19 votes
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Could a mainspring be used to generate train acceleration during starting-up from the kinetic energy stored during its slowing down?

I found that on some Spanish lines, the kinetic energy during braking is converted to electricity and used by other trains from the same line (research paper), but why not keeping the mechanical ...
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  • 8,229
17 votes
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Why does compressed air energy storage use intercoolers?

Not just CAES system, intercooling is desired for multi stage compressors in general, if you checked this diagrams of isentropic, polytropic and isothermal compression processes between the same ...
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  • 2,149
14 votes

Can the Sabatier reaction power a vehicle?

According to Wikipedia: It [Sabatier reaction ] involves the reaction of hydrogen with carbon dioxide at elevated temperatures (optimally 300–400 °C) and pressures in the presence of a nickel ...
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  • 2,149
11 votes

Could a mainspring be used to generate train acceleration during starting-up from the kinetic energy stored during its slowing down?

On the London Underground, many stations use gravity. The line runs uphill into the station, and then departs downhill. This gives a large amount of energy storage, for free, with no additional moving ...
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  • 406
7 votes
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What causes rechargeable batteries to age? What can be done to extend life of these batteries?

One of the problems that plagued older rechargeable batteries (e.g. Nickel Cadmium ($\text{NiCad}$) and Nickel Metal Hydride ($\text{NiMH}$)) was the memory effect. The memory effect occurs when a ...
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  • 2,485
7 votes

Could a mainspring be used to generate train acceleration during starting-up from the kinetic energy stored during its slowing down?

Note also that springs are subject to eventual (and very sudden) failure as they develop cracks with age and a very sudden 5.6MJ energy release inside a railroad car would be exceptionally dangerous!
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6 votes

Why aren't gravity batteries everywhere?

So, this battery costs US$70, weighs 406 grams, and holds around 200,000 Joules of energy. To get the same energy from that weight as a "gravity battery" you'd have to pick it up over 49 kilometers ...
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  • 2,218
6 votes
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Can large capacitors allow power plants to run at full load and store excess electricity?

Capacitors are currently "rather too costly" for this purpose. I've revised my estimated cost after some more research but you appear to be in the 'well over one hundred thousand dollars" range! ...
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5 votes

Is compressed air energy storage economically viable in the home?

It isn't completely infeasible. Just to get a ROM (rough order of magnitude), let's assume that a typical household that isn't using electricity for heating uses about 1 kW on average, and that you'd ...
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  • 6,749
5 votes

Working hours of power plant generators

Nuclear power plants are always working, except circa one month/year for maintenance. It's mainly because stopping the nuclear reaction and cooling the reactor down is a very long and difficult ...
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5 votes

Why aren't gravity batteries everywhere?

Consider 1 kWh = 1000 W * 3600 seconds = 3,600,000 J. 1 kg lifted 1 m = ~10J. Let's use 1 metric tonne. 1000Kg. So we get 10,000 J per meter of elevation. 3,600,000 / 10,000 = 360 meters. Around ...
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5 votes
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What happens to generated electricity if it is not used?

TL;DR: a small portion of the excess energy is stored in the form of rotational kinetic energy, however, generator controls make it so these amounts are not significant. electricity generation (Al ...
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  • 22.6k
4 votes

Can lithium ion batteries solve the world's energy storage problem?

I would like to answer this question slightly differently. The challenge with rechargeable batteries (Lithium Ion), each charge discharge cycle causes internal resistance of the battery to increase. ...
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4 votes

Using a manual pulley system to repeatedly lift a rock and gather its falling energy to store in a power bank

You are describing what is called a gravity battery. See link here: https://en.wikipedia.org/wiki/Gravity_battery Short answer no, and the simplest way to understand it is that you can never create ...
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4 votes

Why no big and slow flywheels for utility-scale energy storage?

What you are missing is that it is cheaper to increase the storage capacity of a flywheel by increasing its rotating speed than it is by making the flywheel bigger. This is the reason why (proposed) ...
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4 votes

Could a mainspring be used to generate train acceleration during starting-up from the kinetic energy stored during its slowing down?

Mechanical energy recovery has been tried on rapid-transit systems, in the form of flywheel storage. This is known as KERS in the motorsport world, but usage on a railway requires much higher ...
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  • 381
3 votes

Do commercial fuel cells actually exist or it is just hype?

Fuel cells have hit the start of commercial success in Japan, where sales so far have been at least 120,000. Given they only became viable commercial products very recently, that's pretty good uptake. ...
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3 votes
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How do you use an insulation jacket's R-value for calculating heat transfer from a hot water tank?

The insulation R-value already accounts for thickness, so you can ignore it. You just have to account for the effect of surface area and temperature difference. The SI units of R are $\frac{K \cdot ...
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  • 206
3 votes
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Storage losses of a heat storage tank

Heat loss due to conductivity of the walls of your container assuming the ambient outside temperature, $$ \frac{\Delta Q}{\Delta t*A}=-k \frac{\Delta T}{\Delta x} =C_{constant}$$ In the above ...
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  • 21k
3 votes

Working hours of power plant generators

There isn't a single answer that covers large power plants around the world. There's way too much variation in generation plant, and way too much variation in the way that plant is used. Some plants ...
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  • 3,701
3 votes

Can the Sabatier reaction power a vehicle?

Algo has given you a good answer about the detail. There is a much broader, more widely-applicable, kind of answer. Converting any form of energy to heat introduces huge inefficiencies. It is the ...
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  • 3,701
3 votes
Accepted

Heat transfer coefficient of a cylindrical hot water storage tank depending on its size

In a tank with no fluid movement and no heat source with steady ambient temperature, the temperature of fluid are layered strata roughly in onion layers but favoring the top of the tank, meaning the ...
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  • 21k
3 votes
Accepted

Does a fully mechanical heat pump make sense?

Virtually every possible way of doing this is already out there. For bolt-ons, you can find propshaft pto chain drives and belt drives, hydraulic and mechanical engine pto systems, and front of block ...
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  • 3,425
2 votes

Is compressed air energy storage economically viable in the home?

The existing answers do a pretty good job of explaining the sizing and the economics, but surprisingly for an engineering site, skip over the equipment. And that's where this becomes totally ...
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2 votes

Is compressed air energy storage economically viable in the home?

I'm going to do some naïve math. So while charging your setup at night, you take in $x$ kilowatt-hours per hour. Multiply this by 7 hours, and you've taken in $7x$ kilowatt-hours. At a cost of $\frac{...
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  • 2,485
2 votes

Can large capacitors allow power plants to run at full load and store excess electricity?

Capacitors typically store power over short periods of time, seconds or minutes. This is too short to be useful for the electrical power grid. Typically peak power demand occurs during the day, ...
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  • 236
2 votes
Accepted

Working hours of power plant generators

There isn't currently any practical means of storing electrical energy on a large scale. There are technologies which can store energy for specific applications but certainly nothing which would have ...
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2 votes

Working hours of power plant generators

A typical conventional power plant may consist of multiple generating units rather than one big huge unit. By having multiple units, the plant is better able to respond to changes in demand during ...
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  • 302
2 votes

Pneumatic Actuators - System Reversibility. Is it possible to use an actuator to store energy?

A,B,C, and D are normally closed solenoid valves. The valves with the arrows above them are pneumatic check valves, such as reed valves, with the arrow indicating flow direction. So basically, ...
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  • 3,525
2 votes

Why aren't gravity batteries everywhere?

Are there some shortcomings that I am missing here? Yes there are a couple of things you have missed. Firstly I will deviate slightly from your question but I believe this is relevant. The need for ...
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