Energy Generation and Storage
Not how electricity is made, but what should power the product in front of you. Reading the constraint out of a brief, then arguing the choice.
Justify the choices, the way you are assessed
Free interactive practice on the decisions the assessment actually asks you to justify.
Start revising freeWhat you'll cover
A different question
A science paper asks how electricity is generated. This one does not. Design and Technology asks what should power the product in front of you, and why that source and not another. The marks live in the *why*. A list of energy sources earns almost nothing; a reasoned choice for a given brief earns the question. So the sources below are worth knowing for what they let you build, not for their own sake.
Where the energy comes from
Know each one by what it means for a designer:
Match each source to what it means for a design
- Solar
- Tidal
- Fossil fuels
- Wind
- can be built into a small product, but the output depends on the light
- can be predicted years ahead, but only works as a large installation
- gives high output on demand, but is finite and high carbon
- costs nothing to fuel, but the output rises and falls with the weather
The first decision
Before any source is chosen, one question settles most of the design: does this product have to work away from a socket?
Which sentence decides it?
Below is a brief from an invented client, written for this module. Tap the sentence that settles how the product must be powered.
- A community garden wants a sign that lights the path after dusk.
- There is no mains supply anywhere on the site.
- The sign should be readable from ten metres.
- The group would like it to look welcoming.
- It must survive being knocked by a wheelbarrow.
What powers the sign?
That garden sign has no mains supply, needs to light the path after dark, and sits outdoors all year. What is the sensible choice?
- A solar cell charging a rechargeable battery during the day
- A solar cell powering the light directly
- A mains supply run out to the sign
- Disposable cells, replaced by a volunteer each month
The five selection factors
Every question on this topic is answered with the same five, so learn them as a checklist: Portability - must it work away from a supply? Power output - can the source deliver what the product actually draws? Circuit and system connections - can it physically connect to what you are designing? Environmental impact - fuel, materials, and what happens at the end of its life. Cost - to buy, and to run over the product's lifetime. Never list all five and stop. Name the one or two that the brief makes decisive, and say why the others matter less here. That is the difference between a describe answer and an evaluate one.
How long will it run?
A product draws a steady 250 mA. It is powered by a rechargeable cell with a capacity of 2000 mAh. For how many hours will it run on one charge?
Order the selection
Put the stages of choosing a power source into a workable order.
- Identify what the product must do, and where it will be used
- Work out the power output it needs, and for how long
- Decide whether it has to work away from a mains supply
- Weigh cost and environmental impact across the options still left
- Check the source can actually connect to the system you are designing
- State the choice, with the factor that decided it
Three products
Three invented briefs. Choose the power source, and notice which factor decides each one.
- A pillar drill for a school workshop, used all day, always in the same corner of the room.
- A safety light worn by a cyclist, used for about an hour on winter mornings and evenings.
- A water-quality sensor left unattended in a river for a month.
Which factors decide it?
For that river sensor, select the TWO selection factors that genuinely decide the answer.
- Portability, because there is no supply anywhere near the site
- Power output and how long it must last between visits
- The appearance of the housing
- The adhesive chosen to assemble the casing
What should power the product
In Design and Technology the question is not how electricity is made, but what should power a _____ product. Mains gives unlimited running time but fixes the product's _____. A battery makes it portable but has a limited _____. The five selection factors are portability, environmental impact, power output, circuit connections and _____. And the marks come from a reasoned argument for the given brief, never from a _____ of sources.
Power the outdoor charging point
A client wants a portable charging point for phones, to be used at outdoor events across a summer, with no mains supply at the sites. Write the argument for the power source you would specify.
- Say which sentence in the brief constrains the choice most, and why
- Name the source and storage you would specify, and how they work together
- Use two of the five selection factors to justify it, and say why the others matter less here
- Give one genuine drawback of your choice, and what you would do about it