Solar Radiation Measurement Technology from Delta-T Devices

Tony Peloe, Distributor Manager at Delta-T Devices talks to AZoSensors about Solar Radiation Measurement Technology.

As one of your key products, how does the SPN1 Sunshine Pyranometer Sensor work to measure solar radiation and sunshine duration?

The SPN1 works in a very innovative way - at least one of the seven individual sensor elements (thermopiles) is always exposed to the full solar beam, whilst at least one is always fully shaded. A microprocessor inside the instrument calculates the global and diffuse irradiance, and from these data the sunshine state (WMO defined) is estimated.

It is the unique design of the shadow mask in the SPN1 that makes such measurements possible. It removes the need for moving parts, and sets it apart from other pyranometer designs.

Sunshine Pyranometer type SPN1. Image credits: Delta-T Devices.

How would you compare the SPN1 product by Delta-T Devices to shade-ring pyranometers, pyrheliometers, and traditional sunshine recorders?

The SPN1 differs principally in price and complexity, compared to more traditional solar tracker sytems, shadow-band technology and sunshine recorders. The SPN1 has no moving parts and no requirement for routine adjustment. The alternative method for measuring global and diffuse radiation involves two pyranometers, one of which is shaded with a shadow-band or shade disk that needs to be automated or adjusted. Likewise, a Campbell-Stokes sunshine recorder requires regular attention.

The simplicity of the SPN1, and the lack of complex automation or mechanisation, makes it ideally suited for use in remote or challenging locations.

Can you provide me with a case study of when the SPN1 product has been used in difficult climate conditions?

Several years ago we supplied the SPN1 to the Finnish Meteorological Institute for use in Antarctica. It worked very well, under extremely testing conditions. The SPN1 was compared with other state-of-the-art solar sensors in that environment and it performed impressively.

Image of SPN1 in Antarctica courtesy of Finnish Meteorological Institute.

Where on this product are the readings displayed for the end-user?

The SPN1 has two connection options. A serial cable can be used and the measurements displayed in real time on a PC using the SunRead software supplied. Alternatively a connection can be made to a data logging system (Delta-T Devices also specialises in these), which can record the three outputs from the SPN1: global radiation, diffuse radiation, and sunshine status.

How does the output from the SPN1 sensor allow for the calculation of direct-normal irradiation (DNI)?

Direct-Normal Irradiance is commonly used in the solar energy sector and is defined as the energy in the solar spectrum incident in unit time at the Earth’s surface on a unit area perpendicular to the direction of the sun.

Since the SPN1 measures global and diffuse radiation on a horizontal plane, calculating DNI can be as simple as subtracting diffuse radiation from global radiation, and dividing by the cosine of the solar zenith angle. This can be done for recorded data using a PC and an Excel spreadsheet supplied by Delta-T. Alternatively, the new GP2 Data Logger from Delta-T Devices will shortly be able to calculate and record DNI values from a horizontally mounted SPN1 in real time.

What are the main areas of application for the SPN1 sensor?

Originally the SPN1 was designed for incorporation into national meteorological networks and for research applications. For the last few years, however, customers from the solar energy sector have dominated. The quality, versatility and simplicity of the SPN1 has proven to be very attractive to this market.

What have you found to be the main challenges for the end-user with regard to this product?

Due to its design, the SPN1 presents very few challenges to the end-user. Normally the only requirement when installing the SPN1 is that it is level, and it has a built-in bubble indicator to facilitate this.

Pyranometer installation can be costly. What efforts have you made to ensure that this product is as economical as possible for its target market?

The SPN1 provides measurements that would normally require three instruments, and so there is a huge potential saving almost immediately. With fewer instruments to install the infrastructure and labour requirements are also reduced. Finally, with no routine adjustments necessary and minimal maintenance, the cost of ownership of the SPN1 is low.

How does the SPN1 pyranometer compare to satellite data?

We normally compare the SPN1 against more accurate ground-based stations. Satellite estimates have become more reliable in recent years, but they always need adjusting for local conditions, or ‘ground truthing’, before they can be used reliably. In general, the SPN1 will still give more accurate results than satellite estimates.

Are there any new areas of application that you hope to explore with your products?

The SPN1 has an extremely fast response time (200mS) and researchers have already been able to apply tilt correction for mounting it on an aeroplane as part of a suite of instruments.
There has also been some work in the US adapting the SPN1 for estimating cloud cover.
Finally, early trials have shown that it may be possible to deploy the SPN1 on marine buoys which are used globally for environmental and climate research.

Where can our readers find further information on your products and services?

They can visit our website or contact one of our distributors. Alternatively they can contact our UK office where we can assist them directly or help them find advice more locally.

About Tony Peloe

Tony Peloe combines an academic background in water science and environmental biology with 20 years commercial experience of science research instrumentation.

He has worked at Delta-T Devices since 2004 and currently performs the role of Distributor Manager for Europe, Africa and the Middle East. His job involves building strong relationships across these important territories and sharing his specialist knowledge of meteorological, and environmental sensing and monitoring applications.