How much voltage and power would an aluminium sheet and a steel sheet make from a 100°C temperature difference?
What volts and amps would I get if I wired a 1 m × 1 m sheet of aluminium to a sheet of steel the same size, heated the aluminium to 100°C, and left the steel at 0°C, from the Peltier effect? I’ve seen a fan on top of a wood burner, and I want to know the power if you scaled it up using basic materials.
– Sydney via the Ask a science question page.
Hi Sydney. This is a great experiment to try out to learn thermoelectric effects. By the way, the actual effect you wanted to quote is Seebeck effect (making a voltage from a temperature difference). Peltier effect is the opposite of that (current through the junction heats or cools it).
Said that, Seebeck effect is what powers the fan on your wood burner.
For your experiment, with plain aluminium and steel, you’d hardly get any voltage. Almost no power, however big you make the sheets.
Let me explain why it’s hard. The measure of the magnitude of the induced thermoelectric voltage in response to a temperature difference across material is called the Seebeck coefficient (S).
The voltage comes from how differently the two metals respond to heat. Measured against platinum, aluminium sits at about +3.5 µV/K and iron at about +19 µV/K. I’m using iron as a stand-in for steel, which shifts a little with the alloy. This gives you 15.5 µV for every degree. So across your 100°C difference that’s about 1.5 mV. In comparison, an AA battery is 1.5 V.
Size doesn’t change that number, because the voltage depends only on the temperature difference. A bigger sheet has lower resistance (because it’s basically resistors in parallel), so it can push more current. But only by letting more heat flow through it. As we know, metals are great conductors of heat, that most of it walks straight across without doing any electrical work. That’s why stove fans use a module of semiconductor pellets wired in series instead.