Harnessing wind and wave power

01 October 2014

Interview with

Dr Richard McMahon, Cambridge University

Wind power is a widely used form of renewable energy, but improvements can stillWind Power 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.  It's 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 that's 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 you've 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 -   It's quite a lot isn't it?

Richard -   I'd agree with you, yes.  I mean, it shows that wind is really making a significant contribution and of course, it's genuine green energy.

Chris -   Indeed, but the wind doesn't always blow.

Richard -   That is quite true.  We've 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, we're having to look at sort of low balancing things, and that's 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 isn't 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.  Who's 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, it's 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 we're 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 it's sometimes hard to envisage, in 30 years, today's 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.  You've 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 we've just got movement and that's 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 we've done is wired some wire into a meter and nothing is happening.  Now, what I'd 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 -   It's moving a lot.

Ginny -   So, the needle is moving backwards and forwards every time you move that magnet in and out of that coil isn't 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 that's 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, wasn't 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, that's very interesting.  If you wiggle a magnet near a coil, you can make some electricity.  But that's 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 it...

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 -   That's right and basically, everything apart from solar power is based on this principle - you move magnets near coils of wire and then produce electricity.

Ginny -   That still doesn't 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 don't 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 it's 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 -   That's right, Ginny.

Ginny -   But you also look at wave generation and waves don't 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 we've got a tidal current, a stream of water from the tides.  But if we want to get power from the actual waves - the bobbing motion - that's difficult.  People have come up with a lot of really clever things going right back to Salter's duck in the '70s tlil today and we've got a lot of things on test.  But we haven't - I think got the right answer yet.

Chris -   What is Salter's duck?

Richard -   Essentially, it's a duck.  It's 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 doesn't work then.  Is that a long answer to say, 'don't work'?

Richard -   No, it's not that it doesn't work.  As we know, we don't want to pay too much for our electricity.  So, we'd like to get the system simpler.  So A, they run longer without trouble and B, it doesn't cost so much money to generate the electricity power.

Chris -   Any questions on air or wind, or waves?  Let's just head this way...

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 that's 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, we'll have bigger wind turbines to capture energy or smaller, more efficient ones?

Richard -   I think both things will happen.  On land, there doesn't 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, 'make it cheap, put them up.'  Offshore, it's a different story because it's 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, we'll see I think growth in offshore size, but on land, I think it'll 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, we're building a prototype at the moment.  So maybe in a year's time, if we're 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 - 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 - a hybrid, so you can bob up and down and collect the wind.  What do you think?

Richard -   It's 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 it's quite a bit of work to make sure it all is reliable and doesn't 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, I'll have to be honest.  Wind turbines do kill birds.  They kill bats.  You said, "Is it a big problem?"  And that's 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 we're quite good.

Steven -   Steven Halliday from Cambridge.  Is there any way of storing electricity which is generated by wind turbines and not used when it's 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, you've got to find out whether it works.  We've 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 we're very happy.

Chris -   I'm not sure if that's 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 you've 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 - the wind cuts through the air and produces some lift.  It's 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 -   That's right, yes.

Chris -   Any other questions or we're 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.  That's particular so in very good sites in the American Midwest.

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