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Solar lantern design and production

Product analysis

The market

The solar lantern was designed for countries with limited supplies of electricity. It was trialed in Kenya, where only 3% of homes have a regular electricity supply.

Technical specification
Power supply: lead-acid rechargeable battery (6.5Ah)
Power output: 5-9 watts
Light operating time: 4.5 hours
Radio operating time: 15 hours
Dimensions: 420 x 135mm
Weight: 3.3kg
Cost: 65

Time taken to fully charge the batteries: 5 hours

Product function

The solar lantern can be used for indoor or outdoor lighting, or as a power supply for a small electrical appliance (like a radio). As a light, it provides a bright beam (equivalent to a 60 watt filament lamp) spread over a 360 area. It can be hung from the ceiling, carried by the handle, or stood on the floor.

A simple lighting circuit is used inside the lantern. The fluorescent lamp is powered by a lead-acid battery and switched on and off using a standard micro-switch. The battery pack is charged by a photovoltaic panel that converts solar energy into electrical energy.

The light comes from a highly-efficient compact fluorescent tube (5-9 watts), which is robust, has a long life and withstands extremes of temperature and humidity.

Materials
The lantern is made from five injection-moulded components - two side panels, a base, a handle and a spacer. Production

The product is designed to be mass produced using injection-moulded parts. Injection moulding is an ideal production process, as components can be made in large quantities to fine tolerances.

Standard electrical components are used for the lamp-holder, micro-switch and connectors. Self-tapping screws, snap and interference fits are used to connect the parts together, making the lantern quick and easy to assemble by semi-skilled workers.

Electrical connections are made using soldered joints for the lighting board and crimp connectors for the battery terminals.

Safety

The lead-acid battery contains potentially hazardous chemicals. So that these cannot leak out, a gel electrolyte is used instead of a liquid.

A jack plug is used to connect the lantern to the solar panel and other electrical products. This helps to avoid short circuits. The lantern mouldings all fit together tightly - the casing is self-sealing and splash-proof. All of the electrical components are inside the lantern body, eliminating the risk of electric shock.

The battery is at the bottom of the lantern, lowering its centre of gravity and making it very stable. However, in case the lantern is knocked over, the lamp is in a protective acrylic diffuser. Safety glass is used for the photovoltaic panel.

Ergonomics
The lantern satisfies basic ergonomic requirements. It:

The lantern is heavy, making it difficult to lift and hang from the ceiling. Changing the lamp or battery is awkward, as you have to unscrew the casing.

Aesthetics
The product's appearance is functional, determined by the layout of its internal components. However, the rounded shape of its casing and diffuser make it more attractive.

The lantern is available in black and orange. Its surface finish helps to disguise small defects in the mouldings and scratches that occur during everyday use.



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Practical Action - Technology challenging povertyEuropean Commission - Department for International Development

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