A Review of the Historical and TMY data now on offer through the API Toolkit

02 October 2019

TMY and Time Series data for the solar powered future

Building off Solcast’s announcement last week that we are now offering historical and TMY data, under the continued banner of deploying data and tools for the solar powered future, it is important to further detail what each of these new data products are, and how they are generated. We’ll dive into this in four parts: a brief review of methods, historical Time Series data, typical meteorological year data and monthly averages.

How Solcast creates solar GIS data

Solcast operates our own unique algorithms and proprietary modelling framework for estimating solar irradiance via geostationary weather satellite data. This geospatial information systems based process has three major steps

  • Detection of cloud cover and the characterisation of that cloud cover in terms of its impact on solar radiance.
  • Modeling the available solar radiance under clear skies, including treatment of aerosols (dust, salt, etc.) and water content
  • Creation of a combined estimate of the amount of solar irradiance reaching the Earth’s surface after it passes through the clouds

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We provide a full flow-chart of our methodology in this effort on our inputs and algorithms webpage, where you can dig deeper into the details. In short, we build a detailed history of global, direct and diffuse solar irradiance availability, worldwide, through the use of the most recently available satellite technologies. It’s a process of directly imaging cloud clover, modelling the interaction of those clouds with incoming solar radiation, and accurately determining how much reaches the Earth’s surface. (It's also the topic I completed my Ph.D. on, so you can naturally assume I find it quite interesting!)

With this detailed history of solar irradiance data in place, we then package the modelling outputs into three unique data products, focused on supporting solar farm prospecting and development as well as project finance, due diligence, and monitoring.

Historical solar irradiance Time Series data


The first historical solar irradiance data product is our Time Series data. Historical Time Series data are a record of past weather data for a specified location. At Solcast, we mean precisely, the location of interest. Not a nearby ‘station’ or ‘region’, but the exact location requested.

Most often, historical Time Series of solar radiation and meteorological variables are used for power modelling of solar farms to estimate year-to-year variability, or the seasonal or intra-day energy generation profile, but are also applied to the calculation of energy estimates for P90 or other probabilistic scenarios. Often, several years of data are used in this work, with a set averaging period for the solar radiation and weather data that matches the use case.

Another application is the use of real-time or more recent (e.g. the past 6-12 months) of Time Series data for solar farm monitoring and operation, to calibrate equipment, or to update/tune local energy modelling tools.

Solcast offers two variants of Time Series data on offer:

  • Basic (hourly granularity only)
  • Extended (all time granularities from hourly down to 5 minute).

Both are available for download in the API Toolkit, and are generally available for your evaluation within a few minutes. You can also directly download a data sample here.

TMY solar data (typical meteorological year)

The second historical data product are TMY data files. TMY stands for “Typical Meteorological Year”, and these files are a collation of all of our available historical weather data for a specified location for a one year period.

Solcast prepare these TMY files to represent the unique weather phenomena and climate of the specified location. This is accomplished through through analysis of multi-year Time Series data so as to provide annual averages that are consistent with long term averages. TMY files are formatted to contain exactly 8760 rows of data, one for each hourly period in an ‘average’, or ‘typical’ year.

Solar engineers routinely use TMY data for PV system simulations, through software like PVSyst, SAM or one of the many others that are now available. TMY data forms the basis of yield assessment, used extensively during prospecting and financing.

Solcast offers two variants of our TMY data for download in the API Toolkit:

  • Basic (P50 only)
  • Extended (P50, P75, P90 & P95)

You can find either available for download in the API Toolkit, where you can begin your evaluation within a few minutes. As was the case above, you can also directly download a data sample here.

Monthly solar irradiance averages

Thirdly, Solcast offers monthly averages of solar radiation data and other weather parameters. We compile these averages by using the entire available solar radiation and weather data history at your site of interest, before compiling them into averages that represent the whole of our historical database.

These monthly averages are meant to be a relatively low-cost way to receive a high-level overview of the solar resource available at a particular site. They are useful during the early stages of solar site prospecting when a coarse energy estimate is acceptable. And, uniquely, you can directly purchase our monthly average data files without an expensive subscription or required additional purchases.

We believe in FREE

At Solcast, we always start our users off with a generous allocation of free data. It’s our philosophy that you should be given a selection of our data, from anywhere in the world to test, validate and explore prior to making any purchasing decisions. This means that every new Solcast API Toolkit registration automatically gets free requests straight-away, no questions asked.

This is not a special offer, doesn’t require a referral or a credit card, no surprise subscription at the end of a set trial period - just FREE. You can access our API Toolkit and download your own sample TMY file or a historical Time Series within minutes of this no obligation registration. Our files come ready to go for PVSyst and SAM, as well as TMY3 and CSV formats!

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Dr. Nick Engerer

Dr. Nick Engerer

Solcast Co-founder • Author

Nick is an expert in the field of solar radiation and distributed solar PV modelling, and has co-founded Solcast out of a sincere desire to enable others to build the solar-powered future.

Read more about Dr. Engerer's scientific papers

Solar Power Forecasting