FAQs - Solar Glossary

The solar glossary contains technical terms & explanation related to Solar energy and PV technology.

NASA-SSE is National Aeronautics and Space Administration 

  • This is the data set contains parameters formulated for assessing and  designing renewable energy systems.
  • Global, regional and site specific radiation and meteorological data allow quick evaluation of potential renewable energy projects for any region of the world. The SSE data set is formulated from NASA satellite- and reanalysis-derived insolation and meteorological data for the 22-year period July 1983 through June 2005.
  • Results are provided for 1° latitude by 1° longitude grid cells over the globe.
  • NASA-SSE is a satellite based data base of Radiation ,wind speed and air temperature along other weather related parameter across the world.

 

SolarGIS

The SolarGIS database is a high resolution database recognised as the most reliable and accurate source of solar resource information. The datababase resides on about 100 terabytes of data and it is continuosly updated on daily basis. The data is calculated using in-house developed algorithms that process satellite imagery and atmospheric and geographical inputs.The database consists of the following parameters

      Solar and PV data 

  • Global Horizontal Irradiance/Irradiation (GHI)
  •  Direct Normal Irradiance/Irradiation (DNI)
  •  Diffuse Horizontal Irradiance/Irradiation (DIF)
  • Global tilted/in-plane irradiance/irradiation for fixed and sun-tracking surfaces (GTI)
  • Optimum Angle (OPTA) for PV modules on fixed mounted construction PV Electricity Yield (PVOUT)

 

       Meteorological data 

  •  Air Temperature at 2 meters (TEMP)
  •  Relative Humidity (RH)
  •  Wind Speed (WS) and Wind Direction (WD) at 10 meters

 

           Geographic data 

  •  Terrain
  •   Landscape
  •   Population

 

Meteonorm

Meteonorm is a comprehensive meteorological reference. It gives you access to catalogue of meteorological data for solar applications and system design at any desired location in the world. It is based on more than 25 years of experience in the development of meteorological databases for energy applications. 

Meteonorm addresses engineers, architects, teachers, planners and anyone interested in solar energy and climatology.

Most of the data is taken from the GEBA (Global Energy Balance Archive), from the World Meteorological Organization (WMO/OMM) Climatological Normals 1961–1990 and from the Swiss database compiled by MeteoSwiss.

The periods 1961–1990 and 2000–2009 are available for temperature, humidity, wind speed and precipitation; the periods 1981–1990 and 1991–2010 for solar radiation.

Monthly climatological (long term) means are available for the following eight parameters:

  • global radiation
  • ambient air temperature
  • humidity
  • precipitation
  • days with precipitation
  • wind speed
  • wind direction
  • sunshine duration

The station data is supplemented by surface data from five geostationary satellites. This data is available on a global grid with a horizontal resolution of 8 km (3 km in Europe and Northern Africa).

There are many losses considered while calculating the final energy generation of your site. 

1. Soiling Loss - Accumulation of dirt and its effect on the system performance is an uncertainty which strongly depends on the environment of the system, raining conditions, etc.

2. Ohmic Loss - It is the wiring ohmic losses between the power available from the modules and that at the terminals of the array. These losses can be characterized by just one resistance parameter R defined for the global array. 

Note: the wire size is not only related to the desired ohmic loss. For a given current and a given installation mode, a minimum wire section is required.

3. Incident Angle Modifier - IAM also known as array incidence loss corresponds to the decrease of the irradiance really reaching the PV cells's surface, with respect to irradiance under normal incidence, due to reflections increasing with the incidence angle.

4. Module Mismatch - Mismatch losses are caused by the interconnection of solar cells or modules which do not have identical properties or which experience different conditions from one another.

5. Inverter Loss during operation -Sometimes the oversized array and high Vmpp ( more modules in series), you have the risk that the over power correction leads to an operating voltage higher than VmppMax, and in this case the inverter has to stop completely ( it cannot find a suitable operating point), leading to high overpower losses.

 

The global formula to estimate the electricity generated in output of a photovoltaic system is:

          E = A * r * H * PR 

= Energy (kWh) 
A = Total solar panel Area (m²) 
= solar panel yield (%) 
H = Annual average solar radiation on tilted panels (shadings not included) 
PR = Performance ratio, coefficient for losses (range between 0.5 and 0.9, default value = 0.75) 

 r is the yield of the solar panel given by the ratio : electrical power (in kWp) of one solar panel divided by the area of one panel

Example: the solar panel yield of a PV module of 250 Wp with an area of 1.6 m² is 15.6% 
Be aware that this nominal ratio is given for standard test conditions (STC) : radiation=1000 W/m², cell temperature=25 °C, Wind speed=1 m/s, AM=1.5 The unit of the nominal power of the photovoltaic panel in these conditions is called "Watt-peak" (Wp or kWp=1000 Wp or MWp=1000000 Wp). 

You can find this global radiation value from solar radiation data which are 

  • NASA-SSE
  • Meteonorm
  • Solar-GIS 

You have to find the global annual irradiation incident on your PV panels with your specific inclination (slope, tilt) and orientation (azimuth). 

PR : PR (Performance Ratio) is a very important value to evaluate the quality of a photovoltaic installation because it gives the performance of the installation independently of the orientation, inclination of the panel. It includes all losses.

