APES Unit 6.10-11 Geothermal Energy + Hydrogen Fuel Cell

Geothermal Energy: Source

Natural radioactive decay of elements deep in earth’s core gives off heat, driving magma convection currents which carry heat to upper portion of mantle, close to earth’s surface

• naturally heated water reservoirs underground are drilled into & piped up to the surface (or water can be piped down into naturally heated rock layers

Geothermal Energy: Process

1. Water can be piped down into the ground and heated by this heat from the mantle

2. Hot water can be converted into steam → turbine → elect. or be used to heat homes directly

Geothermal Energy: Primary Emission or Waste

Hazardous gases and steam that are present in the areas being drilled may also escape geothermal power plants

• Hydrogen Sulfide

Geothermal Energy: Major Economic Barrier

Not being easily accessible everywhere and the expense of drilling multiple deep wells can be high

Geothermal Energy: Environmental Benefit

• Potentially renewable, only if water is piped back into the ground for reuse

• Much less CO2 emission than FF electricity

• No release of (PM/SOx/NOx/CO) as is case with FFs

Geothermal Energy: Environmental Drawback

• Not everywhere on earth has access to geothermal energy reaching close enough to surface to access it

• Hydrogen sulfide can be released, which is toxic and can be lethal to humans & animals

• Cost of drilling that deep in the earth can be very high initially

  • Sometimes so high that it’s not even worth it

Hydrogen Fuel Cells: Energy Source

H2 gas and O2

Hydrogen Fuel Cells: Process

1. H2 gas enters fuel cell where it’s split into protons (H+) and electrons (e-) by an electrolyte membrane that only lets protons pass through

2. Electrons take an alternative route (circuit) around the membrane, which generates an electrical current

3. O2 molecules enter fuel cell break apart into individual O atoms and combine with two hydrogens (H+) to form H2O as a by product (only emissions from F fuel cells)

Hydrogen Fuel Cells: Primary Emission or Waste

NO POLLUTANTS

• NRG

• Water

Hydrogen Fuel Cells: Major Economic Barrier

• Most commercially available hydrogen is produced by an energy-intensive process of using natural gas in order to extract its hydrogen

  • This releases carbon dioxide and other air pollutants

Hydrogen Fuel Cells: Environmental Benefit

1. Because H2 gas can be stored in pressurized tanks, it can be transported for use creating electricity later, in a different location

   1. Unlike solar, hydro, and wind where the electricity must be used as soon as it’s generated & relatively closely to the location of generation

   2. Can also be used as a fuel for vehicles (replacing gasoline) or to create ammonia for fertilizer, or in the chemical industry

2. As a gasoline replacement, it emits no air pollutants (NOx/PM/CO) and only H2O (tech. a GHG) no CO2

   1. Manufacture of many different industrial chemicals requires H2 gas

   2. Can be stored as liquid or gas, making it easy to transport

   3. H fuel cells are ~80% efficient in converting chemical energy in H2 & O2 into electricity (Coal PP = 35% efficient)

Hydrogen Fuel Cells: Environmental Drawback

1. Since 95% of H2 production requires methane (CH4), H fuel cells are based on a non-renewable & CO2 releasing energy source

   1. If electrolysis is used to produce H2, it’s only as sustainable as the electricity source

   2. Widespread H fuel cell use would require building widespread H distribution network (similar to current system for gasoline)

   3. H fuel stored in gas form in vehicles would require much larger tanks than current gasoline tanks

If we use electricity from a coal-fired power plant to create the hydrogen gas for a "clean" fuel cell, is the system truly carbon-free? Why or why not?

No—Coal is a fossil fuel. When burned, old carbon dioxide is released from combustion, increasing atmospheric greenhouse gas levels.

Why can a hydrogen fuel cell be used to power a car in a city, but a geothermal plant cannot?

• Not everywhere on earth has access to geothermal energy reaching close enough to surface to access it

• Hydrogen sulfide can be released, which is toxic and can be lethal to humans & animals

Which of these two energy sources is associated with the release of Hydrogen Sulfide, and

why is that an environmental concern?

Geothermal Energy

• Concern because can cause respiratory failure + explosions + flammable