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Collector Output Calculator

Using this energy calculator you may determine approximately how much energy an Apricus AP evacuated tube solar collector will produce each year.  The values are conservative and so you may be able to get up to 15% more if you are in a hot region or have a large dedicated solar storage tank. 


In order to calculate energy output you must input the following variables:


Solar Insolation Levels

Before you calculate your energy output, you must know your solar radiation level (aka solar insolation). Click here to find values for your location. Take note of the annual average value which can be used below to estimate energy output and savings.

Please note that energy must be input in the unit kWh/m2/day.   

Conversion from US to metric units is:   1 kWh/m2/day = 317.1 Btu/ft2/day


Collector Size

Enter the total number of Apricus evacuated tubes.


Energy Cost

Enter cost per kWh in your local currency (may need to convert from m3 or Therms of gas)

  • 1 therm = 29.3kWh = 100,000Btu = 105.5MJ
  • Natural Gas is 39MJ/m3 = 10.83 kWh/m3
  • LPG Propane (liquid) = 25.3MJ/L = 7kWh/L
  • LPG Propane (gas) = 93.3MJ/m3 = 25.9kWh/m3


For European energy costs click here

Average Annual Insolation Level =     kWh/m2/day
Evacuated Tubes =     
Electricity Cost =     $/£/€ per kWh


(click twice)


  Energy Metric Energy US Cost Savings
Annual Total      kWh   kBtu   $/£/€ 


  • Energy output values are conservative approximations with real life output of -5% / +15% of calculated figures. Actual energy output and overall system efficiency will depend upon installation location, climate, insulation, system configuration and many other factors. On rainy or heavily overcast days energy output will be greatly reduced.
  • Collector peak efficiency is only achieved when ambient temperature and water temperatures are the same. During normal use, this is only likely to happen for a short period of time each day, and usually only when ambient temperatures are high (summer). Therefore during normal use, the solar collector cannot always perform at such a high level of efficiency. This is true for all evacuated tube and flat plate collectors, not only Apricus collectors. In order to provide more realistic figures, the above calculations are based on "normal" operating conditions under which the difference between ambient temp and manifold water temp is around 20-30oC.  For more information on collector efficiency, click here.
  • When making comparisons with other products please take the above point into consideration. Do not simply use the peak efficiency values for energy output, as this will provide inflated figures. IAM values also play an important role in determining total energy output from a solar collector. Please click here to learn more about how to interpret IAM figures.
  • Energy is produced in the form of heat. In transporting and converting this energy, such as for air conditioning or central heating, some energy (heat) will be lost, as no system or insulation is 100% efficient.
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