Kettle on Gas vs Electric Kettle

happyc84

Its interesting that we are focused on the cost to provide the fuel to heat the water. 

We stopped using our kettle for coffee, as we bought a coffee capsule machine.
Was low cost £40, but cost per drink I think works out at 20p.

Instant Jar of coffee is on average £4. number of drinks per jar = 55. cost of  drink is about 8p.
Many variable's in this equation.

So if you want a total cost for your daily cuppa.

1 Cost of fuel
2 Cost of Tea/Coffee or whatever you drink.
3. Cost of water?

You could also add the cost of the cup. Where do you stop!! .

Astria

QrizB said:

And see also:
http://insideenergy.org/2016/02/23/boiling-water-ieq/

Inside Energy spoke with Tom Williams, a researcher at the National Renewable Energy Lab, to break down the rough efficiencies:

• A microwave is about 50 percent efficient. Most of the energy is lost in the process of converting electricity to microwaves (which are part of the electromagnetic spectrum).
• An electric stovetop is about 70 percent efficient, although that varies widely depending on the type of pot or kettle you use. Most of the energy is lost heating the air around the stove.
• An electric teakettle is about 80 percent efficient, although again this varies from kettle to kettle. Electric kettles are generally very well insulated, and the heating coils sit directly in the water, so less heat is lost to the air.
• An induction stove or hot plate is about 85 percent efficient. It creates an electromagnetic current directly in a pot to generate heat, losing very little to the air.

I agree that induction stoves loose very little to the air, but how much energy do they consume compared to how much energy they put into the object on the ring? For example, if a wireless charger for a toothbrush or mobile phone is similar (I don't know if it is or not), they typically draw 2A from the wall to put 1A into your phone.

k_man

Petriix said:

While a gas stove top kettle might only be 40% efficient in terms of heat transferred to water, all of that heat is retained in the house so there will be a corresponding drop in the gas used by the boiler for heating.

 While there will be a small amount of warming from the waste heat, this won't necessarily reduce gas used by the boiler for heating, e.g if the heating thermostat isn't influenced by the kitchen temperature.

 And I suspect this is the case for most homes, in that any extra heat in the kitchen (e.g from cooking) just makes the kitchen hotter than the rest of the house.

Captainkirk54

Astria

"I agree that induction stoves loose very little to the air, but how much energy do they consume compared to how much energy they put into the object on the ring? For example, if a wireless charger for a toothbrush or mobile phone is similar (I don't know if it is or not), they typically draw 2A from the wall to put 1A into your phone"

Exactly that. The magnetic energy is created by a reactive electrical current, but normally the exact current cannot be measured without special equipment. It can be anything from 1.5 to 1.8 times the measured resistive load. In the case of the hob there are more losses involved converting magnetic energy to heat energy. The induction hob would not have got off the drawing board at todays energy prices

The wireless chargers you mention are indeed inductive as Tesla went bankrupt before he could give us wireless power. Electrical inductive loads have higher losses and heavier currents than direct wired resistance loads. The 2A "draw" current you refer to will equate to about 3A inductive current

doodling

Hi,

Captainkirk54 said:

Astria

"I agree that induction stoves loose very little to the air, but how much energy do they consume compared to how much energy they put into the object on the ring? For example, if a wireless charger for a toothbrush or mobile phone is similar (I don't know if it is or not), they typically draw 2A from the wall to put 1A into your phone"

Exactly that. The magnetic energy is created by a reactive electrical current, but normally the exact current cannot be measured without special equipment. It can be anything from 1.5 to 1.8 times the measured resistive load. In the case of the hob there are more losses involved converting magnetic energy to heat energy. The induction hob would not have got off the drawing board at todays energy prices

The wireless chargers you mention are indeed inductive as Tesla went bankrupt before he could give us wireless power. Electrical inductive loads have higher losses and heavier currents than direct wired resistance loads. The 2A "draw" current you refer to will equate to about 3A inductive current

With respect to induction hobs, common sense tells us that they can't be that inefficient as noting but the saucepan is getting hot. In reality, I suspect that there will be something like 10-20% losses in the power electronics which will be dissipated under the counter rather than in the saucepan. That still makes them the most efficient way of heating a pan (but not the cheapest due to the differen in price between gas and electricity),

With respect to inductive phone/toothbrush chargers then yes they will be inefficient, it wouldn't surprise me if they were less than 50% efficient.

