It’s very difficult to explain the concepts of power and energy. People often ask “Can I power my kettle with that?”….
So to try to put the energy in a cup of tea into perspective we built the ‘Cuppa-meter’.
The ‘Cuppa-meter’ shows a cup of tea which lights up as the energy required for a cup of tea is generated. This can be plugged into a pedal generator and people can ‘feel’ the energy required to make a cup of tea.
They can either pedal slowly (and hence low power) for a long time, or they can pedal hard (high power) for a shorter time. The end result (the energy) is the same – a nice hot cup of tea (or rather a lit up image of one).
There is a scrolling LED display at the base of the unit showing instantaneous power.
This plug-in display works with our pedal generators and costs £400 (plus delivery).
We can provide bespoke designs and modifications to suit your application. Please contact us if you would like something like this for your pedal power system.
Energy in a cup of tea
So how did I calculate the energy within a cup of tea?
Firstly lets set the parameters – I am talking about the heat energy requirement to get a cupful of water from room temperature to boiling (100C, at sea level). This does NOT include the energy required to process and purify that water nor the energy embodied in the tea and tea manufacture, nor any milk or sugar added….
In my house kettle (rated at 1500W) enough water for a single cup of tea (around 250ml) takes around 60 seconds to boil.
As Energy (Wh) = Power (W) x Time (h):
Energy (Wh) = 1500 W x 60/3600 (h) = 25Wh
So we need to supply 25Wh of energy to boil a cupful of water.
This could either be provided as 25W for 1 hour, or (as in the case of the kettle) at a much higher rate for a shorter time.
A typical cyclist can provide around 100W, so it will take around 0.25h (15 minutes) to provide 25Wh.
Pedalling at this rate for 15 minutes really works up a sweat, which really drives home the point.
I also did this calculation for a slice of toast:
It takes my 400W toaster around 2 minutes to toast a slice of bread. So the energy required is 400W x 120/3600 (h) = 13.3Wh, or around 1/2 the energy required to boil a cup of tea. I will also make a toast display to pedal for tea and toast.