CA2756521A1

CA2756521A1 - Solar collector

Info

Publication number: CA2756521A1
Application number: CA 2756521
Authority: CA
Inventors: James Thomas Beck
Original assignee: Individual
Current assignee: Individual
Priority date: 2011-10-31
Filing date: 2011-10-31
Publication date: 2013-04-30

Description

SOLAR COLLECTOR

BACKGROUND:
There are a number of solar concentration systems as follows:
1) Solar trough in which sunlight is focused in a linear line in which a solar receiver tube extends the length of the solar trough reflector. These reflectors can be joined together end to end forming long troughs. An adaptation on this is what is called Linear Fresnel lens. This technology is unable to generate high temperatures limiting the operating temperature resulting in the steam tubing operating at significantly lower efficiencies. This is particularly the case in which energy storage is applied since there is a significant drop in temperature through thermal energy storage technologies as it gives up its heat to the steam boiler.

2) Point focus systems are able to generate very high temperatures lending itself well to high temperature thermal storage and higher temperature steam turbines, typical of what would be used in a coal filed power plant. This has the advantage of much higher efficiency operation as well as lower cost since these types of turbines are common compared to specialized lower temperature turbines used in lower temperature solar power generation systems.
SHEC Energy Corporation has developed special solar receiver technology to harness the solar beam in these types of systems with very low emissivity loss.

3) Heliostat with central tower. These types systems use large flat mirrors that focus its energy to the top of a solar tower. These types of systems have to be large scale in order to have the necessary number of heliostats in order to obtain the concentration ratio necessary to generate high temperatures. There are a number of issues when building central tower designs which include:
a) Emissivity loss; A 40 foot dish for example needs to have a very large solar target of at least 40 feet across resulting in a large exposed surface area and resulting very large emissivity loss (radiant energy loss).

b) Dispersion loss; The sun in not a single source point of light and has a diameter of 1.4 million km (865,000 miles) and is (93 million miles) from the Earth. This results in a reflected beam that will spread at a ratio of 1/110. A mirror the size of a point will cause a reflected spot size of 1 meter at a distance of 110 meters from the reflector. The spot size would be 5 meters at 550 meters distance. This is known as dispersion.
This will required an even larger target size to collect the light resulting in even more emissivity loss.
c) Modulation loss. The further a heliostat is from the solar tower, the more easily it can sway on and off target in even mild winds, resulting in substantially reduced power output.
DESCRIPTION OF THE INVENTION
The present invention is able to deploy a matrix of much fewer heliostats around much smaller towers. For example, only 100 heliostats of conventional design would only provide a concern triton ratio of 100 suns. SHEC Energy is able to adapt the geometry of the various heliostat segments to bring the reflected beam from each segment to overlap in the space of one segment, effectively creating a focused beam the size of one mirror segment. For illustration purposes, lets assume a heliostat of 9 mirror segments arranged in 3 rows of 3 coulombs as illustrated in Fig 1.
100 Heliostats with 9 mirror segments each would have an effective concentration ratio of 900 suns. 25 mirrors each, 2,500 suns and so on.
Since Heliostats redirect the solar beam to a tower, the articulating segments adjust to keep the beam in focus. This happens dynamically as the sun tracks across the sky. The entire heliostat moving all the mirror segments adjusts in real time to redirect the sunlight to the top of the solar tower. The centre mirror is fixed to the heliostat but the surrounding mirrors can micro adjust as the sun tracks across the sky. If the segments did not adjust, the focus would become elongated from morning to afternoon.

Figure 2 shows ne row of mirrors in a top down view. As can be seen in this exaggerated view, the geometry of the mirror segments adjust as the entire heliostat is generally steered to redirect the suns solar energy to the solar.
Benefits:
Much small towers can be used, resulting in fewer heliostats per tower to obtain the necessary concentration ratios to generate high temperatures. This will result in less dispersion since the heliostats can be placed closer to the towers. The target size can be dramatically reduced resulting in much less emissivity loss. Modulation losses are minimized do the heliostats being closer the towers. Large scale stations could employ multiple mini towers.
This could add another dimension of station performance as the control system could redirect the reflected solar beam from one tower to the next during certain times of the day to maximize power output. For example, the cross section reflected area becomes smaller at high reflection angles, also referred to as cosine loss, the control system can direct a heliostat to focus on another adjacent tower to minimize this type of loss.
The benefit of this over point focus solar concentration systems is that there is no piping requirement to each solar concentrator, reducing system cost for large scale deployments.