5.4: supply energy sustainably

it is widely recognised that there is a need to.

• optimise efficiency of energy conversions

• reduce fuel consumption & pollutant emissions

what can be used as an alternative energy source to fossil fuels?

biofuels (fuels from plant or organic waste)

• produces less greenhouse gas emissions

limitations of biofuels

• manufactured from crops - using land that would otherwise be used for food production for people & animals

• fossil fuels are likely to be only partially replaced by bioethanol & biodiesel

• biomass used as solid biofuel is inedible & doesnt contribute to food shortages & higher food prices BUT the fuel produced is of low quality that doesn’t produce much energy when burned (methane content significantly lower)

energy supplies need to be:

• sustainable

• minimise CO2 emissions

efficiency of:

• fuel cell

• thermal power stations

• car engines

• fuel cell: 85%

• thermal power stations: 30-40%

• car engines: 25-30%

why are fuel cells more efficient and how is it better?

• single energy transformation (chemical energy → electrical energy), whereas multiple transformations in power stations and internal combustion engines

• substantially lower greenhouse gas emissions

fuel cells can be designed to use which fuels & which fuel is the most popular

• natural gas

• methanol

• ethanol

• ammonia

• HYDROGEN - most popular

hydrogen economy

• fuel cells as replacement for internal combustion engine

hydrogen economy plans

• currently → hydrogen produced by fossil fuels

• if → source of hydrogen were renewable, energy supplies would be more sustainable, drastic reduction in greenhouse gas production and other pollutants without affecting quality of life

development of hydrogen-based fuel cell technologies

• commercial products powered by fuel cells are more widely available and utilised

• increased global resolve to limit climate change

how is hydrogen fuel cell ‘zero emission’

• water is almost the only product apart from electricity and heat

• BUT unless hydrogen fuel is produced with renewable energy, this can result in significant levels of greenhouse gases and otther pollutants

process of hydrogen production from fossil fuels + steam reformming

• ex) natural gas, oil, coal

• process of steam reforming → steam reacts with fossil fuel at high temperatures in presence of nickel catalyst

disadvantages of steam reforming

• hydrogen produced has lower energy content than original fuel

• original chemical energy of these exothermic reacttions is lost as waste heat during producttion

• leads to CO2 emissions

advantages of steam reforming

• as CO2 is produced at site of process, greenhouse gas could be captured and stored, preventing release to atmosphere

• lower cost

2 methods of generating hydrogen susttainably

• using electricty to convert water to hydrogen:

  • electricity generatted from renewable sources such as solar-power farms and wind farms

• collecting biogas from landfill sites & converting methane in the gas to hydrogen by stteam reforming

green hydrogen costs

• hydrogen sources from renewable sources is the most desirable method of production

• energy produced from hydrogen would be sustainable

• costs twice as much as hydrogen from coal and natural gas

hydrogen supply storage

• hydrogen has a very high energy content by mass compared to fuels like petrol

• gas at room temperature

  • established methods for storage in cars is as liquid/compressed hydrogen

  • energy per litre of liquid is much less than that of a petrol → hydrogen vehicle needs larger fuel tank

hydrogen safety

• poses safety challenges

• highly flammable and potenially explosive

• hydrogen sensors to detect leaks

fuel cells likely to have criticalrole in:

• renewable energy

• energy storage

• energy management

• greenhouse gas reduction

elements of fuel cells that need to be developed and optimised

• electrode materials

• electrolytes

• cost

• energy storage

• safety

• lifetime

• performance

renewable energy sources such as…

solar and wind will play an increasing role in the supplly of energy

development of new battery and fuel cell technologies is

• part of move from linear to circular economy

microbial fuel cell (MFC)

• converts organic material to electrical energy by the action of microorganisms

• microorganisms form a film on the surface of the anode and oxidise organic material (producing CO2, protons and electrons)

• microorganisms then transfer electrons to the anode of the fuel cell

• cathode reaction use a variety of oxidants (often O2)

MFC anode cathode reactions

MFC advantages

• operate at or near room temperature

• can use low-grade waste materials

  • soil

  • sediment

  • wastewater

  • agricultural waste

• used for sustainable wastewater treatment and contaminant removal & generating low-power electricity