GB2516888A - Solar shading - Google Patents

Abstract

A shield c which rotates around an evacuated solar thermal tube e to provide shading when required, the shield rotates longitudinally around the solar tubing. The shield may be usable to reflect light onto the solar thermal tube when not used to cover the tube. The shield may be activated by a piston connected to the coolant liquid passing through the solar thermal tubing. The shield may be activated to rotate and cover the tube when the temperature reaches a set point. The shield may extend along the whole solar thermal tube or only part thereof. Preferably the shield is reflective to aid in directing light onto the tube when not covering the tube.

Description

Method of shading for solar thermal evacuated tubes.

This invcntion provides a mcthod to automatically shade evacuated solar thermal heating tubes from the sun to prevent them from over heating.

A common problem with solar thermal heating systems is that due to the widely varying amount of solar radiation between seasons and from day to day due to differing amounts of cloud cover, a solar thermal system which provides sufficient heat on overcast days will overheat and boil on a sunny day. Alternatively a system which is correctly sized for use in summer will not produce sufficient heat in winter. There already exists devices to automatically shade solar thermal tubes but these are either by means of a curtain which requires the tubes to be enclosed, or by coating one side of the tubes and rotating the tube, which permanently loses solar radiation reflecting onto the rear of the tube.

This invention solves these problems by positioning a shield longitudinally behind the evacuated tube which can rotate around the length of the tube to provide shade for the tube and protect from overheating. Many solar thermal panels which use evacuated tubes already have a fixed reflector positioned behind the tube and extending for most of its length to reflect the sun onto the rear of the tube and thereby increasing the efficiency. In this invention this reflector has been modified and utilized to provide a means of reflecting the sun onto the rear of the tube when in the open position, but also to rotate around the tube to provide a shield when the system is overheating. It has been found that an ideal shape and material for the shield is a parabolic reflector made from a bright metal such as polished stainless steel. The invention will now be described using the following diaams.

Figure I shows a view of a typical solar water heating panel which uses evacuated tubes (a) to collect solar radiation which in turn heats water passing through the manifold (b).

Figure 2 shows an example of the reflector (c) which has been created for use in this invention to provide both a reflective surface to direct solar radiation on to the rear of the tube and also provide shade when it is rotated. The loops (U) on the ends provide a suitable method of allowing the reflector (c) to rotate around the length of the evacuated tube. To allow for smooth movement and prevent scratching, loop (d) can be inlaid with a ring of nylon or other suitable material.

Figure 3 shows the reflector (c) which has been slid over an evacuated tube (e) Figure 4 shows a cross sectional view of figure 3 where the reflector (c) is in the open position allowing sunlight to heat the evacuated tube (e).

Figure 5 shows the evacuated tube and reflector described in figure 4 in an overheat situation. The reflector (c) has been rotated around the length of the tube and is now shielding the tube from the sun.

I

Figure 6 shows an evacuated tube (e) with reflective shield (c) in the open position, connected to a suitable linkage (I) and actuator bar (g) which when moved in the direction of the arrow (h) provides a means of rotating the shield around the tubes.

Figure 7 shows the arrangement described in figure 6 in an ovcrhcat situation. The actuator bar has been moved which in turn has rotated the reflective shield around the tube to provide shade.

Figure 8 shows the complcte panel with a motor (5) attachcd. In manifold (b) there are temperature sensors (not shown) connected to the motor by wire, (n) which detect when the panel is overheating and cause the motor to move the actuating bar to close the shield.

Figure 9 shows another suitable method of closing the shading shields. A piston (k) is connected to the actuating bar. The piston is connected to hose (1) which in turn is connected to the pipe work (m) which circulates the cooling liquid. When the cooling liquid overheats and expands the increase in pressure will cause the piston to move and thereby closing the shields. It is recognised that rather than being connected to the pipe work (iii), hose (1) could be connected to a liquid filled bulb placed in a position where the temperature of the panel can be measured, such as within the manifold.

In any of the applications the shading shields could be frilly rotated to provide substantial shade, or partly rotated according to the temperature to provide partial shading and thereby allowing the panel to supply optimal heating capacity.

It is recognised that many other suitable methods of rotating the reflectors can be providcd amongst which arc a means such as a bimetallic strips or cogs and gcars attached to the shields.

It is acknowledged that although parabolic reflectors arc preferred, strips of othcr shapes could be provided. These other strips could be of a non-reflective material but the benefit of increased heat collection in the open position would be lost. For the sake of brevity, within this patent these strips of other shapes and materials will be still be referred to as a shield'.

Curved parabolic reflectors have been used in these examples although it is recognised that straight, v' shaped or other suitable shaped reflector could also be used.

It is noted that the reflector would preferably extend along a substantial length of the tube, although a short reflector could be utilized which extended along a lesser proportion of the tube.