Types of heat generation in Ukraine in 2016 and their cost
Январь 31st, 2016
Main and principal criterion for a trough collector is its ability to concentrate sunrays efficiently and economically on the absorber tube in order to heat the thermal fluid. It is obvious that the knowledge of the flux distribution on the absorber tube is very useful to assess and improve the collector. The objective is to analyze the influence of different parameters of the collector geometry on the collector output. One approach has been made with the PARASCAN (PARAbolic through flux SCANner) system [3, 4], which measures the solar flux distribution at a distance of about 10 cm around the absorber tube along its longitudinal axis, resulting in 2dimensional flux distribution maps. It has a high spatial resolution and provides the result for a 3.5 m long focal area between two absorber tube supports. Figure 5 shows a plot of a PARASCAN measurement.
4000 3500 3000 2500 2000 1500 1000 500 0 tube length [mm] Figure 5: PARASCANFluxmap result at a distance of 10 cm around the 70 mm diameter absorber tube on the EuroTrough collector 
For fast and easy flux distribution analysis the CameraTargetMethod shown in Figure 6 can be used. With this method the flux distribution on a plane perpendicular to the receiver axis can be visualized and sunrays, which pass the absorber tube, can be detected. The digital pictures taken of the diffuse reflecting target are evaluated basing on longtime experience with indirect flux density measurements. Quantitative results of intercept values over the length of large collector areas are possible.
Both methods allow for checking and documentation of proper trough collector alignment and intercept factor impact on receiver performance data. The results of this technique help to quantify the effects of tracking accuracy on the collector performance [4].
Figure 7: Ultrasonic flow meter probe, mounted to the pipe (Flexim) 
Figure 6: CameraTargetMethod method: diffuse reflecting target perpendicular in the focal line of the linear concentrator (left) and flux density map after image rectification and intensity corrections (right) 
02 
After correct assembly of the collectors and positive testing of the flux distributions in the focal line, thermal tests should complete the acceptance tests. In order to reduce cost for sensor mounting and reduce the risk of leakage of heat transfer fluid, clampon sensors might be preferred for this testing, in spite of the lower precision. For temperature measurements, thermally wellinsulated and calibrated surface resistance thermo probes (PT100) in fourwire technique, designed for temperatures up to 400 °C are used. An ultrasonic flow meter can be used for working ranges up to 300°C on a wide range of pipe diameters. One ultrasonic sensor attached to a pipe is shown in Figure 7. The instrument also determines the wall thickness of the pipe in use, which is necessary because this value can vary significantly. Knowing the heat capacity, the specific density, the sound velocity and the viscosity of the fluid for the measured temperature range, mass flow rate can be measured with an accuracy of 1 to 3 percent.
Performance Impact of Geometric Precision
The optical performance of a parabolic trough collector is determined by the optical properties of its key components, the mirrors and the receiver tubes. But of course their properties have to match, and the concentrating collector as a whole has to be manufactured on the appropriate precision level to reach the design performance. The methods for geomet
ric evaluation of concentrating collectors presented in the previous sections provide information about the actual geometry of the product. However the classification in pass/fail categories has been very difficult at some stages. Apart from the common criteria to fit components together, there is a need for appropriate criteria and tolerances that have to be fulfilled in order to reach the design energetic performance of the final product.
Ray tracing has being used to model the capture fraction of the reflected sunrays on the absorber tube. A detailed approach uses finite mirror facet elements and MonteCarlo methods with millions of rays to find out the intercept factor of the solar radiation. If well modelled it reveals the optical efficiency and also the flux distribution of a part of a large collector under certain geometric conditions. This method is not practical for the analysis of large collector fields over longer time periods (e. g. one year).
So different raytracing techniques, as proposed by Rabl [6], have been used for the more extended annual analysis of solar collector fields. Certain simplifications reduce drastically the computational effort required. As usual for studies with a large number of independent, stochastically varying inputs the individual input will be replaced by the statistical model of a Gaussian distribution characterized by the standard deviation. So the beam spread occurring to the sunrays when interacting with the imperfect concentrator is represented by its standard deviation. The same can be applied, within a certain range of validity, for the sunbeam spread due to the size of the solar disc. Basing on this model the effect of irregularities can be respected in dependence of their frequency distribution. The individual effects sum up with their weighted squares:
2 2 ^total = ai Wi
ct total in mrad Figure 8: Intercept factor dependence of the total beam spread for a parabolic trough collector geometry acceptance function (EuroTroughgeometry, 70 mm absorber tube) 
This equation also suggests that the standard deviation for each component (e. g. structure, mirror) is the quality measure, which can be assessed easily from large quantities of measurement results. As given by this theory, the intercept factors for line focusing collectors have a dependence of the total beam spreads. The result for the EuroTrough geometry (and because of identical concentrator and receiver geometry also for the LS 3 collector) is shown in Figure 8.
