This document discusses options for more sustainable energy sources, including exploiting solar energy through photovoltaics, water heating, and building design. It also covers geothermal energy through ground source heat pumps, as well as wind, biogas, and reducing emissions through low-carbon technologies. While renewable sources have potential, each also has limitations to provide energy at scale.

1. Options for energy
sustainability

2. The outline of the problem
• Human activities often require energy
– Power for equipment
– Power for lighting
– Heating for thermal comfort
– Hot water for hygiene
– Cooling in hot weather
• All require external supplies of energy
• Majority of external energy comes from
non-renewable sources - fossil fuels

3. What are fossil fuels?
• All “fossil” fuels are a product of ancient
biological activity
• Living plants capture and fix carbon dioxide
(CO2) and water (H2O) as hydrocarbons
through photosynthesis
– Solar energy is converted to chemical energy,
stored in the hydrocarbons
• All life depends on this process and it also
releases oxygen (O2)
• Ancient plant and animal remains have been
preserved, in some cases, as fossilised
hydrocarbons – fossil fuels

4. Oil and gas: fluid fossil fuels

5. Coal and peat: solid fossil fuels

6. What are the problems with using fossil fuels?
• They are finite resources which will
eventually run out - sustainability?
– There are vast reserves of coal but other
fossil fuels are beginning to run out already
• Burning fossil fuels (combining a
hydrocarbon with oxygen) to release the
stored chemical energy as heat
reverses the photosynthetic process:
Input: methane CH4 + 2O2 >> CO2 + 2H2O Output: carbon
and oxygen dioxide, water and
heat
Heat energy released

7. Why is carbon dioxide (CO2) a problem?
• Carbon dioxide (CO2) is essential for life
and maintenance of life supporting
temperatures, but…
• An increase in atmospheric carbon
dioxide could lead to significant global
temperature rises through the
“greenhouse effect” which will disrupt
human societies
– Rising sea levels - flooding
– Changes in agricultural systems
– Changes in water supply

8. What is the greenhouse effect?
CO2

9. What is the greenhouse effect?
CO2 in atmosphere does not
let long wave infrared (IR)
radiation through
LWIR
CO2

10. What is the greenhouse effect?
CO2 in atmosphere does not
let long wave infrared (IR)
radiation through
LWIR
CO2
SWIR

11. What is the greenhouse effect?
CO2 in atmosphere does not
let long wave infrared (IR)
radiation through
LWIR
CO2
SWIR
The Earth, warmed by short
wave IR, emits long wave IR
which cannot escape through
the CO2 in the atmosphere.
There is a one way traffic in
energy input  temperatures
rise

12. Reducing CO2 emissions aka low carbon technologies
• Use renewable, non-finite energy
sources:
– Direct solar radiation
– Geothermal energy
– Hydro electric power
– Tidal power
– Wind
– Biogas
– Nuclear energy
• Design buildings to make best use of
environmental energy

13. Reducing CO2 emissions aka low carbon technologies
• Use renewable, non-finite energy
sources:
– Direct solar radiation
– Geothermal energy
– Hydro electric power
– Tidal power
– Wind
– Biogas
– Nuclear energy
• Design buildings to make best use of
environmental energy

14. Designing to use the Sun
• Solar energy can be exploited three
ways
– Photo-voltaic electricity generation
– Water heating
– Direct solar heating of the building fabric
• The last two make direct use of the
greenhouse effect themselves

15. Photo-voltaic electricity generation
• Light photons fall on
“photo-cells”, displacing
electrons and thus
generating a current
• Efficiency low and cost
high
• Pay back periods only
economic due to
government sponsored
“feed in tariffs”
• They don’t work in the
dark
• Energy very difficult to
store

16. Solar Water heating
• Black painted water pipes under glass are
heated by direct solar radiation using the
greenhouse effect
• Pay back still very long in UK climate but
should become standard fitting on all new
houses.

17. Direct solar heating of the building fabric
• Exploit solar energy to the maximum
– Consider building orientation
– Exploit the greenhouse effect for building
heating
– Control excessive solar heating through
shading
– Store day time solar heat in mass
construction for night time use

18. Orientation: the sun is in the south…
• Position building and locate
windows to maximise solar gain.
• Build heavy masonry walls to
store the heat to re-emit during
the night

19. Orientation: the sun is high in summer, low in winter

20. Orientation: the sun is high in summer, low in winter

21. Orientation: the sun is high in summer, low in winter

22. Orientation: the sun is high in summer, low in winter

23. Orientation: the sun is high in summer, low in winter

24. The Brise soleil

25. Geothermal energy for individual buildings
• High temperature geothermal energy
– Dependent on hot rocks close to the
surface
– Not viable in the UK but used intensively in
Iceland
• Low temperature “ground source” heat
– Exploits the temperature differences
between the atmosphere and the sub-
surface ground
– Concentrates low quality heat using “heat
pump” technologies

26. Ground source heat
• UK air temperature
varies between
-10 and +30ºC
-10ºC>+30ºC
• 1.5 metres below
ground the
temperature is
constant around
10ºC 1.5m
• This temperature 10ºC
difference can be constant
exploited for heating temp
or cooling.

27. Simplest ground source heating
• Build underground; earth sheltered houses

28. Technical exploitation of ground source heat
Small coiled pipe full of
• “Pump” the heat to refrigerant fluid in the
building
the surface
Pump and valve
• To be effective, air- form the “heat
conditioning pump” which
technology must be concentrates the
heat
exploited, in
reverse. 1.5m
• “Heat pumps” 10ºC
concentrate low constant
temp
grade heat to get Large coiled pipe
full of refrigerant
higher temperatures fluid in the ground

29. Wind energy
• Wind generation of
electricity is
renewable and non-
polluting (when
generating) but…
• It is intermittent
– Where do you get
power from when it is
not running?
• It is highly
dependent on high
wind speeds

30. Is there enough wind energy to be practically useful?
• The theoretical energy output is
proportional to the wind speed cubed
– If the wind speed doubles, the theoretical
energy output goes up eight times (2x2x2)
– If the wind speed halves, the theoretical
output falls to an eighth (2/2/2)
• High steady wind speeds are needed
for useful energy generation
• Domestic scale installations in lowland
areas simply cannot deliver useful
quantities of energy.

31. Biogas generated from waste
• Fermenting organic
waste generates
methane, a main
constituent of natural
gas.
• Digesting farm waste
generates gas and solid
residue is a good
fertiliser
• Food waste can be
digested in urban
locations to generate
biogas and reduce
quantity of waste
• Gas can be burned to
generate electricity or fed
directly into the gas
supply network

32. Summary
• Solar energy can be exploited for
heat/hot water, but electricity generation
is still in its infancy.
• Wind power is ineffective at domestic
scale
• Significant quantities of environmental
energy can be harvested through good
building design
• Biogas generation can potentially
provide fuel or energy, but needs to be
fairly large scale to be significant.