Renewable energy sources like wind turbines, solar panels, and heat pumps provide alternatives to fossil fuels but have some limitations. Wind turbines have low capacity factors of 0.25-0.4 and require high upfront costs of £30,000 for a 6kW system. Solar panels cost £2,000-£4,000 installed for a house and save around £60-£92 per year in electricity bills. Photovoltaic solar cells have high costs of 60-70p/kWh currently and may not be cost competitive with retail electricity until after 2025. Ground source heat pumps can provide efficient heating but require extensive piping installed underground that may have long term temperature effects on the soil.

1. Renewable Energy
A short (and cynical) approach
Stephen Beck

2. Types of Energy
The total energy in a system may comprise all or a
combination of the following:
potential energy - mgh
kinetic energy - ½ mv
2
static pressure - pressure x volume (pV)
internal energy - u
heat - energy transfer due to temp difference
work - integral force with distance
They all have units of Joules (J)

3. HEAT
Heat is the form of energy that is transferred
between two systems (or a system and its
surroundings) by virtue of a temperature
difference.
The amount of heat transferred into a given
system during the process between two states
is denoted by the symbol Q ( kJ).

4. WORK
Work is the energy transfer associated with a force
acting through a distance
The amount of work done by a system is known as
W (kJ)
The base unit of work in the SI system is the
Newton metre (Nm)
1 Nm is also known as 1 joule (J)
(Due to the scale involved in the real world, the kJ (1000 J)
is usually used)

5. The first Law of Thermodynamic
As these are all the energies that we must
consider, we can change between them.
The energy between the beginning and end, and
the heat and work can be added up:
Energy = Heat in - Work out
= change in Potential Energy +
change in Kinetic Energy +
change in Internal Energy +
change in (Pressure Volume)
OR
Q W 1 m C2 C12
2
mg ( z2 z1 ) m(u2 u1 ) p2V2 p1V1
2

6. Energy exchange processes

7. The second law of
thermodynamics.
Imagine a flywheel spinning in an insulated
box that is filled with gas.
Flywheel Flywheel
State B: Flywheel
State A: Flywheel
Stationary, gas
spinning, gas cool
warm

8. Work into heat, or heat into
work?
Is it better to heat something up with a spinning
flywheel or with a gas heater? Producing the
work to get the flywheel going is difficult.
Flywheel
Gas
Heater

9. Some Equations for Entropy (i)
There is entropy increase associated with
heat transfer, and friction, but not with work.
Entropy decreases when a system is cooled
Entropy increases when heat is added to a system.
Thus, entropy increase implies either Heat Input or an
Irreversible Process (due to friction).
The total entropy change is thus made out of the
entropy change due to the irreversibility and that due
to the heat transfer:
Q
S S irrev
T

10. Some Equations for Entropy (ii)
There is also entropy increase associated
Disorder
Boltzmann
S k log W
where k = 1.38×10−23 J K−1 and is Boltzmann's
constant and W is the frequency of occurrence of a
macrostate, the number of (unobservable) ways the
(observable) thermodynamic state of a system can be
realized by assigning different positions and momenta
to the various molecules. In other works, the
complexity of the system.

11. Let’s see what it means
There is a lot of information going around
about renewable energy, putting in a few
numbers helps us to understand what it really
means.
Here are a few examples.

12. •Basically: W A 1
v3
2
Expected energy output per year can Wind
be reliably calculated when the wind
turbine's capacity factor at a given
average annual wind speed is known.
The capacity factor is simply the wind
turbine's actual energy output for the
year divided by the energy output if the
machine operated at its rated power
output for the entire year. A reasonable
capacity factor would be 0.25 to 0.30. A
very good capacity factor would be
0.40.
http://www.awea.org/faq/basicen.html

13. Do the Cameron
• B and Q Windsave Wind
Turbine System -
WS1000PS T2 £1498 1KW
at 12.5 m/s (30MPH)
• Expected Safe Life:10 years
(depended upon actual
conditions the system has
been subjected to)
http://www.diy.com/diy/jsp/bq/nav/nav.jsp?action=detail&fh_secondid=9330400&fh_
search=wind&fh_eds=%c3%9f&fh_refview=search&ts=1174393542806