Conclusions
The systematic analysis and specific measurement systems used until now in solar thermal concentrating technology used to serve for the evaluation and qualification of prototypes in test or demonstration installations. Numerous techniques have been developed and used for measuring and optimizing the performance of prototypes. At the moment of the continuous transition from research and development work to market introduction in large series fabrication, the role of measurement techniques change. Their former application experience however is the basis for its further deployment in concepts for the quality control in largescale projects.
The experience from tedious manual work in geometric measurements, leveling, photo — grammetry and flux density measurements has contributed to the collection of very detailed knowledge about the EuroTrough collector. The fastest and most reliable techniques from R&D experience are now transferred to quality control tools in order to assist the manufacturing and assembly of thousands of trough collector modules for the large solar power plant projects in Spain. Closerange photogrammetry is among the favorites. The contactless measurement with digital camera equipment has been identified to fulfill the precision requirements of trough collector structure assembly. Further effort is underway with the objective to automate the caption and evaluation processes. The work on flux measurement and intercept factor analysis has identified the significant potential of improvement in collector quality, which can be exploited basing on the detailed knowledge gained of the complexity of a concentrating solar collector.
The application of the proposed quality control concepts will reduce the effort on measurements and reworking. But even more: The potential in solar field performance gain amounts to several percent, and savings are reflected in cost reduction for less solar field area needed. In addition the knowledge that has been gathered on how to check and verify in efficient manner the good performance of large parabolic trough collector fields will help to reduce the risk for construction companies and thus cut down solar field cost significantly.
The authors gratefully acknowledge financial support by the German Federal Ministry for the Environment (BMU) within the scope of “PARASOL/OPAL", the contributions by G. Johnston, S. Ulmer, and K.J. Riffelmann, and the collaboration with the SKALET project partners.
Fig. 15 Constant pressure concept; external depressurization, 
Saturated Steam Fig. 16 Steam accumulator with integrated latent heat storage material. 
Although steam accumulators exhibit only a small storage capacity, the availability of these buffer storage systems can contribute to reduce the investment costs for storage capacity if they are combined with storage systems intended for longer periods of discharge. By reducing the requirements regarding response time and discharge rate the specific costs for storage systems with several hours of heat capacity can be reduced.
Acknowledgement
Part of the work presented in this paper has been funded by the German Federal
Environment Ministry under the contract code PARASOL/WESPE and part by the European
Commission within the 5th Framework Programme on Research, Technological
Development and Demonstration under contract no. ENK5CT200100540.
The authors are responsible for the content of this publication.
References
[1] Tamme, R., Laing, D., Steinmann, W. D., Zunft, S., 2002, "Innovative Thermal Energy Storage Technology for Parabolic Trough Concentrating Solar Power Plants”, Proceedings EuroSun 2002, The 4th ISES Europe Solar Congress, Bologna, Italy
[2] Tamme, R., Steinmann, W. D., Laing, D., 2003, „High Temperature Thermal Energy Storage Technologies for Power Generation and Industrial Process Heat", Proceedings FUTURESTOCK 2003, 9th International Conference on Thermal Energy Storage, 1.4. Sept. 2003, Warsaw, Poland.
[3] Tamme, R., Laing, D., Steinmann, W. D., 2004, „Advanced Thermal Energy Storage Technology for Parabolic Trough", ASMEJ. of Solar Energy Engineering, Vol. 126, May 2004.
[4] Eck M., Zarza E., Eickhoff M., Rheinlander J., Valenzuela L.: Applied Research concerning the Direct Steam Generation in Parabolic Troughs, Solar Energy, Vol.
