Energy Storage Systems & Batteries

This lesson examines how energy is stored, with a focus on battery technologies and their application in modern products. Energy storage is covered in AQA GCSE Design and Technology (8552), Section 3.1.2, and is increasingly important as renewable energy and portable electronics grow.

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Why Is Energy Storage Important?

Many renewable energy sources (wind, solar) are intermittent — they produce electricity only when the wind blows or the sun shines. Energy storage systems capture excess energy when supply exceeds demand and release it when demand exceeds supply.

For portable products (smartphones, laptops, electric vehicles), batteries enable operation without a mains connection.

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Types of Batteries

The diagram below classifies the main battery and energy-storage technologies covered in AQA D&T:

graph TD
    ES["Energy Storage"] --> BAT["Batteries"]
    ES --> OTHER["Other Technologies"]
    BAT --> P["Primary Cells\n(non-rechargeable)"]
    BAT --> S["Secondary Cells\n(rechargeable)"]
    P --> P1["Zinc-carbon, Alkaline,\nLithium primary, Silver oxide"]
    S --> S1["NiCd, NiMH"]
    S --> S2["Li-ion, LiPo"]
    S --> S3["Lead-acid"]
    OTHER --> O1["Pumped hydro, Flywheel,\nCompressed air, H2 fuel cells,\nSupercapacitors"]

Primary Cells (Non-Rechargeable)

Primary cells produce electricity from a chemical reaction that is irreversible. Once the chemicals are used up, the battery must be disposed of.

Type	Voltage	Common Uses	Notes
Zinc-carbon	1.5 V	Torches, remote controls, clocks	Cheapest; shortest lifespan
Alkaline	1.5 V	Toys, cameras, portable radios	Longer life than zinc-carbon; most popular disposable battery
Lithium primary	3.0 V	Smoke detectors, medical devices, watches	Very long shelf life (up to 10 years); lightweight
Silver oxide	1.55 V	Watches, hearing aids, calculators	Small button/coin cell format

Secondary Cells (Rechargeable)

Secondary cells use a reversible chemical reaction. When connected to a charger, the chemical reaction is reversed, restoring the battery's charge.

Type	Voltage per Cell	Energy Density	Common Uses	Notes
Nickel-cadmium (NiCd)	1.2 V	Low	Older power tools, emergency lighting	Suffers from "memory effect"; cadmium is toxic
Nickel-metal hydride (NiMH)	1.2 V	Moderate	AA/AAA rechargeable cells, older hybrid cars	Better than NiCd; no toxic cadmium
Lithium-ion (Li-ion)	3.7 V	High	Smartphones, laptops, electric vehicles, drones	Lightweight; no memory effect; dominant technology
Lithium-polymer (LiPo)	3.7 V	High	Thin devices (tablets, smartwatches)	Can be made in very thin, flexible shapes
Lead-acid	2.0 V	Low	Car starter batteries, UPS systems	Heavy; cheap; very reliable; recyclable

AQA Exam Tip: You are most likely to be asked about lithium-ion batteries because they dominate modern consumer electronics. Know their key advantage (high energy density, lightweight) and key disadvantage (risk of thermal runaway/fire if damaged, finite lithium resources).

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Key Battery Terminology

Term	Meaning
Voltage (V)	The electrical pressure or "push" provided by the battery
Capacity (mAh or Ah)	How much charge the battery can store — higher = longer runtime
Energy density	The amount of energy stored per unit of mass (Wh/kg) — higher = lighter for the same capacity
Cycle life	The number of charge/discharge cycles before capacity drops significantly
Self-discharge	The rate at which a battery loses charge when not in use
Memory effect	A phenomenon (mainly NiCd) where partial discharge cycles reduce maximum capacity over time
Thermal runaway	A dangerous condition where a battery overheats uncontrollably, potentially causing fire

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Energy Storage Beyond Batteries

Technology	How It Works	Application
Pumped-storage hydroelectric	Excess electricity pumps water uphill to a reservoir; water is released through turbines when demand rises	Grid-scale energy storage (e.g. Dinorwig, Wales)
Flywheel	A heavy wheel is spun at high speed, storing kinetic energy; the energy is recovered by slowing the wheel	UPS systems, Formula 1 KERS
Compressed air	Excess electricity compresses air into underground caverns; the air is released to drive turbines	Grid-scale storage (e.g. Huntorf, Germany)
Hydrogen fuel cells	Electricity splits water into hydrogen and oxygen (electrolysis); hydrogen is stored and later recombined in a fuel cell to produce electricity	Buses, cars (Toyota Mirai), backup power
Supercapacitors	Store energy electrostatically (not chemically); charge and discharge almost instantly	Regenerative braking, camera flash, rapid-charge devices

Hydrogen Fuel Cells

A hydrogen fuel cell converts hydrogen and oxygen into electricity, with water as the only by-product. This makes it a zero-emission technology at the point of use.

Advantage	Disadvantage
Zero emissions at point of use (only water)	Producing hydrogen often uses fossil fuels (unless electrolysis is powered by renewables)
High energy density	Hydrogen is difficult to store safely (high pressure or very low temperature)
Quick refuelling (minutes, not hours)	Hydrogen refuelling infrastructure is very limited
Quiet operation	Fuel cells are expensive to manufacture (platinum catalysts)

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Batteries and Product Design

When selecting a battery for a product, designers consider:

Factor	Consideration
Size and weight	A wearable device needs a small, lightweight battery (Li-ion or LiPo)
Runtime	Higher capacity (mAh) = longer use between charges
Rechargeability	A product used daily should have a rechargeable battery to reduce waste
Safety	Li-ion batteries in products like e-scooters and hoverboards must include battery management systems (BMS) to prevent overcharging and thermal runaway
Environmental impact	Lithium and cobalt mining causes environmental damage; designers should consider recyclability and end-of-life disposal
Cost	Lead-acid is cheapest; lithium-ion is more expensive but lighter and longer-lasting

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Environmental and Ethical Considerations

• Lithium mining in South America and Australia uses vast amounts of water and chemicals.
• Cobalt mining in the Democratic Republic of Congo has been linked to child labour and unsafe working conditions.
• Recycling rates for lithium-ion batteries are currently low (under 5% globally), but improving.
• The EU Battery Regulation (2023) now mandates recycled content targets and collection schemes.

AQA Exam Tip: If asked about the environmental impact of batteries, go beyond "they can be recycled." Discuss mining impacts, cobalt ethics, and the challenge of low recycling rates. This depth of knowledge targets the top marks.

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Summary

• Primary cells are non-rechargeable (alkaline, lithium); secondary cells are rechargeable (NiCd, NiMH, Li-ion, LiPo, lead-acid).
• Lithium-ion batteries dominate modern electronics due to high energy density and no memory effect.
• Other energy storage technologies include pumped hydro, flywheels, compressed air, hydrogen fuel cells and supercapacitors.
• Designers must balance size, weight, capacity, safety, cost and environmental impact when selecting batteries.
• Ethical sourcing of lithium and cobalt is a significant concern in the electronics industry.

AQA Exam Tip: A common exam question presents a product scenario and asks you to recommend a suitable battery type, justifying your choice. Always link your answer to the product's requirements (size, weight, runtime, safety).

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Worked Example: Sizing a Li-ion Pack for a Cordless Drill