Dr Richard McMahon, Cambridge University
Wind power is a widely used form of renewable energy, but improvements can still be made to better harness the power of the wind. Wave power, however, is much more difficult as the up-and-down motion of the waves is harder to convert into useful energy. Dr Richard McMahon from Cambridge University works on improving the output of both types of technology.
These types of power rely on simple generators. Ginny & Dave explain exactly how and why generators create energy from movement.
Richard - Wind power is relatively mature. Itís making a big contribution to the generation of electricity in many countries. The thing is to reduce cost, improve reliability. I work on generated technology that will achieve that.
Chris - When we say wind power, how are we trying to harness wind power? Is that just with windmills or are there other ways of doing this?
Richard - The way thatís emerged if you like as the sort of standard way of doing it now after a lot of years of development is the thing that I think most of us are familiar with, which is the horizontal axis 3-bladed wind turbine which you see everywhere. People have tried other different forms of wind turbine, but the main one for the foreseeable future is the one I have described, the 3-bladed horizontal axis machine.
Chris - How does that actually work?
Richard - Well, you need some wind to start with and the wind blows on the blades. The force of the wind turns the blades and if you look at these wind turbines, you see the bit behind the blades which is called an nacelle. In there, you think it might all be electrical generator - actually, the generator is about 1/3 of it. The biggest thing is the front bearing because youíve got all those weight of the blades on the front of the turbine and there's probably going to be a gearbox as well to increase the speed from the very slow rotation of the blades to high speed for the generator.
Chris - How much electricity do we produce with wind in Britain at the moment?
Richard - Somewhere around 6% to 7%. I mean obviously, it fluctuates. Some years are windier than others and the aim is by 2020, is to get to 1 in 7 kilowatt-hours produced from wind.
Chris - Itís quite a lot isnít it?
Richard - Iíd agree with you, yes. I mean, it shows that wind is really making a significant contribution and of course, itís genuine green energy.
Chris - Indeed, but the wind doesnít always blow.
Richard - That is quite true. Weíve got a couple of problems to look at. At the moment, we can balance wind with other forms of generation - so, there's no worry about the lights going off. In some countries like Germany and Spain where the wind penetration is getting high, weíre having to look at sort of low balancing things, and thatís where these smart grids come in, can we manage the load, so as to match the generation.
Chris - So, this is where the wind stops blowing. So, we need something else that can step in and fill the gap while the wind isnít blowing.
Richard - Well, depending on the time of day. My friends in the solar business I'm sure could help and of course, my other topic is wave power which, as another colleague points out, you can buy the tide tables for about 20 years ahead.
Chris - Indeed. Whoís got some questions about the future of wind power? Who shall we start with? Hands up. One over here. Let me just get to you.
Nelson - I'm Nelson. How much wind power is produced a year?
Richard - To give it in its sort of form or units, they're actually called terawatt hours - its a little bit difficult But if I go back to a sort of percentage, itís about 7% of our national consumption. We burn about an average of 40 gigawatts which is 40,000 million units of electricity. If somebody is good at sums, you can multiply 7% of 40 gigawatts by 365 times 24. I can't do that in my head I do apologise.
Chris - Neither can I. So, if we already are doing this, what can a researcher like you add? Is it just more turbines or are we trying to make these windmills better in some way?
Richard - Well, the analogy I use is that suppose weíre in the 1930s and we bought a car, we think it was a pretty hot car. We could get to 100 miles an hour, it would be really exciting, but look how much car technology has advanced. I think, although itís sometimes hard to envisage, in 30 years, todayís wind turbines will seem rather basic and the ones of the future will be cheaper and more reliable, less noisy and all the good things that we want.
Chris - Shall we find out actually how we generate electricity with a turbine, Ginny?
Ginny - The way that wind turbines work is they have to convert that motion that the wind is turning the blades around. Youíve got a lovely model of it there, haven't you? So, the wind is going to hit those blades and turn it around. But then weíve just got movement and thatís not what we want. We want electricity. So, how are we going to turn that movement into electricity, Dave?
Dave - First of all, we need someone to produce some movements. So for this, I need a volunteer.
Ginny - What's your name?
Innes - Innes.
Ginny - And how old are you?
Innes - 10.
Dave - So Innes, if you can just stand at the side of this. What I've got here is 2 coils of wire and 2 magnets. The coils of wire are just wired up to this meter which measures how much electricity is being produced. At the moment, how much electricity is being produced?
Innes - Zero.
Dave - All weíve done is wired some wire into a meter and nothing is happening. Now, what Iíd like you to do is to take this magnet and poke it into the middle of the coil. If you move it forwards and backwards, can you start to see that needle moving a little bit?