74 (2003) pp. 341351
[5] Beckmann, G., Gilli, P. V. (1984): "Thermal Energy Storage", Springer Verlag
Hansjorg Lerchenmuller, Max Mertins, Gabriel Morin
Fraunhofer Institute for Solar Energy Systems, Heidenhofstr. 2, 79110 Freiburg email: hansjoerg. lerchenmueller@ise. fraunhofer. de
Dr. Andreas Haberle
PSE GmbH, Solar Info Center, 79072 Freiburg, Germany email:ah@pse. de
02 
Dr. Stefan Bockamp, Dr. Markus Ewert, Matthias Fruth, Thomas Griestop E. ON Energie AG, Brienner Str. 40, 80333 Munich, Germany email: markus. ewert@eonenergie. com
Dr. Jurgen Dersch
German Aerospace Centre (DLR), 51147 Cologne, Germany email: juergen. dersch@dlr. de
Over the last few years FresnelCollectors have attracted a lot of attention within the solar thermal power sector. The main reason is comparatively low investment costs through simple components. The Fraunhofer Institute for Solar Energy Systems,
E. ON Energie AG and German Aerospace Centre (DLR) have carried out a feasibility study in order to assess the technology with respect to technical, economical and ecological aspects.
The mid to long term strategy of solar thermal electricity generation must aim at technical solutions with high solar shares. Thermal storage is not yet technically proven for direct steam generating systems. Therefore special configurations of hybrid operation are an interesting option from a technical and economical point of view. Full load hours of the power plant increase and allow for more stable plant operation. Based on FresnelCollectors, two different types of power plant configurations with low or zero CO2emission are analysed in this paper:
• Hybrid operation of a solar field and a biomass vessel
• From the starting point of a Solar Only power plant, natural gas hybrid operation will be considered and the trade off between high solar share and low cost electricity production will be analysed in detail.
Calculations for this study were carried out in three steps:
• Thermodynamic calculations of the water/steam cycle were done with the commercial process simulation tool Ebsilon [1].
• Thermal and electrical yields were calculated with ColSim [2] for different solar field sizes and different options of hybridization. The simulations are based on the efficiencies of the power cycles — depending on ambient temperature and load — and hourly meteorological data for a site with a DNI of 2’247 kWh/(m2a) [3].
• Based on economic assumptions and on the results of the previous steps, calculations of levelised electricity costs (LEC) and profitability were carried out.
Dipl.Ing. Max Mertins, University of Karlsruhe, Englerstr. 7, 76128 Karlsruhe Dipl.Phys. Hansjorg Lerchenmuller, Fraunhofer ISE, Heidenhofstr. 2, 79110 Freiburg Dr. Andreas Haberle, PSE GmbH, Solar Info Center, 79072 Freiburg Dr. Ing. habil. Volker Heinzel, University of Karlsruhe, FZK, 76131 Karlsruhe
Abstract
The Fresnel solar collector is a promising concept to reduce the electricity cost price in solar thermal power plants. The optical performance of a Fresnel collector depends on material properties, on its geometric layout and on the level of optical accuracy that can be obtained. A variety of geometric parameters, e. g. the height of the absorber, the number, size and distance of primary mirrors influence the shading and blocking of rays and the amount of rays missing the absorber. To evaluate the influence of the parameter variation regarding the electricity cost price and to yield an optimization, the optical performance is assessed with an annual simulation based on hourly weatherdata. To permit a consideration of changes in collector cost according to different geometric layouts, cost factors where allocated to geometric parameters. The paper presents the method and the simulation results of the optimization under different boundary conditions and shows how the developed simulation tool can lead to an optimum collector design with respect to cost price of electricity. The sensitivity of the results will be discussed.
Introduction
Similar to the parabolic trough system the linear Fresnelcollector, which is a piecewise approximation to the parabola, is suitable to produce steam for use in solar thermal power plants. The collector comprises of slightly elastic curved mirrorstripes, which reflect the sunlight to a fully stationary receiver (see figure 1).
secondary concentrator primary mirrors 
insulation glass plane 
W 
The receiver consists of a secondary CPC — type concentrator and a selective coated tubular absorber with no need of a vacuum insulation. Principally the collector is not limited in aperture width[6], therefore a wide range primary mirrors glass plane —
of free geometry parameters is possible. The width of the primary mirrors B has to be
TOC o "15" h z coordinated with their gaps D, their number :
N and, the hight H of the receiver. Several studies ([1], [2]) have certified promising cost
perspectives of the linear Fresnelconcept —— —
but at less specific energy yield. Hence an W ■
optimization of the geometry and the field Figure 1: Principle °f the linear Fresnel size is only meaningful with an economic collector
assessment.
The collector considered in this paper is intended to produce superheated steam at 440 °C
and 50 bar, therefore the collectorfield is divided into sections for preheating, evaporating and superheating.
