Category Archives: EuroSun2008-3

Physical Description

Подпись: Fig. 6. Communication Strategy (SCADA - PLC Tracker) Fig. 7. Prototype built: Electromechanical structure

The prototype built followed the design presented in figure 2. This system incorporates a PV-cell 150mmx150mm, Pmax=1,12W, (Polycrystalline Silicon wafer) and the whole structure is made of aluminium alloy. In fig. 6 the global developed prototype is shown. The control unit was developed using an industrial Siemens S7-300 PLC (Programmable Logic Controller). Figure 7 details the electro-mechanical structure of the developed sun-tracker system.

image164The selected PLC system is a modular device that is constituted by the following modules:

Slotl = Power supply PS 307-2A Slot7 = Analog card AO4 x12bit

Slot2 = Processor CPU 315-2DP Slot8 = FM card — Counter Module (FM350)

Slot4 = Communication module CP 342 -5 Slot9 = FM card — Counter Module (FM350)

Slot5 = Digital card DI8/DO8xDC24V/0,5A SlotlO = FM card — Stepper Motor (FM353)

Slot6 = Analog card AI8 x12bit Slotll = FM card — Stepper Motor (FM353)

Additionally, the PLC-tracker has a modem for GSM communication that provides the system capacity to communicate through the mobile phone network.

Photovoltaic efficiency

Using TRNSYS the PVT system was modelled with a flow rate of 300 kg/hr (0.083 kg/s), equivalent to one building air change per hour, and with zero air flow, as would be the situation for a non-ventilated building integrated PV system. The results showed a difference of at most 1.3% between the PV efficiency operated under these two conditions, however, over the course of the year this small difference in PV efficiency results in quite a substantial increase in electrical output for the ventilated PVT system. This value was calculated to be 135 kWh/annum, assuming a PV cell packing factor of 0.85 and a value of 0.92 for transmission through the glass cover.

Definition of the feed in scenarios

Because electricity can be fed into the distribution grid, grid restrictions are with a moderate penetration of RES actually not the limiting factor. But with a higher amount of decentralised production the transport capacity of the grids will be reached. Variable tariffs give a soft stimulation for operators to shift their operation schedule.

In [6] the Association for Electrical, Electronic &Information Technologies (VDE) suggests a feed-in tariff based on the day-ahead price at the European Energy Exchange in Leipzig (EEX). To the variable EEX-price a constant bonus for decentralised plants will be added during the high demand time from 6 am to 1 am. In the following this scenario will be called VDE.

The described grid in section 1 defines a very weak grid, where the global VDE-tariff might not control decentralised plant sufficient. For an efficient grid operation it is desirable to produce most of the needed power within the grid. For that reason we modified the constant bonus in the VDE-tariff to a local component. This scenario will be called LOCAL. For that the net load (difference between electric load Pel and photovoltaic production PPV) was used. This load was spread to a local time dependent bonus with a minimum at 0°cent and the mean value at the bonus in the VDE-scenario. If the missing power is large the tariff will be high to stimulate further decentralised generation.

To compare the results we assumed the typical constant feed-in tariff for cogeneration in Germany, which is called KWK-G.

Measurement results and system design

3.1. Electrical performance

During this study it was not possible to measure the cells temperature directly since the trough structure is closed. Hence, the average water temperature running inside the thermal absorber at the moment of the electrical efficiency measurement is presented instead. Using the maximum electric power extracted by Solar8 together with the incident beam irradiation it was possible to estimate the electrical efficiency behaviour of the system depending on its working temperature (Fig. 2).

From the linear representations of the electrical performance it is possible to estimate that the electrical efficiency is 8.3% per active glazed area and 6.3% per total glazed area at 25°C average water temperature running inside the thermal absorber. The slope of the electrical performance trend lines fits fairly close the classical 0.4% drop in efficiency per °C in cells temperature increase. For this study, active area was defined as the maximum glazed area the system can make use of.

