Measuring what is needed - energy to cook food

[Ray Leistner]

For the past three days I logged electric use to cook my food.  The average was below 0.6 kWhr per day.  I'm using an induction hotplate, so a regular stove might use 2x as much.  With the induction heater, or maybe a microwave, two solar panels plus a battery could easily support cooking for one person if you want to go with a method that creates no air pollution.

 

I've also tested a small vacuum-insulated cooker, and it did what it was supposed to do - cook food without sustained heating.  The insulation keeps the food at cooking temperature long enough to soften things.  I tried white and brown rice so far.  It would be neat to try the induction cooker to warm the insert for the vacuum container.  This might be my next step.  A variation on this is cooking in a Thermos.

 

Measuring power used when cooking, I found with either the pots + induction or a microwave, that it takes about 20% of the energy value of the food itself to cook the food.

 

Tonight I'll measure heating efficiency of a microwave oven.  To do this I'm going to measure out a quantity of cold water, measure its temperature, and then place it in the microwave, tracking electric power used, and then measuring the final temperature.  Then I'll calculate how much energy it would theoretically take to warm the water that much, and compare that to how much extra energy was used by the real appliance.

[Livetoletlive]

hey id love to see some of these methods ur using to cook. did u build them yourself?

[Ray Leistner]

Nope, cooker was a single burner induction unit that sells for about $80, and the pot was stainless steel with an aluminium layer on the bottom, that cost about $15 from a Chinese grocery store.  I want to test a regular style burner, for comparison.

I think I remember the results of the microwave test.  It was a panasonic Inverter oven, and the water I tested converted to heat about 70% of the energy that came in from the wall outlet.  The induction cooker sent 90% of the electrical energy into the water in the pot, when I did a separate test of just heating water.  Shiny pots help hold in the heat, but they can't be used in a microwave.

Slow cookers could be modified with insulation to lower their energy use, and maybe adding a shiny lid or some kind of fireproof cover like shiny aluminium.

[Livetoletlive]

thank you

[Lianne Snow]

How'd it go?

[Ray Leistner]

Just finished testing - Home Max 1000W single coil burner portable stove.  Electric use dropped as the element warmed up.  I started it cold, and let it stand for 60s after switching off, to allow residual heat to move into the pot.  Pot was flat-bottom w. aluminium layer 2qt., filled with 1500g water at 22.3 deg C.  This ignores the heat capacity of the pot, so actual transfer efficiency to the pot surface is a tiny bit higher.

declining power use over four minutes:

100s x 975W + 80s x 965W + 60s x 960W = 232300 J

4186J/kgC * 1.5kg = 6279 J/Cdegree

232300/6279 = 37 degrees C maximum temp rise

Actual temp rise was 26.2 degrees.  Efficiency 71%

Not bad.