(a) cosinelosses (b) shading (c) blocking Figure 2: Geometric losses of Fresnel type collectors 
The main geometric losses of the Fresnelconcept are shown in figure 2. These effects can be decreased by heightening the absorber and by widening the gap between primary mirrors. On the other hand geometric changes cause losses due to inaccuracy of assembly and tracking of the primary mirrors.
Approach
For analyzing and optimizing the geometry, the optical efficiency is not of primary interest. The optimization for maximum performance of the collector at noon would differ from the one for lowest LEC[7]. The difference would be up to 10% in the LEC between the different optimization targets. Therefore an integral view on the whole system is essential. A link between the optical, thermodynamic and cost models is necessary to take the main influences into account. The electricity yield of the powerblock is calculated via annual simulation based on hourly weatherdata of a certain site under specific boundary conditions. After consideration of the specific cost the LEC is evaluated and chosen to assess the configuration. Hence arbitrary geometries and receiverconcepts can be investigated.
1.1 Technical Description
Within this chapter the integration of a solar collector into a 20 MWei biomass Rankine cycle will be presented with respect to technical and mainly economical aspects. The following benefits will result from the combination of both technologies:
• The plant is operated exclusively with renewable energysources
• Biomass is a limited source of renewable energy. With solar thermal electricity production the amount of biomass substituted by solar energy can be used in other energy applications
• No netproduction of CO2 during operation
• Typical live steam parameters of a biomass plant correspond to those of the FresnelCollector (approximately 450°C and 70 bar)
• The plant can be operated 24 hours a day without the need for heat storage.
• Compared to Solar Only plants, the efficiency of converting solar radiation into electrical energy may be higher in hybrid power plants since the steam cycle always runs at full load.
Figure 1: 20 MWel Hybrid power cycle (biomass / solar thermal), calculation in Ebsilon, efficiency (steam>el, net): 34,836,4%, depending on cooling water temperature) 
In order to use realistic assumptions for the power block within this study, its layout is based on existing biomass power plants of E. ON in Zolling or Landesbergen, Germany. However this kind of system would not be appropriate to be built in Germany because of the limited solar energy yields. The technology as described is applicable for example in South European regions.
Figure 1 shows the water / steam cycle of the hybrid plant. Both heat sources — solar field and biomass boiler — are connected in parallel. In order to supply a constant electricity output (20 MWel), the biomass boiler provides the amount of thermal energy that can not be supplied by
0 50.000 100.000 150.000 200.000 solar field size [m2] Figure 2: Annual solar share depending on the solar field size (24 h/d operation) 
the solar field. To ensure reliable operation, the biomass boiler runs at 50% or more of its nominal thermal load. Accordingly, the solar thermal input rises up to 50% depending on the availability of solar irradiation.
The size of the solar field is varied within these simulations from 0 m2 to 190’000 m2. The solar share, i. e. the percentage of the annual amount of solar steam fed into the turbine is pictured in figure 2. The solar field size 0 m2 corresponds to the pure biomass plant without
solar field.
The amount of solar energy depends approximately linearly on the solar field size between 0 and 65’000 m[1] [2]. Solar fields greater than 65’000 m2 lead to dumping of solar energy during hours with full irradiation, because the solar field must not provide more than 50% of the nominal steam mass flow for the turbine.
For the calculation of the optical performance at a designated sun position the model has to factor in the geometric layout of the primary field and of the secondary concentrator, the angular dependent material properties and the deviation from ideal reflection by optical errors and the sunshape[8]. For obvious reasons there is no closed form of an analytical formula available to calculate the optical performance of the linear Fresnel collector. A common numerical method is the raytrace algorithm, which is a bit slow to compute in view of the needed high amount of rays. For optimization and analysis purposes a time efficient algorithm is more advantageous. As one can treat the distributions of the sunshape 2sun(a) and of the optical errors [9] as statistically independent ([3]) they can lumped via convolution into one effective total relative radiance distribution Zeff[10]. Because of the linearity of the collector the convolution is needed only in one direction and can be expressed by equation 1.
2eff 0 )Tsun(o )dO (1)
*k
The relative angular distribution of the optical errors is assumed to be standard normal with the standard deviation <7, which implies all errors of the primary field6.