Innes - Yeah.
Dave - Try a bigger magnet.
Innes - Itís moving a lot.
Ginny - So, the needle is moving backwards and forwards every time you move that magnet in and out of that coil isnít it?
Innes - Yeah.
Ginny - So, what's going on there, Dave?
Dave - So, if you move a magnet near a coil of wire, what you're actually doing is pushing little tiny subatomic particles which are parts of the atoms, pushing them around those coils, they're called electrons, pushing electrons around the coil, and thatís what we call electricity. And the faster you move the magnet and the bigger the magnet, the harder they're pushed, the higher the voltage, and so, we get a bigger reading here.
Ginny - So, why did it work better with the second magnet than the first, because the first one was a bit rubbish, wasnít it?
Dave - So, yeah, the bigger the magnetic field, the more magnetic field you're changing inside that coil, the bigger the voltage and the molecules that you produce.
Ginny - So, the second magnet was bigger so we got a bigger difference. Brilliant! So, thatís very interesting. If you wiggle a magnet near a coil, you can make some electricity. But thatís not really what's going on inside a wind turbine, is it?
Dave - Pretty much, that is what's going on inside a wind turbine. You're moving magnets past coils of wire. Sometimes the magnets are created by putting electricity through the coils of wire which sounds a bit circular, but it works. Engineers are very good at that sort of thing. And if you move a magnet near a coil of wire, you produce electricity. So here, I've got a whole series of coils with the magnet in the middle. If I turn it upside down so the magnet can roll through itÖ
Ginny - There are little lights on each of the coils and I can see them flash as the magnet falls through that particular coil. So again, this is just a slightly more high-tech version rather than having someone there to move the magnet in and out of each coil. You can turn it and make the magnet fall through the coil.
Dave - Thatís right and basically, everything apart from solar power is based on this principle Ė you move magnets near coils of wire and then produce electricity.
Ginny - That still doesnít seem very efficient. You're having to stop every time and turn it back over. There must be a better way of doing it inside wind power generators and that sort of thing.
Dave - So normally, if you arrange your magnets in a circle, in the coils in the circle, you could keep on going round and round, and round - you donít have to keep starting and stopping. You can also use gears to speed it up. Remember the faster the magnet moves, the more power you generate. So, you can make everything go in circles, and itís much more efficient and you can use a lot of power with quite a small device.
Ginny - And that must be quite easy for wind turbines because they start off by going around in circles. Is that right?
Richard - Thatís right, Ginny.
Ginny - But you also look at wave generation and waves donít go around in circles, do they? They go up and down. Do you have to do something more like what we have here where you actually have something turning over and does that make it more difficult?
Richard - You're spot on, Ginny. Sometimes we can use, if you like, underwater wind turbines where weíve got a tidal current, a stream of water from the tides. But if we want to get power from the actual waves Ė the bobbing motion - thatís difficult. People have come up with a lot of really clever things going right back to Salterís duck in the Ď70s tlil today and weíve got a lot of things on test. But we haven't Ė I think got the right answer yet.
Chris - What is Salterís duck?
Richard - Essentially, itís a duck. Itís a thing that sits on the water that bobs up and down with the waves, and uses that to convert it to oscillatory motion, you know moving motion and then you can do something quite complicated and this is the problem you can pump say, some hydraulic oil, and then you can use that to turn a hydraulic motor which is going around and then you can use what your rotary generated. Sounds complicated, it is a bit complicated.
Chris - So, it doesnít work then. Is that a long answer to say, Ďdonít workí?
Richard - No, itís not that it doesnít work. As we know, we donít want to pay too much for our electricity. So, weíd like to get the system simpler. So A, they run longer without trouble and B, it doesnít cost so much money to generate the electricity power.
Chris - Any questions on air or wind, or waves? Letís just head this wayÖ
Jess - My name is Jess from St. Yves. My question is, have we crossed the threshold where we make more energy than it takes to make the wind turbine?
Richard - Very definitely. If you think about the embedded energy in a wind turbine, sure, there's steel and copper, and concrete in the foundations. But on a good site, you'd expect to pay the energy back in under a year. There's a slightly more subtle question in that as wind turbines get cheaper, you might put them in less windy sites where it takes longer to pay back. So, maybe thatís a worry, but I'm quite comfortable that we can pay the energy back quickly.
Lowen - Hi. This is Lowen from Cambridge. Do you think that in the future, weíll have bigger wind turbines to capture energy or smaller, more efficient ones?
