Influences of climate, load profile and energy storage on the optimum inclination and orientation for thermal and photovoltaic solar energy

collectors

Brian Norton

Dublin Energy Lab Dublin Institute of Technology Dublin, Ireland president@dit. ie Abstract

Climatic and operational factors influencing the optimal orientation of solar energy, primarily photovoltaic, collectors are discussed in the context of relevant previous research. An example is provided of how being in a climate with diffuse components of insolation and winter loads that are generally high gives rise to an optimal inclination with a far greater slope angle than the latitude.

Keywords: Photovoltaics, system design, climate, inclination, orientation.

1. Introduction

When building integrated photovoltaics (BIPV) walls, roofs, and awnings provide fully — integrated electricity generation while also serving as part of the weather protective building envelope [1 — 4]. BIPV can also serve as window shading devices, semi-transparent glass facades, exterior cladding panels, skylights, parapets or roofing systems [5 — 19]. BIPV system output depends on [20 — 22] (i) the availability of and access to solar radiation as determined by climate, inclination and orientation of available building surfaces [23, 24], (ii) PV efficiency and its degradation with time [25], (iii) efficiency of balance of system components. [26], coupling to the electrical network, electrical wiring resistance and voltage drop in diodes [27,28] and (iv) shading, over-shading [29] and accumulation of dirt, dust or snow.

2. Design Issues

Grid-connected PV system economic viability depends on electrical loads and utility prices [30, 31]. PV output varies according to their specific spectral selectivity as direct and diffuse insolation spectra alter with air mass and relative humidity [32; 33, 34], so better spectral matching raises PV efficiency [35]. Larger air mass at low sun angles (the incident spectrum being towards red) decreases PV efficiency. [36]. PV surface reflection loss depends orientation, inclination and location [34, 37, 38]. Measured yearly reflection losses have ranged 6.7% to 10. 8% [39, 40]. Reflection losses are lessened by the inclusion of anti­reflection coatings. Accrual of dirt on a PV surface reduces insolation transmission annually by 2% to 8% [37, 41, 42] but in dry summers could be over 20% [43; 44] depending on the PV surface, local dust sources, cleaning frequency (by rain or manually) [45] and PV surface

inclination [46]. The annual system performance ratio [1] of a roof-mounted BIPV at latitude of 54°N was 18.1% lower than the maximum [47]. At 35.7°N latitude maximum annual energy was obtained for the surface with tilt angle 29°. [48]. For both these locations, these more-inclined optimal inclinations show the contribution diffuse insolation can make to the total solar energy incident annually on a BIPV array. As illustrated in figure 1, there is a broad trend in Europe for diffuse components to be larger (i. e., the clearness index is lower) at higher latitudes [24].

Figure 1. Annual variation of clearness indices with latitude for representative European locations [24]

For seasonally-tracking arrays, annual PV output can be 94% to 96% of the maximum annual PV output when optimum tilt angle is selected only once a year and 99% of the maximum annual PV output if the optimum angle is adjusted twice a year [49]. Different methods are available to obtain optimum tilt of a PV system based on the latitude, local climates, insolation conditions and energy demand [47, 50 — 56] and location-pecific measurements have been reported of the seasonal dependence of PV system performance [57 — 64]. An autonomous solar energy system is defined as not being grid-connected: such are common from free-standing urban street furniture such as solar powered parking charge maters and solar lit and powered ticketing in bus shelters to remote systems ranging from buildings in isolated locations to solar water pumps in deserts [65 — 66]. Such systems satisfy a particular temporal load pattern in the specific weather variations associated with the prevailing climate. From a solar energy system design perspective, climate and load primarily determine the optimal inclination of collection. This interaction is, however complex as the load a function of the climate either directly or indirectly, in time or magnitude. Using a validated simulation model, the maximum annual system performance ratio of a roof mounted BIPV system at a latitude of 54°N in the UK was found to be for a south-facing surface inclined at 20°.[47]. Figure 2 shows the breakdown of influences that cause the optimal inclination in this particular example to 30° different from the latitude

Direct

The example in figure 3 does not have energy storage. The function of energy storage is to enable loads to be met by solar energy systems nocturnally and, more generally, when insolation would be insufficient. The optimal inclination with appropriately sized storage would be the optimal plane position for the collection of both the prevailing direct and diffuse insolation components. Similarly, with storage, there is seldom benefit from non-equatorial — facing (i. e., south-facing and north-facing in the northern and southern hemispheres respectively) orientations. However in applications that make transient use of solar energy such as cooking, incorrect inclination and orientation can lead to poor performance.

