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Power in numbers: Why multiple, decentralized power plants are better

The addition of several small, decentralized generating plants is generally a better solution than adding one large plant in countries such as Azerbaijan, which is experiencing a rapid growth in power consumption, writes Jacob Klimstra.

When Azerbaijan was part of the USSR it had sufficient electricity generating capacity. However, Azerbaijan’s economy expanded steadily in the 1990s and has seen a rapid annual growth of more than 10% during the past years. Economic growth and electricity consumption always have a close link and this rapid growth in the Azerbaijan economy makes the need for energy resources correspondingly greater. Demand is also seasonal, with a 20% energy reserve in summertime but shortages in winter. Electricity sometimes has had to be switched off in winter for several hours a day. Another problem is the poor quality of the country’s power plants. Energy cuts and power fluctuations are a drag on development.

The Astara power plant is one of five decentralized plants aimed to help Azerbaijan achieve energy self-sufficiency
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Figure 1 shows the increase in annual electricity consumption in Azerbaijan between 1997 and 2005; the installed power (5 GW) did not increase fast enough in line with demand, resulting in a capacity utilization of 63% by the end of 2005. The capacity utilization is defined as the annual electricity consumption divided by the installed capacity running at full load during a year. The high utilization of 63% is already close to impossible with modern equipment, whereas some of the power stations in Azerbaijan have operated for as long as 45 years.

Figure 1. Annual electricity use in Azerbaijan, 1997-2005
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In western European countries, a capacity utilization of 50% is generally considered a decent maximum. Sufficient spare capacity is then available to cope with calamities during peak loads and to allow for major maintenance to be carried out. A capacity utilization higher than 55% inevitably leads to regular blackouts.

To solve the problem of insufficient generating capacity, Azerenerji (the national electricity company of Azerbaijan) could have decided to install a new large single power plant of say 750 MW. That would have added 15% to the existing capacity – which might seem sufficient. Apart from the long lead time for such a unit, however, it would not do much to improve the security and efficiency of electricity supply in Azerbaijan. The country cannot rely on obtaining electricity from a high-capacity power interconnection with neighbouring countries in case a large generator fails. The local situation is such that Azerbaijan has to rely on its own electricity production capacity. This resembles the situation on islands such as Sri Lanka, or as in Indonesia and the Caribbean. Consequently, sufficient generating capacity has to be running all the time to compensate for instantaneous failure of at least the largest generator. In such a case, the addition of a single generator that is very large compared with the other generators is – as explained below – cumbersome.

Small versus large power units

Suppose that the electricity demand at a certain moment is 2500 MW while the large 750 MW unit is on line at full capacity. That means that the other generators have to provide the difference of 1750 MW. If the large plant fails, the other units have to additionally generate the failing 750 MW in a split second. Initially, that means they could never run at more than 70% capacity. Taking into account the normal fluctuations in electricity demand, they would probably have to operate at 60% capacity. For power plants, this is not good news for fuel efficiency since the load deviates too much from the 90%-100% load where efficiency is optimal.

Moreover, a load step of 30% in the rated power of a power plant is excessive, giving rise to severe distortions in frequency and voltage. For maximum reliability and stability in the electricity supply system, the golden rule is that a single generator in an isolated system should not produce more than 5% of the total power. The loss of one production unit means that the other units have to make just a 5% load step, which does not create stability problems. All generators can also run much closer to their optimum efficiency. Figure 2 shows optimum and bad matching of size in an isolated generating system.

Figure 2. Optimum and bad matching of the size of the generators in an isolated system
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This example demonstrates that adding new electricity generation capacity to an existing system is a matter of proper matching. It can be very tempting to add a single large generator but that will ultimately create problems with reliability of supply as well as result in an unexpectedly low fuel efficiency of the combined generating system. Moreover, very large power plants also need an extensive transmission grid to bring the power to distant customers. Many studies show that the investment in electricity transmission lines is expensive. In addition, they are an additional source of power interruptions.

Multiple smaller power plants can produce the electricity close to customers, where cogeneration of electricity and heat becomes an interesting option. The much smaller impact of multiple smaller units on the system than one large unit means that all generators can run close to their rated power and achieve high fuel efficiency. Ultimately, less installed power capacity is also required in case of well matched generator sizes since much less back-up capability has to be installed than is the case with an unmatched large generator.

The 90 MW power plant at Astara uses 10 gas engines
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Fortunately, Azerenerji applied the correct methodology for expanding its generating capacity. It opted to install five power plants, each of about 90 MW capacity at the locations where the electricity is needed (Figure 3). The sites for the new plants are in strategically important locations – Astara is situated in the southern tip of the country, Sà‚¸aki (Sheki) is between the borders with Russia and Georgia, Xaàƒ§maz (Khachmaz) is in the north-east of Azerbaijan near the coast, Naxàƒ§rayan (Nakhchivan) is near Turkey and Baku is the capital of Azerbaijan. By the end of 2008, US$2.3 billion will have been invested in Azerbaijan’s energy system.

Figure 3. Locations for the five distributed 90 W power plants in Azerbaijan
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Thus this solution avoided excessive transmission and distribution losses. The original centralized approach meant that, until now, 15% of the generated electric energy was lost in the system. Each new power plant consists of 10 identical 9 MW generators driven by gas engines, with a net fuel efficiency close to 44% under all circumstances. This is markedly better than the existing system, which has an efficiency of substantially less than 30%. The specific fuel consumption of the new electricity generators is therefore at least 50% better than that of the old system. This high efficiency, together with the use of natural gas, has the additional advantage of having very low emissions per kWh generated.

