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  1. 1. Integration and design of renewable energies into new housing developments Integration and design of renewable energies into new housing developmentsEnergy Management 2011-12Sergio Arenas Gayoso 1 Energy Management 2011-12
  2. 2. Integration and design of renewable energies into new housing developmentsIndex1-Introduction Pag. 32-Scheme tariff Pag. 33-Integration of renewable energies Pag. 43.1-Photovoltaic system Pag. 4 3.1.1-Justification Pag. 4 3.1.2-Technical considerations to bear in mind for installing PV systems Pag. 4 3.1.3- Design and implementation strategy for a photovoltaic system Pag. 5 solar radiation Pag. 5 electrical energy consumption Pag. 6 and battery required Pag. 6 design Pag. 7 3.1.4-Payback Pag. 73.2-Wind power Pag. 8 3.2.1-Justification Pag. 8 3.2.2-Required data for installing wind power domestic systems Pag. 8 3.2.3-Design and implementation strategy for a wind power domestic system Pag. 10 of turbine Pag. 10 of turbines required Pag. 11 3.2.4-Payback Pag. 124-Final scheme Pag. 125-Conclusion Pag. 136-References Pag. 13 Number of words (excluding figures/tables and references):2235 2Energy Management 2011-12
  3. 3. Integration and design of renewable energies into new housing developments1-IntroductionA housing developer is interested in the integration of renewable energies into its newhousing developments. The developer is currently at the planning stage of a small site inWest Yorkshire which will consist of affordable 2-bedroom homes. It comprises 4 housing“blocks” in addition to a significant area for communal parking.Acting as a consultant to the developer, the renewable energy sources which could beapplied will be considered and they will benefit from one the UK tariff schemes.The case will be built for the technologies chosen, highlighting the importance of therespective scheme in addition to the economic, societal and environmental benefits. It willbe also suggested a design or implementation strategy for deploying the chosentechnologies on the site, so some basic calculus will be required as well as and conciserationale for the choices.2-Scheme tariffFor this work, has been suggested the Feed in Tariffs (FITs) scheme. The reason for thischoice it is because the Renewable Heat Incentive (RHI) has been discarded as the long-term tariff support is targeted in the non-domestic sectors even though it will be also appliedto the domestic sector by the end of 2012 (DECC, 2011a;b). Figure1. PV systems and wind power systems are only available under the FITs scheme The fact that the RHI tariffs level have not been determined yet as well as other issues around theoperation of this scheme, couple with the need to install renewable energies with a degree oftariff security, have been the deciding factors to go for the FITs scheme as solution for thiscase. With this system, it will not only be boosted the installation of this kind of energysources (apart from the evident improvement on the environmental issue), but also the futurehouseholders will be paid for the electricity produced, and their electricity bill be significantlyreduced as well.Because certain members of the future community work in the green sector, they haveknowledge of wind and solar energy, so they would like to install them whenever possibleand site conditions were favorable. Obviously technical expert advice would be requiredA communal photovoltaic panels and wind micro-turbines with a communal monthly bill to bepaid among the owners could be a possible solution, as the more power installed, thecheaper it is. However, due to the different consumption every household has, anindividualized distribution is finally suggested. 3Energy Management 2011-12
  4. 4. Integration and design of renewable energies into new housing developments3-Integration of renewable energies3.1-Photovoltaic systemIt is widely recognized that photovoltaic (PV) technology can provide an effective electricitysupply with low environmental impact and the use of PV in electricity supply systems isgrowing rapidly. However, the potential contribution of PV to the overall electricity demand ofa country, like England, is highly dependent on both the prevailing climatic conditions andthe nature of the electricity supply and demand within that country (Pearsall et al, 1994).3.1.1-JustificationIn recent years, with the growing pressure on reducing fossil fuel dependence and CO2emission to