Performance of our Solar Water Heaters

A solar water heater’s performance is dependent on the amount of solar radiation present. Remarkably a solar water heater’s performance has very little to do with the outside temperature. This is because the vacuum tube heat pipe technology is so efficient that very little heat is lost externally. Most quality solar water heaters have undergone a certification process by the SRCC (Solar Rating & Certification Corporation), as such there performance has been tested to confirm the energy output based on their size and the solar radiation that they can absorb. This is important when looking at purchasing a solar water heater as this will be a good indicator on how well a solar heater will perform.

The amount solar radiation that fall on 1 m2 is known as the solar irradiance. Solar irradiance is the power per unit area produced by the Sun in the form of electromagnetic radiation. Solar insolation is a measure of solar irradiance over of period of time - typically over the period of a single day. The Maximum solar irradiance is 1000 W/M2 and this is typically found at the equator where the suns angle is most direct and has the least amount of atmosphere to penetrate. Typically solar insolation is measured in days such as Kwhr/day. It sometime is converted to “sun hours” which would be the number of 1000 Watts in a given day. So if the daily solar insolation is 4500w/day there would be 4.5 sun hours. NASA keeps very accurate data on average solar irradiance at every spot on the earth. You can find this data on maps and the data changes during the season. Our special solar simulation software is able to simulate the solar irradiance in any location in the world. This allows us to provide accurate estimates on energy savings a certain sized system will provide dependent on where it is installed. Request a Solar Simulation!

Knowing the irradiance or insolation is important because in any given geographical location it will allow us to calculate how our solar water heating system will perform. As mentioned before, a quality collector will have a SRCC rating that has determined what percentage of the solar irradiance it is able to capture. A collector with a rating of 45% would capture 45% of the solar irradiance per m2 of its size. So a collector measuring 2 meters and having efficiency coefficient of .45 would capture 45 % of the solar energy. Now if the energy at a particular day was 600 Watts/m2 (solar irradiance). We would expect the collector to deliver 600 x .45 x 2 = 540 Watts. However if the sun increase in intensity in a clear summer day to 800 watt/m2 then we would expect the collector to deliver 800 x .45 x 2 = 720 Watts.

So the performance of a collector depends on the size of the collector, the irradiance or insolation where it is located, and its efficiency rating.

Our SunRain TZ58 1800 30R collectors have one of the highest ratings based on the SRCC ratings compared to any other 30 tube vacuum collector. This is based on comparing the amount of energy they produce per area. As we know more area in m2 results in more radiation it can capture so we would expect a larger collector to produce more energy that a smaller collector. Comparing the collectors based on square footage/BTU or KW gives us the best measure of performance. Each TZ58 1800 30R is capable of producing a Maximum of 2.1 Kw of heat energy however this is based on a maximum irradiance of 1000/watt m2. So in reality the output will be less. But we if we had 6 sunlight hours in a given day we would expect approx. 12.6 Kw of performance/day(6 x 2.1 kw).