power calculations are quite easy. Power rating is found by multiplying volts x amps.
For example, when a d.c. resistive load has a 12 volt supply and pulls 12 amps, we use this formula to find the power:
12V x 12A = 144watts
In a.c. circuits, volts x amps doesn’t always equal watts (although sometimes it does!) Read on …
Home appliances use a.c. power and the calculation is handled in a different way. Voltage and current waveforms constantly move from positive to negative in a sinusoidal shape.
If V and I are maximum at the same time, they are said to be ‘in phase’ and volts x amps will really equal watts.
If volts and amps are not in phase, then the equation doesn’t work. We’ll take a look at this later.
How much electricity does a solar powered air conditioner use?
Why is AC rated in tons and not watts?
All air conditioning units have different efficiencies, so if we used their electrical kilowatt ratings for comparison, it wouldn’t reflect their cooling power.
This means that 2 AC units rated at 1.5 kW might not have the same cooling power.
So what is a ton in AC ratings? It represents the amount of cooling required to melt 2000 pounds of ice in one day. It’s commonly known in the trade as a short ton.
The bigger the tonnage, the more air can be cooled each hour. One ton can also be represented as 12,000 BTU/h (British Thermal Units per hour) or 3.5 kW (kilowatt).
This means that a 1 Ton air conditioner has a cooling capacity in Watts of:
(12000BTU x 1055) / 3600 = 3516 Joules per sec = 3516W (cooling)
What is EER value in AC?
EER means ‘energy efficiency ratio’ and it tells you how well an air conditioning unit cools. If you divide an ac unit’s BTU number by it’s electrical rating in Watts you come up with a ratio which indicates it’s efficiency.
An efficient air conditioning unit could have an EER of 11, for example. AC units with an EER rating of more than 10 are recommended for countries or locations with hotter climates.
The EER rating system is based on an outdoor temperature of 95°F, a temperature inside of 80°F, and 50% humidity.
The SEER rating is more common nowadays, as it takes into account an air conditioner’s cooling capacity over a range of outside temperatures – the S means the ratings are ‘seasonal’.
The table below shows the SEER/EER for popular home AC units.
Lennox are making particular gains in supplementing their designs with solar panel support and this will probably become the industry-standard in the not-too distant future.
Table – SEER and EER ratings compared for 5 popular AC brands
Air Conditioner Brand and Model
Lennox Signature Series XC25
Comes with solar option
Amana AVXC20 & Daikin DX20VC
Lennox Signature Series XC21
Maytag M1200 PSA1BG
Carrier Infinity 20 24VNA0
How much does it cost per hour to run an air conditioning unit?
This can vary quite a lot and depends on several factors:
- what is the efficiency of the AC unit?
- how often during the day you run it
- how long the AC unit runs
- the outside temperature
- the cost per kWh of your electricity
As you can see, it can get complicated but is it worth going into all this detail? Let’s examine the factors you need to be aware of.
Air conditioning and solar installers have rule-of-thumb guides for sizing systems. One of these rules states that an air conditioning unit pulls around 7 amps for every 1 Ton of it’s cooling capacity rating.
However, this changes when the Tonnage changes. It’s widely accepted that the relationship of amps vs tons changes as the cooling power increases:
- 2 ton equates to 15 amps
- 3 ton equates to 18 amps
- 4 ton equates to 21 amps
For sizing and installation purposes, this is good. In my case, when I’m designing a solar panel installation, I really want to know exactly what’s going on electrically!
You can get confused about RLA (Rated Load Amps), which can be found on the air conditioning label tag – see image below:
The RLA value is not the AC normal running current – it is the maximum current the compressor motor will pull while the AC unit is running.
In addition, this is not the same as the LRA value, which is Locked Rotor Amps. This occurs is when the compressor motor is stalled, can’t rotate and pulls maximum current.
This value is the same as inrush or surge current when the compressor motor starts from standstill.
The real running current depends on other things.
Air conditioner surge current
When an a.c. motor starts it pulls several times more current than when it runs continuously.
This running current will be dependent on the load, but the surge or inrush current is the highest amps the motor pulls, unless the motor is locked solid and can’t move at all (this is very bad.)
The size of the wiring is based on maximum current when running plus 10%. Surge currents only last for a few seconds normally and the heating effect in the wiring isn’t significant.
However, breakers and fuses need to be sized accordingly, so that they can accommodate this surge without tripping out.
This also has important implications for any solar panel system designed to run air conditioning.
If running during the day without a battery bank used as an energy reservoir, the solar panels wattage rating needs to be big enough to supply this motor surge current.
Solar panel systems designed to run home appliances make use of a device called an inverter to change d.c. (direct current) voltage produced by solar panels into the a.c. (alternating current) power for domestic use.
How many solar panels to power ac unit?
