GB2054131A - Solar energy devices - Google Patents

Abstract

A solar energy device for harnessing energy from the sun comprises a focusser 12 having a cylindrical parabolic face for focusing the rays of the sun onto a fixed elongate hollow tube 13 about the longitudinal axis of which tube the focusser is arranged to rotate, tracking means 14 for tracking the part of the sun with the focusser 12, and means (not shown) for passing fluid through the hollow tube. The tracking means comprises photocells 15 arranged one to each side of a separation blade 16 lying in a plane including the longitudinal axis of the tube. A series of the device acting as master with one or more collectors in slave relationship is described. <IMAGE>

Description

SPECIFICATION Solar energy devices The present invention relates to solar energy devices.

Soiar energy devices are known in which a focusser focusses the rays of the sun onto a receiver. in one construction, the focusser has a cylindrical parabolic face, and the receiver is a pipe, otherwise referred to as a boiler. The pipe is located on a North-South axis and is tilted at an angle to the surface of the earth such that it is substantially normal to the incident rays. Tracking means then serves to rotate the focusser and the boiler whereby the focusser follows the path of the sun, and fluid travelling through the boiler pipe is heated by solar energy.

According to the present invention there is provided a solar energy device for harnessing energy from the sun. The present device comprises a focusser having a cylindrical parabolic face for focussing the sun's rays onto a fixed elongate hollow tube. ĕ focusser is arranged to rotate about the longitudinal axis of the fixed tube.

Tracking means are provided for tracking the path of the sun with the focusser, and the device further includes means for passing fluid through the hollow tube.

With the solar energy devices of the present invention, the focusser rotates about a fixed boiler tube, thereby eliminating the need for rotating joints to the inlet and outlet of the tube.

The tracking means suitably comprises a pair or photocells arranged symmetrically with respect to the cylindrical parabolic face cf the focuses and arranged one to each side of a separation blade lying on a plane including the longitudinal axis of the hollow tube. By balancing the light received by the two photocells, the focusser is aligned with the rays of the sun. To this end the tracking means can include electronic circuitry which will compare the output of the two photocells and seek a balance by actuating a motor causing rotation of the focusser.

It will be appreciated that the sun sets on one horizon and rises on another. Vk&commat; The tracking means could include a reset mechanism which after setting of the sun serves to rotate the focusser back eo a position apprnximately corresponding to that for rising of the sun. However, in a preferred construction employing a pair of photocells, the receiving faces of the photocells lie on respective planes which forwardly include (ie. define) an angle of more than 1800. By selection of a suitable included angle, eg. about 27iso, it can be ensured that with the focusser at the position corresponding to setting of the sun, one of the photocells receives light from the rising sun.As long as one of the photocells give some output at the rising of the sun, the tracking means will rotate to seek a balance.

In order to increase the sensitivity of tracking means which employ a pair of photocells, it is preferred that the separation blade has shadow element arranged to cast matched shadow on the respective photocells when the cylindrical parabola is aligned to focus the sun's rays on the hollow tube and arranged to cast unmatched shadow on the respective photocells when the cylindrical paraboli is not so aligned. When the focusser is out of alignment, there will be more shadow on one of the photocells and less shadow on the other, and a small angular rotation of the focusser will cause a relatively large change in the light received by the photocells.

For preference, the separation blade with shadow elements is ofT-section, the cross bar of the T causing the shadow, and the upright of the T constituting the separation blade itself.

In order to minimize the cooling effect of any local wind, it is preferred to screen the boiler tube with glass. Mitherto the practice has been to employ a glass sheet as a screen for such devices, but this is not essential. Adequate screening against the cooling effect of local wind can be obtained by encasing the tube itself within a glass tube.

The solar energy devices of the invention can be erected by mounting each end of the hollow tubs on a vertical post. Usually the hollow tube will be set up such that it is on a North-South axis and is at 980 to the sun's rays at solar noon and at Equinox. This mode of setting up is nn, essential, and for example the hollow tube could be set up horizontally, although a relatively long focusser might then be needed.

The present solar energy devices can be employed as single units. Alternatively, a series of devices can be used, with one device acting as a master device and serving to operate one or more.

slave devices. The slave devices do not then need tracking means as such, focussing being achieved for instance by the use of follower pulleys carried on the hollow tubes of the slave devices and arranged to be driven by transmission of drive from a driven pulley carried on the hollow tube of the master device.

An embodiment of the present invention will now be described by way of example and with reference to the accompanying drawings, in which: Figure 1 is a perspective view from one side and towards the rear of a master-and-slave arrangement according to the present invention; and Figure 2 is an upper end view of the master device of the arrangement of Figure 1.