environment, integration of PV modules into building construction has become acommon practice (Schoen, 2001). The United Kingdom (UK) faces significant challenges inthe coming years to meet its objective of reducing its CO2 emissions by at least 80% by2050 against a 1990 baseline, and with significant progress to be made by 2020 (OPSI,2008). The UK domestic building sector, as this example, currently constitutes around 30%of the UK’s final energy demand and about 23% of greenhouse gas (GHG) emissions(Hammond et al, 2011).3.1.2-Technical considerations to bear in mind for installing PV systemsOptimum PV inclination and orientation depends on local climate, load consumptiontemporal profile and latitude (Kern and Harris, 1975; Tsalides and Thanailakis, 1985; Bari,2000). Generally, a surface with tilt angle equal to the latitude of a location receivesmaximum insolation. Normally, during summer, the incident insolation is maximised for asurface with an inclination 10-15o less than the latitude and, during winter, 10-15o more thanthe latitude (Duffie and Beckman, 1991). However, for this particular case, the panels will bealways orientated 35o south, as they have not tracking system.PV modules are usually installed on building facade or roof, which creates a warmer interiorthermal condition than that mounted in the free air, and results in a less efficient electricalperformance, which it could be ideal for the Yorkshire area. Currently, the PV electricalefficiency is in the range 6–15%, which is a value measured at the Nominal Operating CellTemperature (NOCT) (Messenger and Ventre, 2003). Figure 2. A typical I-V curve for a photovoltaic cell. Temperature effects on the I-V curve 4Energy Management 2011-12
  5. 5. Integration and design of renewable energies into new housing developments 3.1.3- Design and implementation strategy for a photovoltaic system The system simulation will use as a data base the UK climate conditions (Weather2, 2011) and the calculus simulation will be based on the Technical Building Code (TBC) of Spain (2009 and 2011) as well as on the Institute for Energy Diversification and Saving of Energy (IDAE) of Spain (2009). It is clear that use of the same systems at latitudes with higher levels of solar radiation will improve the performance and make it possible to cover loads with smaller and less expensive systems (Sørensen, 2004). Table 1 shows the initial data for this case. Table 1. Input data for the case of study Area West Yorkshire o Latitude 53 45’ Climate area * I Building 4 housing “blocks” (2-bedroom homes) Panels orientation ** South o Panels Inclination *** 35 Possible shadows No shadows **** * It has been assumed that this climate zone, belonging to a specific area of the North of Spain, has similar characteristics to the West Yorkshire area (TBC, 2011). ** Heat transfer through walls and openings depends on site location of the building, receiving surfaces and orientation (Bekkouche et al, 2011). It is an accepted common practice to install flat solar systems facing south (or north, in the southern hemisphere). In this way, the collector is exposed to the largest amount of total radiation during the day, so that the energy output of the system is maximized (if the energy demand is made during the last hours of sunshine) (Sokolov and Vaxman, 1988); All the houses are facing the south but the block one, so a o special structure should be placed on its roof. An inclination of 35 improves solar generation heat in winter, as the Sun in this station has a lower trajectory in the sky. *** For a typical UK roof pitch of 15-50, and for SE to SW facing installations, the energy available will be increased by approximately 10–15% from these values (BSI, 1989). **** No shading from surrounding buildings or trees. solar radiation To design this system is required the daily incident solar radiation (IE), in order to considerate the most unfavorable month (lowest incident solar radiation) as the technic specifications will be based on it (table 2). Table 2. Incident solar radiation Months J F M A My Jn Jl Ag S O N D oIEday(35 )* 0.92 1.61 2.6 3.69 4.45 4.28 4.65 4.29 3.46 2.26 1.31 0.75(kWh/m2day)days 31 28 31 30 31 30 31 31 30 31 30 31IEmonth** 28.45 45.17 80.52 110.64 137.92 128.4 144 132.99 103.81 70.06 39.24 23.37 * IEday (0o) has been calculated considering monthly solar radiation from IDAE tables (2009); IEday (35o) has been o o calculated with a k (35 ) factor for every month, from IDAE tables (2009) as the inclination of the panels is 35 ** It agrees with Suri et al (2007) as the global irradiation received annually (assuming no shading) on a 2 horizontal surface in the West Yorkshire area could be 900–1000 kWh/m 5 Energy Management 2011-12
