Energy generation and storage
Design & Technology · GCSE · The School
Three kinds of source
NON-RENEWABLE — coal, oil, gas: burned, finite, and carbon dioxide is the product. NUCLEAR: enormous energy density, no carbon at the point of generation, and waste that stays hazardous for a very long time. RENEWABLE — wind, solar, tidal, hydro, biomass: the source is not used up, though the equipment is. Name which of the three before comparing anything.
Storing it is the hard half
Generation is intermittent and demand is not, so storage decides how useful a source is. ALKALINE cells are cheap and single-use. RECHARGEABLE — NiMH, lithium-ion — cost more, last hundreds of cycles, and are far better per use. Both contain materials worth recovering and worth keeping out of landfill. Battery choice is an environmental decision as much as a technical one.
Match the source to the use
A garden light needs a few hours of low power after dark and sits in daylight all day: solar with a small rechargeable cell, obviously. A cordless drill needs high current in short bursts: lithium-ion. A wall clock needs microamps for a year: a single alkaline cell, because a rechargeable would self-discharge faster than the clock uses it. The use decides, not the technology.
PRODUCT: a bus-stop information display, outdoors, running all day, in Britain. MAINS? Trenching a cable to every stop is the dominant cost and rules it out for most sites. SOLAR ALONE? British winter daylight is short and often overcast, so a panel sized for December is absurdly large. SOLAR PLUS BATTERY, sized for the worst week rather than the average, is what actually gets installed — the battery covers the night and the run of dull days, and the panel only has to refill it. WHICH BATTERY: lithium-ion for energy density, but it loses capacity in cold, so the enclosure is insulated and the design accepts a shorter winter runtime rather than pretending otherwise. Notice what decided it: not which source is greenest, but the duty cycle, the worst case and the cost of getting power to the site at all.