References

1. Sick F. & Erge T., (1996), Photovoltaics in Buildings: A Design Handbook for Architects and Engineers, James & James Limited, London UK,

2. Bendel, C., Gummich, D., & Rudolf, U. (1995) Development of photovoltaic facade elements: technical aspects of multifunctional PV-facades, 13th European Photovoltaic Solar Energy Conf, Nice, October, 2168-2170.

3. Bahaj, A. S. & Foote, J. S. (1994) Photovoltaic cladding, a design approach for panels and curtain walling for new and existing buildings, 12th European Photovoltaic Solar Energy Conference, Amsterdam, April, 1097-1099.

4. Brogren M., Wennerberg J., Kapper R., & Karlsson B., (2003), Design of Concentrating Elements with CIS Thin-Film Solar Cells for Facade Integration, Solar Energy Materials & Solar Cells, 75,. 567-575.

5. Bowden, S., Wenham, S. R., Coffey, P., Dickinson, M. R. & Green, M. A. (1993) High efficiency photovoltaic roof tile with static concentrator, IEEE Photovoltaic Specialists Conference, Louisville, May, 1068-1072.

6. Izu, M., Ovshinsky, H., Whelnan, K., Fatalski, L., Ovshinsky, S., Glatefelter, T., Younman, K., Hoffman, K., Banerjee, K., Yang, J. & Guha, S. (1994) Lightweight flexible rooftop PV module, IEEE PV Specialists Conf, Waikoloa,, Dec, 990-993.

7. Hagemann, I. (1996), PV in buildings-the influence of PV on the design and planning process of a building, Renewable Energy, 8, 1-4, 467-470.

8. Bonvin, J., Roecker, C., Affolter, P. & Muller, A. (1997) SOLBAC flat roof system and first installations, 14th European Photovoltaic Solar Energy Conference, Barcelona, Spain, July, 1849­1850.

9. Bahaj, A. S., Ballard, J. R., James, P. A.B & Mucci, P. E.R (1998) A new approach to photovoltaic roof tiles, 2nd World Conference and Exhibition on Photovoltaic Solar Energy Conversion, Vienna, Austria, July, 2690-2693.

10. Zacharopoulos A., Eames P. C., McLarnon D., & Norton B., (2000), Linear Dielectric Non­Imaging Concentrating Covers For PV Integrated Building Facades, Solar Energy, 68, 5, 439-452.

11. Benemann, J. (1994) Multifunctional solar facades — a new challenge for photovoltaic, Conference Record of the IEEE Photovoltaic Specialists Conference, 1, Waikoloa, HI, USA, December, 784­787.

12. Maurus H., Schmid M., Blersch B., Lechner P. & Schade H. (2004) PV for Buildings, ReFocus, December, 22-27.

13. Mallick, T. K., Eames, P. C., & Norton, B, (2002), Asymmetric Compound Parabolic Photovoltaic Concentrators for Building Integration in the UK: An Optical Analysis, World Renewable Energy Cong July 2002, Koln,

14. Mallick, T. K., Eames, P. C., & Norton, B, (2002) App of Comp Fluid Dynamics to Predict the Thermo-Fluid Behaviour of a Parabolic Asymmetric pv Concentrator, World Renewable Energy Cong, July 2002, Koln,.

15. Mallick, T. K., Eames P. C., Hyde T. J., & Norton B., (2004), The design and exp characterisation of an asymmetric compound parabolic pv concentrator for building facade integ in the UK, Sol Energy, 77, 3, 319-327.

16. Mallick T. K., Eames P. C., Hyde T. J., & Norton B., (2004), Exp characterisation of an asymmetric compound parabolic pv concentrator designed for building integration in the UK, Int J of Ambient Energy, 25, 2,85-96.

17. Mallick, T. K., Eames P. C., & Norton B., (2006), Non-Concentrating and Asymmetric Compound Parabolic Concentrating Building Facade Integrated Photovoltaics: An Exp Comparison, Sol Energy, 80, 7, 834-849.

18. Mallick, T. K., Eames P. C., & Norton B., (2007), Using Air Flow to Alleviate Temperature Elevations in Solar Cells within Asymmetric Compound Parabolic Concentrators, Solar Energy, 81, 173-184.

19. Miller W., Brown E. & Livezey R. J. (2005) Building-Integrated Photovoltaics for Low-slope Commercial Roofs, ASME Journal of Solar Energy Engineering, 127, 307-313

20. Kaye, R. J. (1994) A new approach to optimal sizing of components in stand-alone photovoltaic power systems, 24th IEEE Photovoltaic Specialists Conference, Hawaii, USA, December, 1192­1195.

21. Sidrach-de-Cardona, M & Lopez L. M. (1999) Performance analysis of a grid-connected photovoltaic system, Energy, 24, 93-102.

