Renewable Energy - Solar Thermal Panels

Introduction

Thermal solar panels are used to heat the water for domestic use in the home. The heating of the domestic water accounts for about 25% of the total heating bill. Thermal solar panels are also used to heat indoor and outdoor swimming pools.

A typical panel consists of a frame into which rows tubes are fitted and are filled with water. The water is heated by the sun and circulated by a small pump from the thermal solar panel into the top of the domestic hot water tank, returning the cooler water from the bottom of the tank back to the panel.

This is the second article on domestic use of renewable energy and in it we shall examine a modern type of thermal solar panel which uses glass vacuum tubes in place of the normal tubes, and a PV driven circulating pump.

In particular we will take a look at the following,

• Their components & operation
• Their location for optimum output
• Their supply, installation and maintenance costs
• Their payback period
• CO2 emission savings
• Comparison with conventional solar panels in relation to CO2 footprint

The Frame

The frame which holds the tubes is fabricated from a light metal such as aluminum, into a rectangular box shape having sides and a bottom plate, which are insulated against the transfer of heat. After the installation of the components, a UV stabilized, double glazed glass cover is then bolted to the top of the frame completing the panel frame.

The Glass Tube

The glass collection tube component contains a silicon rubber pipe, laid longwise and fixed firmly to a heat absorber plate. The absorber plate runs centrally lengthwise along the glass tube not only acting as solar heat collector but also as a centralizer for the water pipe.

The heat collected by the absorber is transferred to the silicone rubber pipe through which the water is circulated.

The glass tube is then sealed leaving the pipe tails protruding and set under a permanent vacuum, effectively reducing any heat loss to the atmosphere.

A number of the glass tube components are fitted into the frame and the silicone rubber pipe tails are connected to an inlet and outlet manifold at each end of the frame. The manifolds terminate at a single inlet and outlet pipe union.

The domestic water enters the inlet pipe manifold at the bottom of the panel, rising up through the panel as it is heated to exit from the top manifold.

Because there is no antifreeze used in the system the hot water can be circulated through the tank and the solar panels in a direct system of heating. In the case of a solar panel using antifreeze, there had to be another coil fitted to the existing tank or a completely new hot tank with an additional copper coil fitted. This is known as an indirect system and had to be used to keep the antifreeze mixture separate from the domestic hot water.

The water from the solar panel outlet manifold enters the top of the hot water tank, the cooler water at the bottom of the tank being drawn out and pumped back to the solar panel inlet manifold.

Read on to see the orientation and installation costs, payback period and CO2 savings