Ovens and stoves

Hi all
I’m pondering what to put in the new kitchen, obviously with the end goal in mind of going grid tied one day, even maybe off grid.

The boss is pretty firm on a electric oven, so we’ll do that for now and if the off grid happens in future, we’ll reassess.
Is there something like a energy efficient electric oven though, or maybe one brand which is more efficient than another? One of the Defy oven spec sheets say that its energy rating is A, where some other brands doesn’t even mention energy rating.

Then for a hob I was thinking to do a combo of gas and induction. We currently have a gas hob and use a loose standing induction plate for the kettle, plus more and more cooking as well.
Most manufacturers only do gas and electric combos, nobody does gas and induction combos from what I’ve seen, so I’ll have to look at modular systems.
Snappy Chef do a 2 plate gas and 2 plate induction which was designed to match and sit next to each other in a counter top. For the same price I can even do a 4 plate gas from a different manufacturer and then the 2 plate Snappy Chef induction next to it and end up with 900mm.

With the induction plates there will be no need for a electric kettle, we haven’t used one of those in years and there will still be a microwave oven.

Any thoughts, am I missing something or am I on the right track?

I think your best bet will be Defy oven that has a TurboFan mode. Normal elements use about 2kW, but the turbofan use smaller round element that surround the over fan and only use about 1.6kW. You also do not need to preheat the TurboFan saving that power as well.
Then for spares you get them cheap and at every corner.

I have also seen no induction/gas combo hobs. Best would be to make your own combo.
The induction use the wattage of the power level that you set, so that can be anything from 600W-2000W, but it is not a resistive load like an element. We primary use the induction plate (on batteries/solar) and TurboFan oven (only on Eskom).

The Microwave will be around 2000W. It use more power than the induction or TurboFan oven. You will save most power by defrosting naturally than using the microwave, but that need a little bit of planning.

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I’m fairly sure when setting up my Bosch oven it had an option to select 10A or 16A feed in, so they definitely have draw in mind. Ontop of that most oven modes also have eco options so it will pull less energy to get to the target temp. If you are in a hurry you can ask it to pull max amps to get to the target temp.
Once it’s up to temp it really doesn’t use much to keep it going. Just had a look at the graph it seems like 700w to keep it constant at 180 degrees thermofan (No energy-saving modes used)

Kettles are very efficient since the heating element is in the water so all the energy goes into heating the water. This means there is no need to cut out the kettle. I agree with the turbofan Defy oven, we have one and it is great even though I have left it connected to Eskom and not the Inverter.

When considering things like the kettle, oven and microwave for off-grid use you need to consider their energy use, not just their peak power consumption. A kettle may use 2kW, but if it only takes 2 minutes to boil the water then it will only use about 67Watt Hours of energy which is really negligible. The same thing with the Microwave. If you only use the microwave for 1 or 2 minutes at a time to warm something up then it shouldn’t be something to worry about as long as your Inverter is large enough to handle the peak load. What you really should worry about is the oven and hob which are usually used for extended periods during cooking and maybe the microwave if you cook in it. We use a pressure cooker quite happily on the inverter output, it it well insulated with the heating element directly under the aluminium ‘pot’ part. Once it has reached it’s temperature and pressure it doesn’t use a lot of energy to stay there.

By far the items that use the most energy in my system are the things that make up the base load, i.e. Fridge, freezer, PCs, lights at night etc. so these are the items that you should try to get as efficient as possible.

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As a rule of thumb, I say it takes 100Wh to boil a kettle of water. The kettle is usually about 1.5 to 2 liters (ours is 1.7), but if you boil just a liter at a time (a large pot of tea), assume water ambient is 15°C, and you want to take it to 100°C, then 85 degrees Celsius times 1 liter times 1.16 is around 100Wh. It’s a nice round number.

In my experience, the hob is no issue. If you use the right size utensil on top of it, the element really turns on for only seconds in the minute to hold the heat. It doesn’t use all that much energy, even though it has a high peak power consumption. The oven, however, is a different beast, again in my experience (watching the battery charging lag behind on my ESS system on some Sundays when something is roasting).

When it comes to efficiency… an oven can be terrible. Example. We had a container with a nice saucy chicken dish from the previous evening in the fridge (so it was at 4°C). The oven was on anyway, heating something else… so instead of reheating the left-over chicken in the microwave I popped it into the oven for 10 minutes or so… the container got nice and hot… the chicken remained cold inside. A microwave is way better at that job.

Spot on with all of this. And I see exactly the same thing - fridge+freezer combo, bar fridge, and chest freezer.

The last two doesn’t run that efficiently – I basically discovered that they are pretty much always on and building up frost inside. So I ended up putting the chest freezer on a Sonoff TH to better control its temperature and save a little bit of energy.

I have only LED lights throughout the house, with many of them either smart bulbs or on smart switches (e.g. Sonoff minis or shellys). So I did an estimate of each bulbs’ energy usage and added them all together and created a sensor for “Indoor lights power” and “Outdoor lights power” (since I know when they’re switched on). And… I was surprised. More than I thought!

(we’re a family of 5, of which the kids want lights on at night, so focus will have to be on getting them to turn off lights in the rooms where they’re not active/sleeping, or I need to buy more motion detectors).

I can also add that we got an Instantpot Airfryer / pressure cooker combo recently, and it is great to quickly make a couple of fishfingers (yuck) for the kids instead of using the oven!