The stuff above about reactive loads is largely wrong because in the case of hobs they are required to have a power factor near 1, achieved by power factor correction (PFC) on the input, and in the case of phone chargers they are supplied by DC (admittedly from a switching power supply which may or may not have PFC).  I don't know whether electric toothbrush inductive chargers operate at 50Hz so can't comment on them but they aren't very big loads anyway.

coffeehound

Yes can't see how the electric kettle ends up less efficient than induction.  The resistive element is almost 100% inside the water!

doodling

Hi,

coffeehound said:

Yes can't see how the electric kettle ends up less efficient than induction.  The resistive element is almost 100% inside the water!

I was very careful in the wording in my last post to refer to the heating of pans, where induction is no doubt the most efficient form of heating.

If on the other hand you are talking about heating kettles then from an efficiency perspective you can't beat an electrical element immersed directly in the water.

(Hmm, wonders if some form of multi-stage heat pump system might be more efficient then a kettle, probably would be, but only when boiling hundreds (thousands?) of litres of water due to the thermal masses of all the components involved).

All this is of course orthogonal to cost where in the gas vs. electricity the price difference between them dominates.

Petriix

k_man said:

Petriix said:

While a gas stove top kettle might only be 40% efficient in terms of heat transferred to water, all of that heat is retained in the house so there will be a corresponding drop in the gas used by the boiler for heating.

 While there will be a small amount of warming from the waste heat, this won't necessarily reduce gas used by the boiler for heating, e.g if the heating thermostat isn't influenced by the kitchen temperature.

 And I suspect this is the case for most homes, in that any extra heat in the kitchen (e.g from cooking) just makes the kitchen hotter than the rest of the house.

If, however, the kitchen is hotter then that heat must go somewhere. Some will likely be lost to the outside world but most will be distributed around the house - that's just how thermodynamics works.

In my house it's fairly direct in that the main thermostat is in the dining area linked to the kitchen. 

Captainkirk54

doodling

"The stuff above about reactive loads is largely wrong because in the case of hobs they are required to have a power factor near 1, achieved by power factor correction (PFC) on the input, and in the case of phone chargers they are supplied by DC (admittedly from a switching power supply which may or may not have PFC).  I don't know whether electric toothbrush inductive chargers operate at 50Hz so can't comment on them but they aren't very big loads anyway."


Most AC reactive loads were required to be PF corrected to between 0.8 and 0.9.
False unity (1) should not be obtained artificially due to the danger of the destructive resonance condition.

Traditionally inductive loads have been corrected by connecting capacitors as you say, as capacitance is the direct polar opposite of inductance. Both of these conditions are known as reactive power. You can reduce the effect of wasted reactive inductive energy by installing capacitors but these also use reactive power/energy which you have to pay for.

Power companies used to meter and charge PF penalties to large power users. Now we just all pay for poor factor in the form of high electricity prices.

So to sum up 

Real Power – The power supplied to the equipment that performs useful and productive work.

Reactive Power – The power required by equipment such as transformers and motors to produce magnetic fields enabling actual work to be done.

Apparent Power – The vector sum of real power and reactive power

Unity - Artificially achieved cancellation of (XL) inductive reactance and (XC) Capacitive reactance.

The induction hob originated on the basis of safety from touching hot surfaces and easy clean hobs, not energy efficiency.

The induction hob involves changing electrical energy into magnetic energy (Reactive Power) then changing magnetic energy into heat energy - corrected by capacitors using Reactive Power. All of these are energy losses which you have to pay for.

Of course the induction hob is not more efficient than an electric element which is directly
immersed in water.

I do not know enough about phone and toothbrush charger technology to comment - only that in the electrical trade we attract a number of queries about bathroom shaver sockets overheating when used to charge toothbrushes which do not charge fully.

This has been addressed in the trade by the provision of beefed up dual bathroom shaver sockets, which have both charger and shaver logos on them. This issue does not occur when the charger is plugged into a normal 13A socket.

QrizB

We seem to have a difference of opinion re. induction hobs.

The US Department of Energy carried out a study about 8 years ago and concluded induction hobs were slightly more efficient than resistive ones. Wikipedia summarises this as:

For comparable (large) cooking elements the following efficiencies were measured with ±0.5% repeatability: 70.7% - 73.6% for induction, 71.9% for electric coil, 43.9% for gas. Summarizing the results of several tests, DOE affirms that "induction units have an average efficiency of 72.2%, not significantly higher than the 69.9% efficiency of smooth—electric resistance units, or the 71.2% of electric coil units"

The US DoE paper is here for anyone who wants to read it:

https://www.govinfo.gov/content/pkg/FR-2014-12-03/pdf/2014-28212.pdf