SRD100 diffusometer

SRD100: industrial-grade diffuse solar radiation measurement

Hukseflux introduces the SRD100 diffusometer, an advanced, all-digital, heated sensor engineered for reliable and accurate measurement of diffuse solar radiation. When paired with a pyranometer, the SRD100 provides a complete picture of solar irradiance, including both the direct and diffuse components for high-accuracy PV performance monitoring.

The SRD100 diffusometer is a new instrument, tailored for use in PV monitoring systems, but is also well-suited for other applications such as general meteorological monitoring and building physics. 

The diffusometer complies with Industrial-grade Immunity, Emission, Electrical, Environmental, and Safety requirements for demanding outdoor and industrial conditions, greatly improving measurement reliability. The SRD100’s extended functionality and diagnostics further enhance ease of operation.

How it works: diffuse solar radiation

The SRD100 diffusometer features a sensor array and half-sphere shadow mask above the array with a unique Fibonacci lattice hole pattern. All sensors are centrally located under the mask, ensuring that at least one sensor remains in the shade. This shaded sensor is near-homogeneously exposed only to diffuse sky, giving an accurate estimate of diffuse solar irradiance.

Measuring direct solar radiation

When combined with a standard pyranometer, users can estimate direct solar radiation by subtracting the two measurements and dividing by the solar zenith angle, which is typically obtained using data from a GPS sensor.

Optimised for clear sky and partly cloudy conditions

The SRD100 is calibrated under clear-sky conditions, ensuring the highest accuracy for blue skies. It is specifically optimised for conditions most relevant to PV applications, such as clear and partly cloudy skies. Measurement accuracy may be lower under grey overcast skies.

Spectrally-matched solar irradiance

For PV performance data analysis, the SRD100 offers a key advantage: it qualifies as a spectrally-matched reference device, according to IEC 61724-1. Its sensor array is made of the same silicon as the most common PV modules, enabling a more accurate estimate of usable solar resources. When comparing SRD100 measurements to the output of silicon-based PV modules, users can claim to measure “spectrally-matched solar irradiance”, with a spectral response of silicon.

PV System performance monitoring: IEC 61724-1 Class A compliant

The SRD100 diffusometer fully meets IEC requirements for diffuse radiation measurements in Class A PV system performance monitoring, without the need for additional accessories. The SRD100 includes:
 

• onboard heating for dew and frost mitigation
• sensor output traceable to both solar irradiance and spectrally matched solar irradiance

A modern alternative to shadow rings

The SRD100 offers a hassle-free alternative to conventional solutions for diffuse radiation measurement, such as a pyranometer with a shadow ring. Unlike shadow rings, the SRD100 does not require manual adjustment every 2-3 days, offering a low-maintenance solution.

A simpler solution than pyrheliometers and rotating shadow bands

Direct and diffuse radiation may also be measured using pyrheliometers, shaded pyranometers, and pyranometers with rotating shadow bands. While these systems are ideal for scientific applications, they can only attain their potentially high levels of accuracy under ideal conditions. For example, pyrheliometers must be kept very clean – more so than pyranometers - and daily cleaning is recommended. 
The diffuse and direct measurement with rotating shadow bands relies on post-processing of data. For example, a correction factor dependent on the solar zenith angle, to attain the best accuracy. With post-processing, the data lose their traceability, and thus, their bankability. 
Measurement with the SRD100 diffusometer and a standard pyranometer, is a less complicated, low-maintenance and a 100 % traceable alternative.
 

Immunity to high voltages and currents – surge protection

The SRD100 diffuse solar radiation sensor is tested and certified for Industrial Environments per IEC 61326-1 and IEC 61000-6-2 standards. When designing a measuring system, SRD100 users can achieve several levels of immunity.

For enhanced protection, the optional Surge Protection Device (SPD01) increases immunity to 4 kV, protecting up to three pyranometers and diffusometers with a single unit. Alternatively, a third-party SPD with similar specifications may also be used.

RS-485 isolation

The SRD100’s RS-485 interface is galvanically isolated from both the internal electronics and the instrument body, with isolation barriers rated at 1.5 kV. This ensures reliable operation, greater flexibility in system design, and reduced integration costs for all industrial pyranometers and diffusometers.

Remote diagnostics

In addition to solar irradiance, SRD100 provides several alerts and measurements for remote use, most importantly: 

• alert: heating malfunction
• internal humidity

These remote diagnostics minimise the need for (un)scheduled field inspections.