  6. 6. Integration and design of renewable energies into new housing developments3.1.3.2-Household electrical energy consumptionThe table 3, shows average electric consumption considering different devices. Table 3. Average electrical energy consumption* Kind of item Units Power (W) h/d Consumption (Wh/d) Light bulb 10 18 3 540 Light bulb 2 2 8 32 TV 2 50 2 200 Radio 2 20 1 40 PC 3 80 5 1200 Microwave 1 600 0.25 150 Fridge 1 100 - 400 Washing machine 1 150 1 150 Dishwater 1 150 1 150 Total 1564 2862 * IDAE, 2009It has been assumed a 0.9 power output of the inverter (standard technic specification) anda PV system with the technic specifications showed in table 4. Table 4. Average technical specifications of a PV system* Power rating (Pr) 150 Wp Voltage rating 24 V Safety factor (Sf) 1.3 Size 1590x790x39.5 mm * TBC, 20093.1.3.3-Modules and battery requiredDemand energy (ED) (Wh/d)=2862/0.9=3180 Wh/d → 3.2 kWh/dMaximum power of the inverter in direct current (DC)=1564/0.9=1740 WPV power rating (kWp)=(SfED)/IEworst-month=(1.3x3.2)/0.75=5.54 kWp=5546 Wp ≈ 6000 WpIf the system requires 48VDC, then there will be branches of 2 panels in series (300 Wp).It is also necessary a battery bank oversized to account for possible 4-5 days of inclementweather.Thus, the battery bank capacity should be: ED (Wh/d)/Voltage system=3200/48=66.24 AhFor four days: 66.24x4=265 Ah; with a 80% output → 331.25 AhTables 5 and 6 show the final power and area required. 6Energy Management 2011-12
  7. 7. Integration and design of renewable energies into new housing developments Table 5. Number of PV panels and power required 1 house PV = 6000 Wp → 20 panels 1 block 40 panels 4 blocks 160 panels (48 kWp) Table 6. Total area required for installing de PV panels 2 1 panel 1590x790 mm = 1.25 m 2 1 block needs 50 m 2 The residential area needs 200 m3.1.3.4-Final designThe panels could be placed on the top of the parking spaces if the block roof had notenough surface. Therefore, the following 20parking spaces will be used:West zone: V, V, 18, 19, 27, 28, 36, 37, 20.South zone: 26, 35, both disabled parking spaces,V, 12, 13, 14, 15, 16, 17.(It has been assumed a 10 m2 parking spaceroof). Therefore, there will be eight panels in eachparking space designated. Figure 3. There would be 8 panels in every carport3.1.4-PaybackUsing the calculator given on the Solarguide website (2011) and using the “calculating bysize” mode (6 kWp system), the result is as table 7 shows. It seems that the payback wouldbe less than 12 years and the profit over 25 years (4.75% AER) would be basically £40000. Table 7. Payback for the study case Investment in 5.92kWp System £ 17104.41 First year Income from Feed-In Generation Tariff: 16.80p/kWh £ 802.05 Income from exporting energy: 3.10p/kWh £ 96.20 Electricity Saving £ 240.62 Total Benefit £ 1138.86 Payback Time 11y 6m £ 38974.32 Total Profit Over 25 years 9.11% per year (4.75% AER) 7Energy Management 2011-12
  8. 8. Integration and design of renewable energies into new housing developments3.2-Wind powerUrban energy generation such as that produced by small scale wind turbines installed on oraround buildings can be defined as micro-generation (Bahaj and James, 2006). It isestimated that there is a huge potential to utilise this type of technology in the urban builtenvironment not only to satisfy demand and provide decentralised generation but also tohelp tackle fuel poverty and achieve reductions in emissions (DTI, 2005).3.2.1-JustificationMicro-scale wind turbines in the UK are an emerging technology driven by advances indevice design, increasing energy prices and the financial incentives offered to aid theiruptake in buildings (Bahaj et al, 2007). The direct benefit in utilising micro-wind turbines inthe built environment is clearly one of sustainable electrical power generation and henceCO2 abatement and also in financial savings. Indirect benefits are more subtle and span‘softer’ issues such as pride in housing and increased energy awareness to technical issuessuch as generation at point of use and the potential for demand reduction. It can also beargued that the use of micro-generation technologies when combined with occupierperception and behaviour can result in further