RE.SUN Validation (March 2013)


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Validation of mesoscale modelled solar data series for solar resource assessment

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RE.SUN Validation (March 2013)

  1. 1. Re.Sun™ -Validation White Paper, March 2013 page: 1/9 Introduction Understanding the solar resources in areas where local measurements are scarce or unavailable is nowadays possible with state-of-the-art mesoscale numerical weather models and public high quality global weather databases. Since 2009, MEGAJOULE INOVAÇÃO has developed and tested an internal methodology using mesoscale modelling to feed a process of coupling using broadband Clear Sky models (ESRA, Ineichen, REST2) and solar radiation decomposition techniques allowing the assessment of Solar resources worldwide with more detail than usual approaches: Re.Sun™. The Re.Sun™ approach was developed internally and counts with the cooperation of the Physics research department of Aveiro University for validation and optimization of the mesoscale parameterisations. Re.Sun™ - Approach Re.SunTM is a code based on coupling techniques developed to ingest results from WRF–Weather Research and Forecasting mesoscale numerical model. The WRF model is presently used by numerous institutions across the world, and its versatility permits its use in a variety of applications. It consists of a series of modules, which allow the simulation of atmospheric conditions at a large (meso) scale (>1km), as well as assimilation of observed data, through the solution of several equations that describe the dynamics of the physical phenomena. WRF was developed by the U.S. National Center for Atmospheric Research (NCAR) as an evolution of the original MM5. It incorporates the latest scientific developments from the leading research SSoollaarr MMooddeelllliinngg bbaasseedd oonn CCoouupplliinngg TTeecchhnniiqquueess wwiitthh MMeessoossccaallee SSiimmuullaattiioonnss
  2. 2. Re.Sun™ -Validation White Paper, March 2013 page: 2/9 :: Re.Sun.cfg :: > n WRF mesh points to incluide (points to interp) > Transport Radiation model(Global or Indivudual components of Radiation > WRF Mesh aod/TL2 Interpolation > Clear Sky model (ESRA; Ineichen; REST2) > Decomposition model (20 in total ::DIRINT, BRL, Skartveit & Olseth, Maxwell, Reindl and others) :: WRF runs to Re.Sun =>data inputs :: FNL ; CLC Land Use and SRTM for topography) =>set up highlights (2/3 levels nesting ; 2-ways feedback; same radt for all nests; RRTM to LW& Dudhia to SW model) =>output modified (wrfout * tuned, only variables to use in coupling process; 10 min or others time steps) WRF runs wr > Tur bidity, Aer osols, Ozone and Nitr ogen Diox ide Sour ces :: SODA (Solar Radiation Data) :: Aer onet (Aer osol Robotic Networ k) :: MACC Re-analysis (Monitor ing atmospher ic composition & climate, ECMWF) :: OMI V2.1 (Nitr ogen Diox ide, NASA/Goddar d Space Flight Center ) Horizon code >Topogr aphy gr id > number of sector s Hor izon data (*netcdf or *.hdf5) centers, and is the result of decades of research. Over the last years, MJ INOVAÇÃO has “tuned” the WRF configuration for best results in solar assessment. Precursor mesoscale simulations are performed using WRF to solve all meteorological interactions, rendering available fields like Short Wave Radiation, Temperature, Vapour Mixe Ratio and Surface Pressure for posterior use by Re.SunTM . Re.SunTM applies Clear Sky simulations which include current information about aerosols and atmospheric gases (Ozone and Nitrogen Dioxide, in case of the REST2 model), pressure correction and orographic horizon effects. From these runs correction factors are estimated, which are interpolated to the interest points to correcting the local Clear Sky simulations. The correction factors can be estimated in terms of Solar Global index (Global RadiationWRF / Global RadiationClear Sky) or Solar Direct and Diffuse indexes, making use, in this case, of a decomposition model. A flowchart of the process is presented in the figure below. The global weather databases for WRF simulations currently available at MJ INOVAÇÃO are: FNL (Final) Operational Global Analysis from NCEP, ERA-Interim from ECMWF or Reanalysis I and II from NCEP/NCAR. The domain configuration and model parameterizations are studied for a set of cases but they can change according to site features. All WRF simulations make use of SRTM (Shuttle Radar Topography Mission) topography information. Simulations in the European context use Terrain Cover data from the Corine Land Cover 2006 programme, outside Europe, terrain cover data from the Global Land Cover Characteristics Database (USGS, National Center for Earth Resources Observation and Science – EROS, Joint Research Centre of the European Commission) is used.
