17
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 pressure limits you can see that the curve that requires minimum power (area to the left of the process curve) for the same inlet and outlet conditions is the curve ...
14
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 catalyst to produce methane and water. $$ CO_2 + 4H_2 \rightarrow CH_4 + H_2O + \text{Energy} $$
as you can see from the previous chemical reaction, to obtain 1 ...
7
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 rechargeable battery is not fully discharged. It then "forgets" that it has a greater capacity than it thinks it has, and so in the future it discharges less.
A ...
6
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 into the air.
There are applications where picking stuff up and powering things as it falls is useful -- the gravity-powered lighting for 3rd-world countries is ...
6
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!
The dear way: If you were to assemble a 10kF 150 volt capacitor from available smaller capacitors now it would cost around 1 million dollars and store about 30 ...
5
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 like to be able to store a half day's energy, or 12 kWh, which is roughly 45 MJ.
Commercial air compressors can easily achieve 15 bar or so (over 200 PSI). The ...
5
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 process (a few weeks). So "turning on" and "turning off" a Nuclear Power Plant (NPP) is not as simple as pushing a button.
The primary circuit (containing the water ...
4
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 a thousand feet.
Ok. Getting a 15 cm diameter well dug and cased is on the order of \$20/foot. So \$20,000 buys you a 1000 foot deep hole. Use whatever ...
4
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. This causes the usable life of the battery to decrease.
Therefore if the rise internal resistance over time is decreased or fully resolved then the Lithium Ion ...
3
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.
They're generally being used there as domestic CHP systems.
There are still open questions about their long-term reliability.
So yes, they've grown beyond ...
3
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 $\frac{K \cdot m^2}{W}$
Heat transfer increases as the surface area increases, so Q is calculated as:
$$Q_{insulation}=\frac{A (T_f-T_i)}{R}$$ and
$$Q''{insulation}=\frac{(...
3
Heat loss due to conductivity of the walls of your container assuming the ambient outside temperature,
$$ \frac{\Delta Q}{\Delta t*A}=-k \frac{\Delta T}{\Delta x} =C_{constant}$$
In the above equation, the left part is heat loss per unit of area per second and the right side is the thermal conductivity, K multiplied by the temperature gradient which is ...
3
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 will operate for just a few minutes occasionally.
Some will run 24/7 except when closed for maintenance.
And yes, absolutely, the energy is stored before it ...
3
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 lowest-quality form of energy. So if you want to do any work with that energy at all, it is best to do it before it gets turned into heat, whenever possible.
Once ...
3
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 heat is gradually decreasing from the top in ellipsoid layers roughly following the geometry of the cylinder in you question, imagine inverte flames getting ...
2
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 infeasible.
LightSail is arguably the closest to making compressed air energy storage (CAES) economically feasible at any scale. According to LightSail's CEO, the ...
2
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{5.4\text{p}}{\text{kWh}}$, you've paid $37.8x \text{ p}$.
Let's say that when the electricity is on, you use $y$ kilowatt-hours per hour. Multiply this by 17, ...
2
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, often mid-afternoon. Excess power is available at night. To be useful, then, the energy must be stored for many hours. There are many possible technologies for ...
2
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 much of an impact on national level distribution.
For obvious reasons, in a distributed power grid the power demand will vary considerably throughout any ...
2
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 the day or to shut down generating units for maintenance.
By having power distributed by a sophisticated electrical grid, if a plant in one region of the country ...
2
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, with no power, pushing the piston in and out of the air cylinder causes an inlet check valve to open and a check valve to the flask to open and you act to ...
2
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 localised storage has only relatively recently become desirable. With the increase of large scale Solar and in particular wind farm projects the need for ...
2
It sounds like what you are after is increased energy security. You want a backup which would have a very low load factor - it wouldn't get much use each year. You want fast response, times of high power, and a decent amount of storage. But it sounds like you don't need absolute continuity of power - it's ok if power goes out for a few seconds.
Almost all ...
2
In the diagram shown, then if the water temperature of the storage tank falls below the set value, the aux boiler comes in to augment the water temperature.
Other possibilities include the use of a diverter valve so when the tank water temperature is too low, the valve changes to demand water heated by the boiler, if that boiler has a rapid response then ...
2
I'll approach your question from another perspective. This is a very simplistic calculation, but it will serve to make a point.
The following graph presents the cost and gravitational density of Lithium ion batteries.
The data is up to 2013. Let's assume for argument sake that we are at 300 Wh/kg.
Let's take the US residential energy consumption 11$\left[\...
1
In solid-fluid interfaces the heat transfer coefficient (HTC) is dominated by the properties of the fluid and flow, geometry has no effect on the HTC other than promoting zones where flow changes velocity/pressure/turbulence.
In your case, for a simple geometry like a cylinder, the HTC will not change with the change in dimensions (if you keep the magnitude ...
1
You should first "balance charge" the battery to full capacity using a suitable charger. Batteries do vary between manufacturers, and between battery types so check the manufacturer's rated voltage. Most modern chargers are smart enough to recognize the change of resistance as the battery charges to prevent over charging.
Once the battery cells maintain the ...
1
Suspended pipes are heavy and need support - any change of direction also creates a force - and there is the aerial impediment to consider : Birds, parachutes planes etc.
Also some "pipes" are cut directly into the rock saving on material costs and consider that some of these pipes have a water flow rate of 45m3/s so the inertial forces are massive.
1
@geekly: agreed. Also, insulation thickness will increase surface area for external convection, as:
$$ Q_{jacket \to air} = 2\pi (l_{heater})(r_{heater} + t_{jacket})h(T_{jacket} - T_{air})$$
This effect prompted the critical radius of insulation for cyclinders:
https://en.wikipedia.org/wiki/Thermal_insulation:
$$ r_{critical} = \frac{k}{h} = \frac{t_{...
1
It would be a waste of work, if the air did not cool in the storage cavern!
But as you say, it does cool, hence you'll have less pressure available when expanding the air than the pressure you needed to work against when compressing it. The excess pressure could be avoided by compressing in isothermal mode, and as Algo said you approximate isothermal by ...
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