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 CSP- biomass 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 CSP- biomass 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 Politécnica 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.