How efficient is your cooking?

Preparing food is a necessity of life and there are many options that impact your carbon footprint.  Before I go into those, I need to mention that changing what you eat will have a far bigger impact than changing how you cook it.  Choosing a vegetarian or very low meat diet is one of the biggest things you can do to reduce your carbon footprint.  As a family we have reduced the amount of meat we consume, but only our daughter is peskitarian.  

What I set out to discover was which method of cooking is the most efficient and therefore has the least impact on the environment while feeding my family.  The most efficient cooking tool I have found is a multi-cooker/pressure cooker, such as the Instant Pot, because it is insulated, has a perfectly matched heating element to pot size, utilizes pressure to speed up the cooking process and often retains the heat from one cooking step into the next step. With that out of the way, let’s geek out on cooking efficiency numbers.

What are the choices for cooking?

The primary methods by which people in the developed world cook are:

• Electric range
• Electric oven
• Gas range (propane or natural gas)
• Gas oven
• Microwave oven
• Induction range
• Convection/Toaster oven
• Crock pot/Slow cooker
• Multi-cooker/Instant Pot.

Finding efficiency numbers for each method of cooking has been a challenge as it hasn’t been studied extensively and the current administration is opposed to meaningful energy star ratings for appliances. The Trump administration has even changed the rules to remove the standard testing procedure for comparing ranges/cooktops for the Energy Star program.

What I did discover is from some older Department of Energy (DOE) research at Berkeley Labs (formerly Lawrence Berkeley National Lab) that compared the cooking efficiency of electric coil, induction and natural gas ranges.

Cooking Efficiency
Induction cooker – 77.4%
Electric coil – 83.4%
Gas range – 35.2%

All of these numbers were heating water in a large vessel at full power and it should be noted that the test conditions for gas were not the same as the other two and lowered the efficiency artificially. Making the tests identical would still not have brought the efficiency close to the other two electric options.  The research showed that the efficiency of conventional technology was highly dependent on the size of cooking vessel in comparison with the heating element.

According to Alex Wilson at Green Building Advisor, oven efficiency is significantly worse, which makes sense because you have to heat a lot more air to cook the food.  

Cooking Efficiency
Electric ovens – 12-14%
Gas oven – 6-7%
Microwave oven – 56%

In both cases, self-cleaning ovens were more efficient because they have more insulation.

Overall System Efficiencies and Carbon Footprint

In order to understand the environmental impact/greenhouse gas emissions of your cooking tools, it is important to also consider the source of the electricity being used. 

Looking at the energy consumption in the house does not tell the full story in terms of environmental impact between gas and electric because it matters where your electricity comes from.  If you have solar power and buy 100% renewable electricity like we do, then the electricity can be treated as nearly 100% efficient and zero carbon impact.  If your electricity is primarily supplied by Natural Gas from the electric company using combined cycled power plants, then you are looking at 64% efficiency from the gas going into the plant to the electricity in your home meaning that 36% of the energy is loss in the conversion from natural gas to electricity.  When calculating the green house gas emissions, you need to divide by the efficiency to determine the total fossil fuel burned.  The penalty for electricity is even worse if you are primarily supplied by coal, then only 37% of the energy in the coal makes it into electricity.

Revising the numbers based on your electricity source we now have modified planet wide efficiencies as follows:

As you can see from the table, which method is ultimately the most efficient depends greatly on your source of electricity.  I have not found any hard efficiency numbers specifically for toaster/convection ovens, slow cookers or multi-cookers, so, how can I be so certain that the multi-cooker is the most efficient?

I make this conclusion based on the numerous tips available from DOE, Berkeley Labs, Yale, etc. and looking at the features of a good multi-cooker.

• A warped-bottom pot could take 50% more energy to boil water than a flat bottomed pot.
• Putting a lid on a pot during cooking can cut energy use by 8-fold.
• The efficiency of conventional technology is highly dependent on the size of the cookware used.
  • Matching the cooking vessel size to the burner/coil is extremely important.
• Slow cookers use significantly less energy than a stovetop when  preparing soups or stews that take hours to cook.
• Convection ovens also make a difference. The heated air is continuously circulated which reduces cook times as well as the temperatures required. On average you’ll use 20% less energy a month running your convection oven, as compared to a standard oven.
  • Toaster ovens can be even more efficient than full size ovens because they have less air to heat.

What are the features of a good multi-cooker that make it even more efficient?

• Electric coil size is matched to the size of the stainless steel cooking vessel
• The entire cooking vessel is very well insulated
• The cooking vessel is exactly matched to the heating element and designed to be in perfect contact.
• The cooking vessel lid is firmly attached and even sealed for pressure cooking
• The temperature of the cooking is tightly controlled and the multi-cooker only applies heat (uses energy) when needed.  My testing showed that once at temperature during most of the pressure cooking of beans, our multi-cooker only drew 1 W.
• Energy you use to saute or brown foods at the beginning of the process usually carries over into the pressure/slow cooking phase of a recipe as the inner, removable stainless steel vessel stays within the insulated container throughout the whole process.
• Pressure cooking requires less time than stove top cooking 

While I cannot mathematically calculate how much impact each of these seven features has on the overall efficiency of the multi-cooker, it is safe to say that they all improve the efficiency over the already high electric coil/range efficiency.

Our multi-cooker – Zavor LUX LCD 8-QT

I have done some measurements of the energy consumed to cook various foods.  For a simple comparison, let’s look at cooking 1 cup of white rice.  In our multi-cooker (Zavor LCD Lux -8 qt) it consumed 113 Wh to cook 1 cup of white rice.  To see how that compares to cooking with our gas range, you’ll have to check out the next blog post.

One last thing about the benefits of multi-cookers over gas range cooking is that burning natural gas inside the home creates combustion gases that are bad for you.  You should always run your exhaust vent when cooking with gas on the stove or in the oven to vent those harmful gasses out of your home, not just when you burn something.  The venting of the conditioned air inside your home will definitely negatively impact the efficiency of cooking with gas.

Happy Greening!
Jon

If you liked what you just read, please signup below to receive our blog posts and tips via email.