Richard - I think both things will happen. On land, there doesnít seem to be a really big push to increase the size. The plan there is generally a standard unit, you know Henry Ford kind of policy, Ďmake it cheap, put them up.í Offshore, itís a different story because itís a lot of effort to put foundations in. So, if you're going to put a foundation and you probably want to put the biggest wind turbine, you reasonably can. So, weíll see I think growth in offshore size, but on land, I think itíll go for the mass production option.
Edward - I'm Edward from a town called Swavesey. What's the biggest windmill you have ever made?
Richard - Me personally? I've never had the privilege of building a whole windmill because a lot of things go into a windmill, but the biggest generator I've built is a prototype, is 250 kilowatts which is about enough for 200 houses. But the real size ones are now in the megawatts. And actually, weíre building a prototype at the moment. So maybe in a yearís time, if weíre on the show again, I can show you.
Frank - Hello. My name is Frank. I'm from the United States. I was just wondering, is there any kind of technology Ė you say you're doing wave technology as well - but putting these wind turbines on some kind of buoy system if they're going to be offshore to harness the wave energy in, the wind energy at the same time.
Chris - Now, there's an interesting idea Ė a hybrid, so you can bob up and down and collect the wind. What do you think?
Richard - Itís an interesting point. We like, so far, to put our wind turbines on nice solid foundations both on land, and sea. And people are thinking, well, it would actually be quite nice to have some kind of floating system. The only trouble is that itís quite a bit of work to make sure it all is reliable and doesnít tip over and so on.
Alisha - I'm Alisha, I'm from the USA. You always hear about bats and migrating birds and things flying into the wind turbines and getting killed. Is that still a big problem and if so, is there anything being done to mitigate that?
Richard - Well, Iíll have to be honest. Wind turbines do kill birds. They kill bats. You said, ďIs it a big problem?Ē And thatís quite a difficult question. I mean, in terms of things that happens to birds, they're not very likely to get hit by wind turbines. There are much worse fates for birds. So, I'm not pleased that we kill any but I mean, you got to keep in perspective. And I think weíre quite good.
Steven - Steven Halliday from Cambridge. Is there any way of storing electricity which is generated by wind turbines and not used when itís generated? For example, a windy night, lots of energy from wind turbines, no one wants it. Can we store it and use it later?
Richard - Absolutely. The difficulties with that is, we can store it as so-called 'pumped hydro' - you can pump it up to a high reservoir and let it come out. There are other means. You can use batteries. The only trouble is that we would need an enormous number of batteries. At the moment, the economics do not favour a lot of storage. So, we just say, run a gas plant a bit harder or not so hard, or you have Norway as a neighbour.
Holly - This is Holly, and I'm from Florida. You said you're building a prototype. Just exactly what is a prototype?
Richard - When you design something new, youíve got to find out whether it works. Weíve designed a new type of generator. We need to build it, test it, to see whether first of all, does it generate power and does it comply with all the sort of rules and regulations that you need for a wind turbine generator. Actually, we tested it in Norwich and we managed not to blow up the Norwich electrical supply, so weíre very happy.
Chris - I'm not sure if thatís a slight on Norwich or a slight on your engineering.
George - I'm George from Ely. I'm just wondering, how do wind turbines catch the wind?
Chris - Yeah, good question. So how does the blade there that youíve got on your nice model, how does that actually convert the motion of the air into electricity generating motion?
Richard - Well, I can't blow strong enough George, but the wind coming in has a certain amount of momentum and the blade shape is such that the wind is deflected off the blades and that produces the turning force. You know how like an airplane flies Ė the wind cuts through the air and produces some lift. Itís the same principle.
Chris - So, what you're saying is that the air hits the blade and because the blade pushes the air in a certain direction, the air pushes back on the blade. And so, you actually make the blade move in a certain direction.
Richard - Thatís right, yes.
Chris - Any other questions or weíre going to let this man off the hook? We have one more over here.
Joe - Hi. My name is Joe from Caldecote. My question is, as I've heard about wind turbines, that they cost a lot of money to maintain. I just wonder is it efficient and effective enough for the money we generate from the wind turbine to support the maintenance?
Richard - Well, if I were an investor in a wind farm, I would be very concerned about those issues. The general view now is that wind power on land is the cheapest form of generation including the maintenance costs. Thatís particular so in very good sites in the American Midwest.
A video on development of the "Salter Duck" (8 minutes):
The problem with all these technologies is
One method touted to deal with unreliable generation is variable consumption (or "Demand-Side Management", in the jargon).
I think judicious use of a combination of flywheels, capacitors and rechargeable batteries or fuel cells can even out any variability in power generation on the scale of seconds, minutes and months (respectively).
