The performance ratio is only as good as
the irradiance you measured
Site-level solar radiation, wind for the stow decision, temperature, rainfall and tracker position feedback, for solar and hybrid generation sites.
A regional forecast cannot tell you what happened on your site
Solar performance is reported as a ratio against available irradiance. That makes the reference measurement commercial rather than technical: it is the denominator every performance number, every warranty conversation and every underperformance claim is divided by.
A national or regional forecast cannot carry it. It cannot tell you that the cloud sat over the eastern half of the site for two hours, that soiling took four per cent off the front rows after a dry spell, or that the gust which reached row fourteen was stronger than the one the forecast issued for the county.
The same gap sits behind the stow decision. Trackers move to a safe position on a wind threshold, and that threshold is only as good as the measurement it is compared against. Stow too early and generation is thrown away on a day the site could have run. Stow too late, or not at all because a seized cup anemometer is reporting calm, and the damage is structural.
Two measurements on a solar site do commercial work
The first is irradiance. It sets the denominator of the performance ratio, so an error in it moves the reported performance of the whole asset without anything changing on the ground. Measured at the site, over the same interval as the generation data, it turns an argument about yield into an arithmetic question.
The second is wind. It is not a reporting measurement at all: it is a control input that moves several hundred tonnes of steel and glass into a safe position, and it has to be trustworthy at the moment the weather is at its worst.
Everything else on the site supports those two. Temperature explains module derating. Rainfall explains soiling recovery. Position feedback confirms that a tracker actually reached the angle it was commanded to. Humidity and pressure close the picture for forecasting and for the equipment in the compound.
Where a solar site gets its picture
A solar site measures for two different reasons at once: to report what it produced against the light it received, and to protect several hundred tonnes of moving steel when the weather turns.
Irradiance reference
This is the denominator of the performance ratio. Measured badly, it moves the reported performance of the entire asset without a single module changing.
- MaxiMet GMX301 solar radiation only, 0 to 1600 W/m², 0.6 kg, for a dedicated reference node
- MaxiMet GMX501 solar radiation alongside wind, temperature, humidity and pressure in one unit
- MaxiMet GMX551 the same again with rainfall, where soiling recovery has to be explained
Site weather station
One unit, one cable, one output string. The fewer separate instruments on the mast, the fewer things to align, power, calibrate and climb to.
- MaxiMet GMX501 wind, temperature, humidity, pressure and solar radiation, 0.8 kg, IP66
- MaxiMet GMX551 adds rainfall by optical or tipping bucket input
- MetConnect where sensors have to sit at separate heights for WMO-compliant siting
Tracker row wind and the stow decision
The controller stows on this number and has no independent way to know it is wrong. A seized cup and vane does not report a fault, it reports calm.
- WindSonic 60 0 to 60 m/s, 0.5 kg, WMO-compliant gust measurement
- WindSonic 75 0 to 75 m/s where the site sees higher extremes
- WindSonic M heated hard-anodised aluminium, operating to -40 degrees C
Exposed rows and site edges
A single sensor in the middle of a sloping site does not represent the corner that catches the wind first. How many sensors a site needs depends on its size and its terrain.
- WindObserver 75 0 to 75 m/s in a heated 316 stainless open head, IP66, for the most exposed position
- WindObserver 90 0 to 90 m/s where the extremes justify it
- WindUltra 270 g, IP69k, under 100 mW without heating in calm conditions, for self-powered rows
Tracker angle feedback
A stow command is only a command. Position feedback is what confirms the row reached the angle, and a contacting sensor on a mechanism that cycles daily is a wear item.
- Blade360 full 360 degree rotary, configurable range, IP67, sealed for temporary immersion (1 m for 30 min)
- Blade60 60 mm linear or 90 degree angular, analogue and digital outputs
- Blade Dual Output single and dual channel output where the feedback has to be redundant
Rainfall and soiling
Soiling losses are only arguable if you know when it last rained and how hard. A tipping bucket with a moving part is one more thing on the site that needs a visit.