environmental benefits or additionally thatcannot be achieved with traditional supply (ibid).The UK has the most intense wind energy resource in Europe due to its western locationthat is subjected to the main Atlantic weather fronts (Petersen and Troen, 1990). However,micro-wind turbines will not enjoy as favourable locations as large scale devices due to theirsiting at low altitude and in perhaps dense urban terrain.3.2.2-Required data for installing wind power domestic systemsThe following table, shows the kind of data required to install a wind turbine. Table 8. Annual values for wind speed and frequency* Average speed (m/s): 7.56** Height (m): 13*** Direction Frequency (%) Speed (m/s) N 6 6.68 NE 11 6.17 E 10 8.36 SE 13 6.68 S 10 6.00 SW 24 9.77 W 10 9.2 NW 16 7.51* Data estimated from for the North West region** Micro wind turbine looks promising when it is installed in locations having high annual average wind speeds(>6 m/s) (Li et al, 2011)*** 13 m would be good for the domestic sector in this case as Bahaj et al, (2007) took their data from 10 mheight. The more height, the more energy production (Alam et al, 2011), but common sense should be taken intoaccountWith the data above, it is possible to make the wind rose (figures and). It will help in order toknow what is the most probably wind direction and therefore, what should be the micro-turbines orientation. 8Energy Management 2011-12
  9. 9. Integration and design of renewable energies into new housing developments Figures 4 to 5. Wind rose for most probably direction (4); direction of the maximum speed (5) N 4 25 NW 20 NE 15 10 5 W 0 E fr (%) SW SE S N 5 10 NW 8 NE 6 4 2 W 0 E V (m/s) SW SE SAccording to the figures above, it is clear that the micro-turbines should be orientatedtowards SW direction.To know the annual production of one micro-turbine, the data showed in table 9 are required. 9Energy Management 2011-12
  10. 10. Integration and design of renewable energies into new housing developments Table 9. Energy production of a micro-turbine Speed (m/s) h/year* Power (W)** Production (Wh/year) 1 515.1 1.14 586.88 2 801.3 9.11 7303.68 3 958.7 30.76 29491.93 4 1049.9 72.92 76556.96 5 1210.2 142.42 172355.02 6 1368.9 246.10 336885.45 7 1029.8 390.80 402442.45 8 659.4 583.35 384658.81 9 458.2 830.59 380574.24 10 299.9 1139.35 341690.77 11 190.1 1516.47 288281.62 12 104.9 1968.80 206526.60 13 60.3 2503.15 150939.93 14 30.1 3126.37 94103.85 15 13.9 3845.30 53449.71 16 6.8 4666.77 31734.06 17 1.6 5597.62 8956.19 18 0.9 6644.68 5980.22 19 0 7814.79 0 20 0 9114.79 0 21 0 10551.51 0 22 0 12131.79 0 23 0 13862.46 0 Total (kWh/year) 2972.52* Data estimated from for the North West region. Considering 8760 h/year** Power (P), has been estimated using the following relationship P(W)=0.5ρAV 3Cp, where ρ is the density of air 3(1.23 kg/m ), A is the rotor area (for this case a 2 m diameter rotor has been taken since it is a standard size in 2 2the market, therefore A=πr =3.14 m ), V is the wind speed (m/s), and Cp is the coefficient of power and is adimensionless term that has a theoretical maximum value of 0.59 (Burton et al, 2001).3.2.3-Design and implementation strategy for a wind power domestic system3.2.3.1-Kind of turbineAt present there are a number of micro-wind turbines available aimed specifically atdomestic properties. Rated power ranges from 400 W to 1.5 kW. Larger devices areavailable but are better suited to larger multiple occupancy buildings. Whereas traditionalhorizontal axis rotors seem to be favoured for domestic applications vertical axis devices areappearing upwards of 1.5 kW rated power (Mertens, 2003).However, there are some conditions given in the paper of Li et al (2011) which should be inmind in order to install micro-turbines in the domestic sector. They are the following:  The turbine shall not be erected on, or attached to, the house or any building or other structure within its curtilage  The total height of the turbine shall not exceed 13 m  The rotor diameter shall not exceed 6 m  The minimum clearance between the lower tip of the rotor and ground level shall not be less than 3 m 10Energy Management 2011-12
