Evacuated Tube Solar Collector

Running Head: Evacuated Tube Solar Collector 1
EVACUATED TUBE SOLAR COLLECTOR
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Executive Summary
Before modern solar technologies were formed, people still relied on the sun to draw
energy mainly for heating their homes. With time, the methods being used for drawing energy
from the sun have increased immensely. Solar thermal is the name used to refer to these
methods, they require collectors to operate unlike the previously known photovoltaic technology.
Evacuated solar collector tubes are being put to use globally due to their great working
temperatures and great thermal efficiencies when compared to other type of solar collector
technologies. Loss of heat by convection and conduction is significantly minimized by the use of
the vacuum in between the tube collector and absorber. An evacuated tube solar collector is able
to achieve temperatures of between 77 ̊C to 177 ̊ C and usually works efficiently under the right
conditions. The pricing of its cost per unit is higher than its flat plate counterpart. They are best
used in industrial and commercial heating applications as well as refrigeration cycle regeneration
(cooling applications). Domestic application can benefit those staying in cloudy areas by
replacing the flat plate collectors that are cheaper but inefficient. These collectors are made up of
metallic plates that are flat and black coated to increase rate of heat absorption; a polycarbonate
cover or thin, clear glass is used to help capture the heat; liquid filled pipes (commonly a mixture
of glycol antifreeze and water) (Duffie & Beckman, 2013). The heat is captured by the collectors
and transferred to the pipes where the liquid can be heated then transferred to the building for
heating purposes. This paper will focus on the evacuated solar tube collector in the following
sections by giving a brief overview of the system, its key mechanics of operations, the issues to
do with the materials used in design and finally how the climate affects the overall working of
this technology.

Table of Contents
Executive Summary.....................................................................................................................................2
1. Introduction to Evacuated Solar Tube Collector..................................................................................4
2. Heat Pipe Evacuated Tube Collectors..................................................................................................5
3. Direct Flow Evacuated Tube Collector.................................................................................................6
4. Production and operational costs.........................................................................................................7
Component technical details......................................................................................................................10
Outer Glass Tube...................................................................................................................................10
Inner Glass Tube....................................................................................................................................11
Aluminum Fin.......................................................................................................................................11
U-Copper Pipe.......................................................................................................................................11
Climatic Effect on ECT................................................................................................................................12
References.................................................................................................................................................13
Table of Figures
Figure 1-1 Example of Evacuated Solar Tube Collector...............................................................................4
Figure 2-1 Heat Pipe Evacuated Solar Tube Collector..................................................................................6
Figure 3-1 Direct Flow Evacuated Tube.......................................................................................................7
Figure 4-1 Costs in percentages of Production of ECT.................................................................................8
Figure 4-2 Graph of Cost vs. Units per day..................................................................................................8
Figure 4-3 Graph showing increasing production with reduced unit cost...................................................9

1. Introduction to Evacuated Solar Tube Collector
A tube solar collector refers to a successive number of glass tubes, connected to a pipe,
placed parallel to each other. Air is evacuated from the individual tubes creating a vacuum aspect
within them. The vacuum in the tube ensures that the surrounding temperatures are kept at a
certain minimum as well as maintaining the loss of thermal heat to the least. As a result of this
vacuum, these types of collectors are able to give higher temperatures than other collector
alternatives like the flat plate and as such can result to extreme temperatures in the summer
(Sobhansarbandi, 2017). The inner tube has a metal heat pipe running through it which is
attached to a curved or flat copper or aluminum fin. A selected coating is then applied to this fin
which is responsible for transferring heat to the pipes containing the running fluid. A hot bulb is
then used to heat indirectly the header tanks copper manifold, this is achieved by convection;
transfer heat to the hot bulb from the sealed copper heat pipes (Colombo, Bologna, & Masera,
2013). A common manifold joins all the copper pipes and is then used to heat water in a storage
tank. The insulating properties of the tank allow the water to be utilized either during the day or
night.
The evacuated tube collector is formed of certain components that are shown in the
figure below.
(Vijayakumar, Vijayakumar, & Kumar, 2017)
Figure 1-1 Example of Evacuated Solar Tube Collector