Setups and measures

Подпись: 6 12 18 24 Hour
image067

The following results are presented for two setups with different relative demand-to-production ratios, corresponding to different PV penetration levels. The array-to-load ratio (ALR) is the ratio of nominal array peak power to the mean load, in this case the annual mean load for detached houses. Two system setups with ALR of 2 and 8 are used. The relative sizes of load and production are shown in Figure 2. The first setup results in a small overproduction, corresponding to a penetration slightly above optimal from the grid point of view (cfr. [3]). The second setup causes a massive overproduction but nonetheless yields just enough to annually cover the household electricity demand.

Fig. 2. Average load (PL) and production (PS) for the whole year (left) and the summer months May, June
and July (right) at different relative system sizes (ALRs). In addition to the load profile for detached houses,
the corresponding load profile for apartments is shown for comparison purposes.

The main indicator of load matching considered here is the solar fraction, which is the fraction of load covered by PV. Since the overproduced power level is critical from the grid point of view, this is covered briefly.

Model and parameters

The model of the power outputs calculated in the performed simulations is described by the following equations and parameters [2].

P = ‘HobKtaGb +^odGd — a1((Tout+Tin)/2-Tamb)- a2((Tout+Tin)/2-Tamb)2 (1)

where Kta = 1-bo(1/cos0-1) (2)

Подпись: Monitored parameters: P Power from collector (W/m2 ) Gb Beam Irradiance (W/m2 ) Gd Diffuse Irradiance (W/m2 ) Tin Inlet temperature Tout Outlet temperature Tamb Ambient temperature Glazed areas: Aactive elect.= 3.5m2 Solar8 electric active glazed area Aactive tamp 3.7m2 Solar8 thermal active glazed area ASolarS= 4.6m2 Solar8 total glazed area Подпись: Parameters in the collector model: qob Beam efficiency a1 Heat loss factor [W/m2 K] a2 factor [W/m2 K2] Temperature dependence of heat loss a=a1+a2*AT (4) Kta Angle of incidence modifier for beam irradiance bo Angular coefficient Kdiffuse Diffuse incident angle modifier 0 Angle of incidence onto the collector [°]

qod=Kdiffuse*qob (3)

Simulation Parameters:

Table 2. Systems parameters introduced in the performed simulations with Winsun software.

Solar system

Поь (-)

Kdiffuse (-)

aj (W/m2 oC)

a2 (W/m2 oC2)

be (-)

Thermal Solar8 per active glazed area

0.64

0.1

3.09

0

0.1

Electrical Solar8 per active glazed area (50 oC)

0.076

0.1

0

0

0.1

Flat plate collector (50 oC)

0.8

0.9

3.5

0

0.1

PV module (25 oC)

0.16

0.9

0

0

0.1

TECHNO-ECONOMIC FEASIBILITY ANALYSIS OF PV-WIND. HYBRID SYSTEMS FOR SWEDEN

Подпись:F. Fiedler1*, V. Pazmino1, I. Berruezo1, V. Maison1 and E. Wackelgard

1 Solar Energy Research Center SERC, Hogskolan Dalama, S-78188 Borlange, Sweden

Corresponding Author, ffi@du. se

Abstract

PV-Wind-Hybrid systems for stand-alone applications have the potential to be more cost efficient compared to PV-alone systems. The two energy sources can, to some extent, compensate each others minima. The combination of solar and wind should be especially favorable for locations at high latitudes such as Sweden with a very uneven distribution of solar radiation during the year. In this article PV-Wind-Hybrid systems have been studied for 11 locations in Sweden. These systems supply the household electricity for single family houses. The aim was to evaluate the system costs, the cost of energy generated by the PV- Wind-Hybrid systems, the effect of the load size and to what extent the combination of these two energy sources can reduce the costs compared to a PV-alone system. The study has been performed with the simulation tool HOMER developed by the National Renewable Energy Laboratory (NREL) for techno-economical feasibility studies of hybrid systems. The results from HOMER show that the net present costs (NPC) for a hybrid system designed for an annual load of 6000 kWh with a capacity shortage of 10% will vary between $48,000 and $87,000. Sizing the system for a load of 1800 kWh/year will give a NPC of $17,000 for the best and $33,000 for the worst location. PV-Wind-Hybrid systems are for all locations more cost effective compared to PV-alone systems. Using a Hybrid system is reducing the NPC for Borlange by 36% and for Lund by 64%. The cost per kWh electricity varies between $1.4 for the worst location and $0.9 for the best location if a PV-Wind-Hybrid system is used.