  11. 11. Integration and design of renewable energies into new housing developments  The supporting tower shall be a distance of not less than the total structure height (including the blade of the turbine at the highest point of its arc) plus 1 m from any party boundary  Noise levels must not exceed 43 dB(A) during normal operation, or in excess of 5 dB(A) above the background noise, whichever is greater, as measured from the nearest neighbouring inhabited dwelling  No more than one turbine shall be erected within the curtilage of a house  No such structure shall be constructed, erected or placed forward of the front wall of a house  All turbine components shall have a matt non-reflective finish and the blades shall be made of material that does not deflect telecommunication signals  No sign, advertisement or object not required for the functioning or safety of the turbine shall be attached to, or exhibited on, the wind turbine.Taken these points into account, the turbines will be placed in the area open ground on theright of the residence area.Figure 6. Several micro-wind turbines (T-D and L–R): Windsave (1 kW 1.75 m diameter); renewabledevices swift turbine (2.1 m diameter 1.5 kW); Turby vertical axis (2.6 m high, 2 m diameter, 2.5kW); D400 StealthGen (400 W1.1 m diameter) of turbines requiredAssuming that the demand trend and annual electricity consumption in the UK is around6000-8000 kWh/year (Bahaj and James, 2004; Li et al, 2011) and considering that the PVsystem supplies 1000 kWh/year in this study (≈3 kWh/d x 365d/year = 1095 kWh/year), acouple of micro wind turbines could be require for each home. It means 4 micro-turbines/block and 16 micro-turbines in total. It would allow supply the energy for cooking(assuming a 1.9 kW electric cook 2.5 h/d), the boiler for hot water (assuming a 4 kW boiler2.5 h/d) and the heating energy requirement (considering 0.8 kW electric heaters 7 h/d).Due to the different daily energy demand in the houses, it should be considered an auxiliarypower generator, just in case of the shortage of energy production as figure shows. 11Energy Management 2011-12
  12. 12. Integration and design of renewable energies into new housing developments Figure 7. Annual mean wind speeds for each hour of the day at 3 sites in the UK during 2003* 16 14 12 wind speed (m/s) 10 8 Coleshill 6 Coombe Aberdeen 4 2 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Hour of the day* Taken from Bahaj et al, 2007. As it is seems, the peaks normally start at 11-12 pm and end at 19-20 pm3.2.4-PaybackAccording to Li et al (2011), the payback depends on multiple factors and it could vary from20 to 50 years. The first factor would be obviously the kind of micro-turbine, however otherfactor could be the annual mean wind speed (the more speed, within the limits, the lesspayback), the household electrical load, the exported electricity price, the Grant availableand the imported electricity price (all of them vary in the same way as the first factor).4-Final schemeAn example could be like figure 8 shows. Figure 8. Final scheme 12Energy Management 2011-12
  13. 13. Integration and design of renewable energies into new housing developments5-ConclusionIn this work, has been suggested a possible solution for a renewable energy installation in aresidence area under the FITs scheme. The ignorance in relation to the determination of theRHI tariffs level as well as other issues around the operation of this scheme has beendeciding factors to discard it.PV system and wind micro-turbine devices have been presented as a viable way to supplythe annual electrical demand in houses with average electrical energy consumption and fewchanges should be done to the initial site design.The socio-economic and environmental impacts are predominantly related to the fact ofreducing the CO2 emissions and the use of fossil fuels, a lower electric bill and the chanceof giving place a sector on the increase, which generates employment and will contribute toreduce the CO2 emissions by at least 80% by 2050. Furthermore, paybacks seem to beencouraging as they could range to 11-12 years for PV systems and, under favorableconditions, to less than 20 years for wind micro-turbines.However, for this particular case it would be suggested the construction of an isolated roomin order to keep a power generator since the weather conditions would not be alwayssuitable for energy production.6-ReferencesAlam, M., Rehman, S., Meyer, J.P., Al-Hadhrami, L.M., 2011.Review of 600–2500 kW sizedwind turbines and optimization of hub height for maximum wind energy yield realization.Review Article. Renewable and Sustainable Energy Reviews, 15(8), pp. 3839-3849.Bahaj, A.S., James, P.A.B., 2004. Direct indirect benefits of PV in social housing (invited), in:Proceedings of the World Renewable Energy Congress (WREC-VIII), Denver.Bahaj, A.S., James, P.A.B., 2006. Urban energy generation: the added value ofphotovoltaics in social housing, Renewable and Sustainable Energy Reviews.Bahaj, A.S., Myers, L., James, P.A.B., 2007. Urban energy generation: Influence of micro-wind turbine output on electricity consumption in buildings. Energy and Buildings, 39(2), pp.154-165.Bari, S., 2000. Optimum slope angle and orientation of solar collectors for different periods ofpossible utilization. Energy Convers Manage, 41, pp. 855-60. 13Energy Management 2011-12
