class13_w08 - Global primary energy use 1 EJ = 1018 J(per...

Global primary energy use
•
80% of energy from fossil fuels
•
Three-quarters of “Renewables” are from developing countries: biomass
•
Solar + wind together account for less than 1%
•
It is most likely that developing countries will switch from biomass to
fossil fuels as economies develop
1 EJ = 10
18
J
1 W = 1J/sec  ~ 14 TW
(1 TW = 10
12
watts)
(per year )

Passive vs. active solar heating
Passive : relies on building design: greenhouses, thick masonry, dark color
Active : some other source of energy besides solar is also required
•
water circulation to pick up solar energy for heat and hot water
• efficiency improvements for water and energy savings
Active
system

Solar thermal electricity
• Various designs are used for concentrating solar energy into a receiver.
•
Mirrors provide up to 5000-fold concentration of photons
•
High temperatures are produced:
eg, oil flowing in a closed receiver pipeline is heated 
heat transfer to steam electrical generator
• Can be coupled to insulated storage systems to deal with intermittency
•
Dish-engine system is most efficient; T up to 800°C
•
Still more expensive than fossil fuels

photosynthetic
reaction centers
electron
transfer
reactions
oxygen
generated
Light reactions
C-assimilation reactions
C-assimilation reactions
CO
2
IN
NET FIXED
CARBON OUT
Photosynthesis uses light
photons to fix carbon
and generate oxygen

Charge separation in photosynthesis is analogous to the process that
occurs in photovoltaic cells (PV cells)