Now we’ve explored what happens in an air conditioning unit on the the load side, we can take a look at the supply side in some depth.
I’m going to base the rest of the post on using 300 watt fixed solar panels, because the higher panel ratings are a better buy in terms of installed dollars/watt.
*This is the 300 watt solar panel I’m talking about.
How much power can a 300 watt solar panel generate?
A solar panel’s output power in watts depends on these factors:
- solar panel efficiency (monocrystalline panel efficiency is between 20% and 22%)
- solar panel area in square meters
- irradiance (the sun’s energy, which depends on your geographic location)
- orientation (what is the angle to the horizontal and vertical)
- will you be using fixed or auto-tracking for the solar installation
Solar panel ratings given by the manufacturer follow the guidelines laid out in the Standard Test Conditions or STC.
Basically, the panel rating is stipulated when the solar irradiance is 1000 watts/m2 and the temperature is 25 degrees C.
This assumes that the panel is directly under the sun at 90 degrees, but this is hardly ever the case!
Solar panel output reduces when the angle to the sun becomes more acute. Unfortunately, it also reduces at other angles, if the temperature is above 25 degrees C.
The power output goes down at a rate of 0.5 watts for every degree increase in temperature.
If the sun’s energy is low because of the irradiance level in your geographical location, then solar panel output will go down proportionately.
How does a solar inverter work? Some basics
Solar panels produce direct current (d.c.) but home appliances need alternating current (a.c.) – that’s why you need an inverter to convert d.c. to a.c.
An inverter chops up the direct current into packets or pulses, and re-shapes them electronically into the smooth sinusoidal waveform, just like the power fed into your home by utility companies.
How many solar panels to run 5 ton ac unit?
Air conditioner is needed when it’s hottest, which is the four hours around noon-time in most locations.
This is a lucky break, because this is the same window of time when the sun’s energy is high and solar panel power output is at a maximum.
1 Ton of air conditioning cooling capacity is about 1.2kW, so if you run it for 4 hours it would consume 4.8kWh over that time.
Logically, a 5 Ton air conditioning unit will consume:
4.8kWh x 5 = 24kWh
A 300 watt solar panel can produce 300 watts x 4 hours for the same time period (if the sunshine conditions are ideal) which equal 1.2kWh.
The basic formula for finding the number of solar panels to run a 5 ton ac unit is:
AC energy consumption (24kWh)/energy produced (1.2kWh) = 20 solar panels (300 watt rating)
How many solar panels to run a 2 ton ac unit?
Let’s say we’re going to run the AC for 4 hours again in the hottest part of the day.
The basic calculation appears below, and assumes continuous running, surge current ignored:
9.6kWh/1.2kWh = 8 solar panels (300 watts)
Can I run a 1.5 ton AC on solar without batteries?
Small air conditioning units are easier to power using solar panels. The basic calculation for a 1.5 ton air conditioning unit is:
- 7.2kWh/1.2kWh = 6 (300 watts rating)
So it’s possible run a 1.5 Ton AC unit on 6 x 300 watt solar panels, provided the sun is shining!
What about the AC inrush current?
Inrush current is pulled when the compressor motor starts from being stationary, for example when it starts a compression cycle when the temperature drops.
Starting when the motor is cold is the worst possible situation and in this case the motor could pull 3 or 4 times it’s normal current in. In fact,it’s best to assume 4 times for safety.
This means a 5 ton air conditioner could need 4 times more energy to get the cycle started, which would mean installing 80 solar panels!
Clearly, this isn’t practical, so what is the answer? And what about running the AC unit on a cloudy day or at night?
The solution is to install a bank of batteries for energy storage. This ensures a reservoir of extra power when it is needed and means you can run air conditioning when there’s no sun.
Key takeaways about solar air conditioners
Unlike an RV air conditioner a central air conditioner has a much higher power consumption and a solar array needs to have enough power to accommodate the current surges.
Generally, it’s better for a solar power system to incorporate solar batteries, even for a relatively low power appliance such as a window air conditioner. (A 5000 BTU air conditioner is considered small for window use.)
Battery systems also have the advantage of delivering energy during a power outage, so the home isn’t deprived of cool air. In general, 1000 watts of solar panels is needed for every 1000 Btu of ac. The size of the battery bank will determine the number of hours air conditioning can run. A solar charge controller is required for any solar system using batteries and lithium batteries are strongly recommended as solar battery storage.
A single solar panel will not have enough power to run AC, even in direct sunlight. The heavier the AC then the higher number of panels needed.
An off-grid system may be used and adequate roof space is needed, which should be sized up to make sure the amount of power generated is adequate, which depends on the energy consumption of your air conditioner.
The exact number of solar panels is determined by the average annual energy consumption taken from the manufacturer’s name plate. As a general rule, 2.5kw of power with batteries is adequate for a small AC unit.