Sunny countries are often poor. A shame, then, that solar power is still quite expensive. Eight19, a British company by Cambridge University, has, however, invented a novel way to _ this. In return for a deposit of around $10 it is supplying poor Kenyan families with a solar cell able to generate 2.5 watts of electricity, a battery that can deliver a three amp  current to store this electricity, and a lamp whose bulb is a light-emitting diode . The firm thinks that this system, once the battery is fully charged, is enough to light two small rooms and to power a mobile-phone charger for seven hours. Then, next day, it can be put outside and charged back up again. The trick is that, to be able to use the electricity, the system's keeper must buy a scratch card--for as little as a dollar--on which is printed a reference number. The keeper sends this reference, plus the serial number of the household solar unit, by SMS to Eight19. The company's server will respond automatically with an access code to the unit. Users may consider that they are paying an hourly rate for their electricity. In fact, they are paying off the cost of the unit. After buying around $80 worth of scratch cards--which Eight19 expects would take the average family around 18 months--the user will own it. He will then have the option of continuing to use it for nothing, or of trading it in for a bigger one, perhaps driven by a 10-watt solar cell. In that case, he would go then through the same process again, paying off the additional cost of the upgraded kit at a slightly higher rate. Users would therefore increase their electricity supply steadily and affordably. According to Eight19's figures, this looks like a good deal for customers. The firm believes the average energy-starved Kenyan spends around $10 a month on oil--enough to fuel a couple of smoky lamps--plus $2 on charging his mobile phone in the market-place. Regular users of one of Eight19's basic solar units will spend around half that, before owning it completely. Meanwhile, as the cost of solar technology falls, it should get even cheaper. How much would users pay for the cell and scratch cards before they own a 2.5-watt solar cell?
Around $10. Around $80. Around $90. Around $180.