- TruMet PW100 infrared optical rain gauge, no moving parts, pairs with GMX550 and GMX551
- MaxiMet GMX551 rainfall by optical or tipping bucket alongside solar radiation
- MaxiMet GMX603 optical rainfall 0 to 200 mm/hr at 5 per cent or better, integrated
The wind half of a hybrid site
On a hybrid connection the wind sensor stops being only a safety input and starts explaining generation, which raises what the measurement has to support.
- WindObserver 75 heated 316 stainless, 0 to 75 m/s, for a permanent site mast
- WindMaster Pro 3-axis, where turbulence intensity and inflow angle matter as well as speed
- WindUltra 0 to 75 m/s, IP69k, heated as standard, for a remote or unattended mast
Calibration and verification
When a yield number is questioned, the instrument behind it is questioned with it. Traceability is what ends that conversation rather than extending it.
- Labcal air velocity UKAS-accredited calibration of anemometers, Pitot tubes and thermal probes
- Labcal temperature and humidity thermometers, probes, transmitters and data loggers
- Labcal pressure gauges, transducers, manometers and transmitters
The denominator of every performance number
Performance ratio compares what the plant generated with what the available light says it should have generated. The generation side is metered precisely. The irradiance side is whatever instrument the site was given, so that is where the uncertainty lives.
MaxiMet measures solar radiation from 0 to 1600 W/m². The GMX301 does that and nothing else, which suits a dedicated reference node. The GMX501 carries solar radiation alongside wind, temperature, humidity and pressure in a single 0.8 kg unit on one cable, and the GMX551 adds rainfall on top.
Where the reporting standard a project is being held to sets a particular sensor class or mounting plane, tell us which one and we will say plainly whether it is met. We would rather answer that question before the mast goes up than after the first performance review.
0 to 1600 W/m² solar radiation measurement
Explore weather stationsThe gust that stows the trackers has to be a number you trust
A stow threshold is usually written against a gust, not an instantaneous reading, which means the averaging matters as much as the sensor. WindSonic produces a WMO-compliant gust from a rolling average, so the gust figure is defined the same way every time it is compared with the threshold the structural engineer wrote.
Every output carries an instrumentation status code. That is the difference between a controller that knows its sensor has failed and a controller that quietly believes a dead sensor reporting calm, which is the failure mode that costs trackers.
There are no bearings in the measurement, so there is nothing to ice, foul or seize, and nothing to replace on an annual visit. Accuracy is 2 per cent RMSE at 12 m/s with 2 degrees on direction, from a starting threshold of 0.01 m/s.
A status code on every output, so a failed sensor cannot read calm
Explore wind sensorsA hybrid site is a solar site with a second source on the same connection
Hybrid usually means solar generating alongside wind, increasingly with battery storage, sharing one grid connection and one export limit. The commercial logic is that the two resources rarely peak together, so the connection is used for more hours of the year.
The measurement follows the same logic. Irradiance, wind, temperature, humidity, pressure and rainfall are wanted on both halves of the site, and one compact station can serve both rather than two separate installations reporting into two separate systems.
What changes is the weight the wind measurement has to carry. On a solar-only site it is a protection input. On a hybrid site it also explains generation, which pushes it towards a permanent mast, a heated stainless head, and in some cases 3-axis measurement where turbulence and inflow angle matter as well as speed and direction.
That is why solar and hybrid sit on one page here rather than two. The site is the same site. The question is how far up the measurement has to move when the second source arrives.
More than the irradiance sensor
Environmental measurement for the performance number, wind measurement for the stow decision, and position feedback for the trackers themselves.
Environmental measurement
MaxiMet
Compact all-in-one weather stations
The site station. One unit, one cable, one output string, and no moving parts in the measurement.
TruMet PW100
Infrared optical rain gauge
Rainfall without a tipping bucket, so soiling recovery can be explained without adding a moving part to the site.
WindSonic
Lightweight 2-axis ultrasonic anemometer
The tracker protection workhorse, and the sensor most often multiplied across a large or sloping site.
Exposed positions and tracker feedback
WindObserver
Heated 316 stainless open-head 2-axis anemometer
For the corner of the site that catches the weather first, and for the permanent mast on a hybrid connection.
