Solar panels on the roof
Put 2 to 10 solar panels on a roof and choose how many sunny hours a day it gets. See how many kilowatt-hours they make a day and a month, how many LED bulbs that lights for an evening, and how much CO₂ it saves against coal power.
Core concept
Energy = power × time: a 0.4 kW panel in 5 hours of sun gives about 0.4 × 5 × 0.8 = 1.6 kWh, after the losses of heat, dust and wiring
Topic: Energy and technology
A solar panel turns sunlight into electricity. Its rating, say 400 W (0.4 kW), is the power it gives in full, bright sun. energy: What is needed to make things move, heat up, light up or grow. All key words is power × time, so a 0.4 kW panel working for 5 hours could give 2 kWh, the unit on an electricity bill. In real life heat, dust, cloud and the wiring take away about a fifth, so we use 80% of that: 1.6 kWh a panel. More panels or more sunny hours give more energy. A 10 W LED bulb lit for 5 hours uses 0.05 kWh, and every kWh made by the sun instead of a coal power station keeps about 0.82 kg of carbon dioxide out of the air.
What you will learn
- Use energy = power × time to find the kWh a solar roof makes.
- Explain why real panels give less than their rating.
- Compare the energy with what LED bulbs use and the CO₂ it saves.
Before you start
- Know that power is measured in watts and energy in kilowatt-hours (kWh).
Materials
- An electricity bill (to see the kWh your home uses in a month)
Equipment
- None
Procedure
- Record the starting roof: 4 panels and 5 sunny hours.
- Put 10 panels on the roof and record.
- Change the sunny hours to 4 and then 6, and record each.
How this simulation is simplified
- Each panel is rated 400 W (0.4 kW) and gives 80% of its rating over the sunny hours.
- A 10 W LED bulb lit for 5 hours uses 0.05 kWh; a month is 30 days.
- Coal power gives about 0.82 kg of CO₂ for each kWh.