[Stoves] solar cooker response (changing thread name)

[Crispin Pemberton-Pigott]

Dear Andrew

When we were looking at the claim that simmering a pot could produce an 'efficiency' and fuel consumption 'per litre simmered', Yixiang and I investigated induction cookers in the 1800-2100 W range. All were single plate, like a gas fired wok cooker. Some have six settings for power, down to 300 W.

The 88% efficient were marked C, the 90% were marked B and the 92% were rated A. That is a Chinese national rating system.

‎In Canada there were, for a time, no powerful ones. All were under 1 kW.  It could easily be run on a 1 kW inverter. Given the coincidence  of the voltage being half and the power being half, I am wondering it the guts are same, just that it runs on a lower voltage. They are still rare in Canada except for expensive built-ins, 4 or 5 plate glass tops.

That is all an aside. What we measured was the direct heating of the water and it was a lot less than 90% efficient. The stability of the power consumption was excellent. Yixiang reported the efficiency in the 70's.  ‎It is possible that the pot itself has an effect of the efficiency of the induction. That is going to affect the battery life.

Regards
Crispin



On 12 June 2017 at 20:35, Crispin Pemberton-Pigott
<crispinpigott at outlook.com> wrote:

> There are two kinds of induction heater that I have seen at the bottom of the market: single and double plates. The double one has a high power (often 1000-1100 W) and a 700 W one. Both plates on is about ten amps.

Mine was the cheapest I could find locally and is rated at 2100W but
you seldom use high power, indeed my first few tries I burned food
when frying

https://www.amazon.co.uk/Tefal-Everyday-Induction-IH201840-Ceramic/dp/B00ER445UQ
>
> ‎The efficiency of the single plate units is 88-92%. That is much higher than an electric hot plate.

Yes and because it heats the pan directly there is no loss involved in
heating the hob, it does have the parasitic load of a cooling fan for
the electronics.

>
> So running the big plate for 30 minutes is 0.5 kWh. 500 Watt-hours. That is roughly a quarter of a regular car battery (1800 Wh). Is that reasonable?
>
> A large car battery can store about 4.8 kWh. It is fine for cooking, but not heating water.

Because it is fast you don't need it on for long, it also has various
sensors and a timer for things like gently heating milk, or porridge,
without it burning on the bottom of the pan.

If no one else has figures I will try and monitor its electricity
consumption, we tend to only have two for meals in this household and
I don't believe I have ever used it for more than 15 minutes at a
time.


A typical lead acid battery for a large diesel engined car is about
95Ah but you seriously damage it's life if you run the voltage below
11.5V, in practice as long as you have the capacity for the peak load
you would use a similar rated leisure battery but still only get about
24Ah from it, so about 0.5kWhr. This just about matches your
calculated usage.

My panels actually run at 300V and I would be looking to a lithium ion
storage battery if I were not grid connected.

I guess this sort of thing is for the remote but middling affluent
users rather than the sort of people we normally think would benefit
from improved stoves as the capital investment is large.

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