NOVELTY - Seaweed grown at sea by hydroculture is harvested, dried and burnt to produce electricity. Combustion gases are returned to the sea water so that carbon dioxide can be used for photosynthesis. The ash is added to the seawater as nutrient salts for the seaweed.    USE - For generating cheap electricity used for heating buildings, or for the electrolysis of water to produce cheap hydrogen for vehicle, ship or aircraft fuel cells.    ADVANTAGE - Energy can be generated from a cheap and easy to grow naturally renewable resource without releasing large amounts of greenhouse gases into the atmosphere.    DETAILED DESCRIPTION - Seaweed is grown at sea in an open or closed hydroculture system with the aid of nutrient salts obtained from the sea itself or from the ash of burnt seaweed. A small amount of the seaweed (e.g. 0.1 %) harvested for burning is cut into pieces with a size of e.g. 1 cm and thrown back into the sea so that seaweed continues to grow. The rest of the seaweed is dried and burnt, the combustion gases generated when the seaweed is burnt are treated to remove carbon dioxide, by passing the gases through the seawater. The carbon dioxide is useful to the growing seaweed for photosynthesis.    DESCRIPTION OF DRAWING(S) - Figure 1 shows a schematic view of an open system for growing and distributing seaweed, and dissolving carbon dioxide in seawater.    Suck-press compressor for seawater (1)    Suck-press compressors for combustion gases (2, 3)    Suction pipe for seawater (4)    Pressurised pipe for seawater (5)    Suction pipe for combustion gases (6)    Pressurised pipe for combustion gases (7)    Combustion gas with reduced carbon dioxide concentration (8)    Pressurised pipe for combustion gases (9)    Combustion gas with low carbon dioxide concentration (10)    Filter (11)    High-pressure one-way check valves (12, 13)    High-pressure check valves (16, 17)    Pressurised carbon dioxide holding areas (18-21)    Porous filter comprising e.g. plastic mesh or mineral wool or glass wool fibre (22)    Pressurised region for carbon dioxide and seawater (23)    Porous filter comprising e.g. plastic mesh or mineral wool or glass wool fibre (24)    Pressurised region for carbon dioxide and seawater (25)    Valves (26-29)    Traps for combustion gases with reduced carbon dioxide concentration (30, 31)    Combustion gas with reduced carbon dioxide concentration (32)    Combustion gas with low carbon dioxide concentration (33)    Seawater containing carbon dioxide (34-37)    Atmosphere (A)    Seawater (Z)