Charge of the potatoes

16th February 2007 at 00:00
Producing electricity from potatoes is more than a half-baked idea. Jonathan Hare offers some exciting, and messy, ways to get pupils thinking

This has to be the best laboratory ever. I am sitting in front of a bench covered with bits and pieces outside a beachfront house. Just a few feet away rolling breakers from a turquoise sea carry warm, salty air rich in spices. I am in Zanzibar, east Africa, with the Rough Science TV crew...

who says science is not glamorous?

We scientists have each been set a challenge by Kate Humble, our presenter.

Kathy Sykes and Ellen McCallie have the job of making Kate a life jacket.

Mike Bullivant, our chemist, is to make an emergency flare. My task is to make emergency lights for the life jacket so it can be seen at night. I decide to power some little LED lights I have salvaged from a rusty old radio and set about making a sea water battery to power them. The idea is that, once in the water, these life jacket lights will be powered by the Indian Ocean.

One night Kate tests our inventions at sea. Our little sea-powered LEDs help guide the way and we eventually find her safe and sound, kept afloat by a Rough Science life jacket.

This all seems a bit like a dream now as I show a clip from the programme to a group of pupils as part of a Brighton Science Festival workshop.

It was so sunny and hot there; now snow drifts down outside the classroom windows. But it doesn't matter, we are having fun.

Richard Robinson, the festival's founder, and I are halfway through a 30-workshop tour of Sussex schools to help build up the start of the 2007 festival. In Zanzibar I used sea water to make the battery. In these workshops we are using potatoes. It's less messy when you have 30 or more pupils wiring their own inventions.

Richard and I are hoping the classmates will be inspired to devise their own homemade batteries after the workshop and bring them along to the festival's school day on February 23.

We divide the children into six groups of five to make the batteries. They use zinc-plated screws and carbon rods (the graphite in pencil "leads") for the electrodes. They find that one or two potatoes will power an LCD calculator. Two or three will power a flashing LED circuit.

On the way they also discover that a series of circuits adds voltages enabling these two devices to work but that a buzzer, needing more current, works best with three or four potato cells wired in parallel.

They start to see that you can't just wire them up randomly, they need to work it out.

Finally, when we have six working batteries from each group, we bring them together and wire them up in parallel to make a super-spud battery. I have brought along a radio and this time all our connections seem to be good because in the excited hush we hear voices and music.

Reactions to the potato workshops have been interesting. At first many of them said "oh no, not potatoes" or "we have done this before with lemons", and were sometimes quite negative.

However, once they got going making their own batteries, trying to puzzle out the wiring and getting them to power the electronic devices, they realised there was a lot more to it than they initially thought. By the end of every workshop they appeared to have got a lot out of it. Many told us it was a "fab" lesson - they seemed to love it.

So, we're hoping for something more imaginative than potato batteries from these pupils at the festival next week.

Perhaps we might get a sea water battery or two, but we hope they are more creative than that. Perhaps they can make a fruit juice or tomato sauce battery; perhaps even a Marmite toast battery. At least you could eat the evidence if it didn't work well.

We want them to look again at everyday objects and from the science they have learnt in the workshops, invent for themselves. TV, radio, mobile phones, computers, washing machines, heating, lighting and medical equipment. The list of useful and life-transforming inventions and discoveries made possible by the use of electricity is mind-blowing.

Electricity is so effective we hardly notice it is there most of the time - we take it for granted. Perhaps we only begin to think about it when occasionally the light doesn't go on when we flick the switch, when the filament blows, then we just get annoyed. But all this technology did not just appear; it was created by scientists.

We hope these little workshops will help pupils appreciate the wonder of electricity and also that it is possible for them, like the investigators of the past, to understand it for themselves and perhaps even make their own inventions

Jonathan Hare has appeared in six series of the BBC show Rough Science. He runs The Creative Science Centre and is part of the Vega Science Trust at the University of Sussex


The principle is simple: when two conductors are immersed into liquid such as salt water (or chemicals that are found in a potato) each will become electrically charged because of their relative re-activities.

Metal ions come off into solution, leaving an equal and opposite charge behind on the metals.

Essentially one will appear positive and the other negative and a simple cell is formed. We are using chemical energy to make electricity.


Find details about the Rough Science series, homemade batteries and the Brighton Science Festival from the websites below.

Brighton Science Festival runs from February 18 to 25, with family days on February 24 and 25. Details and online ticket purchases can be made at

For information about the Creative Science Centre visit and

OU Rough Science facts can be found by looking at www.open2.netroughscience.

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