You joined the Green party when you were 15. What were the values that you saw in the party then that made you make that decision?

The key realisation was that we live on a planet with limited resources, on which you can't have unlimited growth. To sum it up in one image: the Greens had a poster at the time which said: "We've only borrowed the Earth from our children." That single sentence still sums up the philosophy of my party for me. We need responsible lifestyles: we need to make sure that we don't use up the resources that belong to other generations, but also that we don't use up the resources of other countries. Fairness shouldn't end on Germany's doorstep.

The nice thing is that the idea of sustainability translates very well from ecology to economics. It's in the DNA of my party that we aren't just OK with the idea of a balanced household budget, but that our very founding philosophy tells us that we shouldn't burden the next generation with mountains of debts.

How has the Green party and their typical voter changed since then?

The Greens are more at ease with German society and its values: this is our country, not an enemy we have to fight against. We want to change and improve this country because we like it. And society as a whole has become greener too. When I joined, I would have never believed that the world's fourth largest economy would eventually agree to phase out nuclear energy – and that even though the Greens were in opposition. What used to be considered alternative ideas are now mainstream policy.

For example?

When I was young, I used to collect rubbish in my home town and recycle in my spare time. At school I had learned how hard and energy-inefficient it was to produce aluminium, and how hard to break it down again. So my friends and I developed a concept whereby we would start aluminium collection points around the town and then take the bins to collection points outside the city. My mother used to curse me, because we ended up with piles of aluminium in our basement. But eventually the local council cottoned on to the scheme and started doing the same thing professionally.

Why is the Green party so much more successful in Germany than in the UK?

I wouldn't say that. Let's not forget that the British Greens once got 15% at European elections – we've never managed that much. The French managed more than 16%. Feeling a bond with nature isn't a uniquely German phenomenon. Of course, the debates can run differently at times. For example, the debate on nuclear power takes on a different course in Germany – the famed "German angst" does play a role, and I think that's correct. In the UK, the nuclear debate is more of an argument about cost. But that's not to say that the end results aren't similar: ie, that hardly anyone builds nuclear power stations these days. Everyone is more realistic about the dangers of nuclear.

How would you sell the benefits of wind energy to the Brits?

That's easy. It's not about ecology: there are pragmatic economic reasons for taking wind energy seriously. Onshore wind energy is cheaper and faster; offshore is more expensive and takes longer to build. It's that simple. For those who think it spoils their view of the landscape: would you rather have a nuclear power station plonked in the middle of the countryside? I find that logic strange. And of course no one in the Green party thinks you should just put windfarms anywhere – there are parts of the countryside that should be off limits.

In the past, the energy market in Germany used to be run by four big players. Since the shift to renewables that we helped to bring about, regional authorities and cities council have become empowered to act as players in their own right, buying back the networks that they sold to private companies in the past. In Germany, a large number of windfarms are regionally owned: that helps to decentralise power and encourages competition.

What do you say to critics of Germany's nuclear phaseout, who argue that it will merely end up having to import more dirty coal energy from abroad?

We are looking at a third industrial revolution, and just as there were once those who opposed the invention of the steam engine, there are now those who hark back to nuclear energy. In Germany we now have just over 20% of our energy coming from renewable sources. All predictions from the past have turned out not to be true: when I went to school, my teachers used to say that maybe, just maybe we might have 3% of renewable energy one day. Angela Merkel says we'll have 35% by 2020; we at the Green party say it'll be 45%. My guess is: we'll both be wrong, because it'll be even more than that.

And at any rate, don't listen to what Cem Özdemir has to say on this, don't listen to what the Greens have to say, listen to what Siemens is doing. Siemens are not switching from nuclear to clean energy because they want to lose money: they want to make profit. And I'd warn anyone who questions whether they'll manage: industrial policy, that's one thing the Germans know how to get right. If the Brits would rather hand the first mover advantage down to us, then so be it – as a German, I thank them for it. We already cater for many of the markets for renewable energy around the globe, and our future competitors are more likely to come from China than from the other side of the Channel.

