In December 2012, another combined heat and power plant (CHP) from Stadtwerke Gießen (SWG) went into trial operation in Winchesterstraße. This is the fifth identical power plant that SWG has installed and connected in the past 18 months. SWG is also already working on a sixth unit in Versailler Strasse. It is due to start up at the beginning of this year.
The engines of these power plants each deliver 2400 kilowatts (kW) of thermal output and an electrical output of 1999 kW. One each feeds into the electricity and district heating network at the former US depot, at the East substation and in Schlachthofstrasse. The fourth is located on the Stadtwerke premises in Lahnstraße. All five plants currently in operation produce 50 million kilowatt hours of electricity every year. That is enough for around 12500 households.
SWG commissioned its first CHP plant around 30 years ago and has gradually expanded CHP generation since then. The municipal utilities now produce around 40 per cent of the electricity they supply to their private customers in their own CHP plants. The remaining 60 per cent comes from TÜV-certified hydropower plants. All private customers in the basic supply and with PowerPack products therefore automatically receive climate-friendly and nuclear-free electricity with the "Giessener Grünstrom" label.
By massively expanding its generation capacity, SWG is also helping to achieve the ambitious new target set by the German government. The aim is for combined heat and power (CHP) to cover 25 per cent of Germany's electricity requirements by 2020. A new CHP law, which provides for subsidies among other things, is intended to accelerate the expansion.
Matthias Funk, Head of the District Heating Department at Stadtwerke Gießen, and Jens Hanig, Project Manager for the new CHP plant, explain in an interview why CHP is so successful in Gießen and what else Stadtwerke plans to do with this efficient technology in the future.
The German government has re-evaluated combined heat and power generation with a new law and a clear target. How do you rate this decision?
Matthias Funk: First of all, we would have built our six combined heat and power plants even without the new legislation. Simply because we have enough experience and can estimate that our strategy will work in the long term. But of course we welcome the fact that the German government has changed its previous course. In my view, it was long overdue to categorise combined heat and power generation, which has been tried and tested for years and is as efficient as solar and wind energy.
Why is that?
Matthias Funk: Because the technology is comparatively simple, reliable, highly efficient and therefore economical. We have been proving this for 30 years: our first CHP unit went into operation in 1982. The unit still produces electricity and heat today. Of course, we have since modernised the system and made it even more efficient. But the engine block, the centrepiece, is still the same.
Where does this economic efficiency of combined heat and power generation come from?
Jens Hanig: A CHP unit doesn't just generate electrical energy. The heat generated during electricity production is also utilised. This makes this technology around 40 per cent more efficient than generating electricity and heat separately. We now operate smaller and larger plants with a total electrical output of around 30,650 kilowatts and a thermal output of 6,600 kilowatts. They generate 109 million kilowatt hours of electricity, which Stadtwerke Gießen supplies to its customers.
Matthias Funk: "Apart from that, we design our CHP units in such a way that they solve the biggest problem of photovoltaic and wind power plants. These two energy sources are highly volatile. In other words, we either have a lot or very little wind and solar power in the grid. These fluctuations need to be balanced out in order to keep the power grid stable. And it is precisely for this stabilisation that our CHP units are ideally suited. Because our grid can store a relatively large amount of heat, we are able to switch individual plants on or off as required. CHP is therefore not a competitor to solar and wind, but the ideal complement if planned correctly. One that we cannot do without in the medium term. As long as there is no way to store large quantities of electricity, we will need 0.8 kilowatts of conventional power plant capacity available at the touch of a button for every installed kilowatt of solar or wind power.
But CHPs burn natural gas and therefore emit CO2 ...
Jens Hanig: That's true. But compared to all other conventional solutions, it's unrivalled. And over the next few years, our CHP units will become increasingly greener because we are gradually converting the engines to bio natural gas. When a CHP unit burns bio natural gas, it produces highly efficient green electricity and green heat. And when we have reached our target - 50 per cent in-house production from CHP by 2020 - the real eco share should be 20 per cent.
Matthias Funk: We have been successfully focussing on different fuels for years. Never ideologically, however, but always under the premise of combining ecology and economy. And we've managed to do that quite well so far. We still burn around 85 per cent natural gas and 15 per cent waste and biomass in all our heat generators. By 2020, we want to cover only half of our fuel requirements with natural gas.
Surely you need more plants for that?
Matthias Funk: That's right. We will have to invest a million or two for this. But in a really good cause. We are currently planning to build a second TREA - in other words, to utilise even more processed substitute fuel from waste thermally. In addition, the plans for another biogas plant in Heuchelheim are already very concrete.
Jens Hanig: A very important advantage of this strategy is that the more electricity we generate here locally, the more added value we keep in the region. If everything materialises as we envisage today, new jobs will certainly be created.
One crucial problem remains: where to put all the heat? It's warm enough here for at least half the year. That doesn't add up, does it?
Jens Hanig: Yes, our calculation also works in summer. First of all, at least as much hot water is needed for showering in the warm season as in winter. Apart from that, we have the biggest peaks in electricity demand in summer because more and more air conditioning systems are in operation. The cooling for buildings could be produced much more efficiently with our district heating. Several customers in the city centre already use this low-cost method of air conditioning. Interested parties can experience such a system in action at our customer centre on the market square.
Dare to take a look ahead. What do you think will happen in the next few years in terms of energy, or rather the energy transition?
Matthias Funk: It's really not easy for me to make such a prediction. Because I believe in people's common sense, I think that politicians will get their act together and reorganise the framework conditions. In Germany, we can no longer afford to be as lax as we have been with subsidies for too much longer. This is already leading to excesses that are profitable for investors, but are questionable from the point of view of a sustainable and secure energy supply. We have therefore only ever pushed ahead with things that we are 100 per cent behind. Without patting ourselves on the back, I really believe that our concept could be transferred to many other cities. Not overnight, of course. But the principle of decentralised combined heat and power generation works. Anyone can come and see for themselves.
15.01.2013