This week, we’re pleased to present a guest post from GroundWork® Renewables’ Director of Data and Analytics Julie Chard.
At GroundWork, we’re committed to delivering high-quality solar-meteorological (MET) data to reduce uncertainty in solar resource assessments. With more than 15 years of experience supporting the solar development community, our observational MET programs combine best-in-class equipment and our rigorous data quality program, GroundWatch®, to deliver the highest field accuracy possible.
Why observational MET programs matter
Accurate in situ irradiance data significantly reduces the uncertainty of the solar resource assessment and results in a measurable return on investment during project financing. Serving the solar development community since 2009, the GroundWork ReyTM MET program has continuously provided high-quality equipment and its rigorous data quality program, GroundWatch, to achieve a field uncertainty as close to the instrument uncertainty as possible.
Furthermore, high-quality MET data can be used in combination with SolarAnywhere® satellite data for more accurate resource assessment, especially at project locations in complex climates.
MET program best practices
Timing and siting
For utility-scale solar projects, developers typically deploy MET equipment when project AC capacity is 10 MW or greater and land acquisition is complete. Ground campaigns are run for a minimum of one year to capture seasonal variations. Climate variability and increasing project sizes have motivated some clients to extend ground campaigns to 18 to 24 months to maximize the uncertainty reduction (see Figure 1) and protect against the impact of anomalous weather events. Campaign extensions are cost-effective for our clients, as continued maintenance and data services represent only a fraction of the total cost of the campaign.
Figure 1: GroundWork and SolarAnywhere Site Adaptations Reduce Solar Resource Bias and Uncertainty
Example uncertainty reduction obtained with a campaign length of 12 and 24 months relative to native SolarAnywhere Data Version 4.0 from Clean Power Research. Extending a Rey MET campaign by six months accounts for less than 10% of the total resource assessment campaign budget. However, this extension can yield substantially higher returns due to the further reduction in uncertainty.
Site selection and deployment
Collaboration with developers and landowners to properly site the MET system is key. Many factors are considered to ensure data quality, allow access for proper maintenance and maintain security of the system. Our MET systems are mobile, fenced and equipped with data loggers to transmit real-time information to our secure servers.
High-quality equipment for precise data
Irradiance is paramount
Global Horizontal Irradiance (GHI) is the foundation of solar resource assessment, and accurate GHI data is crucial for modeling energy production.
Groundwork measures GHI with redundant ISO 9060 spectrally flat Class A pyranometers. These instruments provide a best-case measurement uncertainty under laboratory and/or controlled conditions of 2%. With redundant measurements and reliable maintenance, GroundWork achieves a fielded measurement uncertainty of 2.5%1, representing real-world performance as close to the instrument uncertainty as possible.
Diffuse horizontal irradiance (DHI) data further aids energy modelers in determining the energy available at the plane of the array. This is particularly useful for single-axis tracking arrays.
Ancillary MET measurements
Robust observational MET programs include additional meteorological data points required for energy modeling and utility compliance. GroundWork MET systems measure and monitor:
- Relative Humidity
- Ambient Temperature
- Wind Speed and Direction
- Barometric Pressure
- Rainfall
Meteorological data is often required by the utility contracted to purchase power. Wind speed and ambient temperature measurements in particular are critical to the energy modeling process and to inform array design. An optional snow depth measurement add-on can aid accurate assessment of snow losses in PV energy modeling and validation of albedo measurements. It can also help developers understand where heavy snowpack can impact tracker tilt limits, or hinder access for operation and maintenance (O&M) activities.
Soiling measurement
It is cost effective to measure site-specific soiling trends in conjunction with the Rey MET campaign as GroundWork’s soiling measurements leverage the MET system’s data logging and data transmission infrastructure. GroundWork deploys a matched pair of small solar modules. One module is allowed to soil while the other is cleaned weekly during the maintenance technician’s regular visits. Particulate matter and rainfall measurements are included as standard on the GroundWork soiling kit for soiling loss modeling.
The resulting data provides critical insights for modeling soiling losses as a component of energy modeling.
Albedo measurement
With the proliferation of bifacial modules in utility-scale PV solar installations, albedo measurement has become a valuable addition to the GroundWork Rey MET System. Snow cover, seasonal vegetation and soil moisture conditions all influence the albedo. Characterization of how site-specific albedo varies throughout the day and year is important for accurate modeling of PV performance, including bifacial gains.
Using GroundWatch® to ensure data quality
Onsite maintenance and data integrity
Meteorological instruments require routine maintenance to sustain measurement accuracy. Pyranometers, for instance, are sensitive optical devices that can collect dust and debris, leading to skewed irradiance readings and increased uncertainty. To maintain data integrity, our technicians conduct weekly site visits to:
- Clean and level irradiance sensors
- Inspect ancillary meteorological sensors
- Verify equipment security
As-found and as-left conditions are reported and a comprehensive set of photos is taken. The resulting metadata accompanies the dataset through the financing process, in support of data accuracy.
Real-time data monitoring and issue resolution
With a dataset that is so valuable, safe data transmission, storage and analysis is essential. Our automated data quality algorithms detect anomalies to flag data and alert our data team. On a daily basis, trained analysts also perform visual review of irradiance curves, soiling, albedo and meteorological data to identify potential issues.
A smart investment for solar developers
A quality in situ measurement campaign can be performed for a nominal cost relative to the total capital expenditure of a utility-scale solar project. When used in conjunction with satellite data such as SolarAnyhwhere, ground-based measurements reduce the uncertainty of the solar resource assessment, resulting in lower financing costs and more accurate energy production estimates. At GroundWork, we are passionate about our part in accelerating the solar industry’s success.
About our guest author
Julie Chard is director of Data and Analytics for GroundWork. She is well-versed in solar-meteorological system instrumentation and configuration. She closely follows the work coming out of U.S. National Laboratories and regularly participates in specialized conferences in order to stay current on solar industry standards and best practices for achieving the lowest uncertainty data sets.
Julie is keenly focused on ensuring that the industry-leading data sets generated by GroundWork equipment and services meet or exceed the expectations of GroundWork clients and independent engineers.
1 Peterson J, Chard J, Bryan A. June 2023. Quantifying Real-World Sources of Error in Redundant GHI Measurements. 2023 IEEE 50th Photovoltaic Specialists Conference (PVSC). DOI:10.1109/PVSC48320.2023.10359797. Link