Passive solar heat collector

The present invention relates to a method and an improved passive apparatus for absorbing, transferring and storing solar energy as heat, economically and effectively, without pumps, solar tracking devices or electric power. The apparatus comprises an improved trough-type concentrating collector, a heat pipe heat absorber and an insulated storage tank. Solar energy is reflected and focused by the concentrator onto the absorber where the energy is absorbed as heat. The absorber, made of one or more slightly tilted gravity-assisted heat pipes partially filled with a volatile liquid, transfers the heat by evaporation, vapor transport and condensation into a slightly elevated heat storage reservoir. A method for filling the heat pipes is disclosed. The absorber serves as the main axial support for internal structural ribs over which are fitted a flexible transparent top cover and a flexible reflective bottom cover that comprise the concentrator. The apparatus collects solar energy, stores heat during the day and automatically shuts off to minimize heat losses at night. The apparatus may be refocused periodically to increase the temperature of the heat collected.

I claim:

1. An improved passive solar heating apparatus of the type having a solar energy concentrator structured to reflect and focus solar energy into a linear region of small volume so as to increase the temperature in the linear region, having a linear heat absorber of at least one heat pipe, with a first and second end with the first end serving as a heat absorber section located in the high temperature linear region of the concentrator to absorb the focused solar energy as heat and transfer it into the second end that serves as a heat removal section, wherein the improvement comprises:

a. a concentrator made of a durable and flexible solar energy reflecting material along the bottom surface to reflect and focus the solar energy into the linear region of small volume, a durable and flexible transparent material along the top surface to help minimize heat losses, and internal structural ribs located along the concentrator to support and give shape to the flexible solar energy reflecting material and the flexible transparent material;

b. a linear heat absorber of at least one heat pipe having the first end closed and the second end provided with a closure means and being made of material capable of serving as the main axial support structure for the concentrator and capable of serving as a hermetically sealed vessel containing a volatile liquid that transfers heat by evaporation in the heat absorber section and condensation in the heat removal section, said absorber being tilted with the heat removal section above the heat absorber section so that condensed liquid will flow from the heat removal section to the heat absorber section by gravity force and thereby provide heat transfer into the heat removal section but not out of it;

c. a heat sorage reservoir containing a heat absorbing fluid is connected to the heat removal section of the absorber

c. to absorb and store heat, and is provided with inlet and outlet passages for the heated fluid to be drawn off for external use and cool makeup fluid to flow in and is provided with external thermal insulation to minimize heat loss to the surroundings; and

d. a support structure attached to the absorber and to the heat storage reservoir adapted to support the apparatus on whatever base it may be placed in a proper orientation to receive the solar energy and to allow the apparatus to be rotated about the linear focal axis so that the concentrator can focus the solar energy onto the absorber.

2. The apparatus recited in claim 1 wherein the absorber comprises:

a. a selective surface coating on the outside surface of the absorber that gives high absorptivity and low emissivity of solar energy; and

b. a longitudinal transparent cover around the linear heat absorber that may be sealed at both ends and evacuated of air and other gases to further minimize heat losses.

3. The apparatus recited in claim 1 wherein the absorber comprises at least two heat pipes arranged in a planar geometry along the high temperature linear region of the concentrator to intercept the solar energy reflected from the concentrator.

4. The apparatus recited in claim 1 wherein the absorber comprises at least three heat pipes arranged in a V shaped geometry along the high temperature linear region of the concentrator to intercept the solar energy reflected from the concentrator.

5. The apparatus recited in claim 1 wherein the absorber comprises at least three heat pipes arranged in a Y shaped geometry along the high temperature linear region of the concentrator to intercept the solar energy reflected from the concentrator.

6. The apparatus recited in claim 1 wherein the absorber is made of at least one section of extruded metal with at least one hollow heat pipe formed within it.

7. The apparatus recited in claim 1 wherein the absorber of at least one hollow heat pipe is provided with at least one longitudinal fin securely attached and extending radially out from the pipe to provide additional surface to intercept the solar energy reflected from the collector.

8. The apparatus recited in claim 1 wherein the absorber of at least one hollow heat pipe is provided with internal circumferential screw threads or other porous material lining the inside wall to serve as a circumferential capillary wick to allow the volatile liquid to wet the internal surface for enhanced evaporation and condensation.

9. The apparatus recited in claim 1 wherein the absorber of at least one hollow pipe is made of a transparent pipe material and a dark colored porous wick that allows solar energy to be absorbed directly into the liquid saturated wick.

10. A method for filling the absorber of at least one heat pipe recited in claim 1 wherein:

a. cleaning the absorber;

b. filling the absorber partially full of the volatile liquid;

c. heating the absorber along the heat absorption section so that the volatile liquid is heated to a temperature above its normal boiling point;

d. venting the air, other non-condensing gases, and excess volatile liquid from the absorber by opening slightly the closure means on the second end; and

e. closing and sealing the closure means.

11. The apparatus recited in claim 1 wherein the solar energy concentrator comprises:

a. a longitudinal cylindrical trough along the bottom;

b. internal structural support ribs of cylindrical shape along the bottom to give shape to the flexible solar energy reflecting material attached along the bottom, the ribs being made of a low cost, easily fabricated material and coated with a protective coating to provide long lifetime and to reflect sunlight, the internal ribs having an open structure to provide minimal obstruction of the solar energy rays, and the ribs being attached to the absorber.

12. The apparatus recited in claim 1 wherein the solar energy concentrator comprises:

a. a longitudinal parabolic trough along the bottom;

b. internal structural support ribs of parabolic shape along the bottom to give shape to the flexible solar energy reflecting material attached along the bottom, the ribs being made from a low cost, easily fabricated material and coated with a protective coating to provide long lifetime and to reflect sunlight, the internal ribs having an open structure to provide minimal obstruction of the solar energy rays, and the ribs being attached to the absorber.

13. The apparatus recited in claim 1 wherein the solar energy concentrator comprises:

a. a longitudinal Trombe cusp trough along the bottom;

b. internal structural support ribs of the Trombe cusp shape along the bottom to give shape to the flexible solar energy reflecting material attached along the bottom, the ribs being made of low cost, easily fabricated material and coated with a protective coating to provide long lifetime and to reflect sunlight, the internal ribs having an open structure to provide minimal obstruction of the solar energy rays, and the ribs being attached to the absorber.

14. The apparatus recited in claim 1 wherein the solar energy concentrator may be rotated around the absorber so that the concentrator can focus the solar energy onto the linear heat absorber.

15. The apparatus recited in claims 1 wherein a plate having a small pinhole is located on the top edge and in the center of each of the two end ribs of the concentrator so that a small spot of sunlight falls directly on the absorber when the concentrator is properly aligned and focused.

16. The apparatus recited in claim 1 wherein the heat storage reservoir contains baffels comprised of two plates located on either side of the absorber to induce natural convection mixing of the heat absorbing fluid.

17. The apparatus recited in claim 1 wherein:

a. the heat absorbing fluid contained in the heat storage reservoir is a gas that flows over the heat removal section of the absorber to remove and transfer heat; and

b. the absorber is provided with external fins in the heat removal section to enhance convective heat transfer from the absorber to the gas.