Did it last night during loadshedding and while the fans on the inverter did spin up, it was still way more efficient than the oven (I don’t have it on a smart plug yet, so can’t measure direct energy usage).

Thinking about it logically, an oven really just needs to be insulated well. So firstly the glass should not be radiating a lot of heat (probably much better not to have glass to begin with) and the interior should be lined with proper insulation. Oh, and the door should close properly (not like our Defy Gemini that looks like a steam train).

After an oven is hot (just heating the air inside surely can’t take that much energy), it also just switches on a little bit every now and then, but how often that needs to happen will depend on the insulation.

Oh and maybe to add, our Gemini is useful quite efficient in one respect - It has the smaller oven at the bottom and the larger one on top. We often only use the small oven (has a smaller element but also less losses - presumably) if we aren’t making many dishes.

To note - Hot air likes to rise and when we use the small bottom oven, the top one gets hot enough (after a while) to use it as a warm drawer… So I assume the insulation between the two ovens are pretty crap. And so maybe it isn’t as efficient as the top one, because the top one might be isolated better at its top…

Those oven with the four compartments should be quite nice. Use the size you need (assuming equal insulation).

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Thanks for all the replies.
I didn’t even mention the air fryer, there’s that as well. For now I only want to focus on the items which will be bought new. Things like the air fryer, microwave and fridges will get attention at a later stage when it’s time to replace them.

Our fridges isn’t that old, but still far from the A plus energy rated stuff you buy these days, I know fridge consumption can quickly add up.

As for the electric kettle, as said we anyway haven’t used one in years, we are used to boiling a kettle on the induction plate. Last I did some testing the electric kettle and induction practically took the same time to boil the same amount of water, but I believe the induction use less electricity than the resistive element of a electri kettle.

In theory, a kettle should use less energy.

The element is inside the water, so you have close to 100% efficiency in transferring that heat to the water. Some of that heat then transfers to the container, and then radiates off into space.

With a container on an induction plate, the heat is generated in the container, and then has to transfer to the water, while some of it doesn’t transfer into the water and instead radiates off into space directly.

Unless I am missing, basic principles dictate the induction method must be less energy efficient.

Can you also look for other signals that basically come down to energy efficiency…

Our oven (a Smeg gas hob / electric oven) doesn’t market its efficiency at all, but does make a big deal about its “cool touch” / child-safe front glass.

You can literally touch the front oven glass with your bare hands, and while it’s definitely warm, you won’t burn. They achieve this with 3x glass layers in the door, which makes a huge difference to the oven’s efficiency, even though it doesn’t directly affect the current drawn. Turning on the turbofan mode also makes a big difference to heat-up time as other have noted.

Another thing to look for is whether you can plug it into a normal 16A socket instead of hard-wiring it in. The salesman won’t know, but the manual was pretty clear that it’ll be fine in our case.

You mention not replacing the microwave now, but for when it’s time…

When you select < 100% power on a normal microwave, it just toggles the magnetron between on & off while it’s running. You can see this with a cup of water on a < 100% setting: the water will alternate between boiling and not while the cycle is running. You will also hear the “whoom… WHOOOOM” noise change, and if you measure the current, the cycle between max & standby will be plain as day.

In contrast to this, LG’s NeoChef microwaves drive their magnetron through an inverter, so the power output and draw is a lot smoother: the magnetron stays on the whole time, but at a lower power level. This is kinder to everything else on the circuit and actually heats better. For something like defrosting, as mentioned earlier, this makes a big difference to what else you can run from solar or batteries at the same time since the peaks are gone.

I’m sure other brands will have something similar, but again, it’s not always marketed well.

Regarding the microwave, MIGHT be different for those inverter types, but yeah, the normal ones just full blast on and off vs always on.

You made me get the meter, now I look like a crazy person on the internet. Again.

You can see full power (“1200”) is about 1800W, then @ 20s “1000” is about 1600W, and @ 44s “400” is about 600W. You can see the nice slow ramp-up in all cases and fairly steady during.

And now you’ve watched a Youtube video about microwave power levels, congrats. \o/ :slight_smile:

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Now that’s interesting. I would love to learn the mechanics. Far as I know, the physical design of the magnetron is based on the frequency it will run at (60Hz models don’t work on 50Hz power, and so on), because it has to be at the resonant frequency of the device. So this inverter device will probably be a bit different to the VFD-type you use to drive an induction motor at different speeds.

But since it likely requires some kind of converter, that means it could potentially run at higher (more efficient?) frequencies too. You also don’t use the voltage to control the power level (you need a pretty high voltage to even get started). So the control would be entirely current-based, most likely just PWM’ing the duty cycle.

Nice! So basically, I should’ve spent the extra money and got the inverter type. :sweat_smile:

I must say, after I got an inverter aircon, I’m definitely on the inverter bandwagon. Just really cool watching how it can ramp up and down on energy usage. And this is a 24,000 BTU unit.

(I turned it up a degree 19:00 and off 20:00)

For reference ovens do chow power though (depending on what you consider a lot of power) this is a smeg oven with @ 180deg C, used ~ 1kWh using just the thermofan.

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Hah, I see it’s a “Critical Load” :slight_smile:

Also want to do a changeover for mine to we can run it if we need to, but still do our own Stage 2 loadshedding. Don’t want to lose touch with reality too much.

Amen!