22. Imamura, M. S., Helm, P. & Palz, W. (1992) Photovoltaic system technology a European Handbook, H S Stephens and Associates, Bedford, England.

23 Norton, B., (1992) Solar energy thermal technology, Springer, Heidelberg, Germany

24. Waide, P. A. & Norton B. (2003) Variation of insolation transmission with glazing plane position and shy conditions, ASME Journal of Solar Energy Engineering, 125, 182-9

25. Simmons, A. D. & Infield, D. G. (1996) Grid-connected amorphous silicon photovoltaic array, Progress in Photovoltaics: Research and Applications, 4, 381-388.

26. Miguel, A. D., Bilbao, J., Cazorro, J. R.S. & Martin, C. (2002) Performance analysis of a grid — connected PV system in a rural site in the Northwest of Spain, World Renewable Energy Congress VII, Cologne, July.

27. Baltus, C. W.A, Eikelboom, J. A. & van Zolingen, R. J.C. (1997) Analytical monitoring of losses in PV systems, 14th European Photovoltaic Solar Energy Conference, Barcelona, Spain, July, 1547­1550.

28. Bahaj, A. S., Braid, R. M. & James, P. A.B. (2001) An assessment of the building integrated pv facade and it’s operational mismatch losses at Southampton Univ, Renew En in Maritime Island Clim, Belfast, Sept, 111-118.

29. Alonso, M. C., Arribas, L. M., Chenlo, F. & Cruz, I. (1997) Shading effect on a roof integrated grid — connected PV plant, 14th European Photovoltaic Solar Energy Conference, Barcelona, Spain, July, 1891-1893.

30. Watt M., Kaye R. J., Travers D., & MacGill I., (1998a), “Assessing the Potential for PV in Buildings”, 14th European Photovoltaic Solar Energy Conference and Exhibition, Barcelona, Spain, 1879-1882.

31. Mondol J D, Yohanis Y G. & Norton B (2008), Solar radiation modelling for the simulation of photovoltaic systems, Renewable Energy, 33, 1109-1120

32. Hirata, Y. & Tani, T. (1994) Evaluation of photovoltaic modules considering spectral solar radiation, Electrical engineering in Japan, 114, 8, 93-105.

33. Nann S. & Emery, K. (1992) Spectral effects on PV-device rating, Solar Energy Materials and Solar Cells, 27, 189-216.

34. Bucher, K. (1997) Site dependence of the energy collection of PV modules, Solar Energy Materials and Solar Cells, 47, 85-94.

35. Ruther, R. & Dacoregio, M. M. (2000) Performance assessment of a 2 kWp grid-connected, building integrated, amorphous silicon photovoltaic installation in Brazil, Prog. in Photovoltaics: Research & App, 8, 257-266.

36. Pratt, R, G. & Burdik, J. (1988) Performance of a 4 kW amorphous-silicon alloy photovoltaic array at Okland Community College, Aurban Hills, Michigan, IEEE Photovoltaic Specialists Conf, Las Vegas,, Sept, 1272-1277.

37. Reinders, A. H.M. E, Dijk, V. A.P., Wiemken, E. & Turkenburg, E. (1999) Technical and economic analysis of grid-connected PV system by means of simulation, Prog in Photovoltaics: Research & Appl, 7, 71-82.

38. Martin, N. & Ruiz, J. M. (2001) Calculation of the PV modules angular losses under field conditions by means of an analytical model, Solar Energy Materials and Solar Cells, 70, 25-38.

39. Lanzerstorfer, S., Bauer, G. & Wilk, H. (1995) Losses by reflection of crystalline PV modules, 13th European Photovoltaic Solar Energy Conference, Nice, France, October, 2294-2297.

40. Preu, R., Kleiss, G., Reiche, K. & Bucher, K. (1995) PV-module reflection losses: measurement, simulation and influence on energy yield and performance ratio, 13th Euro Photovoltaic Sol Energy Conf, Nice, Oct, 1465-68.

41. Goossens D. & Kerschaever E. V., (1999), Aeolian Dust Deposition on Photovoltaic solar cells:

The Effects of Wind Velocity and Airborne Dust Concentration on Cell Performance, Solar Energy, 66, 277-289.

42. Gonzalez, C. (1986) Photovoltaic array loss mechanisms, Solar Cell, 18, 373-382.

43. Maag, C. R. Jr. (1977) Outdoor weathering performance of solar electric generators, Journal of Energy, 1, 6, 376-381.

44. Townsend, T. U. & Whitaker, C. M. (1997) Measured vs. ideal insolation on PV structures, 26th IEEE Photovoltaic Specialists Conference, Anaheim, CA, October, 1201-1204.