  3. 3. Re.Sun™ -Validation White Paper, March 2013 page: 3/9 The aerosols or the TL2 (Linke Turbidity for an air mass equal to 2) can be derived from the SODA (Solar Radiation Data) programme or from MACC Re-analysis (Monitoring Atmospheric Composition & Climate) project (ECMWF). MEGAJOULE INOVAÇÃO has processed the two databases and has created its own database. The SODA project has monthly Worldwide Linke Turbidity Information already available, which is a result of assembling estimates of TL gathering different background layers, METEOTEST (Redmund et al. 2003). The MACC Re-analysis project does not contain TL2 information, but this can be estimated using the aerosols information for different wavelengths and water column data. To obtain TL2 from MACC information we have used two formulations: Redmund et al. 2003 and a multivariate fit calculated from beam irradiance with Solis model and the Kasten pyrheliometric formula (1996). Depending on the Clear Sky model used, we have different information to characterize the atmosphere purity. In case of the ESRA model the equations make use of TL2. Simplified version of Solis model (Ineichen model), use as input the aerosol optical depth information for a wavelength of 700nm (AOD700). Independently of the source of the aerosols or TL2, the data are used with a daily frequency. The monthly values of SODA are interpolated linearly from monthly to daily values and the MACC average daily values come from the insolation period with three hours of sampling. Regarding the atmospheric gases, ozone data is obtained from MACC and Nitrogen Dioxide values from OMI V2.1 programme (NASA/Goddard Space Flight Center). The REST2 (Reference Evaluation of Solar Transmittance, 2 bands) model is currently in implementation and its performance will be tested and results published in further editions of Re.SunTM White Paper. In a few words, the REST2 is a high performance model to predict cloudless-sky broadband irradiance, illuminance and photosynthetically active radiation (PAR) from atmospheric data (Christian A. Gueymard, 2007). REST2 was developed to precisely account the effect of aerosols, using for that two bands separated at 700nm where band 1 covers the UV and visible ranges (290nm to 700nm) and band 2 covers the near-infrared range (700nm to 4000nm). The Re.SunTM software thus provides a package of data that includes Solar Radiation (Global, Direct Diffuse on horizontal/tilted plane and Beam) and Meteorological (Temperature, Relative Humidity at 2m and Wind Speed/Direction at 10m) variables at site/project scale.
  4. 4. Re.Sun™ -Validation White Paper, March 2013 page: 4/9 Diffuse / Global Radiation ratio, (kd), Complex/Coastal site, Corvo, 06 October 2011, Re.SunTM Why no Pre-Calculated Solar Data ? Mesoscale weather numerical modelling is a complex science and in constant development. Calculation domain and several model parameterizations depend on the effects of prevailing climate and local topography features. The WRF model is also in continuous development and constantly tested. By not making use of pre-calculated solar maps or series MEGAJOULE INOVAÇÃO ensures that our Clients get the best modelling options available for each case and at any given time. Typical application from Re.Sun™ Typically, Re.SunTM is best suited for: • Country, Regional or Urban prospection of Solar Resource; • Complex terrains (high altitudes and varied soil occupations), sites where the atmospheric conditions are changing constantly; • Urban environments where the shadow effects of buildings, aerosols and micro-climates are features which affect the Solar Resource. The approach proposed by MEGAJOULE INOVAÇÃO was conceived to gather and model the main drivers which affect the Solar Resource modelling, performing a more realistic assessment than usual techniques based on interpolations. Traditional products are: • Solar Resource Mapping at Country, Regional or Urban scale (flexible output data – GIS, Google Earth, etc…); • Solar Data Series TMY (Typical Meteorological Year) for annual energy estimates; • Long Term reference solar data (for Long Term extrapolation of local measurements). The main outputs are: Global1 , Direct1 , Diffuse (Horizontal1 ), Beam2 Radiation, Temperature, Relative Humidity at 2m and Wind3 speed/direction at 10 m. 1,2,3 - The estimates in tilted planes, Solar Beam Radiation and Wind Speed/Direction are provided at an additional cost.
