Two types of solar panels are generally available: photovoltaic electrical generation and water-heating.
My idea is to combine the two into a single panel: the water panel atop the solar cells. I have discussed this with a number of vendors, and nobody sells nor is aware of a panel with this combination of functions of operation. The water panel would be transparent, allowing sunlight to reach the photovoltaic panel.
Please note in my drawings that the top of the water panel (the side facing the sun) is arched, with the intention being to shape the panel as a "lens", which would help to concentrate more light into the panel during a wider angle of the sun’s transit, increasing efficiency and productivity. The dual panel would be constructed as a single enclosed unit, to assure no contamination between the two panels.
The water-panel section would be a sealed unit with a water-depth of about two inches and have standard plumbing connections at top and bottom, to circulate human-potable water to a holding hot-water tank / heater. Input water could come in at the panel bottom from the holding tank, or optionally from a normal ambient water source. Reflection of heat from the dark photovoltaic panel would be reflected back into the water panel, increasing the production of heated water. The water return is at the top, assuring the warmest water possible.
The photovoltaic section would have standard electrical connections to transfer electricity into the building's electrical system. Connections would be at the panel bottom, to reduce exposure to weather. Any type of photovoltaic panel type would work, but obviously the more advanced and recently-developed solar panels would be better. This includes those with embedded devices and computer-managed cells to generate AC current in-phase with electricity coming into the building from the local utility, manage current-flow on days with heavy cloud-cover, etc.
Panel size would be determined by commercially-attractive (home, business, etc.) demands, but a 4'x8' panel size would probably be standard for home roofs, with a number of panels placed side-by-side to cover most of the roofing area. The more panels used, the greater the production of electricity and heated water.
A number of variations are possible, such as using the generated electricity to circulate and further heat the water, or to use the heated water as part of the building's HVAC, but these are after-the-fact alternate uses of the panel's outputted products.
The main component I am presenting is the combined solar panels to generate electricity and hot water. This combined panel utilizes as much solar energy as can be obtained using all currently-available and applicable technologies and techniques.