A hybrid photovoltaic-thermal system provides co-generation of electrical energy and thermal energy. Electrical energy is efficiently generated by photovoltaic panels that are cooled by heat exchangers attached thereto, and the cooling of the photovoltaic panels improves the energy output efficiency of the photovoltaic panels. The heat exchangers flow fluid through its channels, and the fluid collects heat from the photovoltaic panels to which the heat exchangers are attached. The heated fluid is then received at and stored in a thermal battery. The thermal battery can be a fluid tank that encourages the fluid to retain the heat collected from the photovoltaic panels. The thermal battery can then supply the heated fluid to thermal loads as thermal energy.

A solar thermal collector and an accessory structure of a building are provided. The solar thermal collector includes at least one heat absorbing plate and at least one heat insulating plate. Each of the heat absorbing plate includes at least one first slab and first engaging parts connected with the first slab. Each of the heat insulating plate includes at least one second slab and second engaging parts connected with the second slab. The first engaging parts are respectively engaged with the second engaging parts, and a gap is maintained between the first slab and the second slab to define a heat collecting channel, through which a heat transfer medium flows between the heat absorbing plate and the heat insulating plate. A heat conductivity of the heat absorbing plate is at least 30 times greater than a heat conductivity of the heat insulating plate.