Hybrid solar - biomass plants for power generation; technical and economic assessment.

Environmental, economic and strategic reasons are behind the rapid impulse in the deployment of renewable energy sources that is taking place around the world. In addition to overcoming economic and commercial barriers, meeting the ambitious objectives set by most countries in this field will require the development of novel technologies capable of maximising the energy potential of different renewable sources at an acceptable cost. The use of solar radiation and biomass for power generation is growing rapidly, particularly in areas of the globe where these resources are plentiful, like Mediterranean countries. However, solar energy plants necessarily suffer from the intermittency of day/night cycles and also from reduced irradiation periods (winter, cloudy days, short transients). Biomass power plants have to confront the logistic problems associated with the continuous supply of very large amounts of a relatively scarce and seasonal fuel. Hybrid systems may provide the solution to these limitations, maximising the energy potential of these resources, increasing process efficiency, providing greater security of supply and reducing overall costs. This work provides a practical introduction to the production of electricity from conventional Concentrating Solar Power (CSP) and biomass power plants, which is used as the basis to evaluate the technical and economic benefits associated with hybrid CSP-biomass energy systems. The paper initially analyses alternative configurations for a 10 MWe hybrid CSPbiomass combustion power plant. The Solar Advisor Model (SAM) was used to determine the contribution of the solar field using quasi-steady generation conditions. The contribution of the biomass and gas boiler to the power plant was estimated considering the available radiation throughout the year. An economic assessment of a 10 MWe power plant based on conventional CSP, biomass combustion and hybrid technology is calculated. The results show that investment costs for hybrid CSPbiomass power plants are higher than for conventional CSP and biomass combustion plants alone. However, owing to the shared use of some of the equipment, this value is significantly lower (24% saving) than a simple addition of the investment costs associated with the two standard technologies. In contrast, effective operating hours and, therefore, overall energy generation, are significantly higher than in conventional CSP (2.77 times higher) and avoids the need for highly expensive heat storage system. Owing to the lower biomass requirements, hybrid plants may have larger capacities than standard biomass combustion plants, which implies higher energy efficiencies and a reduced risk associated with biomass supply. Universidad Politecnica de Madrid (UPM) is currently collaborating with a consortium of private companies in the development of a first commercial hybrid CSP-biomass combustion power plant that is expected to start operating in 2012.