Solar Tracker Optimizer

STO is a system that tests and optimizes the tracking accuracy of single-axis solar trackers.

It accurately monitors second by second the inclination of PV modules, analytically calculates the deviation from the optimal tilt, and generates the tilt-correction parameters delivering optimized alignment and maximized energy production.


  • Suitable for all types of single-axis solar trackers
  • Battery-powered
  • Optimal tilt curve calculated also in uneven ground conditions
  • Easy clamp-on installation
  • Automatic calculation of the production loss (Kw/h) generated by the error detected with respect to the optimal tilt curve implementable

Maximizing energy production from single-axis solar trackers

The optimal angle is calculated by STO itself through a combined set of algorithms:

(i) the ephemeris algorithm, which calculates the position of the sun on the basis of time and local GPS coordinates

(ii) the shadowing algorithm, which calculates the mutual shadowing generated by adjacent trackers

(iii) the ground tilt algorithm, which calculates the mutual mismatch due to the East-West tilt of ground in any possible ground configuration.

Optimal inclination, grow revenues

Very often the tracking accuracy of mono-axial systems is lower than expected. Minor undetected mismatches between the actual and the optimal tilt curve can easily cause the Performance Ratio to drop below the contracted value, resulting in financial penalties and in lost annual revenues ranging from tens of thousands of Euro for a 5 MW installation, up to a million Euro for a 250 MW plant.
STO has been conceived for delivering accurate insight on the tracking accuracy of such systems, and for optimizing their operating parameters during the phases of field test and of plant operation.


Testing and operation optimization of single-axis solar PV plants during the phases of field test and of operations.

STO has been tested by

Enel Green Power in the Finis Terrae (Chile, 160 MhW), Ituverava (Brazil, 254 MhW), and Villanueva (Mexico, 754 MhW) power plants, delivering an average annual production increase between 2% and 5%.

STO is a sunto proprietary technology. Patent pending.

STO is composed by three different hardware units:

  • The battery-powered inclinometer (STO/a), to be installed on the tracker you want to monitor. It measures the current tilt of the module and transmits measured data to the receiver as soon as it asks for them. In order to maximize battery life, the inclinometer is set in sleep mode when not in use. When set in monitoring mode, the tilt angle is measured every minute. To do so,  the inclinometer remains in sleep mode for 57 seconds and wakes up 3 seconds before the scheduled time in which the receiver is expected to ask for the next dataset. The data communication between the remote device and the receiver is performed via free band radio transmission at 868 MHz, in compliance with the ETSI EN 301-489-1 V1.9.2 (2011-09) standard.
  • The remote receiver (STO/b) that communicates with the inclinometer in order to read the tilt data and send it to the data-logger. The receiver generates the two cool contacts to control the tracker motion.
  • The industrial tablet, complete with cable, battery charger and user and installation manual (pdf format).

The system is delivered in a wheeled waterproof box  containing the above listed units, and complements and spare parts ( No. 24 clamps, No. 3 spare battery chargers with cables, No. 1 universal travel adapter, No. 1 multiplug, No. 2 spare micro-SD cards, No. 6 complementary micro-SD cards adapters, No. 1 screwdriver, and No. 2 mini-USB cables)

The dimensions of the waterproof box are 595 x 475 x H 270 mm and its weight is 16.5 Kg.

STO/a unit specifications

Weight0,5 Kg
Dimensions190 x 80 x 63 mm
International ProtectionIP 65
Power supply0.5 W Max, battery supplied
Battery specifications2200 mAh, 11 V, 200 g, 3 cells (8.1 Wh/each)
Autonomy3 weeks in monitoring mode
Measuring error0.3 degree

STO/b unit specifications

Weight0.5 Kg
Dimensions190 x 80 x 63 mm
International ProtectionIP 65
Power supply0.5 W Max, battery supplied
Battery specifications2200 mAh, 11 V, 200 g, 3 cells (8.1 Wh/each)
  • 2 days in correction mode (device always on)
  • 3 weeks in monitoring mode
Measuring error0.3 degree
Detachable cool switch cable length6 m
Cool contacts resistance> 1 GOhm when open; < 0.5 Ohm when shorted
Cool contacts current strength 0.5 A max

Industrial tablet specifications

Weight1 Kg
International ProtectionIP 65
Power supply100-240 V AC; 5 V, 3 A DC
Autonomy8 hours
Full charging time4 hours
Battery capacity10.5 Ah @3.8 V
Radio power25 mW
Radio range300 m in open air
Max occupation band0.6% (duty cycle radio on/off)
Typical occupation band0.03% (duty cycle radio on/off)
Compliance to standardsETSI EN 301-489-1 V1.9.2 (2011-09)


DescriptionItem CodeQuantity
Solar Tracker Optimizer. Supplied in a wheeled waterproof box containing No.8 STO/a units, No. 2 STO/b units, No. 1 industrial tablet, complements, spare parts, and User GuideSTO1-BRD