hands-on energy and climate projects in schools chris waltham ubc physics & astronomy 2015.10.23

Hands-on Energy and Climate Projects in Schools

Chris WalthamUBC Physics & Astronomy

2015.10.23

A large fraction of the energy we use is in the form of electricity; this has to be made from some other form of energy:

• Fossil fuels (burn)→ Heat (boiler) → Kinetic energy (turbine) → Electricity (generator)

• Biomass (burn)→ Heat (boiler) → Kinetic energy (turbine) → Electricity (generator)

• Hydro (solar/rain)→ Potential energy (dam) → Kinetic energy (turbine) → Electricity

• Wind (air flow) → Kinetic energy (turbine) → Electricity (generator)

• Solar (light) → Electricity (photovoltaics)

• Waves (solar/wind)→ Potential/kinetic energy (waves) → Kinetic energy (turbine) → Electricity (generator)

At each step energy is “lost” to heat

Background: Electricity Generation

Energy (J)

= Force (N) Distance (m) (Mechanical)

= Potential difference (V) Charge (C) (Electrical)

Background: Electricity Generation

Revisit: energy definition and foundation of SI units

Power (W)

= Force (N) Velocity (m/s) (Mechanical)

= Potential difference (V) Current (A) (Electrical)

Circumference of circle 20 cm

Period of revolution 2 s

Force 1 N (9.81 kg weight)

Mechanical Power = 0.2 W = 100 mW

Voltage reading = 0.5 V

Current reading = 100 mA

Electrical Power (heats load resistor) = 50 mW

Electrical conversion efficiency = 50 mW / 100 mW = 50%

Tactile! Feel what a newton is like, what 100 mW of output is like

Activity: Hand Crank Exercise

Using the geared motor as a generator and the supercapacitor for storage, students can feel the resistance to turning the generator when the supercap is connected into the circuit.

Beyond formal curriculum:

Air density, ≈ 1.2 kg/m3

So a swept area () of 0.1 m2 and a wind velocity of 3 m/s cannot produce any more power than 1 W.

You’ll be lucky if your turbine produces 100 mW.

Background: Wind Turbines for Energy

Sun → Heat → Linear kinetic energy of air

→ Rotational kinetic energy of blades/turbine → Electrical energy

How?

Factors that affect amount of power generated

Activity: Constructing a Wind Turbine

Similarly, water...?

Measure electrical output (simple voltage reading at lower grade levels)

Optimize blade configuration: possible at all grade levels

Optimize gear configuration (higher grade levels)

Optimize load (higher grade levels)

Hotter things radiate at smaller wavelengths, and vice versa

At 6000 K (e.g. the Sun’s surface), the peak power wavelength is 500 nm, middle of the visible range (green)

At 300 K (e.g. the Earth, us), the peak power wavelength is 10 μm, in the thermal infrared

i.e. 20 x the temperature, the peak power wavelength goes down by a factor 20

Background: Electromagnetic radiation

Anything with a non-zero temperature radiates electromagnetic energy with a broad spectrum

An infrared thermometer works by measuring the intensity of emitted thermal infrared

Activity: Playing with Infrared Thermometers

• Asphalt

• Grass

• Wet things

• Trees

• Car windows

• The sky

• Exterior of buildings

• Low-e glass

Environmental Measurements

Most dramatic variations on clear-sky days/nights

Learn how to collect data and produce a map

Background: The Greenhouse Effect

http://barrettbellamyclimate.com/page15.htm

Radiation from Sun and Earthmsemac.redwoods.edu

What gets throughour atmosphere

Activity: Measuring Passive Solar Heating

Use probe thermometers

Observe the temperature of small cubes of various colours and transparency exposed to direct sunlight

Need to take some care with experimental design

Watch the sky

Plot data as a function of time

Light → Electricity

Optimize power generated by photocell

Compare indoor and outdoor lighting levels

Activity: Photovoltaics and Lighting

Electricity → Light

Use kill-a-watt meter to show power requirements of various (household) light bulbs

Use hand-crank activity to estimate comparative efficiencies of small low-voltage light bulbs

Light → Electricity → Light

Use photocell to light a small bulbNote efficiency (qualitatively)