  5. 5. Re.Sun™ -Validation White Paper, March 2013 page: 5/9 Validation of Simulated Solar Data Series During 2012 MJ completed its first validation programme for Re.Sun™, the solar coupling code with mesoscale numerical model WRF, using Global Solar data from 9 locations. This validation was based in WRF meshes of 5x5 km and 1x1 km resolution, depending on site complexity. The weather input used was the NCEP FNL (Final) Operation Global Analysis data set. The simulated data was compared against local measurements for 9 complex sites, due to their challenging orogrophic and/or atmospheric conditions, located in Portugal. One in continental Portugal, in urban context, one in the Azores archipelago in Corvo Island under the influence of the well-known Azores anticyclone weather pattern. The remaining sites, 7, are located in Madeira Island. The climate throughout the year in Madeira is also directly influenced by the Azores anticyclone weather pattern. Due the privileged geographical location and east to west orientation the island can be split in two climatic regions, the south, warm subtropical, and the north, humid temperate. The two climatic regions combine to produce an exceptionally mild climate, with an overall average temperature of 22°C in the summer and 16°C in the winter, along with a moderate level of humidity. The island has many micro climates due to its extreme complex orography. The local measurements in Corvo and Sintra were carried out by MEGAJOULE and all measurements in Madeira were courtesy of LREC (Laboratório Regional de Engenharia Civil). The test sites vary from flat to very complex, coastal (< 10 km to shoreline) to inland and also urban to rural environment. This set of tests contains all the main drivers in the context of solar modelling. In the urban environment aerosols play an important role on the attenuation of radiation, and the shadowing effects from neighbour buildings are crucial. The orographic complexity is also present which normally leads to added shadowing effects, always considered in Re.SunTM simulations, as well as contributions from fog and cloud formation due to increased humidity on the slopes not exposed to direct radiation. Sintra Corvo
  6. 6. Re.Sun™ -Validation White Paper, March 2013 page: 6/9 Example of mean Daily values of Global Radiation Complex/Coastal site, Corvo October 2011, Re.SunTM (Orange), Measured (Green) Example of 10 minutes correlation of Global Radiation Complex/Coastal site, Corvo October 2011, Re.SunTM Example of Cumulative Density Function (CDF) of Global Radiation, sampling 10 minutes, Complex/Coastal site, Corvo, October 2011, Re.SunTM (Orange), Measured (Green) Results showed (table 1) a relative RMS error (Root Mean Square) of 4.00 % and a relative MB error (Mean Bias) of 0.64 %. The cumulative distribution of results (table 2) showed that for 80 % of cases, average Annual Global Solar Radiation (in horizontal plane) was below 4.14 % and below 2.77 % for 50 % of cases. 5 10 15 20 25 30 0 50 100 150 200 250 Day Irradiance[W/m 2 ] Modelled Measured 0 100 200 300 400 500 600 700 800 0 100 200 300 400 500 600 700 800 Measured [W/m2 ] Modelled[W/m 2 ] 0 100 200 300 400 500 600 700 800 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Irradiance [W/m2 ] CDF Modelled Measured Day 06 Day 17
  7. 7. Re.Sun™ -Validation White Paper, March 2013 page: 7/9 (Mapping of Mean Daily Global Radiation based on time step of 10 minutes, 06 October 2011, Re.SunTM (Mapping of Mean Daily Global Radiation based on time step of 10 minutes, 17 October 2011, Re.SunTM Table 1 Global statistics for Annual Average Solar Global Radiation comparison rMB (%) rRMS(%) rSTD(%) 0.64 4.00 4.19 Table 2 Maximum relative Mean Absolute BIAS (rMAB) for different frequency levels Frequency [%] Maximum rMAB (%) 50% 2.77 80% 4.14 90% 5.94
  8. 8. Re.Sun™ -Validation White Paper, March 2013 page: 8/9 Conclusions The statistics above show the usefulness of Re.Sun™ code for: solar applications in Thermal and Photovoltaic, solar series for energy building simulations and analysis of solar potential at urban scale. An 80 % probability was found that real average Annual Global Solar Radiation (in horizontal plane) will be within an interval +/- 4.14 % of the simulated value and within +/-2.77 % for a probability of 50%. The complexity of the sites involved in the validation process included the main drivers in the solar modelling context, rendering the worldwide application of this methodology more reliable. Further releases of this White Paper will integrate: i) a new validation set based on WRF weather dataset input ERA-Interim; ii) validation results of one year of energy production simulated against real energy production for a PV central of 1MWp; iii) validation of Global, Beam and Diffuse Radiation using stations from the SURFRAD network. Further Info.:
  9. 9. Re.Sun™ -Validation White Paper, March 2013 page: 9/9 Annex - List of sample sites ID Complexity Elevation [m] Data Period Data Recovery Rate [%] Sampling rMB R 1 Complex / Coastal / Rural 390 Oc11 - Sp12 78% 10min 1.7% 0.94 2 Complex / Coastal /Rural 675 Ja11-Dc11 98% 1hour -0.1% 0.95 3 Complex / Inland / Rural 1622 Ja11-Dc11 100% 1hour -3.0% 0.99 4 Complex / Inland / Rural 1017 Ja11-Dc11 99% 1hour -2.3% 0.97 5 Complex / Coastal / Rural 1020 Ja11-Dc11 90% 1hour 9.0% 0.98 6 Complex / Inland / Urban 260 Ja11-Dc11 100% 1hour -5.2% 0.94 7 Complex / Inland / Rural 1215 Ja11-Dc11 94% 1hour 2.8% 0.98 8 Complex / Inland / Rural 874 Ja11-Dc11 92% 1hour -0.5% 0.95 9 Flat / Inland / Urban 188 Ja11-Dc11 100% 1hour 3.4% 0.99