What is solar thermal cooling?

To many, the idea of adding heat to the air conditioning/refrigeration cycle appears counterproductive. But we must remember that most air conditioning systems and chillers are essentially heat pumps that cool buildings by moving heat out of them. The vapor compression cycle used in most heat pumps is driven by a high-temperature and/or high-pressure refrigerant. To generate these high temperatures and pressures, electricity is used to drive a compressor. A solar thermal cooling system uses solar energy to reduce the electricity needed for the process.The diagram below shows the typical vapor compression cycle supported by a solar thermal panel. The thermal collection unit is installed on the discharge side (hot gas side) of the compressor. Free solar energy is injected into this hot refrigerant gas, increasing the kinetic energy of the molecules and the velocity and temperature of the refrigerant. The higher temperature of the refrigerant gas increases the delta temperature (Delta T) between the condenser coils and the outside air, which increases the heat flow out of the system. The increased heat flow means the gas reaches the equilibrium point (the conversion of the refrigerant from gas to liquid) earlier within the condenser coil, which also improves the effectiveness of the heat transfer and conversion to liquid.

The Simple Science

In Layman’s terms

Controlled vs. uncontrolled systems.

In simple terms: Our intellectual property adds an element of the heat which would under normal circumstances be generated by the compressor, allowing the compressor or compressors to unload. This process accelerates the heat transfer at condensation point, thus improving the quantity of liquid flow through the expansion valve, in other words reducing or eradicating flash gas. (see our video) As a result, the cooling capacity in the evaporator is enhanced, a process which the systems normal control logic recognises allowing the variable flow compressor system to slow down (or if staged - shut down), thus achieving substantial energy reductions.

Over recent years the ‘old’ single fixed speed compressor (un-controlled) has started to be replaced by more efficient rack systems (staged fixed speed compressors), and more recently variable speed systems (frequency controlled). The single fixed speed system is exactly that, it comes on at one speed and goes off at one speed. Therefore it would run at full speed (and energy consumption), even if the building or refrigerator required only a small load.

Today’s staged and variable technology however provides us with an ‘engine’ with variable speed, therefore we now have a system with a considerably improved correlation between demand and production. We now have an engine (the compressor), which has the ability to slow down in variable or staged modes, simply because the we implement a ‘tail wind’ (the third party heat source i.e. a Solar Thermal Collection System) allowing the engine to take advantage of that tail wind, therefore achieving the original speed (the cooling capacity) without the additional fuel consumption..

Thermodynamics of Solar Cool

The well-known compressor technology is enhanced with a proprietary developed solar thermal collection system. We now have a super advanced compressor system.

Solar Cool uses an exclusive patented process, of placing a 3-party heat exchanger between Compressor and Condenser. Utilizing the free available energy from the sun to heat the refrigerant & subsequently reducing the workload of the compressor/s..

As the free energy from the sun heats the refrigerant, it is provided with thermal energy, this in turn raises the internal energy (the sum of all microscopic kinetic and potential energy of the molecules).

The molecules now move with a higher value of kinetic energy, which simply implies each molecule moves with a higher velocity than before. Now the molecules collide more often with one another and rebound with an increased energy…

…which in turn creates an improved Delta T at the condenser, increased sub-cooling and  better quality of liquid at expansion

- resulting in an unequaled cooling and heating process.

The hotter the sun shines, the more the solar takes over the heating of the gas and the more power is saved. The compressor acts now mainly as a pump, providing the necessary cycle flow.

The reason clients use our systems for heating

How the heating system works

In heating mode the system works in almost the same way, but now the flow changes compared to the cooling mode. The additional free heating of the refrigerant in the solar panel allows the compressor to reduce its load, and therefore, its power consumption. Dependent on sun levels, COP figures (heating capacity vs power consumption) of over 8 are possible!

Again the more the sun shines, the more the solar panel takes over the compressing of the gas and the more power is saved, as the compressor now acts mainly as a pump providing the necessary cycle flow.

Due to the ultra UV absorbent design and glass vacuum tubing, the ambient external temperature has little if any impact on the temperature of the gas. The only natural element driving this positive process is the free energy provided by the sun's rays.

The system is also fitted with the innovative Solar Bypass Valve. This allows the gas to bypass the panel in heating mode, when the sun is non-existent. i.e. night-time and heavy rain-cloud.

Learn how the sun’s heat can make your system more efficient during summer peaks!

This 54-panel thermal collection system below was installed on a 1MW fruit packaging facility in the UK.
Solar thermal technology isn’t new under the sun. For centuries, it’s been utilized for heating water. But the integration of solar thermal into the HVAC refrigeration cycle is new – and it offers significant energy savings.
The introduction of variable load HVAC/R systems (VRF, inverter, staged, screw, digital scroll, etc.) has made the integration possible. While you may have heard over the last decade of some unsuccessful applications of thermal cooling, a new approach has succeeded where others failed. This article will provide an overview of the technology and show documented energy savings of this approach reducing energy consumption of HVAC/R usage by 30-65%.

As the refrigerant passes from the condenser toward the evaporator, the heat pump’s internal monitoring components will recognize that more than enough of the liquid refrigerant is of sufficient quantity and quality to allow the evaporator to be effective. With this excess cooling capability, the compressors can then slow down or stage off. The energy savings begin as the solar energy “substitutes” for some of the energy formerly used by the compressor(s).

Benefits of solar thermal cooling include the following:

  • Sustainability and reduction in greenhouse emissions due to using the sun’s free energy.

  • Adaptability for retrofits and new installs– These systems can be used on new or existing HVAC systems that have variable flow capability and compressors able to slow or stage down.

  • Forward compatibility– When replacing an existing HVAC/R system, the solar thermal components can just be re-piped into the new system with minor adjustments.

  • Internal rates of return (IRR) of 15-65% on investments prior to any tax, utility, and/or other incentives.

  • Scalability – No system is too large or too small.

  • No moving parts and small footprint

  • Reduction in overall HVAC/R energy consumption of 30-65%, even when including evenings and winter seasons.

  • Peak demand reduction – The hotter the sun, the more efficient the system becomes. The highest efficiencies are achieved during peak hours, when demand savings may be available.

Solar Cool explained for a car with tail wind


  • Imagine you have a car which runs along with a speed of 100 km/h. It may not run faster, because the tyres and brakes don’t allow that.

  • Now while running it, you experience a very strong tail wind of 30 km/h. This would push the car to 130 km/h depending on the engine you have:

  • Uncontrolled “systems”: If you have an engine which runs only 100 km/h and nothing more or less (of course this sounds ridiculous, because all cars have gear boxes and engines with variable speeds, but let’s imagine that the car has only one speed, because that is what compressors of on‐off units do), you have the potential to push the car to a speed of 130 km/h. But in reality you can’t because tyres and brakes don’t allow it. So you had the potential, but you are not able to realize it.

  • Controlled “systems”: If you have an engine with variable speed, then you could take your foot off the gas pedal, because the engine now with 70 km/h plus the tail wind of 30 km/h sum up to a total speed of 100 km/h and you are back at the original speed. Of course you would now save a lot of gas, because the tail wind is pushing you for free.

  • And that is exactly what SolarCool does. We use an engine = compressor, which may slow down, but in the end with the booster from the solar collector achieves the original speed, or for air conditioners the cooling capacity.


35 Main Rd Gonubie,
South Africa




Tel : 043 732 1749

©2018 by Solar Cool (Pty) Ltd