[Closed] Storing Renewable Energy

I didn't listen to it but I think it's something that we should be throwing a lot more money at.

I do find it amazing that we haven't come up with a practical way of storing electricity yet.

If we perfect this, self-charging electric cars, and nuclear fusion then we may well stand a chance... if it's not already too late.

Electrolysis of salt water produce hydrogen, chlorine and sodium hydroxide using wind power, maybe wave power. Slow steady pretty much constant grinding the stuff out.
My thoughts anyway...

Hydrogen FTW, pump it into the gas grid for more win.

in the shorter term smart usage makes a bit more sense, I know some people who are equipping entire buildings with micro controllers and sensors that can up the heating system or air con etc. when surplus energy hits the grid from renewables (high wind days etc.) smoothing demand would make a big difference to the ability of the system to cope.

It was interesting. Compressed air in bloody great holes in the ground - hadn't thought of that.

Problem with hydrogen is that generating it using electricity [url= http://en.wikipedia.org/wiki/Hydrogen_economy#Electrolysis_of_water ]seems to be 50-80% efficient[/url], then you have the losses when converting it back to heat/movement/electricity. And it creates an awful lot of CO2. My understanding is that hydrogen is also a bugger to store and transport.

I tend to the view that the hydrogen economy is a distraction when talking about energy storage.

Compressed air underground: I'm no expert on rock, but you know how you get subsidence above old mine workings? What could possibly go wrong when you pump them full of compressed air? Not to mention the energy losses in the system. (I've also seen what happens when an air-pocket in a uPVC water pipe 2m underground lets go when somebody closes the outlet valve but doesn't turn off the pumps)

Given current technology my money is on [url= http://en.wikipedia.org/wiki/Pumped-storage_hydroelectricity ]pumped storage[/url] (Ffestiniog style), thermal storage in sodium or oil (as discussed in the focussed array thread) and batteries/smart-grid (even more so as electric cars become more widespread).

We had some solar PV people (Irish-German joint venture) visit us with a view to installing a 20MW plant: their installation was going to include several containers full of batteries and a few MW of diesel generators in order to guarantee supply. And needed 40Ha of land (~650m x 650m).

I've recommended it before and will do so again: [url= http://www.withouthotair.com/ ]Sustainable Energy Without The Hot Air[/url] puts energy use and energy generation into perspective, without seeming to have any particular axe to grind.

Hopefully somebody will be along shortly with a "disruptive technology" (a modern equivalent of the spinnning jenny or steam engine) that will give us a practical, economical method for storing energy.

Hydrogen would be perfectly easy to transport using existing gas infrastructure as I already said. You only need to do anothjer 70's style conversion like they did when converting to LNG from town (coal) gas.

As for generating CO2 - only if you're using coal power, electolysis using water produces only hydrogen and oxygen. You can also pull it from other chemical processes. Efficiency isn't so much of an issue if you have plenty of power to throw at it and it can be used to power a CCGT or peaking plant at the usual efficiencies.

[i]It was interesting. Compressed air in bloody great holes in the ground - hadn't thought of that.[/i]

A bit like this, although +100 yrs later 🙂

http://en.wikipedia.org/wiki/Hydraulic_power_network

I wonder if there are softer approaches - the problem with renewables is trying to make using then fit our current patterns of consumption. But our current patterns of consumption were deliberately shaped to fit the purposes of the energy production and distribution. So rather than try and bend on model of generation to behave like another - and incur huge infrastructure costs and losses in efficiency - it would be smart to change our lives so they fit the resources that are available to us

The reason, back in the day, the shops on the high street that sold electrical goods were run by your local power company is because those companies had to market goods and lifestyles to the population that shaped the demand we make on the grid. For instance they had to sell the idea of needing fridges and freezers to smooth out the demand between night and day. Incentives for off peak power - like storage heaters - existed for the same reason. Street lighting serves much the same purpose.

So while its important to take certain steps to store power its also important that we adapt to using power as and when its available - make hay while the sun shines - and expect that its not always available.

Hydrogen would be perfectly easy to transport using existing gas infrastructure as I already said

Wouldn't the hydrogen simply permeate through the pipework and be lost to the atmosphere or does that just take too long? Also what would be the impact on the Wobbe index, would there be a need to change out burners on cookers/boilers and the like?

it would be smart to change our lives so they fit the resources that are available to us

Absolutely, but with people wanting more electronic devices and bigger cars all the time, I can't see this happening.

I'll try and listen to the program but I wonder if HVDC interconnector grids were mentioned.

