Your web browser is out of date. Update your browser for more security, speed and the best experience on this site.

Update browser

Multiple utensils or fuel stacking?

10th October 2022

By Dr. Simon Batchelor (Gamos Ltd.; Loughborough University).

While many of the team are at the Clean Cooking Forum, I have space this week to put a few thoughts that are emerging in our research into a blog – so this may be the first of many from me.

We have been focused for a while on the energy efficiency of the electric pressure cooker (EPC). It offers an opportunity to cook any ‘long cook’ meal for a fraction of the cost of other urban fuels such as charcoal or LPG. The recent Ghana cookbook evidences this clearly.

However, no one device is a solve all, and one of the pushbacks we get is that the EPC can’t cook chapati or Roti. I returned last week from a visit to India which was very informative, and encouraging in terms of modern energy cooking for the masses moving forward, and visited a women’s community there. They had LPG gas, but they lit their Chula every day to cook the Roti. They said that LPG-made Roti wasn’t easy to do and took a lot of gas. 

(During the trip there was a lot of debate as to what temperature you need on the flat plate to get a good Roti, opinions seemed to vary between 200 degrees and 300 degrees. When the women were asked how did they know the plate was ready for the Roti mix, they just laughed and said – “We don’t know, we just know”. Watch this space as we will try to answer this question with field measurements).

Anyway, the point was that despite having gas, the Chula was lit every day. And indeed the household had electricity and used electricity to heat water for washing. 

We have all known that ‘fuel stacking’ exists. Movement from one fuel to another rarely results in the older fuel being completely unused. A very common set up in many of our research locations is LPG for ‘quick foods’ (e.g. stir fry) and charcoal for the longer cooking (e.g. beans, etc). This has often been masked by the single national survey question ‘What is your primary cooking fuel’ but more recently the Multi Tier Framework has been giving more nuanced data and the picture is becoming clearer.

However, as well as fuel stacking, there are multiple utensils. The problem with chapati in electric pressure cookers, is not that they can’t be done (with skill they can since an EPC can fry), but that few people on this earth cook their chapati at the base of a deep pot! It’s difficult to get them out and to flip them. In theory, an EPC with a Sauté mode that got to 280 degrees could do Roti, but i) EPCs are set to switch off at about 180 degrees in Sauté mode, and ii) it would be very difficult to reach in and turn the Roti by hand (which most people do), without burning your wrists on the side of the pan.

I don’t want sound like Roti is the only problem, an EPC can do a fried egg, but getting it out sunny side up is a challenge.  

So what we perhaps need is a device that can use a flat pan, or shallow frying pan, for the quick frying.  

Induction stove I hear you cry.  It is said induction stove can do everything.  Well yes, it can but at a cost for multiple utensils, and for wasted energy. 

The EPC has four mechanisms for energy efficiency –

(a) It makes a tight and good connection between the heating element and the pot so minimal losses of heat transfer at the base,

(b) It has an air gap around the pot providing insulation (A pot half full of water and beans simmering radiates about 200 to 300W),

(c) It uses pressure to cook faster for the long cooking, and

(d) It switches itself off and on during the pressure phase to minimise wastage from over heating and releasing steam.  

Induction is great at (a). It excites the pot itself through a magnetic flux, and the pot heats up with minimal loss in that heating phase. But once it is doing ‘long cooking’ it is just like the gas – any simmering pot sits there radiating heat and ‘wasting’ money. (And of course we all know cooks who don’t put a lid on their pots!). But even with a lid, the sides are radiating ‘lost’ heat. And regarding (c), using induction with a ‘stove top’ pressure cooker doesn’t have the air gap and therefore uses more electricity than the EPC which utilises (b) and (d) so well, as evidenced by the India eCookbook, page 53.