(2) 
‘Q2 
XeffH cos i 
da 
Ip = Ib T a1 Figure 3: Explanation of the optical model 
(c) integral of If a) 
For calculating the irradiance IP at a Point P (see Fig. 3) that is reflected from the sun at a mirrorsegment M, only the bounding angles and a2 between the ideal reflection l’ of the sunvector l have to be regarded. To consider sunpositions that deviate from the transversal plane with the angle 9, the rayexpansion can be factored in with its cosine.
In order to compute the flux distribution of the reflection of a single mirror at the aperture of the secondary concentrator, the contribution of each finite mirrorsegment has to be summed up for each point. As shown in figure 4 the raytrace algorithm reaches the smooth profile of the convolution algorithm only after a huge amount of rays. The profit in time without losses in accuracy is significant.
a ^ 0.00349 <7sun ^ 0.0041 50e3 rays Figure 4: Comparison between raytrace and convolution algorithm 
a ^ 0.00349 <7sun ^ 0.0041 5e5 rays 
To describe the angular dependent optical performance of the collector, it is sufficient to calculate the incident angle modifiers (IAM) of the transversal Kx and the longitudinal K plane (see figure 5). A common interpolation formula is the factorization of the IAM [4]: 
r? opt = Щ KX(0J K 
(3) 
Instead of 0 in formula 3, the incident angle 0^, which is the angle between the transversal plane and the sunvector, is used in the model in order to get higher accuracy. Beside the angular dependent material properties the main influence on K is the increasing amount of rays missing the absorber due to the increasing length of reflected rays. The angle that influences the length of the rays is 9, therefore this angle is the best appropriated for the use in in the interpolation. With 0 the annual yield is underestimated in a range of 2 to up to 5% at higher latitudes. Economic Optimization and EvaluationFirst the economic assumptions in a conservative approach will be described before presenting the results of the LEC calculation. At last there will be an analysis under the economic conditions and the legal framework for renewable energies in Spain. Assumptions The economic assumptions are given in the following table: Table 1: Economic assumptions
Cost assumptions apply for the second or third plant to be built, having under control the unexpected difficulties related to new technologies. The first demonstration plant will have considerably higher solar field costs. SHAPE * MERGEFORMAT
Thermodynamic ModelFor describing the thermodynamic behavior of the collector, a semi stationary model, based on an energy balance, is used. With equation 4 the reachable massflux M of a collector segment is calculated via the absorbed radiation Iabs = r? optIb, the heat of in and outflow. 
referred to direct horizontal irradi — ance Ibh 
% 
losses qloss and the enthalpydifference zih (0opt(0zCr) lbq! 
M 
) Ac 
4hi 
The whole collectorfield can only reach the lowest massflux of the three sections: 
7в = arcsin(cos(7)sin(0z)) 
(a) 5 x 104 rays (b) 5 x 105 rays
M = min^, M2, M3) (5)
This way matching losses between the sections are taken into account. To make sure, that the collector is in operating conditions to produce its corresponding output, a dynamic thermal node at each end of collectorstage is used as shown in equation 6.
(mcp)l dt — (Ubs^loss) Wap (6)
The thermodynamic model is implemented in the simulation environment Co/S/m[5] which was developed at the Fraunhofer ISE to simulate solarcollector systems.
Power Block
(a) flow sheet 
(b) part load of a simp/e fresh water coo/ed process Figure 6: Powerblock Cost Model The cost model is based on a first estimation for a starting configuration with N = 34, H = 7.5 m, D = 0.075 m and an absorber tube with a diameter of 15 cm. The specific direct cost8 of this collector would be Cc = 90 €/m2 for the mentioned configuration. This figure corresponds to cost estimations of the Solarmundo collector. The cost estimations were evaluated and seem reasonable for a third plant. All changes in cost due to mutations of the geometry are assumed to be linear. The specific direct collectorcost Cc is expressed by equation 7. Cm N + Ch (4m + H) + Cd (N1) D + Ca Cc ^ NB (7) The whole investment Бр of the solar field, power block, infrastructure, land and engineering can be calculated with: 
The power b/ock is assumed to be a simple process with only the fresh water tank as a preheater (see figure 6). The condenser is cooled by fresh water. The part load behavior is integrated into simulation via lookuptable.
TE — (CcAc + TO) x (1 + «e) + CAc(1 + ^^21 + 2pb The LEC is calculated via annuity «a and the annual electricity yield.
(8) 
LEC = 
(«a + K. + ^Mt1 + «c)TE
Ja Eeldt
Table 1: 50 MW Faro DNI = 2247 kWtlm2a

The assumptions of the cost model are shown in table 1.