14. Dear editor
• Mine was installed on 27th November, and after
10 weeks it has produced only 48 kW despite
being mounted on the gable end apex of my
house with uninterrupted winds from the SW.
The variable low frequency drone can be heard
throughout the house. In gusty conditions the
stair rods rattle. I have estimated my pay-back
time at around 50 years. Needless to say, I will
be contacting Windsave for an explanation.
http://www.bettergeneration.co.uk/wind-turbine-models/the-windsave-ws1000.html

15. Financial benefits?
At the rate the is
delivering power at our
test site, it would take
several millennia for the
product to pay for itself in
savings—not the 56
years it would take even
with the 1,155 kWh
quote we received.
http://savonius-balaton.hupont.hu/128/wind-tronics-inc-canada
http://www.masterresource.org/2012/08/microwind-consumer-reports/

16. Cost and payback
• 6KW Proven about £30K
Site Average Wind 4.0 5.0 6.0 7.0 8.0 9.0
Speed m/s
mph 9.0 11.2 13.4 15.7 17.9 20.2
Av. Yearly Energy 6,765 11,622 16,900 21,944 26,216 29,467
Output (kWh)
Saving (12p/kWh) £812 £1,395 £2,028 £2,633 £3,146 £3,536
current costs for onshore wind in good sites
are in the region of from 2.5–3.0 p/kWh
http://www.solarwindworks.com/Products/Wind_Turbines/Proven/Proven_Output/proven_output.htm
http://www.esru.strath.ac.uk/EandE/Web_sites/01-02/RE_info/photovoltaics.htm

17. Solar panels
• Get hot water
Clear Cover plate
Air space
Black Absorber
Plate
Circulating Fluid
Insulation

18. Cost of Solar Panels
• The cost of a commercial flat plate
system, including installation, for an 'average'
house ranges from about £2,000 to £4,000.
• Paul Jones of the EST says the average
saving on electricity bills would be roughly £60
to £92 a year, though he stressed that this is
"dependent on property and usage". This does
not sound a great deal of money, so it seems
the only real reason to install the system is for
environmental purposes.
http://www.cat.org.uk/information/catinfo.tmpl?command=search&db=catinfo.db&eqSKUdatarq=20020210164613
http://news.bbc.co.uk/2/hi/programmes/moneybox/2002080.stm

19. Photovoltaics
• Convert photons directly
into electricity
• Efficiency 4-20%
www2.northumberland.gov.uk/reports/nreg/about.asp

20. Photovoltaics - cost
• BRITISH PV ASSOCIATION say that PV
technology has a long way to go before
establishing itself competitively with
conventional electricity and other Renewables.
Photovoltaic technology costs typically range
from 60-70p/kWh and is viewed by the
government as a long term project with
anticipated price by 2020 of 10–16 p/kWh, with
the possibility of becoming cost competitive with
retail electricity in the UK around 2025.
http://www.esru.strath.ac.uk/EandE/Web_sites/01-02/RE_info/photovoltaics.htm

21. Cost of Solar PV
http://blogs.scientificamerican.com/guest-blog/2011/03/16/smaller-cheaper-faster-
does-moores-law-apply-to-solar-cells/

22. Feed in Tariff
• Don’t even get me started on this…
• Too late!
• These were too high (46p per kWh) and
turned into a scam. The Fit should reflect
the price.
• Dropping 23p per kWh April 2012 (now
15.44p per kWh).

23. Ground
Source
Heat pumps
Underground temperatures
at the Royal Edinburgh
Observatory, average
1838-1854 (after data from
Everett, 1860)
As can be seen from measurements dating as
far back as to the 17th century, the
temperature below a certain depth (neutral
zone, at about. 15-20 m depth) remains
constant over the year. Without extraction!

24. Horizontal heat recovery
For the ground heat
collectors with dense
pipe pattern, usually
the top earth layer is
removed
completely, the pipes
are laid, and the soil
is distributed back
over the pipes.

25. Vertical heat recovery
The need to install
sufficient heat
exchange capacity
under a confined
surface
area, favours
vertical ground heat
exchangers
(borehole heat
exchangers).

