Solar resource assessment and forecasting

The International Energy Agency (IEA) Solar Heating and Cooling Programme (SHC) Task 46 project: ”Solar Resource Assessment and Forecasting” has two goals: 1) To understand short-term resource variability caused by clouds; 2) To assess the application of short term forecasts for planning the operation of multiple solar energy systems. The international task has been prolonged to last to 2016; we plan to continue the Danish participation accordingly. The Danish partners in SHC Task 46 are the Danish Meteorological Institute (DMI) and the Department of Civil Engineering at the Technical University of Denmark (DTU). The cooperation from 2011 to 2015 has been very good - both nationally and internationally. Below a list of our results so far and our plans continuing into 2016 can be found:

- New design reference years (DRYs) for solar heating and buildings have been developed based on ten years of Danish meteorological data from 2001 to 2010. These include global radiation data from DMI weather stations and calculated diffuse irradiances based on algorithms developed by DTU. The new DRYs have been made freely available.

- DRYs include meteorological data from 12 typical months. The effect of meteorological variability on the thermal performance of solar collectors during all 120 typical and untypical months in the period 2001-2010 analyses has been tested. The investigation was presented at the solar heating and cooling conference SHC2014 in Beijing.

- In 2014 DMI took the lead of activity B5 in the SHC Task 46. This activity includes making a review of all the different types of yearly meteorological data sets used for modeling different types of solar energy systems. Recommendations on how to design and document such meteorological data sets will be made.

- Benchmarking of DMI weather models against several other models has been carried out for the period March 2013 to February 2014. The first results have been published in the 2015 NREL report: NREL/TP- 5D00-63112. Further results will be published during 2015.

- At DTU the angular distribution of global radiation is now monitored with 2 minute time resolution. The first results from these measurements were presented at the solar heating and cooling conference SHC2014 in Beijing.

- DMI has made a theoretical model of the variability of angular irradiance. It includes the variability effect of inhomogeneous cloud cover. The model utilizes the cloud optical thickness, which is a novelty compared with empirical models, such as the Perez angular distribution model. This model will be published in 2015.

- Moving into 2016, a main goal will be to utilize our increased understanding of the angular distribution of solar irradiances for the solar heating plant in Hedehusene. Our working hypothesis is that improved understanding and monitoring of the angular distribution of the solar resource will enable improved design and operation of solar heating plants and PV plants.