Observations of Indirect Solar irradiance – A Pilot project (IEA-SHC Task 46)
Nationwide observations of both indirect and direct solar irradiance will be of value for designing solar energy systems, energy optimization of buildings and architects. Currently, DMI only monitors the total solar irradiance. This is a pilot project to test the quality and usefulness of measuring also the indirect solar irradiance.
The energy from the Sun comes to us in form of either direct solar irradiance or scattered solar irradiance. Solar irradiance is scattered when this is refracted or diffracted from cloud droplets, cloud ice particles, microscopic aerosols or Rayleigh scattered from atmospheric molecules, which makes the sky blue. The fraction of the scattered solar irradiance and scattered solar illuminance as compared with the total solar irradiance is great importance to building engineers, architects, and for optimal utilization of solar heating and photovoltaic systems. In the greater scheme of things, increased knowledge about the distribution of solar irradiance is important for the optimal management of power plants in the Danish smart grid.
Currently, DMI measures only the total solar irradiance. This is done at 28 stations at locations across Denmark. Here we make a pilot study where several types of instruments for measuring the scattered irradiance also are tested over a period of at least one year. This test will be done in parallel with the international collaboration in the IEA SHC Task 46 expert group, where using and making new standards for low maintenance pyranometers that measure also the scattered solar irradiance is a priority.
Measurements performed over several years at DTU Civil Engineering of the total and scattered solar irradiance show that the fraction of the solar irradiance that is scattered is highly variable over time, and, that a simple correlation between the total solar irradiance and the scattered solar irradiance does not exist (EUDP 64011-0085001; Dragsted og Furbo 2012, DTU Civil Engineering Report R-275).
Solar irradiance is scattered when this is refracted or diffracted from cloud droplets, cloud ice particles, microscopic aerosols or Rayleigh scattered from atmospheric molecules, and when this is reflected from the surface. The fraction of the scattered solar irradiance and scattered solar illuminance as compared with the total solar irradiance is of great importance to building engineers, architects, and for optimal utilization of solar heating and photovoltaic systems. In the greater scheme of things, increased knowledge about the distribution of solar irradiance is important for the optimal management of power plants in the Danish smart grid. Thus, there is a need for nationwide monitoring of scattered solar irradiance and including these into the meteorological measurement network of the Danish Meteorological Institute (DMI). Currently, DMI measures only the total solar irradiance. This is done at 28 stations across Denmark.
In this pilot study instruments for measuring the scattered irradiance have been tested over a period more than one year. The study has been coordinated with the IEA SHC Task 46 expert group. Two instruments have been tested: The RSR2 from Irradiance Inc. (Lincoln, Massachusetts 01773 USA) and the SPN1 from Delta-T Devices (Cambridge, CB25 0EJ UK). It is important that the instruments chosen are: 1) Sufficiently accurate compared to state-of-the-art instruments; 2) Solid and capable of being operated continuously over many years without frequent maintenance. It is recommended that DMI installs SPN1 pyranometers at its current radiation stations.
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Participants
| Partner | Subsidy | Auto financing |
|---|---|---|
| Danmarks Meteorologiske Institut | 0,34 mio. DKK | 0,07 mio. DKK |