26. Some pictures
Trenching for horizontal coils
Drilling holes for
vertical piles

27. Some pictures
Spiral collectors
Coils in trench

28. Some pictures
Domestic pump Under floor heating
unit

29. Long term problems
Measurements and simulations can
visualise the temperature development
during operation as well as the
thermal
recovery
after
operation:

30. The Useful heat
COPHP
Performance of a Work input
Heat Pump
As well as moving
COP times the amount
of heat that was put
into the compressor as
work, the amount of
heat that will end up in
the house is one more
than this: COPHP COPR 1

31. Coefficient of Performance (COP)
For refrigeration systems we define how good
they are by how much heat (Watts) can be
moved from a cold place to a warm one for each
Watt (electricity generally) work input.
Useful heat
COPHP
Work input
The maximum COP is limited by the second
law of thermodynamics such that
Th
COPHP (max)
Th Tl
Where Th and Tl are the top and bottom
temperatures of the cycle in Kelvin

32. Typical COP values for a GSHP
system
• Under floor and hot air heating
(35 C), COPHP = 4
• Low temperature radiators (45 C) COPHP = 3
• Hot water (65 C) COPHP = 2.5

33. Air Source Heat pumps
• The idea is the same, but instead of the
heat coming from the ground, it is
extracted from the air.
• This is similar to an air conditioner run in
reverse.

34. Outside heat exchanger
http://www.flickr.com/photos/goins/2484039387/

35. ASHP Typical COP values
Due to engineering issues and heat transfer,
real COP’s are much lower.
• Under floor and hot air heating (35 C), from
air at -10 C COPHP = 3 (3.5)
• Hot water (65 C) from air at 0 C COPHP = 2.0
• Conventional Radiators(75 C), from air at -
10 C COPHP = 2 (1.5)
There are also issues about condensation etc.

36. Getting the electricity (I)
If the electricity is produced burning fuel, there is
an inherent inefficiency in conversion, limited by
the second law of thermodynamics.
Th Tl
Th
Where Th and Tl are the top and bottom
temperatures of the cycle in Kelvin
Typical conversion rates ( ) vary from 30% for
open cycle gas turbine systems through 42% for
coal fired plant to 53% for the latest gas fires
combined cycle stations.

37. Getting the electricity (II)
As the GSHS system needs electricity for
run, this needs to be taken into account.
It will be seen that savings are possible, but
this needs to be taken into account.
If however, the electricity is produced using
renewable resources (hydro, wind) then
will be unity and the energy savings far
greater. We will be getting far more heat
than we are putting in as primary energy.

38. Getting the electricity (III)
1
Proportional saving 1
COPR 1
COPHP of GSHS
2 3 4 5
0.3 -0.67 -0.11 0.17 0.33
0.4 -0.25 0.17 0.38 0.50
0.5 0.00 0.33 0.50 0.60
1 0.50 0.67 0.75 0.80

39. So
• If you need to heat by electricity, then this
is better that resistance heaters.
• However in cold weather, you’re better off
with a gas system,
• Or why not…

40. Biofuels or Biomass
• Burning fossil fuel releases locked in CO2..
• If you grow something, burn it and replant
it then this is a renewable.
Typical Fuels
• Straw
• Willow
• Pellets
• Offcuts.

41. Typical
biomass
boiler Boiler
Heat
exchanger
Rotation
combustio
n chamber
Moving
grate Primary
air valve
De-asher
Feed screw
Biofuel Boiler

42. Costs
Capital costs depend on the type and size of
system you choose. Stand alone room heaters
generally cost £1500 - £3000 installed. A typical
20kW (average size required for a three-
bedroom semi-detached house) pellet boiler
would cost around £5000 installed, including
the cost of the flue and commissioning.
Running costs: Unlike other forms of renewable
energy, biomass systems require you to pay for
the fuel. This is a bit cheaper than oil, and gas.
http://www.est.org.uk/myhome/generating/types/biomass/

43. But
―Environmentalists are also concerned at new
subsidies for burning wood pellets in power
stations. They say the huge scale of imported
wood is unsustainable.
Oxfam's policy adviser Tracy Carty said the MPs'
decision made no sense because it would only
increase the burning of harmful biofuels in UK
power plants.
"Biofuels, like palm oil, produce more carbon
emissions than they save, fuel land grabs and
increase global food prices," she said.‖
http://www.bbc.co.uk/news/science-environment-21692673

44. The Rankine Cycle.
Invented in the late 19th century, this is a cycle
that uses steam to run.
Steam engines, coal and early nuclear power
stations used this

45. Q in
The four 1 Boiler (A) 2
processes W out
are: W in
Pump
Turbine
(B)
(D)
Condenser
4 (C) 3
T Q out
1a A
2
TH
A) Heat addition at
1 B constant pressure in a
TL
D C boiler from the
4 3
compressed water
region to the saturated
s vapour point

46. The four
processes
are:
T
1a A
2
TH
B) An isentropic
1 B expansion in a turbine
TL
D C from the saturated
4 3
vapour line to the wet
region (Q = 0, S =
s 0), (2-3).