WindUltra
Compact, IP68 and IP69K, heated as standard
For self-powered tracker rows, floating arrays and any position where the power budget is measured in milliwatts.
Blade position sensors
Non-contact linear and rotary position sensing
Angle feedback on a mechanism that cycles every day of a twenty-five year life, with nothing in contact to wear.
Where solar site measurement does the work
Six positions where the measurement changes a decision rather than filling a log file.
Utility-scale tracker arrays
Single-axis tracker rows stow on a wind threshold. The sensor count follows the size and the terrain, because a sloping site does not see one wind.
Performance ratio reporting
Site-level irradiance measured over the same interval as the generation data, so yield questions become arithmetic rather than argument.
Soiling and cleaning schedules
Rainfall and irradiance together show when the array last recovered and whether a clean is due or has already been paid for by the weather.
Hybrid solar and wind connections
One station serving both halves of a shared grid connection, with the wind measurement raised to explain generation as well as protect the structure.
Construction and commissioning
A temporary mast gives the wind number that stops a lift or a panel install, and the baseline the site is handed over against.
Remote and self-powered installations
Low-power sensing where each row carries its own panel and controller, and a sensor drawing milliwatts is the difference between fitting the budget and not.
UKAS-accredited calibration for six measurement parameters
Labcal is an independent UKAS-accredited calibration laboratory, Lab 0625, operating to ISO/IEC 17025:2017. It provides calibration across gas and air flow, air velocity, liquid flow, pressure, temperature and humidity, all under one roof.
For a solar site that covers the anemometers behind the stow decision, the temperature and humidity probes behind the derating figures, and the pressure instruments in the compound. Labcal supports equipment from Gill and other manufacturers, so a site can consolidate an instrument schedule that was never bought from one supplier.
01 · Gas and air flow
Gas meters · Mass flow controllers · Dispensing systems
02 · Air velocity
Anemometers · Pitot tubes · Thermal probes
03 · Liquid flow
Flow meters and sensors · Process control equipment
04 · Pressure
Gauges · Transducers · Manometers · Transmitters
05 · Temperature
Thermometers · Probes · Thermocouples · Data loggers
06 · Humidity
Hygrometers · Probes · Transmitters
The measurement has to arrive where the decision is made
A stow threshold is enforced by a tracker controller. A performance ratio is calculated in a monitoring platform. Neither reads a datasheet, so the output format decides whether the measurement is usable on the day it is installed.
Gill supports environmental monitoring, industrial sensing, embedded electronics and systems integration, so the measurement can be brought into tracker controllers, SCADA and asset management platforms from specification through commissioning.
Outputs and options
- Modbus RTU : Two-wire RS485, into SCADA and tracker controllers
- SDI-12 : Into loggers on a shared bus across a large site
- RS422 / RS485 : Serial into an existing control system
- Analogue : 0 to 5 V, 0 to 20 mA or 4 to 20 mA where the input is fixed
Why solar programmes specify Gill
Nothing in the measurement wears
Ultrasonic measurement removes the bearings that ice, foul and produce a false calm on a cup and vane sensor. That is the failure that costs trackers.
A gust you can match to the threshold
WMO-compliant gust from a rolling average, so the gust figure is defined the same way every time it is checked against the number the structural engineer wrote.
A status code on every output
The controller can tell a healthy sensor from a failed one, instead of acting on a plausible reading from a dead instrument.
Lower cost of ownership
Mechanical sensors are replaced and revisited. Ultrasonic sensors have no moving parts, which is where the total cost of ownership case on a large site is won.
One unit for the site picture
Solar radiation, wind, temperature, humidity, pressure and rainfall from one 0.8 kg station on one cable, rather than six instruments to align and power.
Evidence when the yield is questioned
Independent UKAS-accredited calibration across six parameters, for equipment from any manufacturer, not only ours.
Questions about solar and hybrid site measurement
Irradiance for the performance ratio, wind speed and direction for the tracker stow decision, and air temperature for module derating. Rainfall, humidity and pressure complete the picture for soiling, forecasting and the equipment in the compound.