The fuel efficiency of the new engine-driven power plants will be high, irrespective of their load. The control concept is such that, if the power demand decreases, individual engines can be switched off so that the remaining engines will keep running close to their rated power. If more power is needed again, engines can be started up quickly. The manufacturer of the power plants, Wärtsilä, calls this the ‘cascading principle’. Engines that are not running do not wear, so this approach also minimizes maintenance costs.

Moreover, the reliability and availability of these power plants beat every other concept. Failure of a single engine- generator combination means that only 10% of the maximum production capacity of the 90 MW power plant is lost. In most cases, the remaining engines can even carry the extra load. The probability that two engine-generator sets fail at the same time is less than 0.15%. Such well matched modular power plants means that the risk of supply system instabilities and blackouts due to failure is close to zero.

Azerbaijan chooses five plants

The first 90 MW power plant at Astara was delivered in only 10 months in the desert at a former Soviet military base and is now up and running. This illustrates the short lead time for a decentralized power plant based on modular units. The President of Azerbaijan, Ilhan Aliyev, inaugurated the power plant in February 2006. He expressed his confidence in the concept of local electricity production with these highly efficient engine-driven power plants. The plant at Astara has a generating capacity of 87 MWe provided by ten 20-cylinder Wärtsilä 34SG gas-engine generating sets. Wärtsilä supplied all the equipment for the power plant, which was built by a local company.

The Astara power plant was delivered in 10 months, illustrating the short lead time of a decentralized power plant based on modular units
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The four remaining plants are under construction; two are due to be handed over this autumn and the other two at the beginning of next year. When they are ready, Azerbaijan will have the power capacity to match its economic growth.

At the plant at Sà‚¸aki, Azerenerji is investigating the potential use of the heat released by the power plant for product chilling and in greenhouses to stimulate crop growth. Heat exchangers have already been installed.

The 20-cylinder 34SG engines that serve as prime movers for the installations have been manufactured and supplied by Wärtsilä. The power capacity of a single unit is 9 MW, ideal for setting up a modular power plant of a suitable size. In case power plants larger than 150 MW are needed, Wärtsilä can use the same principle with its 17 MW gas engines.

Advantages of modular plants

In summary, power plants for local electricity generation based on multiple modular units have the following advantages:

  • the right size for increasing system reliability, stability and fuel efficiency
  • 50% better fuel efficiency than existing centralized systems
  • short lead time
  • low maintenance costs
  • potential to use the heat released
  • high flexibility in plant size.

Jacob Klimstra is a Senior Energy and Engine Expert with Wärtsilä Power Plants, Helsinki, Finland.
e-mail: jacob.klimstra@wartsila.com

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Azerenerji and Wärtsilä work together in Azerbaijan

The Azerbaijan President gave Azerenerji the task of providing the energy that would allow the country to develop its economy. The President’s programme aims to create 600,000 new jobs in five years, but every workplace requires an additional 1.5 kW of energy capacity; new factories and other commercial establishments add to the total.

Wärtsilä has a contract with Azerenerji for five plants with a combined electrical output of 454 MWe to serve as decentralized power plants supplying the national grid and burning local natural gas. The aim is to keep Azerbaijan independent of foreign energy and to take advantage of the country’s own reserves of energy. After four years, there should be sufficient power to allow exports to Iran and other neighbouring countries.

‘What we signed with Wärtsilä was not just an energy agreement,’ says Dr Majid Aliyev, a commercial and financial adviser with Azerenerji. ‘For our country it has both strategic and social implications. In situations where people can’t even watch television in the evenings, a stable energy supply is a very important issue. Both general welfare and public opinion will improve, which is more important than figures can show’.

Wärtsilä was chosen as a partner because of the technologies it offered. According to Dr Aliyev, the advantages of Wärtsilä technology include on-time delivery, very good levels of efficiency (up to 44%), and engines that need gas at only six bars of pressure.

In Astara, site manager Marek Fijalkowski is proud of the results achieved by his international team. ‘We have people here from Finland, the Netherlands, Russia, Poland and Azerbaijan’, he says. ‘We had to find a common language and we did.’ Jorma Màƒ¤kelàƒ¤ from Wärtsilä’s construction office in Azerbaijan gives most praise to local people – most of the construction workers came from Azenko, a local company. ‘For them, the importance of the power plant was twofold – their own welfare, and proving they could do things better and faster than anybody else in the world’.

The next manager of the Astara station will be Teimur Ahmedov, who started as fitting manager just five months ago and was promoted to head of shift. When he looks at a computer screen, he knows the location of every single wire it is monitoring. According to Teimur Ahmedov, his young specialist team has had the best possible experience in these five months.

Wärtsilä has almost completed work on the Astara project, but two men will stay on for 24 months to guarantee the plant’s performance. The rest of the team members are travelling to other locations in Azerbaijan or elsewhere in the world.

Wärtsilä’s delivery to Astara included all the plant equipment and required more than 100 containers – 10 engines, pipes, all screws and fixings, and everything else right down to the very smallest parts. Construction materials, including the flooring plates, were also delivered from Finland.

ABB supplied five transformers, and computer programs designed specifically for the Astara power plant were written at Wärtsilä’s facility in Vaasa, Finland. Local personnel handled fitting, welding and construction work. More than 500 specialists worked on the plant under Wärtsilä supervision.
– Peep Ehasalu, freelance writer