And of course to use a stove top pressure cooker on an induction stove, would require acquiring an induction ready pressure cooker. Indeed one of the issues with induction stoves is that the household often needs a new set of utensils to work with the stove (as opposed to their existing aluminium ones). And while the induction stove itself is cheaper than an EPC, it plus the cost of a new set of utensils is often higher than an EPC. (See the India eCookbook page 15)

Multiple utensils? – so is the issue ‘fuel stacking’ or actually multiple utensils? If an EPC could accommodate a shallow frying pan, then perhaps it could do even more of the menu than it currently does? (……And there are some interesting ideas emerging about raising and exposing the heating element to create such an effect).

However, that doesn’t address another reason people have multiple utensils. They want to cook more than one dish for the meal at the same time. A limit of the EPC is that it comes with one pot, and while you could use it sequentially and there is a preference among households for 2 pots (so one dish can sit in the pot while the other is being cooked), there is perhaps more desire for parallel cooking – to use the Indian example the main dish on the LPG while the Roti and chapati are on the Chula.

All of this suggests the simplest answer is 2 devices?  In Cooking with Electricity | A Cost Perspective the team suggested that a ‘clean stack’, LPG and electricity, was a cost effective way forward in order to accommodate the different needs of the cook. Induction and EPC also present a clean stack.  However, two sets of equipment whether LPG or induction plus EPC, suggests two upfront costs? Or as some proponents of induction suggest – two induction hobs for parallel cooking – much cheaper than LPG plus EPC, but less energy efficient than induction plus EPC. 

I think we have previously assumed that the ideal was a single device that could so all the cooking – after all isn’t a three stone fire that – a single heating source which the cook uses with multiple utensils to do multiple dishes. That may still be the goal for the very poor and vulnerable, however what the Cooking with Electricity | A Cost Perspective also shows is that over the lifetime of the device, the upfront cost is small compared to the potential savings on the fuel costs. It’s small but it’s a cost the consumer doesn’t have. 

Enter the Carbon and Results-Based Financing work. Using these, programmes are mitigating the upfront cost, and encouraging uptake beyond those users who can afford the cash price. Indeed, the user can mitigate not just the upfront costs but the ongoing costs. 

So perhaps the weakness of a two hob induction stove compared to an induction plus EPC, is the loss of energy. ‘Scott et al. in some recent work, as yet unpublished but used to inform Gold Standard’, shows how our data suggests how an induction (in real life use – not lab use) saves about 15 to 20% of energy compared to a reasonable hotplate, while an EPC saves 50%. That 30% difference is real money to the consumer. If two induction stoves are being used, the consumer is foregoing savings in ongoing fuel costs, and as Cooking with Electricity | A Cost Perspective have said over the lifetime of the device that dwarfs the upfront cost. So even with savings from say carbon credits payments, both the user and the world are foregoing potential carbon savings.

So where does that leave us? First we should acknowledge that people want multiple utensils, and maybe need multiple devices to heat them at the same time. In our quest for that lets not abandon the savings that can be made by using an EPC. The double induction stove does seem ‘user friendly’ but it will cost the consumer more than an EPC for the same meal (although in most urban settings, still less than LPG and Charcoal). 

Finally – induction or infrared or hotplate? Many have latched onto induction stoves because of their efficiency in transferring energy to the pot and heating the food. Actually a good fitting infrared stove is almost as efficient at that as induction in quick food cooking and does not require steel pots. I emphasise good fitting, because that’s the key issue. And indeed a good fitting resistive heater can also transfer the heat as well as induction in quick food cooking, as evidenced by the EPC which has a bespoke pot fitted to a resistive heater. IF the device is only going to be used for quick cooking (shallow frying), then the differences are minimal.  A forthcoming working paper will evidence these statements, and as a final word I acknowledge that the danger of offering a good fitting hotplate is that some cooks may use ill-fitting pots on the same hotplate (a problem that induction avoids).


Featured image: Women’s focus group in Pune (image credit: Simon Batchelor, Gamos Ltd.).