Why do solar panels have to be flat, why can we not make a square box with a magnifying lense to heatour water

Answer 1

The absorption of solar energy is maximized for a surface at right angles to the incoming rays of light. (Incidentally, this is why we have seasons... the inclination of the earth's axis alternately causes either the northern or southern hemisphere to be more perpendicular with respect to the angle of the sun.) This principle is equally appropriate to both heating water and generating electricity using solar energy.

Since the light from the sun is coming from so far away, the rays of light can be considered essentially parallel. Since we have a set of parallel incoming rays of light, the only surface which can be oriented so as to be perpendicular to all of them would have to be flat. Computerized motors can be used to tilt the panel so as to always have it facing the sun, maximizing the power output.

Note that the energy is also proportional to the surface area of the collector. For this reason, a lens would be no better than a flat panel of the same size; either would collect the same volume of incoming light. The lens would concentrate the collected energy onto a smaller area beneath it, but the total energy collected would be the same.

Answer 2

A number of reasons come to mind.

Assuming a roof mount:

1. Flat collector panels are easily mounted to a roof line, compared to a cumbersome (and heavy) sized tank.
2. Their weight is not as much of a concern, as a large tank would also add the weight of the water.
3. The time the water takes to heat up is proportional to the
amount of water in contact with the surface area of the collector.
No good having a large tank if there is insufficient heat to do the job.
4. Flat panels can be made modular and just joined together for extra surface area, therefore more heat equals less time to heat the designed volume of water.
5. There are two types of flat panel systems I know of, one has the tank mounted adjoining the collector panels, the other has a remote storage tank with pipes connecting back to the panels, but they both work on the thermosyphon principle.

Answer 3

Some solar collectors are tubes with cylindrical lenses and a pipe up the center. They have to be placed perpendicular to the path of the sun so that rays are focused on the tube as the sun move E to W across the sky and angled so as the sun goes higher and lower in varous seasons the angle is good most of the time. They are much more expensive than flat collectors although they should be more efficient and get the water hotter.
Big separate magnifying lenses are expensive.

Answer 4

Some system do work with a small collector and a magnifying lens. However the advantage of a flat panel is simplicity. A flat panel works well without having to track the Sun. When you use a magnifying lens the system becomes very directional and must track the Sun so that the spot is on the collector at all times. (Otherwise you might burn your roof).

Answer 5

They don't have to be flat. Just need to absorb the maximum amount of solar heating available.