Solar Due Diligence Services

    Product Description
    Vaisala's Solar Energy Due Diligence Services take into account all of the factors that impact solar production to deliver the net energy estimates needed to make critical investment and financing decisions. Solar resource intensity and variability is a key indicator of future success, and understanding how it directly impacts energy generation is the most sensitive variable for predicting a solar plant's revenue potential.


    Experience and Information You Can Trust

    With experience delivering over 6 GW of performance estimates at utility-scale PV plants around the world, Vaisala's expert team is one you can trust. We make use of our full long-term resource records when determining our power estimates because it is the best method for quantifying risk and predicting how much revenue will vary month-to-month and year-to-year over a project's lifetime. Our team follows a rigorous process for creation of the energy due diligence including a two stage review by experienced scientists and engineers to ensure the best practices are always followed.

    Vaisala’s Solar Energy Due Diligence services have been used to support project design, project financing and refinancing, portfolio reviews, energy auction bids and second opinions. Our team will work with you on your timeline to ensure the right level of analysis and deliverables that meet your needs.

    Services Customized to Your Project

    We quality control and incorporate all available on-site observations to enhance the accuracy of our methodology. In addition, we tailor losses, degradation schedules, and other inputs to each project site based on the project’s design and the local climate. If you aren’t certain of your project’s design Vaisala’s experts can collaborate with you to ensure the most energetic outputs possible at your location. Our holistic solar risk framework uncertainty analysis means that both the developer and the financier can be confident of the results and fully informed of potential risks. ​



    Technical Overview

    ​Produ​​​ct Features

    Solar Energy Due Diligence Analysis Report containing:

    • Executive summary
    • Project specifications
    • Meteorological data overview and methodology
    • Power generation overview and methodology
    • Uncertainty discussion with probability of exceedance tables
    • Results
      • Losses
      • Yield and performance metrics
      • Inter-annual variability
      • Lifetime of plant generation
    • Also included are data files for resource and energy

    Optional Features

    • Project design layout
    • 10-minute interval resource data

    Delivery Method

    Portable Document File (PDF) report and data files in an easily integrated, comma-separated value (CSV) format.


    As a leading innovator in atmospheric sciences, Vaisala offers Solar Energy Due Diligence Analysis for assessing large-scale solar projects anywhere in the world. By deeply analyzing the long-term satellite derived irradiance time series in the exact spot where the project would be located, the developer gets in-depth information about the interannual variability of the resource, which provides essential information about the future availability of the resource. It is an exhaustive study of solar conditions at the site, determining the suitability of the project and giving the developer confidence to move the project forward.

    We also analyzes other meteorological variables, such as wind speed and temperature that affect project performance, to give a broad and complete picture of the resource of the site, and the necessary information to understand project feasibility. By incorporating other meteorological variables our report provides a clearer picture of the conditions that affect the long-term production potential of your project. In addition to the long-term irradiance time series we also provide an accompanying data file with hourly wind and temperature values.

    Learn more about our Solar Resource Assessments by clicking the tab at the top of this screen.

    As a single assessment provider with global capabilities, Vaisala allows you to make more informed decisions whether you are developing projects in California or Rajasthan. While the solar energy resource is a key indicator, most developers want to know how much energy can be generated at a given site before continuing to invest in a project site. A Solar Energy Due Diligence Analysis is a simulation of the hour-by-hour electrical production of a specific, but yet-to-be-built solar generating station. Production estimates are highly complex and involve dozens of specific assumptions and considerable exercise of professional judgment, which Vaisala has through its specialized personnel.

    We take the stated capacity and choice of technology, and produce an annual yield estimate based on manufacturer’s specifications, industry best practices and our own experience at similar sites. The power is based on 3TIER Service’s long-term resource time series or a Typical Meteorological Year and contains a thorough uncertainty analysis. This gives you net energy estimates with losses, derates, and overbuild needs. This estimate is an indication of the annual yield and therefore of the revenue to be achieved at a proposed plant.


    Comparing year-1 yield distributions from a TMY standard deviation methodology and a long-term time series Kernel Density Estimation methodology


    Learn more about our energy uncertainty methodologies by downloading this recent paper {Pellend Solar 2016}

    Global Solar Dataset

    Vaisala produced the first global solar irradiance map and time series dataset at roughly three times the resolution of previous US solar datasets and at thirty times the resolution of global datasets available from NASA. Based on over a decade of satellite imagery and cutting-edge technology, our uniform methodology is supported by a large scientific and research community and results in a consistent map and dataset, enabling more accurate point-to-point comparisons.

    The dataset is based on actual, half-hourly, high-resolution visible satellite imagery observations via the broadband visible wavelength channel at a 2 arc minute resolution. These data have been processed to hourly GHI, DNI, and DIF values. Vaisala processes the satellite images based on a combination of in-house research and algorithms published in peer-reviewed scientific literature. These algorithms contain parameters and coefficients that are based on empirical fits to observational data. The specific satellites and length of time varies slightly by region due to differences in the availability of data from region to region. See the chart below for more details.

    Regions Satellites Temporal Coverage

    Western Hemisphere

    GOES 8 - 14

    January 1997 – ​last month

    South Asia & Middle East

    Meteosat 5, Meteosat 7

    January 1999 – last month

    East Asia & Oceania

    GMS 5, GOES 9, MTSAT 1-2, Himari-8

    December 1998 – last month

    Europe & Africa

    Meteosat 7, Meteosat 9-10

    July 1998 – last month

    To develop and validate our model, Vaisala used observations from:

    • SurfRad
    • Baseline Surface Radiation Networks
    • National Solar Radiation Database
    • Bureau of Meteorology (Australia)
    • National Institute of Water and Atmospheric Research (New Zealand)
    • Indian Meteorology Department
    • NREL Annex II
    • Linke Turbidity Database from Ecole des Mines de Paris
    • National Snow and Ice Data Center (high-resolution snow dataset)
    • MODIS Aerosol Optical Depth and Water Vapor Datasets

    Find our validation paper here.

    Customer Requirements

    In order for us to process this report, you must provide the center latitude and longitude of your solar site and one year of high quality, solar irradiance observations taken within 2​0km of the solar site. In addition, we require full equipment specifications, operations and maintenance plans, transformer data, and shade study.​

    ​If you are unfamiliar with the technical terminology on this page, please visit our Glossary for more information.​​​