Build Solar Water Heater

there are several ways of doing this, but a common way is through light energy absorbance by the electrons leading to a charge disparity that drives electron movement. The electrons get excited to the higher energy of the diffuse cloud surrounding the alloy or ceramic or whatever particular material is present and become free to move beyond the confines of their original atom. This can create a negative charge that will be offset by a positive “hole” that also can migrate.
A lot of times the substance consists of layers that impart a direction to the flow (one side excites and the other receives the excited electrons).

cost.If not, is there any organisation doing research on it

For best results the panel should be in 90 degrees with the solar radiations to get the best out of this flux. think of it as if u have a hose and spraying water through a 3 feet far window, more water will cross the window if the window was straight, if it is incline the opening willdirectly get smaller and thus less water will get in.
same thing for solar, if angle is not 90 degrees less radiations get in, if the angle is less than 30 degrees radiations do not penetrate.
cos θ = (sin δ sin φ cos β) – (sin δ cos φ sin β cos γ) + (cos δ cos φ cos β cos ω) + (cos δ sin β sin γ sin ω ) + (cos δ sin φ sin β cos γ cos ω)
θ: Incidence angle
δ: Declination
γ: Surface azimuth
β: Tilt angle
φ: Latitude
ω: Hour angle