Renewable Energy Projects There is no Need to Reinvent the Wheel. Dipl.-Ing. Dirk Neumann. Dipl.-Ing. Christian Fricke. STEAG Energy Services GmbH

Transcription

1 Renewable Energy Projects There is no Need to Reinvent the Wheel Dipl.-Ing. Dirk Neumann Dipl.-Ing. Christian Fricke STEAG Energy Services GmbH Germany Page 1 of 11

2 Table of Contents 1. Preface Background and boundary conditions for conventional and renewable energy generation Lessons learned from traditional energy projects Lessons learned from renewable energy projects Grid connection items Recommendations for the future development and realization of renewable energy projects List of Abbreviations IPP: TQB: CSP: TSO: PCC: OLTC: Independent Power Producer Time, Quality, Budget Concentrating Solar Power Transmission System Operator Point of Common Coupling On-load-tap-changer Page 2 of 11

3 1. Preface At present, there are some players involved in renewable energy markets who have already been experienced in conventional power and heating plants for decades. Their view on the relatively young renewable sector is different and thus will help to improve the performance of renewable energy projects. One of these players is STEAG GmbH, a German IPP (Independent Power Producer) with a fleet of power and heating plants worldwide, consisting of conventional as well as of renewable plants. STEAG Energy Services GmbH, the wholly-owned subsidiary of STEAG GmbH, has among others, special expertise as an Owner s Engineer, power plant operator and IT solutions developer for national and international power plant projects and clients. In the following, experience with traditional and renewable power and heating plant projects are presented and finally recommendations for renewable energy projects will be given. 2. Background and boundary conditions for conventional and renewable energy generation Most players on the conventional field of power generation in Germany made their first steps with coal-fired power plants. Later they gained experience with the planning and operation of gas-fired units in addition. For decades they learned about the effects of the constant scale-up of unit size and about increasing efficiency and availability as well as about optimizing operation and maintenance. They acted responsibly for a save and high available energy supply of the public grid and the industrial sector. In an energy generation market free of price regulations by the state, profits were solely the result of successful economic management. Compared to conventional power plant engineering and operation, the experience with renewable energy projects is quite young. The renewable era was initiated by single private households and organizations of citizens, who had the idealistic wish to give the generation of green energy in smaller units in their neighborhood a chance. As soon as renewable energy generation was subsidized by the state in Germany and in other countries, capital investors who were newcomers in the energy generation business decided to make investments in this field. Because of the profitable subsidies, these investors had greater interest in the rapid realization of larger renewable power plant units. Finally, only about a decade ago, listed energy suppliers, Stadtwerke and other utilities, which already had an expertise in conventional energy generation, joined the competition in the green energy market. 3. Lessons learned from traditional energy projects Owners and operators of conventional power plants learned that it is of economic worth to care for a long technical lifetime of a plant, to ensure a so called golden end with much higher profits after the depreciation period. For a long technical lifetime, e.g. 40 to 60 years, an overall optimized plant is necessary which is free of defects from the planning phase and operated and maintained on the basis of best practice. Page 3 of 11

4 The technical planning and quality management mustn t be left to the power plant suppliers and manufacturers alone, because these companies always keep the economic optimization of their contract in sight. From their point of view this is somehow understandable but the lifetime of a power or heating plant doesn t end after the warranty period. warranty period (= contract balance period of plant supplier(s)) depreciation period technical lifetime time golden end Figure 3.1: Periods during power plant lifetime As the basis for a sufficient lifetime of a power or heating plant is already prepared at the beginning of a project, it is advantageous for the owner to install an Owner s Engineer with excellent technical expertise and operational experience from the start on. This Owner s Engineer should follow a supplier independent approach and be familiar with all project phases of planning, permission and realization. To avoid time, quality or budget (TQB) relevant deviations during the term of a project and to allow corrective actions, the owner is highly recommended to set up professional and close monitoring and controlling of these variables. The so-called critical path of the time schedule must always be visible. With respect to a later best practice operation and maintenance of the power or heating plant, it is essential to take maximum care of a detailed as-built documentation of the plant in the course of the project. In this context one should not forget to equip the plant with sufficient and informative measuring points and a suitable data collection and evaluation. By our experience, for all the prior recommendations it does not make a difference if the project is realized as turn-key or lot structured. The decision if a turn-key or a lot structured project is the best solution strongly depends on the project s boundary conditions and constraints. 4. Lessons learned from renewable energy projects In the following some typical findings with renewable energy projects are addressed, which of course cannot give a complete but certainly representative overview for the different technologies. Page 4 of 11