Keywords: Techno-economic feasibility, PV-Wind-Hybrid systems

1. Introduction

In the Nordic countries stand-alone PV systems are mainly used to supply electricity to remote weather and telecommunication stations, traffic signals/lights and for other remote applications with a relatively low power demand. Due to the extensive developed electrical grid only a few remote residential buildings for all year round usage are supplied by stand-alone systems. An obstacle for the use of stand-alone PV systems is also the uneven distribution of the solar radiation causing high costs if the system needs to be sized for a constant load throughout the year. As the example for Gothenburg in Figure 1 shows has wind power the potential to compensate at least to some extent the low irradiation during the winter. The average wind power at the most locations in Sweden is higher during the seasons with low irradiation. Another reason why the combination of PV — and wind-alone systems can be economical interesting is that the costs for PV modules per Watt peak are still higher than the cost per Watt peak of wind turbines. If there will be a cost benefit or not depends of course also on other parameters, especially on the available local wind speed.

1st International Congress on Heating, Cooling, and Buildings " ‘ 7th to 10th October, Lisbon — Portugal *

image046

Fig. 1. Monthly average wind power at 10 m height and monthly average horizontal solar radiation for

Gothenburg (TMY weather data).

Studies have performed for several other locations worldwide showing often that PV-Wind-Hybrid systems can be more cost effective than PV-alone or wind-alone systems [1-5]. The results presented in this paper are based on two Master theses reports of students of the European Solar Engineering School in Borlange/Sweden [6, 7].

2. Aims

In this paper PV-Wind-Hybrid systems have been studied for 11 locations in Sweden. The aim was to evaluate the system costs, the cost of energy generated by the PV-Wind-Hybrid systems, the effect of the load size and to what extent the combination of these two energy systems can reduce the costs compared to a PV-alone system.

A COOLING SYSTEM FOR A HYBRID PV/THERMAL LINEAR CONCENTRATOR

D. Chemisana1* , J. Cipriano, M. Ibanez, B. Abbdel Mesih, A. Mellor

1 University of Lleida, 25001 Lleida, Spain.

Daniel Chemisana, daniel. chemisana@macs. udl. cat

Abstract

This paper presents the thermal evaluation of an evacuated PVT collector designed to operate under concentrated radiation (15 suns). Finite volume 3D numerical computations have been carried out in order to study the thermal characteristics of different rectangular cross section aluminium pipes and to test the performance of the PVT collector with several laminar flow rates. Experiments with the same laminar flows show the same behavior than in the numerical results.

Keywords: linear concentration, active cooling, PVT.

1. Introduction

Within the field of solar collectors, there is a group of hybrid photovoltaic/thermal (PVT) generators, which simultaneously convert sunlight into electrical and thermal energy. Electrical energy is produced by photovoltaic cells. Thermal energy is produced by means of a circulation of fluid around the hottest parts of the system (namely the photovoltaic cells). Due the difference in temperatures, heat is transferred to the fluid providing an energy source whilst cooling the cells.

PVT systems can operate under concentrated or un-concentrated light. The system analysed in this research, will operate under linear concentrated radiation.

These PV/T systems have an inherent contradiction: from the point of view of the electricity generation, the temperature of the PV cells must be kept as low as possible, which leads to low outlet temperatures of the thermal fluid, by contrast, from the thermal energy point of view high outlet temperatures are needed. Hence, a balance between PV efficiency and thermal energy production must be chosen.