  14. 14. Integration and design of renewable energies into new housing developmentsBekkouche, S.M.A., Benouaz T., Yaiche, M.R., Cherier M.K., Hamdani M., Chellali F., 2011.Introduction to control of solar gain and internal temperatures by thermal insulation, properorientation and eaves. Energy and Buildings, 43 (9), pp. 2414-2421.BSI, 1989. BS 5918. British standard code of practice for solar heating systems for domestichot water. London.Burton, T., Sharpe, D., Jenkins, N., Bossanyi, E., 2001. Wind Energy Handbook, John Wileyand Sons, Ltd.DECC, 2011a. Meeting Energy Demand. Renewable energy policy, Feed-in Tariffs.Available at:<> [Accessed 29 November 2011].DECC, 2011b. Meeting Energy Demand. Renewable energy policy, Renewable HeatIncentive. Available at:<>[Accessed 29 November 2011].DTI, 2005. Potential for microgeneration study and analysis, Final Report. Available at:<> [Accessed 22 November 2011].Duffie, J., A., Beckman, W., A., 1991. Solar engineering of thermal processes, 2nd ed.Wiley.Hammond, G. P., Harajli, H.A., Jones, C.I., Adrian B., 2011. Winnett Whole systemsappraisal of a UK Building Integrated Photovoltaic (BIPV) system: Energy, environmental,and economic evaluations. Energy Policy, 40, pp. 219-230.IDAE, 2009. Instalaciones de Energía Solar Térmica. Pliego de Condiciones Técnicas deInstalaciones de Baja Temperatura. Available at:<> [Accessed 13November 2011]Kern J., Harris, I., 1975. On the optimum tilt of a solar collector. Sol Energy, 17, pp. 97-102. 14Energy Management 2011-12
  15. 15. Integration and design of renewable energies into new housing developmentsLi, Z., Boyle, F., Reynolds, A., 2011. Domestic application of micro wind turbines in Ireland:Investigation of their economic viability. Renewable Energy, in press.Mertens S., 2003. The energy yield of roof mounted wind turbines. Wind Engineering 27, pp.507–518.Messenger, R.A., Ventre, J., 2003. Photovoltaic system engineering. 2 ed. Florida (USA):CRC Press, pp. 54-5.Pearsall, N.M., Hil,l R., Claiden, P., 1994. PV-cladding as an energy resource for the UK.Renewable Energy, 5 (1-4), pp. 348-355.Petersen, E.L., Troen, I., 1990. The UK wind resource and the European wind atlas, in:Proceedings of the 12th BWEA. Wind Energy Conference, pp. 129–135.Sokolov, M., Vaxman, M., 1988. On the dependence of thermosyphonic solar systemperformance on collectors azimuthal orientation. Energy Conversion and Management, 28(3) pp. 257-263.Solarguide, 2011. Solar PV (Photovoltaic) Feed-In Tariff Calculator. Available at:<> [Accessed 22November 2011].Sørensen, B., 2004. Renewable energy,3 ed. Academic Press, pp. 637-646.Suri, M., Huld, T.A., Dunlop, E.D., Ossenbrink, H.A., 2007. Potential of solar electricitygeneration in the European Union member states and candidate countries. Solar Energy,81(10), pp. 1295–305.TBC, 2009. Documento Básico HE 1-5. Ahorro de energía. Código Técnico de laEdificación. Ministerio de Fomento Secretaría de Estado de Vivienda y ActuacionesUrbanas Dirección General de Arquitectura y Política de Vivienda. Available at:<> [Accessed 16 November 2011]. 15Energy Management 2011-12
  16. 16. Integration and design of renewable energies into new housing developmentsTBC, 2011. DA DB-HE1. Zonificación climática en función de la radiación solar globalmedia diaria anual. Documento de Apoyo al Documento Básico DB-HE. Ahorro de energía.Código Técnico de la Edificación . Ministerio de Fomento Secretaría de Estado de Vivienday Actuaciones Urbanas Dirección General de Arquitectura y Política de Vivienda. Availableat:<>[Accessed 16 November 2011].Tsalides, P., Thanailakis, A., 1985. Direct computation of the array optimum tilt angle inconstant-tilt photovoltaic systems. Sol Cells,14, pp. 83-94.Weather2, 2011. Local Weather, West Yorkshire Climate History. Past weather includingmonthly averages for West Yorkshire, United Kingdom. Available at:<> [Accessed 8November 2011]. 16Energy Management 2011-12