In Germany, industry is now starting to thank us for pestering in the past, because it forced them to go through the kind of innovations that the rest of the world is now catching up with. The Brits are still discussing whether they should insulate their houses better in the future, and we insulate them.

Germany is proud of its export industry. But in order to make Europe work, doesn't Germany need to start importing more as well?

I don't think it's a matter of either/or. The traditional left's mistake is that they've only read half of Keynes, namely the first bit about not making a recession worse by trying to save money. You learn that in the first term at university. But the second part of what Keynes says, that you have to pay your debts back in the end, that bit isn't so easy. It's a nice idea, but in reality no one does it – especially when you're dealing with four- to five-year electoral cycles.

Germany's mistake under Merkel has been to assume that a country like Spain can get rid of its debt problem purely through austerity. So it's not a matter of "either/or", but a matter of "and": we need debt brakes, but also a long-term perspective for growth. And in order to get there, you have to deal with bad interest rates: our suggestion would be a "sinking fund" to pay down excessive sovereign debt in the eurozone.

When, or if Europe emerges from the current crisis, what will it look like?

Europe's problem isn't that Germany exports too much. The problem is that we haven't done enough to increase demand in Germany. The recent increase in pay rates was a small step, but the lack of a basic minimum wage is a problem. That's an absurd German quirk: it doesn't make sense for our British friends to have a minimum wage but not us.

Europe's other problem is that there are some countries within the eurozone who are no longer capable of being competitive. Too much debt is certainly a problem in Greece, but not everywhere across the eurozone. Our main problem is that we need to become more competitive, and Germany shouldn't just stand by the sideline and comment but become an active member of the community.

There's a theory that says we're looking at a trend towards ever smaller parties across Europe, who cater exclusively for regional and specialist interests. Is Germany on the path to Belgian conditions?

That's hard to say. We saw the rise of a new party with the Pirates in Germany, but we are currently seeing a decline in their polling results. It's certainly true that the days of lifelong voter loyalty are over – all parties notice that. But you see that in Great Britain too, even if you have a majority voting system. If you look at the power of Ukip in some parts of the country, and the effect it is having on Tory policy, then you can see that even a party that gets 3-4% can wield a lot of influence. In every country in Europe there is currently a lot of insecurity, and populists are trying to exploit that.

Does Germany still have a problem with the far right?

We have to be honest enough to admit that there is a problem, particularly in the east. In most parts of Germany, we make a point of not entering a dialogue with the NPD [the National Democratic party] – we regard them as an anti-democratic movement. But we have to realise that there are small pockets in the country where that isn't the case, because the other parties have simply withered away. There are no short-term fixes for that, but we shouldn't ignore it completely either.

We have to make sure that we don't just try to ban the extreme right, but also that we support those movements and those citizens that stand up to the far right. There's still plenty Germany can learn from countries who have more experience with diversity: one important step would be to make sure that the police force reflects the ethnic diversity of the population.

Does Germany have a problem with the way it treats its migrant population?

For a long time, Germans only knew non-whites living in Germany as Ausländer, "foreigners". Then they started talking about Einwanderer, "immigrants". But I'm not an immigrant, I migrated to Germany via the maternity ward of a German hospital. When I speak to my American friends and they ask me what generation immigrant I am, I tell them that in Germany, I'm considered a second-generation immigrant. But to them, I would be a first-generation immigrant, because I was born in Germany.

When the Greens were last in government, we changed the law so that people who were born in Germany would also be legally certified as Germans – replacing a law introduced by Kaiser Wilhelm in 1913. If we win the next election, we want to extend the citizenship law further – not because we want to make things easier for immigrants, but because we think it's in Germany's interest that people who have lived in the country for a long time are recognised as citizens. Solving problems is always easier among citizens than between citizens and non-citizens.

In 1998, I said I wished that people with a similar background to mine could play football for Germany. I got into lots of trouble for that: a lot of Germans shook their head and I got criticised in the Turkish press. And look at the national team now.