TL;DR: power saving with a lid comes from the fact that you can use a lower power-mode on
your cookstove. Energy used to bring the water to the boiling point is roughly the same with or without the lid, energy saving occur after that point.
I'm afraid that the question and the current discussions are quite ambiguous on one capital point.
In case it is not obvious to everyone, I will therefore make it explicit here.
First: using a lid is more efficient, no questions, but it's much better if you make
full use of it.
What's the catch?
Unless you really optimize your cooking and do things faster when using the lid (which, from
experience is not that significant, at least for me), then using the lid will save
almost no energy .
This is simply because the cookstove is sending the same amount of power to your pan or pot whether
or not the lid is on.
Using the lid enables to reduce water evaporation and the associated energy loss, as well as some
radiative loss (probably negligible).
Now, if you're cooking pasta, using the lid will usually make you save energy because you'll have
to reduce the power to avoid overflow, but if you're frying stuff, then you might keep the same
power as without the lid, in which case you're basically not saving much...
I have induction at home, and my small stove varies between 160 and 1400 W when I vary the power setting
from 1 to 9.
I'll assume here that the power varies linearly (might be wrong but I did not find an answer to
So let's make some pasta (200 g) using 1L of water.
With the lid:
- Power 9 for 4.5 minutes -> water boils, add pasta
- Power to 4 for 10 minutes -> pasta cooked
Without the lid:
- Power 9 for 4.5 minutes -> water boils , add pasta
- Power to 6 or 7 for 10 minutes -> pasta cooked
Power consumption is
P(N) = 160 + 1240*(N-1)/8 Watt
Energy consumption is
E = (boiling_time * 1400 + cooking_time*P(N)) J
Here, this gives:
- with the lid, 10 minutes at 625 W (power on 4) gives a total consumption of 753 kJ or 0.52 kWh
- without the lid, at 935 W (power on 6, for me), one gets 939 kJ or 0.65 kWh
- without the lid, at 1090 W (power on 7, for my girlfriend, who thinks it does not boil strongly enough at 6), one gets 1032 kJ or 0.72 kWh
So with the lid, lowering the power to 4 enables me to save between 186 and 279 kJ on pasta,
without changing anything about the time that it takes to cook it nor the exceptional quality
of the final dish!
To give an order of magnitude, the average energy consumption per day is around 10 kWh in Europe so
this energy saving is roughly 2 percent of that value, but can get much larger if you simmer a dish
for a long time.
 Note that this would be quite different if a pressure cooker was used, but I'm assuming a regular
 Note that the time necessary to make the water boil is the same with and without the lid, which is
perfectly normal since, before it boils, we are not wasting energy into liquid-to-vapor transition
and the other energy transfers are very small.