When comparing collectors, it is better to use efficiency values from the normal operating range rather than peak efficiency levels, as this will better represent average annual performance. The "normal operating range" refers to the normal delta-t range (Tm - Ta) that the collector is exposed to. For domestic water heating an average value of 30-40oC is common.
Every region has different ambient temperatures and different insolation levels, but for the purpose of a comparison we can use a "standard" set of environmental conditions.
In a moderate climate, an "average" intermittently clouded day in Spring can provide an insolation level of 3.5kWh/m2/day. The solar radiation distribution throughout the day from sunrise to sunset is displayed in the following graph.
Solar Collectors Comparison
It can be seen that 90% of the radiation falls between 9:00am and 4:00pm with an average insolation level during this period of 400W/m2.
We now have a full set of factors in order to do a comparison:
1. Insolation Level = 400Watts/m2 (G)
2. (Tm-Ta) = 35K
3. (Tm-Ta)/G = 0.0875 (x)
4. SunSurfs:
- Performance variables: h0 = 0.717, a1 = 1.52, a2 = 0.0085 (SPF)
- IAM adjustment = 1.2(K)
5. Leading Flat Plate:
- Performance variables: h0 = 0.8, a1 = 2.99, a2 = 0.023 (SPF)
- IAM adjustment = 0.97(K)
1. Insolation Level = 400Watts/m2 (G)
2. (Tm-Ta) = 35K
3. (Tm-Ta)/G = 0.0875 (x)
4. SunSurfs:
- Performance variables: h0 = 0.717, a1 = 1.52, a2 = 0.0085 (SPF)
- IAM adjustment = 1.2(K)
5. Leading Flat Plate:
- Performance variables: h0 = 0.8, a1 = 2.99, a2 = 0.023 (SPF)
- IAM adjustment = 0.97(K)
The calculations for the two collectors are therefore as follows.
SunSurfs: Performance = 1.2 * 0.717 - (1.52 * 0.0875) - (0.0085 * 400 * 0.08752)
= 1.2*0.717-0.133-0.026 = 70%
Flat Plate: Performance = 0.97 * 0.8 - (2.99 *0.0875) - (0.023 * 400 * 0.08752)
= 0.97*0.8-0.26-0.07 = 44.6%
Given the set of variables used, the SunSurfs solar collector would provide approximately 57% greater heat output throughout the day for a given absorber area.
The same calculation can be completed with other collectors using performance variables and IAM values. Please note this is just a rough estimation based on average variables only. For a complete comparison a modelling software package such as FCHART, or TRNSYS should be used.
Please note: SunSurfs Solar Energy does not guarantee the accuracy of these calculations and will not be held liable or responsible for any activities relating to their use. SunSurfs Solar Energy does not permit the use of these graphs or data for commercial use of any kind.