Energy Solutions to Air Pollution and Global Warming - Air Pollution and Global Warming: History, Science, and Solutions - page 322

warming-relevant gas and particle emissions from such
vehicles over their lifetimes is nearly zero (Figure 13.1).
Another advantage of a BEV is that it can travel
up to five times further per unit of input energy than
can an internal combustion vehicle (km/kWh-outlet vs.
km/kWh-gasoline). As such, BEVs require less energy
than do internal combustion vehicles, and a conversion
from internal combustion to BEVs will reduce energy
demand for transportation fuel by a factor of up to 5.
Contemporary BEVs use lithium ion batteries, which
do not contain the toxic chemicals associated with lead
acid or nickel cadmium batteries.
HFCVs use a fuel cell to convert hydrogen fuel and
oxygen from the air into electricity that is used to run
an electric motor. A fuel cell is a device that converts
chemical energy from a fuel into electric energy. HFCVs
are truly clean only if the hydrogen used by them is
generated by electrolysis (passing electricity through
water to split water, producing hydrogen), where the
electricity is obtained from clean WWS technologies.
To reduce storage space in a vehicle, the hydrogen
must be compressed. Because energy is required dur-
ing electrolysis, hydrogen compression, and fuel cell
use, HFCVs are less efficient than are BEVs; how-
ever, they are more efficient than internal combustion
vehicles. HFCVs emit only water vapor during their
operation. The only other emissions associated with
them aside from those resulting from vehicle and elec-
trolyzer manufacturing and decommissioning are emis-
sions associated with manufacturing and operating (if
any) the WWS technology producing the electricity for
electrolysis.
Liquid (cryogenic) hydrogen for air transportation
is not a novel idea. Such hydrogen has been used in the
space shuttle for decades and was tested in demonstra-
tion flights for the Soviet Union's commercial aircraft
Tupolev Tu-154B, beginning on April 15, 1988. In the
latter case, the aircraft was fitted with a thermally insu-
lated fuel tank behind the passenger cabin that contained
liquid hydrogen at a temperature of 20 K. The hydrogen
powered a third engine on the aircraft.
Liquid hydrogen requires 4.2 times the volume of jet
fuel for the same energy. As such, a liquid hydrogen
aircraft requires a larger fuel tank than does a jet-fueled
aircraft, increasing drag. However, jet fuel weighs 2.9
times more than does liquid hydrogen for the same
energy, so a liquid hydrogen aircraft weighs much less
than does a jet-fueled aircraft, offsetting much of the
efficiency loss due to the greater drag. The advantage
of a liquid hydrogen aircraft is the elimination of car-
bon dioxide, black carbon, carbon monoxide, reactive
hydrocarbon, and sulfur dioxide emissions from the

exhaust. Because the aircraft still requires combustion,
nitrogen oxides are produced, water vapor is emitted,
and thus contrails still form.

13.2.9. Use of Wind, Water, and Sunlight
Power for Heating and Cooling
Forwater and air heating in buildings, WWS energy
technologies include heat pumps and electric resistance
heaters. Heat pumps are efficient devices that extract
heat from the air or ground, even at low temperature.
The heat is either used to heat water or forced through
vents into a building to heat air. Heat pumps can act in
reverse as air conditioners. A heat pump that extracts
heat from the ground is a ground-source heat pump ,
whereas one that extracts heat from the air is an air-
source heat pump (Figure 13.11). One that extracts
heat from water, such as a swimming pool, is a water-
source heat pump .The advantage of a ground-source
heat pump over an air-source heat pump is that temper-
atures under the ground are relatively stable and warm,
even when the air outside is cold; thus, ground-source
heat pumps are more efficient under cold air conditions.
The advantage of an air-source heat pump is that it is
easier to install and maintain because none of its parts
is buried underground.
Electric resistance heaters can also be used for air
and water heating, but they are less efficient than are
heat pumps. Rooftop solar hot water heaters have

Figure 13.11. Air-source heat pump, installed
outdoors but used for indoor air heating and cooling.
Photo by Mark Z. Jacobson.