James Prescott Joule - Wikipedia
However, there is a relationship between them. To find it, you must know the amperage, the voltage, and the wattage (number of joules per second). The wattage. What is the difference between a kW and kWh? 1 Watt is a rate of energy usage of 1 Joule every second, or 1 Joule per second (J/s). The unit of energy is the "Joule" - a Watt is just a flow of one Joule per second. But here we must make a clear difference between thermal energy and output.
So kW means kilowatt which is Watts. It is a measure of power. Notice that, if you like to keep anal electrical engineers like me happy, the correct way to write it is always with a small k and a capital W. The size of a solar system is defined by its peak power. A kWh is a measure of energy not power. If your solar panels for example continuously output 1 kW of power for a whole 60 minutes, you will have produced 1 kWh of energy.
The amount of electricity you use or generate is defined in kWhs. Why is the difference between Energy and Power important? It is very common for people to mistakenly interchange the terms energy and power as if there is no difference.
James Prescott Joule
Most people do it all the time without noticing. It drives electrical geeks like me up the wall. Especially when I read it in national newspapers and books!
If someone is talking about their electricity usage and says: Well it is actually quite important if you are buying a solar system. If someone says they need a solar power system to produce 8 kW, they might end up being quoted an 8 kW solar power system. If you do you may end up with a solar system that is completely the wrong size!
How do kW and kWh relate to batteries? When buying batteries, you need to think about both the power of the battery and the energy storage capacity of the battery you are looking at.
The energy storage capacity of the battery is measured in kWh. Its power is 5 kW, so it can charge or discharge at that rate. At full power, then, it can fully discharge in under 3 hours. The more energy kWh a battery has the more you can store and the longer it will last, the more power it has the faster you can get that energy in our out of the battery, In other words the more power it has, the more appliances you can power with it and the more energy it has, the longer you can power those appliances.
For normal household use, you want enough energy to get you through the night and at least 5 kW of power for speedy charging.
Top tip for filtering out the worst solar and battery salesmen: He measured the heat generated against the work done in compressing a gas. In many ways, this experiment offered the easiest target for Joule's critics but Joule disposed of the anticipated objections by clever experimentation. Joule read his paper to the Royal Society on 20 June however, his paper was rejected for publishing by the Royal Society and he had to be content with publishing in the Philosophical Magazine in I conceive that this theory Joule here adopts the language of vis viva energypossibly because Hodgkinson had read a review of Ewart's On the measure of moving force to the Literary and Philosophical Society in April Joule wrote in his paper: He wrote a letter to the Philosophical Magazine, published in September describing his experiment.
Much of the initial resistance to Joule's work stemmed from its dependence upon extremely precise measurements. Such precision was certainly uncommon in contemporary experimental physics but his doubters may have neglected his experience in the art of brewing and his access to its practical technologies. Joule's experiments complemented the theoretical work of Rudolf Clausiuswho is considered by some to be the coinventor of the energy concept.
Joule was proposing a kinetic theory of heat he believed it to be a form of rotational, rather than translational, kinetic energyand this required a conceptual leap: Joule's ideas required one to believe that the collisions of molecules were perfectly elastic.
We should also remember that the very existence of atoms and molecules was not widely accepted for another 50 years. Although it may be hard today to understand the allure of the caloric theoryat the time it seemed to have some clear advantages. Carnot 's successful theory of heat engines had also been based on the caloric assumption, and only later was it proved by Lord Kelvin that Carnot's mathematics were equally valid without assuming a caloric fluid.
Though both men had been neglected since their respective publications, Helmholtz's definitive declaration of the conservation of energy credited them both. Also inanother of Joule's presentations at the British Association in Oxford was attended by George Gabriel StokesMichael Faradayand the precocious and maverick William Thomsonlater to become Lord Kelvin, who had just been appointed professor of natural philosophy at the University of Glasgow.
Stokes was "inclined to be a Joulite" and Faraday was "much struck with it" though he harboured doubts. Thomson was intrigued but sceptical. Unanticipated, Thomson and Joule met later that year in Chamonix.
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Joule married Amelia Grimes on 18 August and the couple went on honeymoon. Marital enthusiasm notwithstanding, Joule and Thomson arranged to attempt an experiment a few days later to measure the temperature difference between the top and bottom of the Cascade de Sallanches waterfall, though this subsequently proved impractical. Though Thomson felt that Joule's results demanded theoretical explanation, he retreated into a spirited defence of the Carnot-Clapeyron school.
In his account of absolute temperatureThomson wrote that "the conversion of heat or caloric into mechanical effect is probably impossible, certainly undiscovered"  — but a footnote signalled his first doubts about the caloric theory, referring to Joule's "very remarkable discoveries".
Surprisingly, Thomson did not send Joule a copy of his paper but when Joule eventually read it he wrote to Thomson on 6 October, claiming that his studies had demonstrated conversion of heat into work but that he was planning further experiments.
Thomson replied on the 27th, revealing that he was planning his own experiments and hoping for a reconciliation of their two views.
Though Thomson conducted no new experiments, over the next two years he became increasingly dissatisfied with Carnot's theory and convinced of Joule's. In his paper, Thomson was willing to go no further than a compromise and declared "the whole theory of the motive power of heat is founded on As soon as Joule read the paper he wrote to Thomson with his comments and questions.
Thus began a fruitful, though largely epistolary, collaboration between the two men, Joule conducting experiments, Thomson analysing the results and suggesting further experiments.What is a Kilowatt hour?