Solar energy conversion through seaweed photosynthesis and zero emissions power generation

The present paper is aimed at describing a “closed cycle” power plant scheme (Solar Oxygen Fuel Turbine (SOFT)) with macroalgae (seaweed) cultivation in a pond, combustion of its organic matter in a fluidized bed boiler using the Rankine cycle, and return of the combustion products to the pond to feed the algae. The oxygen used for combustion is released to the atmosphere during photosynthesis. It is further elaborated in a paper presented at ECOS2005 in Trondheim. As a renewable fuel, the seaweed Ulva lactuca is selected. Its growth rate in many experiments (in the literature) is 0.1–0.2 per day, the heating value of its dry weight is 19 MJ/kg, and its optimal concentration in salt water is 1:1000. The energy efficiency is less than in photovoltaics, but the energy expenditures to construct the pond as a solar energy receiver are much less, so it gives some economic benefits. For a power unit of 100 kW, the pond surface is about 4 hectare. The cultivation of seaweed in sea-water ponds is well developed in Italy and Israel for water cleaning and chemical production. Construction in the future of a SOFT system near the Dead Sea in the Israeli desert would provide the country with needed power, chemicals, and fresh water using solar energy. The system is protected by United States Patten no. 6 477 841 B1 dated 12.11.2002 with priority in Israel dated 22.03.1999. Many more benefits to the customer than are in the patent text are highlighted in the paper, including fresh water by desalination. In view of the active work in Italy on water cleaning using Ulva and contaminants in the water as nutrients for an increase of the biomass productivity, an additional target of the SOFT cycle might be incineration. Some suppositions of the use of a desert surface for massive scale use of ponds are given.