Referring to the drawings, a master-and-slave arrangement of solar energy devices comprises a master device 1 0 and two slave devices 11. Each solar energy device has a focusser 12 with a cylindrical parabolic face for focussing the rays of the sun onto a fixed elongate hollow tube 13 (shown in Figure 2). The hollow tube acts as a boiler, and the respective focusser is arranged to rotate about the longitudinal axis of the tube 13.

The master device 1 0 further includes tracking means 14 for mraclcing the path of the sun and ensuring that all three devices are aligned so as to receive the incident rays frnm the sun and focus them on the respective hollow tube 13. A pump (not shown) or other means serves to pass fluid through the hollow tubes of the master device and of the slave devices.

In more detail, the tracking means comprises a pair of photocells 1 5 arranged symmetrically with respect to the cylindrical parabolic face of the focusser of the master solar energy device 10. The photocells are arranged one to each side of a separation blade 1 6 lying on a plane including the longitudinal axis of the hollow tube 13. The receiving faces of the photocells lie on respective planes which forwardly includes an angle a which in this instance is 2700. The separation blade has shadow elements 1 7 such that the separation blade and shadow elements are of T-section (see Figure 2).

The tracking means further includes a servomotor 18 and a driven pulley 1 9 secured to the hollow tube of the master device 10. Each of the slave devices 11 has a follower pulley 20, and a cable 21 extends from a pulley of the motor 18 to the driven pulley 1 9 and thence to the follower pulleys 20. The tracking means further includes an electronic device (not shown) which compares the ouputs of the two photocells 1 5 and seeks a balance by actuation of the motor 1 8.

As shown in Figure 1 ,the master and the slave devices are mounted by means of vertical posts 22 attached to the ends of the respective hollow tubes 1 3. In this instance each hollow tube is set up such that it is on a North-South axis and is at 900 to the rays of the sun at solar noon at Equinox.

When there is output from the two photocells 1 5, the motor 18 is actuated, causing each of the focussers to be aligned with the rays of the sun.

As a result, the rays are focussed onto the hollow tubes, and fluid passing through the tubes is heated. The sensitivity of the tracking means is high because when the focusser of the main device is out of alignment, one of the shadow elements 1 7 casts a larger shadow on its associated photocell 1 5 than does the other shadow element 1 7 on the other photocell 1 5.

Moreover, and because of the way in which the receiving faces of the photocells are arranged, at least one of the photocells 15 will receive light at sun rise, even if the device is at the position corresponding to sun set.

If desired, it can be arranged that the means for passing fluid through the hollow tube comes into operation only when there is output from one of the photocells. In this way, the pump or other means is switched off when there are no incident rays from the sun.

Claims (10)

1. A solar energy device for harnessing energy from the sun, the device comprising a focusser having a cylindrical parabolic face for focussing the sun's rays on to a fixed elongate hollow tube about the longitudinal axis of which tube the focusser is arranged to rotate, tracking means for tracking the path of the sun with the focusser, and means for passing fluid through the hollow tube.

2. A solar energy device according to Claim 1, wherein the tracking means comprises a pair of photocells arranged symmetrically with respect to the cylindrical parabolic face of the focusser and arranged one to each side of a separation blade lying on a plane including the longitudinal axis of the hollow tube.

3. A solar energy device according to Claim 2, where the receiving faces of the photocells lie on respective planes which forwardly include an angle of more than 1800.

4. A solar energy device according to Claim 3, wherein the included angle is about 2700.

5. A solar energy device according to Claim 2, 3 or 4, wherein the separation blade has shadow elements arranged to cast matched shadow on the respective photocells when the cylindrical parabola is aligned to focus the sun's rays on to the hollow tube and arranged to cast unmatched shadow on the respective photocells when the cylindrical parabola is not so aligned.

6. A solar energy device according to Claim 5, wherein the separation blade and shadow elements form a T-section.

7. A solar energy device according to any preceding claim, wherein the hollow tube is encased in a glass tube.

8. A solar energy device according to any preceding Claim, wherein the hollow tube is mounted at each end on a vertical post.

9. A solar energy device according to any preceding Claim, wherein the hollow tube is set up such that it is on a North-South axis and is at 900 to the sun's rays at solar noon at Equinox.

10. A solar energy device according to any preceding Claim, when constructed as a master device for use with one or more slave devices in a master-and-slave reiationship, together with the one or more slave devices which each comprise a focusser having a cylindrical parabolic face for focussing the sun's rays onto an elongate hollow tube about the longitudinal axis of which tube the focusser is arranged to rotate, there being means for passing fluid through the hollow tubes of the slave devices as well as of the master device.

1 A master and one or more slave solar energy devices as defined in Claim 10, wherein the hollow tubes of the slave devices each carry a pulley arranged to be driven by transmission of drive from a pulley carried on the hollow tube of the master device.