Solar Energy Perspectives - IEA

Solar Energy Perspectives: Solar fuels
sometimes called “bio-coal”, could possibly benefit from using solar energy as a heat source.
The process is sometimes claimed to be self-sustained, as the torrefaction produces the
emission of gases, notably carbon monoxide (CO) and hydrogen (H 2 ), thus some sort of
syngas, which is being burnt to generate the middle-temperature heat (200°C to 300°C) that
sustains the process. Other sources suggest a few percent of the solid output needs to be
burnt in the process. In both cases, if solar heat is introduced to run the process, the desired
output would be increased, as would the possibilities of valuing the syngas generated
together with the bio-coal.
Figure 9.4 Solar-driven biomass gasification
2
3
1
4
Notes: 1. Concentrated solar power from heliostats on the ground is directed into the thermochemical reactor on top of a tower.
2. Finely ground biomass is delivered by pneumatic tube into a feeder unit above the reactor. 3. Feedstock is dropped through the
reactor’s solar furnace, where temperatures of 1300°C gasify the material. 4. Syngas is collected and delivered to the adjacent
biorefinery to create green gasoline or diesel fuels.
Source: Sundrop Fuels, Inc.
Key point
Solar heat can gasify biomass and increase biofuel production.
Using solar fuels
Solar thermal hydrogen production costs are expected to be USD 2/kg to USD 4 /kg by 2020
for efficient solar thermodynamic cycles, significantly lower than costs of solar electricity
coupled with electrolysis, which are expected to be USD 6/kg to USD 8/kg when solar
electricity cost is down to USD 80/MWh. Solar-assisted steam reforming of natural gas would
become competitive with natural gas (as an energy source) at prices of about USD 11 /MBtu.
168
© OECD/IEA, 2011