A compact station such as the MaxiMet GMX551 carries all of those in a single unit on one cable. A GMX301 covers solar radiation alone where a dedicated reference node is wanted.
Trackers move to a defined stow position when wind exceeds a set threshold, because a row of panels held at an extreme angle in a storm is far more exposed than a fixed array. The measurement is what triggers that move, so it is a protection device rather than a reporting instrument.
A large or sloping site usually needs more than one sensor, because the corner that catches the wind first is not the middle of the field.
It depends on the site area and the terrain. A large flat square site needs fewer sensors than a hillside or sloping site of the same size, because the flat site sees closer to one wind across the whole array.
Tell us the layout, the export capacity and the stow threshold and our team can work through the sensor count with you rather than quoting a rule of thumb.
A cup and vane sensor has bearings. They wear, they ice, and they seize. When they seize the sensor does not report a fault, it reports calm, and a controller acting on that will not stow.
An ultrasonic sensor has no moving parts in the measurement, so there is nothing to replace on an annual visit. The purchase price is higher and the total cost of ownership across a site with many sensors is lower.
A stow threshold is normally written against a gust rather than an instantaneous reading, so the averaging behind the gust figure is part of the threshold. WindSonic produces a WMO-compliant gust calculated from a rolling average.
Check that gust definition against the period the structural specification assumed instead of the two being compared on different bases.
WindSonic 60 and 75 publish their accuracy across the full measuring range, with a resolution of 0.01 m/s and a starting threshold of 0.01 m/s. Direction covers 0 to 360 degrees with no dead band.
For a permanent mast on an exposed or hybrid site, WindObserver 75 measures 0 to 75 m/s in a heated 316 stainless open head.
MaxiMet measures solar radiation from 0 to 1600 W/m². The GMX301 measures solar radiation only. The GMX501 adds wind, temperature, humidity and pressure, and the GMX551 adds rainfall on top of that.
Where a project is held to a particular reporting standard with a stated sensor class or mounting plane, share the clause with us and we will confirm plainly whether it is met.
Not for the measurement. A hybrid site generates from more than one source on a single grid connection, usually solar with wind and increasingly with storage, and it wants the same parameters from the same station.
What changes is the weight the wind measurement carries. On a solar-only site it protects the structure. On a hybrid site it also explains generation, which pushes it towards a permanent heated mast and, where turbulence matters, 3-axis measurement.
In most cases yes. A GMX501 or GMX551 gives irradiance, wind, temperature, humidity, pressure and rainfall from one unit, which covers the environmental picture for both halves.
A separate, higher-specification wind measurement is usually added where the wind generation is material, because the accuracy and mounting requirements for explaining yield are not the same as those for triggering a stow.
Through the protocol the system already accepts. WindSonic offers RS232, RS422 and RS485 with ASCII and NMEA, an SDI-12 option and a Modbus RTU option on two-wire RS485, plus analogue at 0 to 5 V, 0 to 20 mA or 4 to 20 mA.
WindUltra offers dual RS485 or RS422, SDI-12, USB and a configurable Modbus RTU string, which suits shared buses across a large site.
Yes. The Blade range is non-contact inductive position sensing in linear and rotary formats, with a full 360 degree rotary option, a dual-channel variant where feedback has to be redundant, and IP67 construction, sealed for temporary immersion (1 m for 30 min).
The sensor and the target are separate parts, so there is nothing in contact to wear on a mechanism that cycles every day of the asset life. The sensors also report their own health, including sensor fault and whether the target is in range.
Instruments behind a commercial number are usually on a calibration schedule set by the asset owner or the reporting standard. Labcal is an independent UKAS-accredited laboratory, Lab 0625, operating to ISO/IEC 17025:2017 across six parameters including air velocity, temperature and humidity.
It calibrates equipment from any manufacturer, so a site can put its whole instrument schedule through one laboratory rather than splitting it by supplier.
Speak to our team
Tell us what you need to measure, where and under what conditions. We’ll help you work out the appropriate approach.
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