Sadly our need for light when it is dark and heat when it is cold will always remain. I guess times of day for heating up food could be up for grabs I suppose.

Whenever I have conversations about this sort of thing I always am reminded that reducing demand has to be the number one priority. But then I sit here typing on a laptop via wifi consuming numerous other resources so I am just as much part of the problem as anyone else.

Pump storage still seems like a good one, we've got stacks of reservoirs around the country, some of which are going to be suitable. And dam hydro's got the advantage of being very "switchable"

I don't really know how effective it is but small and microhydro are just really nice ideas. Locally a community project just put a microhydro generator on an old water reservoir- it's no longer used for water but is part of a flood prevention network now and has a constant spilloff, absolutely ideal. The flow's now slightly regulated for peak times too- a very low impact approach but could be made higher impact if required

Must be tons of reservoirs and old mill lades and watercourses and such all round the country that could usefully have generating capacity added, and little projects are much easier to fund and build. Often right on the demand as well.

Northwind - Member

Pump storage still seems like a good one, we've got stacks of reservoirs around the country, some of which are going to be suitable.

thing is, they're not suitable.

you need a big reservoir, AND it needs to be a good few hundred metres above the power station - to create the pressure

(pressure = density x g x height)

(power = pressure x volumetric flowrate)

basically, you need mountains, which are in short supply round these parts. the short supply gets even shorter when you start asking if you can flood a valley.

I did a little work on this a while ago, i'll dig out the trusty spreadsheet...

edit: to give you a couple of GW, for a couple of hours, you'd need 2 reservoirs, each capable of holding 1.5million cubic metres, that's a reservoir 50m deep, 500m along each side. Not extactly massive by reservoir standards, but try sticking 2 of them up a mountain in the Cairngorms...

yes, you could achieve the same thing with multiple, smaller reservoirs, but you still need significant height, and if you accept that it'll be tricky to build ONE pump storage plant in an area of natural beauty, imagine trying to build dozens...

(technically, it's possible, but there'd be a little protesting)

Hydrogen would be perfectly easy to transport using existing gas infrastructure as I already said

But sadly its not true. The existing gas infrastructure is not leak-proof to molecules the size of hydrogen.

Why does it have to be a big drop? I mean, I know that's the traditional approach, and if you're building one from scratch then sure, it makes sense. But where you've got a smaller drop or volume of storage, sure you've got less generation/storage capacity but also less infrastructure need- a smaller pump/return system and less local impact.

So, for example, back water from Loch Treig back up to Loch Laggan (the connection between the two doesn't have any hydro generation, I think, from memory it's a pretty shallow tunnel, but Laggan dam supplies Loch Treig with water for its hydro scheme.

You don't need to transport the hydrogen. You transport the electricity. It only takes a small series of imaginative leaps to envisage a future whereby we all store our energy at home in small CHP units

Surplus renewable electricity + water = hydrogen, oxygen and heat. Use the heat to heat the home (or heat water), store the hydrogen.

When renewable electricity is in short supply or there is excess demand we burn the hydrogen at home to provide heat and the electricity. The heat is again used in the home and electricity, if not required is fed back into the grid.

It's technically feasible to do this now. What will be needed is a refinement in cost, safety, etc etc. And a change in our thinking. Our gas network will become a thing of the past, and we become self-sufficient in energy production.

Existing gas infrastructure is not good enough to transport hydrogen as I understand it. Leakage would be a bit high. Perhaps natural gas with a percentage hydrogen.

Edit: Ah beaten to it.

Northwind - Member

Why does it have to be a big drop? I mean, I know that's the traditional approach, and if you're building one from scratch then sure, it makes sense. But where you've got a smaller drop or volume of storage, sure you've got less generation/storage capacity but also less infrastructure need- a smaller pump/return system and less local impact.

you need lots of height, OR lots of flow-rate.

power = pressure x flowrate.

a higher flowrate would mean you'd need bigger reservoirs - and that's MORE infrastructure, not less. MORE impact, not less.

higher flowrate means higher efficiency losses in the pipes feeding the turbines.

if you want efficiency, you need height, and it needs to drop in short distance.

As for transporting the electricity, you may need to upgrade the low voltage network into homes and businesses, cause that's built around an ADMD of 2kW or so.

As for transporting the electricity, you may need to upgrade the low voltage network into homes and businesses, cause that's built around an ADMD of 2kW or so.

My kettle is 3kW, I guess were buggered! A small series of imaginative leaps

Surplus renewable electricity

ahwiles - Member

you need lots of height, OR lots of flow-rate.

power = pressure x flowrate.