Example of losses details that gives the PR value (depend on the site, the technology, and sizing of the system) : 
- Inverter losses (4% to 15 %) 
- Température losses (5% to 18%) 
- DC cables losses (1 to 3 %) 
- AC cables losses (1 to 3 %) 
- Shadings 0 % to 80% !!! (specific to each site) 
- Losses weak radiation (3% to 7%) 
- Losses due to dust, snow... (2%) 
- Other Losses 

Tariff is charges against the per unit (kWh) consumption of energy called Energy tariff.

The price at which electricity is sold is known as tariff for electricity and several factors come into play while determining the tariff. Normally the tariff of electricity is mentioned in rate per kilowatt hour of power consumed or rate per kWh.

1 kWh refers to the amount of electricity consumed when an appliance of one kilowatt power rating runs for one full hour or sixty minutes. 1 kWh is also known as one unit of electricity.

Capacity utilization factor refers to the relationship between actual output that is actually produced with the installed equipment, and the potential output which could be produced with it, if capacity was fully used. 

Thus, a capacity utilization is the (weighted) average of the ratios between the actual output of firms to the maximum that could be produced per unit of time, with existing plant and equipment. 

 

The performance ratio under the influence of certain factors, may exceed values of 100 %. This is because performance characteristics of the PV modules are used in the calculation of the performance ratio that have been determined under standard test conditions (1,000 W/m2 solar irradiation and 25 °C module temperature).

The following factors can have influence to the PR value:

• Environmental factors

  • Temperature of the PV module
  • Solar irradiation and power dissipation
  • The measuring gauge is in the shade or soiled
  • PV module in the shade or soiled

• Other factors

  • Recording period
  • Conduction losses
  • Efficiency factor of the PV modules
  • Efficiency factor of the inverter
  • Differences in solar cell technologies of the measuring gage and of the PV modules
  • Orientation of the measurement gage 

The Performance ratio (PR) is ratio of AC Energy generated (kWh) to multiplication of  irradiance (kWh/sq.m) on panel, Active area of PV module (sq. m) and PV module efficiency.

Basic calculation formula for Performance ratio is 

PR =Actual reading of plant output in kWh p.a / Calculated, nominal plant output in kWh p.a
 
 
 

NASA-SSE is National Aeronautics and Space Administration - Surface meteorology and Solar Energy. 

This is the data set contains parameters formulated for assessing and designing renewable energy systems.

It contains new parameters recommended by the renewable energy industry and is more accurate. Global, regional and site specific radiation and meteorological data allow quick evaluation of potential renewable energy projects for any region of the world. The SSE data set is formulated from NASA satellite- and reanalysis-derived insolation and meteorological data for the 22-year period July 1983 through June 2005.

Results are provided for 1° latitude by 1° longitude grid cells over the globe.

NASA-SSE is a satellite based data base of Radiation ,wind speed and air temperature along other weather related parameter across the world.

A "PXX" denotes the annual energy production level that is reached with a probability of XX%.

P90: P90 denotes the level of annual sun-driven electricity generation that is forecasted to be exceeded 90% of the year. A P90 value of 10,000 kWh would mean that the system is likely to generate over 10,000 kWh 90 % of the time. 

P75: There is a 75% chance that the annual energy production level will be reached.

P50: There is a 50% chance that the annual energy production level will be reached. A P50 value of 10,000 kWh for the annual output of a solar power system means that there is a 50 % likelihood that the system’s output will be greater than 10,000 kWh.

The PXX values are widely used by potential investors and banks as basis for financing decisions.

Solar GIS provides irradiation ,air temperature and wind speed of each 15 minute to hourly daily ,monthly ,and long term average value ,TMY.

It is a geographical information system designed to meet the needs of the solar energy industry. It integrates solar resource and meteorological data with tools for planning and performance monitoring of solar energy systems.

SolarGIS accurately calculate PV electricity potential within minutes.

The performance ratio (PR) is stated as percent and describes the  relationship between the actual and theoretical energy outputs of the PV plant. It is independent of location and it therefore often described as a quality factor. 

Performance Ratio (PR) of a plantperiod of time =Energy measured(kWh)/(Irradiance(kWh/m2) on the panel x Active area of PV module(m2) x PV module efficiency)

Global Horizontal Radiation also called Global Horizontal Irradiance; total solar radiation; the sum of Direct Normal Irradiance (DNI), Diffuse Horizontal Irradiance (DHI), and ground-reflected radiation; however, because ground reflected radiation is usually insignificant compared to direct and diffuse, for all practical purposes global radiation is said to be the sum of direct and diffuse radiation only:

      GHI = DHI + DNI * cos (Z)

      where

      Z is the solar zenith angle. 

 

Meteonorm is proven data base for accessing meteorological data i.e. irradiation, temperature and more weather related parameter across the world. Meteonorm having approximately 8233 ground based station for measuring these weather parameters.

As fossil fuel based power generation are getting costlier day by day along with serious environmental issues, We need long lasted, eco friendly source of energy generation, and that is solar energy.  

Although there are numerous other methods of generating electricity, solar plant have a number of considerable advantages for both the consumer, the producer, and the environment.

Solar Power plants, is arranged to generate commercial electricity, are becoming more and more frequent nowadays.

Electricity generated from solar panels is free, nearly infinitely abundant, and non-polluting.

Many environmentally-minded communities across the world have set up solar power stations to help generate private or commercial solar energy.

Powering homes with solar power has also been a major part of the solar revolution the last two decades have seen. Solar panels can be placed on the roof of homes, businesses, or remote research stations, and can be used independent of or in conjunction with the local power grid.