5 The technologies in the center of attention are: Biomass Power Plants Concentrating Solar Power Plants (CSP plants) Wind Farms Biomass Power Plants The definition of the achievable equivalent full load hours is always a major subject of discussion in the planning phase of biomass power plants. 7,500 hours per year have been proven to be a realistic value for wood-fired plants in Germany. With a very well-trained and experienced operating personnel a few hundred hours more are possible. Equivalent full load hours of 8,200 and more in the design calculations are the basis for economic imbalance. The wear and tear and corrosion phenomena as well as the cleaning necessities are underestimated carelessly. Owners and operators of biomass power plants rely too much on the fact that they can expect a perfectly treated fuel by their suppliers throughout the power plant s lifetime. Experience shows that biomass deliveries often content wrong materials and therefore need to be treated on power plant site before reaching the firing. This on-site-treatment of the biomass often initially not considered and calculated helps to reduce the maintenance costs of the plant considerably. Figure 4.1: Wrong materials from wood deliveries Observations of existing biomass-firing systems lead to the result that the combustion sequence is frequently not optimized. As a consequence, higher operation and maintenance costs and a reduced availability may result in a profit setback of the biomass plant. Thus, a qualified engineering during the design phase accurately has to take into consideration all the variety of parameters which influence the burning behavior and quality. Page 5 of 11

6 On the contrary, the expenditures for maintenance increase with the lifetime of the biomass power plant, the in time availability of spare, wear and tear parts is getting a more and more challenging factor. Therefore it makes sense to think of pooling possibilities for these parts at an early state of the project. For the early recognition of undesirable developments and the analysis, a longtime data acquisition is advisable. This data function is often missing in biomass plants. In nearly every biomass plant project the harmonization of the personnel concept and the automation level of the power plant means a major challenge. High expectations to availability can easily be destroyed if low automation and few personnel meet each other. Poor plant documentation is likely to intensify this negative effect. Concentrating Solar Power Plants (CSP plants) The profitability of CSP plants strongly depends on the solar harvest and the yearly power generation. The overestimation of the importance of solar mirrors and optical effects on the one hand and the underestimation of the influence of all other components and standards (which should be well-known from traditional power plants) on the other hand are typical of CSP plant projects. It doesn t really make sense if the reflection factor of new solar mirrors had been improved by a thousandth but these mirrors later cannot be cleaned as sufficiently as necessary. The routes between solar collectors often cannot absorb rainwater soon enough to ensure that cleaning trucks can drive on them shortly after the rain. Consequently it might be not possible to clean the neighboring solar mirrors for weeks. By the way: Even the general accessibility of some collectors in special areas of the solar field cannot be guaranteed. Figure 4.2: Furrows in the solar field after rain Page 6 of 11

7 Likewise the accessibility of components, valves and fittings from ground level can be difficult. Then scaffolds have to be risen where normally platforms should exist. Some balance of plant systems of the CSP plant, like for example water treatment or cooling water cleaning, do commonly not match the longtime proven standard and quality of traditional power plants and cause unnecessary trouble with the power plant s availability. The operation of CSP plants frequently has potential for optimization with regard to the power block. This in particular concerns the start-up process because an extended warm-upperiod for example can lead to high losses in power generation. On the other hand, if steam generators of parabolic trough systems, which are fed by hot thermal oil and produce superheated steam from feed water, and steam reheaters are stressed too quickly, the occurrence of leaks between the thermal oil system and the water-and-steam-cycle will increase. The right type of gaskets and the way of making the tube-to-tubesheet joints play an important role for the thermal behavior and hence the reliability of these components. Therefore, the technical design of the steam generator and the reheater should be made by experienced engineers who have a long-standing core competence in the construction of steam generators. The level of automation and process analysis of CSP plants are to some extent deviating from the higher standards found in conventional power plants. The operator s personal experience with successful actions in similar situations concerning weather, load condition, storage content etc. in the past, still plays an important role for the maximization of power generation. For example, the operation of CSP plants could be improved by applying software optimization tools well-known in other types of power plants. Wind Farms Simple-minded people will tell you that you buy a wind turbine like you would buy a car. The wind turbine is wrongly seen as a standard product from the catalogue. These people ignore that even for cars more and more extra equipment and wishes are possible today. And the buyer of a fleet of cars will take special care that his fleet concept is free of multiplied defects. So, what should be the adequate attention to a multi-million Euro investment in a wind farm with dozens of turbines installed on hundreds of hectares? This question almost answers itself. Today s equipment for wind turbines regarding lubrication oil handling and monitoring is still below the quality of steam and gas turbines. Future improvements for wind turbines in terms of redundancies, e.g. oil filtration units, and oil monitoring are possible of course. In this case the customer is asked to accelerate the development also. Although wind turbine manufacturers expect a more or less unhindered performance of their works until the taking over by the customer, this doesn t mean that the customer has no rights in terms of inspections, receipt of reports and documentation. The customer rather has to pay attention to express these rights precisely and explicitly in his contract with the manufacturer. The same contractual precision is necessary to get access to operation parameters with highest available resolution, because it surprisingly has not been common sense in the wind energy business that the plant owners know all the operation parameters so far. Page 7 of 11