OK but to ask the same question in a different way, why does all of the height and flowrate have to be in a single location. I can see there'll be a minimum efficiency threshold but why couldn't 10 existing paired reservoirs with a small scheme each do the job of one massive pair?

(frinstance, cruachan can produce 440mw, loch treig produces 65mw. Treig might not be a great example as I imagine the smelter is a pretty much 24/7 power consumer but it just happens to be one I know the physical locations of!)

ADMD = after diversity maximum demand.

An ADMD of 2kW will happily run a 3kW kettle. It's just that it won't run all 100 houses on the estate's 3kW kettle at the same time.

If everyone wants to use surplus energy at the same time (they may not want to use it, but if they do it will be at the same time) then we may just have a tiny little problem.

The Fenland Alps should be perfect location for pump-storage for the North London commuter belt 😉

Where does the surplus come from? Letting a windmill spin when it's not needed, or unnecessarily
letting the top reservoir of an HEP scheme drain to the bottom one or something?

That's what the thread title is about. Dealing with a future whereby the energy mix consists of a lot of generating power that generates at a time we don't necessarily use it. Wind turbines spinning at night. Wave/tidal sources at night.

Mr 'Wind,

i think i've done a bad job of explaining myself. Of course we can approach things creatively, i'm sure we will (we'll have to).

but, let's not under-estimate the scale of the job.

we need to store gigawatt-hours, if pump storage is the answer, prepare to make lots of people very angry.

it'll be like the third runway at Heathrow, but without any rich buisness people fighting FOR it.

So in effect using the fact that electricity generated by wind at night to electrolyse water in to H2 and O2, then burning them in a heat engine to produce heat that turns a turbine in the home to produce electricity another time is as efficient as turning that wind tubine at the time it's needed?

What most of them up there said:

- hydrogen causes normal metal pipe to become brittle, you need stainless steel or composites (not sure how well plastic pipes would work - I remember seeing a hydrocarbons pipeline installed through Wiltshire in the 90s that I think was plastic).

- there already exists a vast infrastructure for transporting electricity, the only issue is economics with respect to turning expensive high-grade energy (electricity) back into low-grade energy (heat) for cooking and space-heating. Sadly the only alternative for cooking is to burn things (solar stoves not really being a practical proposition in many places). Solar-thermal and heat-pumps could work for water- and space-heating though, even in higher latitudes.

- generating hydrogen on-site with electricity is also (currently) wasteful: electrolysis is poor at room temperature and atmospheric pressure. Scientists busy working on it though. Current CHP installations as far as I know are economical because they run on natural gas or byproducts from other processes (landfill methane, biodigestors)

- focus needs to be on reducing energy usage: see the graphs of what we use energy for in the Without Hot Air document. "Stuff" is the embedded energy in the things that we buy.

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there already exists a vast infrastructure for transporting electricity

Yes, but not big enough for some of the suggestions we've seen here.

So in effect using the fact that electricity generated by wind at night to electrolyse water in to H2 and O2, then burning them in a heat engine to produce heat that turns a turbine in the home to produce electricity another time is as efficient as turning that wind tubine at the time it's needed?

The wind cannot be arranged to blow when we need it. Hence we must store the energy. Efficiencies of electrolysis and hydrogen combustion appear poor because of the wasted heat - but if we collect that surplus heat and use it meaningfully, that changes things.

I think everyone who rushed out a brought a 29er, when they were trendy last year, and who now probably has a 27.5er, can donate their old wheels to be used as "flywheel" storage.............

More seriously, the issue with all of these schemes is that modern technology can pretty much deliver a solution to any of these issues. Unfortunately, modern capitalism cannot AFFORD those solutions! i.e. small scale, low pumped storage whilst technically feasible, is not (currently) financially feasible.......

Efficiencies of electrolysis and hydrogen combustion appear poor because of the wasted heat

At the moment 100% of the surplus is not used. If hydrogen generation can capture 50% surely that's better than not doing it.

CHP is certainly one of the more promising wind storage ideas though.

[url= http://en.wikipedia.org/wiki/Wind_hybrid_power_systems#Wind-hydrogen_system ]link to wiki[/url]

Yep, definitely can't argue with that ahwiles. Suppose the only counter is that the existing big schemes show that hydro can be pretty sympathetic to the environment- Dinorwig being a shining example, take an area you've already trashed and make it better. Not that this means there's no impact but then, that's modern life isn't it, not building them will have an impact too.

The wind cannot be arranged to blow when we need it. Hence we must store the energy.

my money is on nukes.

