lectures 1-2: estimates, energy use, wind, cars

Renewable Energy

Neil Greenham

ncg11@cam.ac.uk

Aims

• To develop the skills to be quantitative about energy generation, storage and use

• Order of magnitude estimates from simple physics • To understand the physics/chemistry/materials science behind some (non-

PV) renewable energy technologies, for example • Hydrogen • Batteries • Biofuels

Absent Friends

• Prof. David MacKay

• Chief Scientific Adviser, Department of Energy and Climate Change (2009-2014)

• Regius Professor of Engineering

The book:

• Available at all good bookshops

• Free online at http://www.withouthotair.com/

Water-Powered Car Might Be Available by 2009

“Forget cars fuelled by alcohol and vegetable oil. Before long, you might be able to run your car with nothing more than water in its fuel tank. It would be the ultimate zero-emissions vehicle. While water is not at first sight an obvious power source, it has a key virtue: it is an abundant source of hydrogen, the element widely touted as the green fuel of the future.”

http://www.newscientist.com/article/mg19125621.200-a-fuel-tank-full-of-water.html?full=true

Nuclear versus Wind

“If we’re going to cut greenhouse gases by 60%, there’s no other possible way of doing that except through renewables” “Anybody who is relying on renewables to fill the energy gap is living in an utter dream world and is, in my view, an enemy of the people “We have a huge amount of wave and wind” “Nuclear is a money pit”

Anne Leslie, Journalist

Sir Bernard Ingham, former press secretary to Margaret Thatcher

Michael Meacher, former environment minister

We need numbers, not adjectives!

What is in the course?

Lectures 1-2 Lectures 5-6

• Estimates • Energy use • Wind • Cars

• Hydrogen • Storage • Batteries

• Heating and cooling • Exergy • Solar thermal

Lectures 3-4

• Energy and charge transfer • Photosynthesis • Biofuels

Lectures 7-8

Rate of energy use of average UK person?

kW kW h day-1

Some answers

NB. Electricity use ~16 kWh/d/person

106

Possible UK renewable energy sources

Some answers

NB. Electricity use ~16 kWh/d/person

103

Realistic renewables?

53 TWh/year = 2.3 kWh/person/day Digest of United Kingdom energy statistics (DUKES)

Current renewables (2013)

Hydro Landfill

Bio PV

Onshore wind

Offshore wind

How many wind turbines does it take to run a car?

Average family car, 33 m.p.g = 12 km per litre

Distance travelled per day: 50 km

Wind turbine diameter: 25 m

Average wind speed: 6 m s-1

Wind

David Cameron’s chimney

Microwind

An Ampair '600 W' micro-turbine.

The average power generated by this micro-turbine in Leamington Spa is 0.037 kWh per day (1.5 W)

Real data – 27 m turbines, Norfolk (‘225 kW’)

Photo by Andrew Dunn Average output (1 turbine): 42 kW

Refinements?

Betz’s law

32

8vdPower πρ= ?

Best power when vafter = vbefore/3

32

8590 vdPower πρ.max =

In practice, more like 0.5 ⇒ 35 kW

Wind power per person in UK?

Spacing ~ 5 times diameter

• Cover 10% of UK

• Population 60m

• Area 244 000 km2

Cars

Where does the energy go?

Why does a car do 33 m.p.g.?

Air resistance?

Acceleration and braking

Efficient transport

• Have small frontal area per person • Have small weight per person • Convert energy efficiently • Go slowly • Go steadily

Solar power per person in UK?

10% of land area

Other people’s sun?

600 km × 600 km, 15 W/m2 ⇒ 1 billion people at 125 kWh/d

145 km × 145 km, 15 W/m2 ⇒ UK population at 125 kWh/d

Just electricity? Each blob 1500 km2

Half filled at 15 W/m2

⇒ 10 GW average per blob

65 blobs ⇒ 1 bn people at 16 kWh/d each

HVDC transmission 2 GW

3.1 GW, 1360 km 1.9 GW, 1420 km

0.7 GW, 580 km

HVDC cables

Finland – Estonia 350 MW in 2 cables Photos: ABB