47. The four
processes
are:
T
1a A
2
TH
C) Heat removal in a
1 B condenser from the
TL
D C wet region to the
4 3
saturated liquid point
(W = 0, P = 0), (3-4).
s

48. Power station condensers.
http://www.flickr.com/photos/freefoto/3844250043/sizes/l/in/photostream/

49. The four
processes
are:
T
1a A
2
TH
D) An isentropic
1 B compression using feed
TL
D C pumps from saturated
4 3
liquid point to the
compressed water region,
s (Q = 0, S = 0), (4-1)

50. Getting the electricity (I)
Once again the efficiency is limited by the second
law of thermodynamics
Th Tl
Th
Where Th and Tl are the top and bottom
temperatures of the cycle in Kelvin
Typical conversion rates ( ) vary from 30% for
open cycle gas turbine systems through 42% for
coal fired plant to 53% for the latest gas fires
combined cycle stations.

51. Combined heat and power
• Basically an electricity generator that uses
its hot exhaust gases to heat buildings and
processes.
• Total energy use varies from 70-90%
http://www.bartonwillmore.co.uk/townplanning/project_sheet.asp?id=61

52. Power and fuel
Cycle Engine Fuel Exhaust Temp. ( C) Power
Diesel Internal Oil/biodiesel 400 50-200kW
combustion
Brayton Gas turbine Oil/gas 600 5-100MW
Rankine Steam turbine Anything 100 50-2000MW
25-02-2002
A team of Greenpeace volunteers
today shut-down and occupied
Britain’s ―flagship‖ waste incinerator
in south London to protect the
health of Britain’s children.
http://www.greenpeace.org.uk/contentlookup.cfm?
CFID=1044260&CFTOKEN=&ucidparam=20020225085523&MenuPoint=G-A

53. Building Insulation
As well as looking at ways of
acquiring energy from renewable
resources, let’s look at where the heat
goes

54. Conduction is heat transfer Conduction
through a material due to a heat transfer
heat difference between its
two surfaces it is:

Q U A(T2 T1 ) (W), where
T1 - T2 (or T) is the
temperature difference
between the two surfaces,
A, is the surface area
UA is the conductance
(W m-2 C-1).

55. Conduction through multiple
materials.
With two or more
T1 materials, the temperature
drops linearly through
each material from the hot
side to the cool side.
T2 The gradient of the
temperature drop is
greater through a poor
conductor.

56. Conduction through multiple
materials.
1
The U in the conduction heat transfer
equation can be equated to a thermal
resistance for the wall.
1 da db dc
....
U ka kb kc
where
U = Heat transfer coefficient (W m-2 C-1)
d = Thickness of each of the materials (m)
k = Thermal conductivity of material (W m-1 C-1)

57. Thermal conductivity at 25 C
-3
Material Thermal conductivity Density (kg m )
-1 -1
(W m C )
Air (stationary) 0.0263 1.2
Aluminium Alloy 170 2780
Brick, common 0.72 1920
Concrete 1.4 2300
Concrete block 0.67 -
Glass 1.4 2500
Glass fibre 0.036 105
Plaster 0.22 1680
Plywood 0.12 545
Polystyrene, expanded 0.027 55
Steel, mild 61 7854
Vermiculite flakes 0.063 80

58. Insulation Values

59. Insulation Values

60. Payback periods (very approx)
Effect Cost Payback
Filling cavity walls £400 3 Years
Double glazing £4000 50 years
Roof insulation £400 2 Years
Low energy light 99p 4 months
bulb

61. Payback periods (very approx)
Effect Cost Payback
Filling cavity walls £400 3 Years
Double glazing £4000 50 years
Roof insulation £400 2 Years
Low energy light 99p 4 months
bulb
Wearing jumper £20 (lower thermostat) 4 months

62. The end
news.bbc.co.uk/2/hi/uk_news/scotland/2224466.stm