8 In general, the standard final documentation for wind turbines does not fulfill the requirements of the level for traditional power plants. Wind turbine manufacturers intend to withhold detailed information and documents of their scope of work by arguing that the later service and maintenance will be performed by themselves. In case that the customer himself intends to perform operation and maintenance after the expiry of the service agreement with the manufacturer, he should secure the delivery of the required extensive documentation and information by contract. Figure 4.3: Wind turbine supply agreement 5. Grid connection items The following issues will summarize examples where the longtime experience with conventional power plant projects led to improvements in the process of achieving the Grid Connection Contract of a wind farm and in the realization of the grid connection. Optimal concept for the grid connection It s the typical procedure that the Transmission System Operator (TSO) first advises a location for the Point of Common Coupling (PCC) where the applicant shall connect the wind farm to the transmission system. This usually is either an existing substation, where a feeder for the new wind farm needs to be added, or it is a power line which has to be cut and redirected to a new substation. It is of utmost importance to develop a feasible and stressable technical concept for the connection of the wind farm to the transmission system. The concept not only has to fulfill all technical requirements, it also needs to adhere to legal and commercial conditions. Before the negotiations with the TSO start, the concept needs to be finalized and proven to avoid time delays or, even worse, a Grid Connection Contract that is not realizable due to technical, legal or commercial aspects. Page 8 of 11

9 As an example, the influence of other wind farms which may be allocated to the same PCC needs to be analyzed. A joint operation company for the wind farms may be necessary from the technical side but is legally forbidden. Also different wind farms with the same PCC require a coordinated control of voltage and reactive power which directly impacts the operational cost by the wind farms share of reactive power. A separately used grid connection may be requested to be paid by the applicant and handed over to the TSO. Such equipment also needs to be in line with the TSO s own technical requirement to ensure the later taking over by the TSO. Figure 5.1: Typical grid connection of a wind farm Steady state and dynamic studies The relevant grid code shows strong technical requirements which a power plant has to stick to. For conventional power plants the requirements exist for a long time and therefore are well known. In recent years, as the share of renewable power plants increased in some countries, also the renewables impact on the electric grid has grown. This has led to stricter conditions also for renewable power plants - a still ongoing process. Experience shows that standard concepts for the wind turbine generators and for the wind farm internal electric infrastructure do not pay sufficient attention to this development. Page 9 of 11

10 We have developed simulation models to perform both steady state and dynamic studies; not only to verify the above requirements but also to optimize the grid connection concept and the wind farm internal structure. This results in an economic wind farm structure without central capacitive and inductive compensation, or at least with minimized compensation. The structure of the medium voltage cable grid is optimized to be economic but also robust to voltage variations and high load. Optimization of the unit transformer Beside the medium voltage cable grid, the unit transformer represents the main equipment which allows optimization. The unit transformer of a wind farm needs to follow similar requirements as the unit transformer of a conventional power plant, but specific requirements are different. A basic requirement of all grid codes is the provision of reactive power during power production and the zero-exchange of reactive power during no-load operation. The experience with unit transformers of conventional power plants shows the impact of the transformer s onload-tap-changer (OLTC) on reactive power. Further to its basic, function to control the windfarms voltage, we design the OLTC to optimize reactive power control in addition. By using the voltage tolerance, the reactive power flow is adapted to reach exactly the requested value. The huge length of the medium voltage cable grid is specific for a wind farm. Due to the cable capacitance between phase and ground the huge total length may cause a standing arc and dangerous step voltages during an earth fault. Therefore, the medium voltage is operated grid compensating by using a neutral grounding reactor. To save cost for a separate medium voltage cubicle and to increase availability, the unit transformer is star-connected on the medium voltage site and the reactor is connected directly to its neutral. Figure 5.2: View of a substation for a wind farm Page 10 of 11

11 6. Recommendations for the future development and realization of renewable energy projects The customer for renewable power plants must be encouraged to make use of the same rights, methods and standards as state of the art for traditional power plant projects. For the project success the following principles are essential: Renewable and conventional power plant technologies are from the same planet. Meanwhile manufacturers and suppliers for renewable plants are used to customers coming from the traditional power plant sector. Therefore, the customer shouldn t hesitate to apply well-tried methods and standards also to renewable projects. With respect to a long lifetime and golden end of the power plant, the customer should take an active position in control and examining of the technical planning and quality management, e.g. by assigning an experienced Owner s Engineer. These tasks must not be left to the power plant supplier alone because his optimization time is only the warranty period. Not every secret of the power plant supplier must remain a secret. The customer should secure rights and access to data, information and documentation by a sound contract arrangement. Page 11 of 11