45. Hoffman, A. R. & Maag, C. R. (1980) Airborne particulate soiling of terrestrial photovoltaic modules and cover materials, Proc, Ann Tech Meeting-Institute of Environmental Sci, Philadelphia, PA, USA, May, 229-236.

46. Nakamura, H., Yamada, T, Sugiura, T., Sakuta, K. & Kurokawa, K. (2001) Data analysis on solar irradiance and performance characteristics of solar modules with a test facility of various tilted angles and directions, Sol En Mat and Sol Cells, 67, 591-600.

47. Mondol J D, Yohanis Y G. and Norton B (2007a), Comparison of measured and predicted long term performance of grid a connected photovoltaic system, Energy Conversion and Management, 48, 1065-1080

48. Soleimani, E. A, Farhangi, S. & Zabihi, M. S. (2001) The effect of tilt angle, air pollution on performance of photovoltaic systems in Tehran, Renewable Energy, 24, 459-468.

49. Balouktsis, A., Tsanakas, D. & Vachtsevanos, G. (1987) On the optimum tilt angle of a photovoltaic array, International Journal of Solar Energy, 5, 153-169.

50. Tsalides, P. & Thanailakis, A. (1985) Direct computation of the array optimum tilt angle in constant-tilt photovoltaic systems, Solar Cells, 14, 83-94.

51. Kern, J. & Harris, I. (1975) On the optimum tilt of a solar collector, Solar Energy, 17, 97-102.

52. Bari, S. (2000) Optimum slope angle and orientation of solar collectors for different periods of possible utilization, Energy Conversion and Management, 41, 855-860.

53. Mondol J D, Yohanis Y G. & Norton B (2007b), The impact of array inclination and orientation on the performance of a grid-connected photovoltaic system, Renewable Energy, 32, 118-140

54. Mondol J D, Yohanis Y G. & Norton B (2006a), Optimal sizing of array and inverter for grid — connected photovoltaic systems, Solar Energy, 80, 1517-1539

55. Mondol J D, Yohanis Y, Smyth M & Norton B (2006b), Long term performance analysis of a grid connected photovoltaic system in Northern Ireland, Energy Conversion and Management, 47, 2925­2947

56. Mondol J. D., Yohanis Y. G., Smyth M. & Norton B. (2005), Long-term validated simulation of a building integrated photovoltaic system, Solar Energy, 78, 163-176

57. Ruther, R. (1998) Experiences and operational results of the first grid-connected, building integrated, thin film photovoltaic installation in Brazil, 2nd World Conf on Photovoltaic Sol Energy Conv, Vienna, July, 2655-2658.

58. Marion, B. & Atmaram, G. (1990) Seasonal performance of three grid-connected PV systems, Conference Record of the IEEE Photovoltaic Specialists Conference, 2, Kissimimee, FL, USA, May, 1030-1037.

59. Oladiran, M. T. (1995) Mean global radiation captured by inclined collectors at various surface azimuth angles in Nigeria, Applied Energy, 52, 317-330.

60. Akhmad, K., Belley, F., Kitamura, A., Yamamoto, F. & Akita, S. (1994) Effect of installation conditions on the output characteristics of photovoltaic modules, IEEE Photovoltaic Specialists Conf, Hawaii, Dec. 730-733.

61. Sopitpan, S., Changmuang, P. & Panyakeow, S. (2001) Monitoring and data analysis of a PV system connected to a grid for home applications, Solar Energy Materials and Solar Cells, 67, 481­490.

62. Pearsall, N. M., Hynes, K. M. & Hill, R. (1997) Analysis of operation of the Northumberland building photovoltaic facade, 14th European Photovoltaic Solar Energy Conference, Barcelona, Spain, July, 1968-1971.

63. Molenbroek, E. C., Leenders, F., Kil, A. J., Hoekstra, K. J., Deege, P. & Schoen, A. J.N. (1998) Field experience with grid connected, roof integrated amorphous silicon PV systems in the Netherlands, 2nd World Conference on Photovoltaic Solar Energy Conversion, Vienna, July, 2583-2586.

64. Itoh, M., Takahashi, H., Fujii, T., Takakura, H., Hamakawa, Y. & Matsumoto, Y. (2001) Evaluation of electric energy performance by democratic module PV system field test, Sol Energy Mat & Sol Cells, 67, 435-440.

65. Odeh, I., Y. Yohanis and B. Norton, Influence of pumping head, insolation & PV array size on PV water pumping system performance, Solar Energy. 80, 51-64, 2006

66. Odeh I., Y. G. Yohanis and B. Norton., Economic viability of PV water pumping systems, Solar Energy. 80, 850-860, 2006