[edited] a grid of millions of capacitors each one individually and digitally controlled to release or accumulate power, can then be strung along and around the mains lines, built into walls and roofs of any existing or new structures, and releasing power in the correct direction, quantity and phase so as to emulate the AC. Then gradually lower the power needs at peak hours to use the accumulated power from off-peak.
Until the large utility companies buy into the technology (and buy it off), small companies can use it to accumulate off peak night-time power, or to store night-time wind or marine current energy, or to run an off grid solar power station at night.
[Edited - the following section was added]: Sets of capacitors are set to be connected or disconnected via controlled switching, so that they are charged during different times of the AC cycle, with some charging from the current one way, and others set to be charged when the current is the other way. When needed, they are then discharged in sequence in a controlled manner so as to emulate the AC current on the mains.
The control system could be distributed, or made central for every group of capacitors, using PLCs, distributed DSCs and other advanced low cost industrial control systems.
Efficiency of regular capacitors can be extremely high, with almost no loss of power or energy (see link)
An industrially manufactured product in these lines can presumably cost much less than comparable battery systems.-- pashute, Sep 30 2014 Raising capacitor efficiency (reducing energy loss) http://www.smpstech.com/charge.htm [pashute, Oct 01 2014] AC power storage shameless self promotion [xaviergisz, Oct 07 2014] So these are magic capacitors which work in alternating current then? And they're cheaper than normal capacitors but don't have any charge leakage?-- Loris, Sep 30 2014 Capacitors are hellishly inefficient at storage. An order of magnitude worse than batteries. Supercapacitors are better, but then you are limited to low voltage and the losses associated with voltage conversion AC/DC problems. Batteries are expensive and less efficient than pumped storage. Which is why we use pumped storage.-- bs0u0155, Sep 30 2014 I wouldn't worry about charge leakage much but, while caps are really really fast and very robust and long lasting, they aren't very efficient. Also they're rather expensive per kWh in terms of both cost and size/weight.-- FlyingToaster, Sep 30 2014 In terms of energy conversion efficiency, caps can be pretty good. On an AC system, to charge a cap, just connect it between hot and neutral just as the voltage crosses 0 then disconnect it when the voltage reaches the peak. To put the power back on the grid, connect it when the voltage is at it's peak (matching the voltage on the cap), and let the cap dump its charge until the voltage reaches 0 before disconnecting it. With a large number of caps you could connect one (or more) each 60Hz cycle to have fairly fine control of how much power is being added or removed from the grid.
This results in a very simple control circuit for each capacitor, but the problem is that you need to have a whole lot of capacitors. Say for example that during a typical day you want charge for 6 hours, discharge for 6 hours and be idle for 12 hours. To accept charge for 6 hours, you need one cap for each cycle = 60Hz * 60s/min * 60min/hr * 6hr ~= 1.3 million. There needs to be a high voltage switch with low leakage for each cap and each needs to be able to handle the peak current that an equivalent battery system would use. I suspect those 1.3million transistors will be quite a bit more expensive than the electronics to convert between AC to DC and back for a battery based system.-- scad mientist, Sep 30 2014 To benefit from off-peak electricity, simply buy a long extension lead and find a like-minded friend who lives 180° away from you.-- MaxwellBuchanan, Sep 30 2014 great, now I need a friend in the mid pacific who's also on 120V 60Hz.-- bs0u0155, Sep 30 2014 Well, maybe you and a friend could share a 230V donation from the rest of the world?
Hmmm.....aha, reversible lightning.-- not_morrison_rm, Sep 30 2014 [Scad mientist] clarified what I thought I had described in enough detail. No magic here [Loris], but actually some quite simple electronics. Capacitors can be dirt cheap. Regular capacitors, and that's what I'm talking about. Yes they take up much space, but if distributed as I described it can be practical.
The cost of control (transistors) can be lowered by using PLCs, extreme low-cost DSCs, and other industrial control systems.
Of course to get this going a serious investment would be needed, but that doesn't mean the idea is not worth its while.
And about capacitor efficiency - it can be set to almost 100%, with any regular capacitor. See link.
I'm editing the idea for clarity.-- pashute, Oct 01 2014 No, it is an issue.
I'm not saying it won't be possible to use capacitors to store useful amounts of energy in future, if better capacitor technologies come along.
However, distributing current technology capacitors like you propose just has ridiculous issues.
The specific energy capacity of capacitors compared to batteries is a joke. They're great for power - they can dump their energy quickly - but they can't hold much energy per unit weight. Large, cheap capacitors leak like sieves. Controlling circuits - well, you seem to have missed the bit where scad mientist pointed out how expensive even his simple system would likely be. I'll get back to this later.
But hey, let's suppose for the sake of argument that we get a really efficient energy storage system. Why the hell would we run it along power-lines? I can imagine that this might be handy for everyone to have a bit of storage in their property. If it's really small, we could have it all in one compact unit. Fine. Spread out through the walls and roof? Nope. We've already decided it holds a lot of juice, so ... well, maybe you could mull on why some electrical devices have warnings about opening them up even when the power is off (hint - they're the ones with big capacitors in). Alternatively, what if they're cheap and efficient, but really large? Wouldn't it make more sense to have them all in one facility? What do you gain from strewing them along the power lines? I mean, other than disadvantages in maintenance, control, security and safety.