My money is on compressed air storage.

The financial and logistical issues of nuclear are pretty horrendous too- even just replenishing our declining nuclear capacity's challenging.

Really big ****-off flywheels, that's what we need. We can see if planes can take off from them.

we'll be relying on foraging for berries and seeds before UK is 90%+ renewables.

"surplus" isn't really a surplus. It's more over-provisioning than current over-provisioning margin, with a lower effective efficiency on that surplus over-provisioning. sub 50% if there's a something to heat to electricity conversion.

plus all that hydrogen will be needed to run the furnaces needed to smelt the glass for the glass fibre used to make the turbine blades, and to make the concrete for all the installations, when the oil runs out. there will be no carbon fibre when the oil has run out.

edit: although I quite like the idea of micro solar furnace for those instances where the energy source required is heat. if there's a big bright burning thing in the sky kicking out heat, may as well capture that as heat, rather than convert, store, convert, heat...

I thought that [url= http://tidallagoonswanseabay.com/proposal-overview-and-vision.aspx ]Swansea Bay[/url] looked like an interseting project*

*[i]Didn't listen to the R4 programme ,was it mentioned ? [/i]

Really big ****-off flywheels, that's what we need. We can see if planes can take off from them.

if we can attach a treadmill to the flywheel, that should stop them

Compressed air underground: I'm no expert on rock, but you know how you get subsidence above old mine workings? What could possibly go wrong when you pump them full of compressed air? Not to mention the energy losses in the system. (I've also seen what happens when an air-pocket in a uPVC water pipe 2m underground lets go when somebody closes the outlet valve but doesn't turn off the pumps)

Not that hard actualy, and done regulalry. We store ethylene in the rock under Teesside. The only problem is after 40 odd years of constant pressurising/depressurising they're starting to crumble (not a danger to the surface, if you have a cave, and the roof falls in, effectively the caves just moved a few meters close to the surface, but unlike the coal mines, is still a long way down).

Absolutely, but with people wanting more electronic devices and bigger cars all the time, I can't see this happening.

you can change what people want though. People didn't want fridge freezers, they were encouraged to want them.

Really big ****-off flywheels, that's what we need. We can see if planes can take off from them.

Had those as a 'kinetic UPS' at a datacenter.

Problems were:
1. You had to have 2 as one was always inder maintenance.
2. They were always under maintenance 🙂

Worked out expensive and unreliable compared to good old batteries unfortunately.

Encouraging consumers to spread the load would certainly be a help as it mitigates the need for peaking plant and spreads base load better.

As for hydrogen not being suitable for existing infrastructure, there seems to be no real data available to suggest this is the case and in any event proven hydrogen infrastructure seems to be of a similar cost to our compressed natural gas infrastructure so improvements could easily be made through natural wastage until further research proves the viability (or not) of existing pipework.

I'm not really sure what the Wobbe index is; I'm an engineer, not a chemist. However I do know from previous study that dilution of existing gas supplies by up to 10% hydrogen content is possible without the need for any modifications to burners. As I said, anything more and we would need to do a national refit as last seen in the 70's. You can also fit microgeneration boilers that produce electricity as well as heat (like CHP but the bias is reversed) which can help spread the load a little.

Pumped storage is also perfectly viable, you do not need a massive pump head to achieve a viable output - look at the Galloway hydro scheme or the likes of the Kielder dam. The whole Severn Barrage idea hinges on this principle! Existing hydro infrastructure is already being refurbished for higher generation potential (more efficient turbines) and there are plenty of reservoirs that could be retrofitted to produce power. As said though microgeneration and small scale hydro is the better option as it has less of a detrimental environmental impact (hydro is one of the least green options and most destructive of all renewables).

On nuclear - the challenge in replenishing our existing stations is more seated in the actions (or lack thereof) of previous governments and a lack of incentive for investment. We could have got the ball rolling when we owned British Energy but instead decided to pass on the ownership plus any subsequent investment returns to the French. The long term high level waste issues need to be addressed as well although 4th gen (breeder type) reactors should go a long way to reducing existing and future medium and high level waste. With the correct financing though, there is no reason why nuclear couldn't have a similar cost to hydro. Lets face it, the existing fleet will but a bawhair off 50 when it comes to the present end of life projection.

Flywheels are also viable, don't know much about them but did read an interesting article about them recently which explained how they could work in large scale.

Finally - as knottinbotswana alluded to, 'Without The Hot Air' is worth a read (free to DL here: http://www.withouthotair.com/download.html). A lot of similar content to OU texts from what I can see and describes things quite well IIRC