Last month (a warm September) there was no wind above 5 knots over England for more than 10 days. As wind turbines produce power accordiing to a v3 law, this means that if , say, 20% of grid power was generated by wind, we would need a storage capacity of about 500 kWh per capita to maintain our present standard of living under perfectly normal circumstances. That's 500 car batteries per person, assuming 100% efficiency. You would need to double that to cope with average winter conditions, and at least double it again to cope with peak demand, like cooking breakfast.
The problem is private enterprise reselling, Wind power is more a problem of equipment reliability than cost for a DIY consumer, true it is expensive but it is quite possible with only mild care at choosing modern household appliances to be able to live the same life as grid electricity with 8Kw hybrid kit.
If I read your figures correctly, a 230 kg 2volt deep cycle unit will give you 3000 Ah. That is 6 kWh, so you need 24 of these to supply 20% of one person's energy needs for 5 days. Add in the controller and connectors, and we are talking about 40 tonnes of battery pack per household. Most believable price today is about $500 per cell, so $50k or so per household for the batteries alone. And then there's the small problem of dealing with 4 tonnes of scrap lead and a few gallons of sulfuric acid every year.
Car batteries are not the solution, for many obvious reasons, as Alan has laid out quite well. However, power to gas conversion might have a chance. Electrolysis of one liter of water will produce 4.5 kWh worth of hydrogen, so only about 120 L of water would be required to store that 500 kWh value put forth earlier. Of course the hydrogen takes up space too--at atmospheric pressure, 500 kWh worth of hydrogen gas would require 141 m3, or a sphere of radius of 3 meters. This is unreasonable to have in a house or apartment, but if large wind or solar farms had a substation to store and dole out energy, it would make sense to produce and store highly compressed or even liquified hydrogen (or methane).
The hydrogen economy can be set up at very low cost as we already have the necessary distribution network for most stationary purposes. Centralised storage isn't a problem: oldfashioned gasholders worked at low pressures, modern LPG farms can handle several atmospheres' compression, and the bigger the storage vessel, the more economical it is to fill it with liquid hydrogen.
Read energy or extinction by Fred Hoyle from the 1970's its a great small book.
Real world capacity factors
The problem with capacity factors is that they are arbitrary. If I put a 100 kW blade on a 150 kW alternator (which makes sense, because blades are a lot more expensive than alternators, and you certainly don't want to do it the other way round!) I can put a 50 kW rating plate on it and claim 20% capacity factor even though it only produces 10 kW. alancalverd, Fri, 10th Oct 2014
I know that we use pumped hydro and compressed air to store energy now, but it is a tiny percentage of the energy consumed, and requires enormous reservoirs. They are some of the most energy efficient methods employed these days, but in terms of space and water required, there must be something better (pumping 10000 m3 of water to a height of 100 m won't even store 3 MWh). Additionally, most of the geographic formations that allow for this are already employed in this way.
I'm no mathematician, so please correct me, but:
Just do the maths instead of shouting.
First however, i'd deal with the problem of government corruptions subversive media , derogation and demeaning against wind power capabilities, along with the generous personal support of having its own electric wind power to be two faced.
Corruption, certainly. Taxpayers are forced to support wind farms which only damage the stability of the grid, so some politician's brother in law must be making money out of the scam. alancalverd, Tue, 21st Oct 2014
Apologies for screwing up the decimal points earlier! Dinorwig capacity is published as about 6.5 GWh (1.3 GW for 5 hours). UK energy consumption is about 300 GW, so it could run the country for 78 seconds. alancalverd, Wed, 22nd Oct 2014
Thanks Alan for clarifying that. teragram, Thu, 23rd Oct 2014
You say the problem is space for wind turbines, looking at some of the newer small turbines that have a large number of blades and mounted on a
The problem isn't the size of windmills, though there is a practical limit to hiow big you can make them, but the energy density of wind. Wind speed squared, multiplied by air density, comes out as watts per square meter, so if you want more watts, you need more square meters of wind, not just sail area. You then design the sail to optimise the power extraction from th area you have got, and it turns out that multiple baldes work well for high windspeeds and small areas, but two or three blades are best for low speeds and large areas - it's the difference between a jet engine and a helicopter!. alancalverd, Fri, 24th Oct 2014
Alas, no. Friction and inertia are not the problem. It's all a matter of conservation of energy, the lack of appreciation of which seems to run through all your posts!
How sad that every scientist and engineer has got it wrong all these years. All you need to extract unlimited power from a gentle breeze is lots of oil on your bearings, and once it starts rotating you can get rid of the supporting mast! alancalverd, Wed, 29th Oct 2014