NOVELTY - The photovoltaic-thermal (PV-T) based desalination system comprises arrays of photovoltaic (PV) cells in thermal communication with an excitation source, a cooling system in contact with the PV-T system, and a desalination system. A fluid that traverses the cooling system cools the PV cells and makes a heated water byproduct. The desalination system is configured for capturing and using a thermal energy from the heated water byproduct in a desalination plant, and comprises reverse osmosis, nanofiltration, electrodialysis, electrodialysis reversal, and/or electrodeionization processes.    USE - The photovoltaic-thermal system is useful for desalination of water or a fluid in a desalination plant (claimed).    ADVANTAGE - The photovoltaic-thermal system is capable of economically desalinating the water with less power consumption, and exhibits high efficiency and performance and improved durability.    DETAILED DESCRIPTION - The photovoltaic-thermal (PV-T) based desalination system comprises arrays of photovoltaic (PV) cells in thermal communication with an excitation source, a cooling system in contact with the PV-T system, and a desalination system. A fluid that traverses the cooling system cools the PV cells and makes a heated water byproduct. The desalination system is configured for capturing and using a thermal energy from the heated water byproduct in a desalination plant, and comprises reverse osmosis, nanofiltration, electrodialysis, electrodialysis reversal, electrodeionization, capacitive deionization, membrane distillation, and/or evaporative desalination processes. Lenses or mirrors are configured to intensify the thermal communication with the excitation source to harvest a form of energy. INDEPENDENT CLAIMS are included for:    (1) a method of cooling photovoltaic cells in a photovoltaic-thermal based desalination system;    (2) a method of converting solar energy to electrical energy with an energy conversion device and a heat sink; and    (3) a method for desalination of water or a fluid.