Sunreign Reference: Solar Thermal Energy

Solar Thermal Energy

Solar thermal energy is the energie in sunlight. It can be harvested in different ways. Solarthermal panels and vacuum tubes are the most common methods.

Solar thermal panel vs. Vacuum tube

Solart thermal panels are ususally cheaper than vacuum tubes, and they are more reliable (easier to repair). The vacuum tube on the other hand is more efficient and performs better when it's cold in the winter, because less heat is lost once it is captured.

You can find a good analysis of the comparative efficiencies here.

Two graphs below show the thermal and optical efficiency of flat panel vs tubular (vacuum tube) collectors. The article concludes that flat plate colletors have matured and the technology is probably at its maximum performace. There is a new design based on concentrating solar rays onto finned heat pipes that does deliver higher temperatures and performance.

Thermal losses and optical efficiency for flat plate

Thermal losses and optical efficiency for tubular

Seasonal effects

Important factors with the two types of solar thermal collectors are the environment temperature and insolation. These factors change throughout the year. Below you see that the two technologies (on the left a vacuum tube with flat fin collector, on the right a traditional flat panel collector) have different yields and yield profiles.

from Solar corp NZ

Good thermal panels produce 1/3 rd to 1/10th in comparison to good vacuum tubes in summer and winter.

Relative advantages

The vacuum tube and flat panel collectors both have advantages. For applications where heat is most needed in the summer, for instance for solar cooling, flat panels will do fine as their yield follows the demand. Also for hotel water heating where most guests arrive in summer, the flat pannels are a good reliable low maintenance option. Thermal storage makes it even more sensible to go for an easily maintianed system.

There higher performance throuhot the year is desired, and space is limited, or where higher temperatures are needed one can use vacuum tubes. It is possible to run a turbine uising vacuum tubes, which makes them usefull for off grid power generation. Parabolic through collectors can do the same but are more robust. Vacuum tubes are pushed with a relatively high price point because the gas industry does not want their wide adaption and still sets the price of heating. As the prices of gas rise business should consider the use of solar thermal power to augment their heating requirement, as it has predictable cost.