Now, controlling circuits. You explicitly want each one to be controlled independently - fine, but that's going to cost extra. Both financially and in efficiency. Does each one have a clock so it knows when to charge or discharge? Let's assume not. So how do you propose to ensure that they play nicely with the rest of the power system? A side-channel? Or were you hoping to communicate with them via mains frequency changes? That's not going to be easy when every single other capacitor you've installed is investing its energy fighting your control.-- Loris, Oct 04 2014 Are you sure I have not given adequate answers to all your questions?
It is switched off the mains with a PLC. Not fighting with anyone for anything. Modern switching can run dirt cheap for millions of switches. And take a minute amount of power to run.
Simple standard modern capacitors have almost zero leakage current when switched off from the circuit, and storing electricity, mind you, if you have not heard, is one of the major challenges that any electric company has, let alone when managing a distributed (renewable energy) grid. So this could be a better solution than CAES or RESS. No big capacitors, all are relatively small and harmless (say standard 50 volts each, 2200mf caps).-- pashute, Oct 06 2014 I will dispute your claim of dirt cheap. While it is true that you can get millions of transistors for less than the cost of a bag of topsoil, those are on a VLSI chip and can't handle anywhere near the voltage or current you would need. If you get switches big enough, but only use them for 16ms out of each day, you'd be better off making an inverter with switches that are 1000x larger, but are used for many hours each day.
I started doing the calculations to see what switch you would need for a system with a million 2200 uf caps, compared to a inverter system with lead- acid battery bank with similar power and capacity, but then decided I didn't have that much time to burn right now.
Now I would not be hugely surprised if someone actually did (or has already) found a cost effective way to build capacitors designed for stationary operation. The key would be making them ultra- cheap and not worrying about weight or size. But even if that worked out, using them in an ultra- distributed system like this won't be as cost effective as using a fairly standard inverter but enhanced to handle the higher voltage range of a capacitor compared to a battery.-- scad mientist, Oct 07 2014 So Bath County Pumped storage can run for about 16 hours on a full reservoir. At 3003 MW. That's 176,644,800,000,000J.
Total cost 1.6 billion in 1985. About 3.5 billion now.
Capacitor: 75 Joules per $ Car battery: 170,000 Joules per $ Pumped Storage: 50469 Joules per $
I'm surprised, and writing a letter regarding car batteries to the government.
I'll probably get a letter back regarding longevity, charging efficiency, and there not being 103 million spare batteries.-- bs0u0155, Oct 07 2014 isn't charging low voltage batteries pretty horrific efficiency wise? Inverting it afterward? hmm, web suggests transformer rectifier can be 95%, lead acid charge/discharge can be 60-95% and inverters 94-96%.
So 1,700,000 in, assuming Transform/rectify> charge> discharge> invert at 95>90>90>95% gives 1,700,000> 1,615,000>1,453,500> 1,308150> 1,242,743J. about 73% of the original.
Pumped storage is up in the 80% region. Still ballpark. You get some free when it rains too, if you have catchment area.
I think they should be coupling power stations physically. i.e. Fuel>Steam>turbine> pump. Then let it out when you need. Cuts out steps Fuel> steam> turbine> generator> transformer> transmit> transformer> pump.-- bs0u0155, Oct 07 2014 So we conclude that pumped storage facilities are less economical than lead-acid batteries for starting your car in the morning?-- pocmloc, Oct 07 2014 //So we conclude that pumped storage facilities are less economical than lead-acid batteries for starting your car in the morning//
And people say we're wasting our time.-- bs0u0155, Oct 07 2014 //Are you sure I have not given adequate answers to all your questions?// Quite sure.
//It is switched off the mains with a PLC. Not fighting with anyone for anything.// I don't think you understand the issue. How are you telling the capacitors to store or release their energy? There are basically three options. 1) By timer. 2) Through the mains. Changing either the amplitude or frequency of the AC. 3) Through a side-channel.
(1) means as many clocks as you have capacitors, and is not responsive to supply and demand. (3) means you need all the infrastructure of the side-channel, and all that entails. (2) is how load is already regulated to some extent, so we know that method works for a decent fraction of power -sinking- devices (apparently some behave in the opposite manner to what you'd want). However, if you have millions of very relatively stupid power -sources-, I think there might be issues.
And you haven't explained why you want to string them along power lines, or in peoples walls or roofs despite all the disadvantages of doing that.-- Loris, Oct 07 2014 isn't the issue more to do with capacitors being ideal for very short term storage/release <1 second. And the storage demand being on a different scale >1 min. Then add in the capacity issues. The occasional computer controlled capacitor bank could be useful for local conditioning, say at the sub-station level. Where grid spikes could be absorbed and minor local brown-outs smoothed.-- bs0u0155, Oct 07 2014 random, halfbakery