Delta-T Devices Ltd.

- Model BF5 - Sunshine Meter for Solar Power System

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The BF5 Sunshine Sensor is a versatile, multi-purpose solar radiation sensor. It uses an array of photodiodes with a unique computer-generated shading pattern to measure incident solar radiation. A microprocessor calculates the global and diffuse components of the radiation and determines the sunshine state. The BF5 Sunshine Sensor is protected by patents EP 1012633 and US 6417500. Two analogue voltage outputs give global and diffuse radiation, from which direct and diffuse radiation are derived. The sunshine state is indicated by a digital output. The three outputs can be connected to appropriate channels on the GP1, GP2 or DL2e data loggers, or other loggers commonly used for environmental monitoring. An internal heater keeps the BF5 Sunshine Sensor clear of dew, ice and snow down to -20 degrees C.

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  • Measures global and diffuse radiation
  • Sunshine duration
  • No moving parts, no shade rings
  • PAR reference sensor for SunScan System 
  • Outputs can be PAR (mmol.m-2.s-1), Energy (W.m-2) or Lux

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The BF5 Sunshine Sensor measures sunshine hours indirectly using a simple equation based on the total PAR radiation (Photosynthetically Active Radiation), and the ratio of total to direct PAR. This sunshine algorithm corresponds closely to the World Met Office threshold of 120 W/m-2 in the solar beam for sunshine duration. The BF5 Sunshine Sensor does not need to be adjusted or repositioned to track the sun – a distinct advantage over devices with shadow rings. There are no complex electro-mechanical assemblies and no burnt paper tracks to interpret.

The BF5 Sunshine Sensor can be used as an integral component of the SunScan Canopy Analysis system. The SunScan Probe is a 1 metre long light sensor array suitable for measuring PAR interception by plant canopies and estimating LAI ( Leaf Area Index). The BF5 Sunshine Sensor improves the accuracy of the SunScan system and enables it to be used even under variable light conditions.

In addition to its role in the SunScan System, the BF5 Sunshine Sensor’s alternative outputs enable it to be used in the study of photosynthesis, illumination and solar energy measurement.

For building energy management systems, the ability to control the response of powered blinds and louvres to sunlight is a tricky challenge. For example, total incident radiation may be high, but if the radiation is arriving as diffuse light there may be no need to adjust the blinds. On the other hand, the total solar radiation level could be low, but if most of the energy is in the direct beam (e.g. low level winter sun), louvre adjustment may be necessary to shield occupants from glare. The BF5 Sunshine Sensor offers system developers a unique tool for obtaining diffuse and direct solar radiation from a single, compact device. In addition it does not need to be adjusted or repositioned to track the sun – an advantage over devices with shadow rings.

The SPN1 Sunshine Pyranometer is a precision version of the BF5 Sunshine Sensor and although the two instruments have some features in common, there are important differences. These are summarised in the document: “SPN1 and BF5 Comparison Data Sheet” which can be found in Product Resources section (accessed by menu button above).

REFERENCES: Wood J, Muneer T, Kubie J (Feb 2003), “Evaluation of a new photodiode sensor for measuring global and diffuse irradiance, and sunshine duration” Journal Solar Energy Engineering.

  • Accuracy: Sunshine hours: ±10% compared to the WMO definition
  • AccuracyCosine correction: ±10% of incoming radiation over 0-90° Zenith angle
  • AccuracyAzimuth angle: ± 5% over 360° rotation
  • Temperature coefficient: ± 0.15 % /°C (typical)
  • Temperature range:
    • -20 to + 50°C with Alkaline batteries
    • -20 to + 70°C with Lithium batteries
  • Stability: Recalibration recommended every 2 years.
  • Response time: < 250 ms
  • Spectral response: 400-700 nm
  • Latitude capability: -90° to + 90°
  • Environmental : Sealing: IP65 ( shower and dust proof)
  • Sunshine status :
    • contact closure: No sun = open circuit
    • Sun = short circuit to ground
  • Internal battery: 2 x 1.5 V AA alkaline batteries
  • Power requirement: 2 mA (awake ), <30 µA (asleep)
  • Heater power: 12 V – 15 VDC, up to 1.5 A
  • Battery lifetime: 1 year (typical)
  • Input voltage range – powered from internal battery: 1.4 to 3.6 VDC
  •  Input voltage range – external power: 5 to 15 VDC
  • Fuse trip point, on sunshine status signal, (when in switch-closure mode): 0.5 A, 30 V (self-resetting)
  • Max applied voltage to sunshine status output, in contact closure mode: 0 to 24 V
  • RS232 connector: 5-pin M12
  • Signal output & power-in connector: 8 pin M12
  • Mounting options:: Camera tripod socket (¼inch Whitworth). Holes for 4 x M4 bolts at corners of box.
  • Size & Weight: 120mm x 122mm x 95mm, 635g