Control Algorithm

The software used for the PLC programming was the Siemens Simatic Step 7 [13], with the Simatic S7 Prodave V5.5 [14] needed for the communication between the Scada system and the PLC network.

The designed control algorithm was implemented using the Ladder Diagram language [15].

The developed control algorithm is illustrated in fig. 8.

A short description of the tasks performed by the tracker controller, regarding the above referred algorithm, is described beside the algorithm.

Thermal efficiency

The average thermal efficiency as modelled in TRNSYS was 22%. This value for thermal efficiency agrees with values for thermal efficiency as illustrated in graphical results of Tonui and Tripanagnostopoulos [10] for a PVT system with a channel depth of 0.15m. The convective top heat loss coefficient of the PVT system varies with wind speed according to the equation used by Cox and Raghuraman [11],

hg = 1.247 x[ — Ta)x cos#] + 2.658 x Vw (5)

where hg is the convective top heat loss coefficient from the glass cover, Tg is the temperature of the glass cover, Ta is the ambient temperature, 0 is the tilt angle and Vw is the wind velocity. The simulated values for the convective heat loss coefficient were reasonably high as inspection of the Sydney TMY2 weather data revealed an annual average wind speed of 5 m/s.

2. Conclusion

The PVT and building energy modelling and simulation shows promising potential for PVT systems to be integrated into well insulated residential houses in the Sydney climate. The results presented in this paper illustrate that a covered PVT system could feasibly provide adequate thermal comfort for occupants while also achieving the aims of eliminating the need for heaters, increasing the electrical output from the photovoltaic system and further reducing the energy requirement of the household. Further investigations into the pressure drops and required fan power to operate the PVT system and also the use of the building integrated PVT system with an air/earth heat exchanger for both winter heating and summer cooling will continue on from this work.

References

[1] EMET Consultants, (2004), Energy Efficiency Improvement in the Residential Sector. Report prepared by EMET Consultants Pty Ltd for the Sustainable Energy Authority of Victoria.

[2] P. G. Charalambous, G. G. Maidment, S. A. Kalgirou, K. Yiakoumetti, (2007), Photovoltaic thermal (PV/T) collectors: A review. Applied Thermal Engineering, 27, 275-286.

[3] M. Posnansky, S. Gnos, S. Coonen, (1994), The Importance of Hybrid PV-Building Integration. Conference paper: WCPEC 1994 Hawaii.

[4] A. Lloret, J. Andreu, J. Merten, J. Puigdollers, O. Aceves, L. Sabata, M. Chantant, U. Eicker, (1998), Large Grid-connected Hybrid PV System Integrated in a Public Building.

[5] B. P. Cartmell, N. J. Shankland, D. Fiala, V. Hanby, (2004), A multi-operational ventilated photovoltaic and solar air collector: application, simulation and initial monitoring feedback. Solar Energy, 76 (2004) 45-53.

[6] M. Bakker, H. A. Zondag, M. J. Elswijk, K. J. Strootman, M. J.M. Jong, (2005), Performance and costs of a roof sized PV/thermal array with a ground coupled heat pump. Solar Energy, 78, 331-339.

[7] U. Eicker, (2003), Solar technologies for buildings. Wiley, Hoboken, NJ.

[8] ASHRAE, (2008). ASHRAE Publishes Energy Performance Comparison Standard. Available online: http://www. ashrae. org/pressroom/detail/16438 (Accessed 22/07/2008).

[9] M. Hart, R. de Dear, (2004), Weather sensitivity in household appliance energy end-use. Energy and Buildings, 36, 161-174.

[10] J. K. Tonui, Y. Tripanagnostopoulos, (2007), Air-cooled PV/T solar collectors with low cost performance improvements. Solar Energy, 81, 498-511.

[11] C. H. Cox, P. Raghuraman, (1985), Design considerations for flat-plate photovoltaic/thermal collectors. Solar Energy, 35, 227-241.