1 kwh, what is it?

[bernardd]

there is no confusion but equivalence between all forms of energy (I did not take into account the yields, of course).

There is theoretical equivalence at first glance only, but it is necessary to take into account the "potential" of energy, which will influence the efficiency of the real transformation between heat and mechanical work.

For example, if you have 1 kWh of thermal energy in a liquid at -10 ° C / 263 ° K, you will have a lot of trouble extracting any mechanical work from it.

The example is true without taking performance into account, but it is not realistic, hence Remundo's remark which indicated a ratio of 3 to 1 when we try to transform thermal energy into mechanical work, in real life.

There would thus really be 400l of water raised at 300m, and that is always more than what I would do in a single trip :-)

At the rate of 1h / 300m ascent on foot, with a 40kg bag, I would need more than 10h ... not counting the descent.

On the other hand, 2/3 of the thermal energy which could not be transformed into mechanical work remains to be dissipated in the form of heat, for example to heat water in the house: this is the principle of cogeneration . More useful in winter than in summer :-)

[oiseautempete]

With the same idea:

When the steam engines began to replace the horse, an attempt was made to measure their power in relation to the power that a horse could develop.
A horse being able to lift a mass of 75 kg at the speed of 1m / s, we deduce an equivalent power of 736W.

Yes, except that this is completely wrong, the horse's power has been very undervalued because it is on the order of 12 horsepower on average ... and again, its pullout capacity since stopping
(= starting torque) is enormous where that of a heat or steam engine is very low ...
When raising 1,2 tonnes of water with 1 kW, it only works in theory ...

[jmarc3]

I see that I do not master the quotes!

Bernardd wrote:
There is theoretical equivalence at first glance only, but it is necessary to take into account the "potential" of energy, which will influence the efficiency of the real transformation between heat and mechanical work.

For example, if you have 1 kWh of thermal energy in a liquid at -10 ° C / 263 ° K, you will have a lot of trouble extracting any mechanical work from it.

The example is true without taking performance into account, but it is not realistic, hence Remundo's remark which indicated a ratio of 3 to 1 when we try to transform thermal energy into mechanical work, in real life.

There would thus really be 400l of water raised at 300m, and this is always more than what I would do in a single trip

Excuse me, Bernardd, there is no equivalence only at first glance, the equivalence between all forms of energy is a basic principle of physics (hence the famous E = MC2).
So 1kwh is 1200l high 300m.

That said, you're right, each time we go from one form of energy to another, we lose part of it in the form of heat (hence the thermodynamic principle of irreversibility).

In real life, if we wanted to mount 1200 liters of water at the top of the Eiffel Tower, we would use a pump and we would consume 1 kWh divided by the efficiency of the pump, maybe 1,4 or 1,5 kWh (I am not a pump specialist!), the difference being dissipated as heat.

[bernardd]

In real life, if we wanted to mount 1200 liters of water at the top of the Eiffel Tower, we would use a pump and we would consume 1 kWh divided by the efficiency of the pump, maybe 1,4 or 1,5 kWh (I am not a pump specialist!), the difference being dissipated as heat.

You seem to be talking about a pump with an electric motor. Is that the case ?

Your example would then be valid in countries with a majority of hydroelectric production.

In France, the majority of electricity goes through a thermal stage, and it would then require 4,2 to 4,5KWh thermal to obtain this result ... without counting transport losses.

In reality, we would be between 7 and 7,5KWh with a real yield, including transport, of 20% for nuclear power, which represents 80% of electrical production.

[Christophe]

Here is a good subject which puts back a few "points on the i's" ... we now have our Jean Marc ... Jancovici on econology!

[jmarc3]

It doesn't matter whether the pump is electric or pedal operated!

It takes 1 kWh of 'useful' mechanical energy to raise this water, as the pump does not have 100% efficiency, it will take more than 1 kW of primary mechanical energy to activate it. If you want to nitpick, there are also friction losses in the pipes etc.

If you consider that the pump is powered by an electric motor, that electricity is produced from such or such primary source of energy, it is another debate.

[Christophe]

It doesn't matter whether the pump is electric or pedal operated!

Indirectly according to the use of the kWh in question I think that it matters.

Because if the Kwh in question is used to make exclusively thermal, well the primary energy, also thermal therefore (unless this kWh comes from an Enr source ...), must be taken into account in order to compare 2 quantities of the same energetic nature.

So to "do well" you have to compare:

- electrical kWh and mechanical Kwh (close to generator output near = 0.8 to 0.9)
- Electric thermal kWh and "flame" thermal kWh (factor 2.5 to 3 approximately)

[tigrou_838]

hello, great what forum.

I have a question for the professionals, we are talking about donkeys, horses, petrol, cars, electricity.

have you think of food and other for animals, what is in kwh the consumption to feed a horse, so that it can develop the x kwh of power and mount the 1200litres of water at the top of the eiffel tower.

oopssss

[jmarc3]

Here is a good subject which puts back a few "points on the i's" ... we now have our Jean Marc ... Jancovici on econology!

Very flattered to be compared to the other Jean-Marc whose unfortunately I do not have the skills.

[Christophe]

have you think of food and other for animals, what is in kwh the consumption to feed a horse, so that it can develop the x kwh of power and mount the 1200litres of water at the top of the eiffel tower.

The overall CO2 balance would be much worse than oil ...