LELABSINES
Technical page

LORENTZ PSk hybrid
solar pumping

The PSk family makes the photovoltaic array and a second energy source work together, on the same pump and continuously. The PSk3 carries its alternating-current input inside the controller, for systems of 8.3 and 16 kVA. Above that, the PSk2 receives the same capability through the smartPSUk2, up to controllers of 100 kWp of solar input and 75 kW of motor power. The smartStart adds automatic control of the generator.

Continuous blending of the two sources PSk3: built-in AC input PSk2 + smartPSUk2 Day and night
The principle

Both sources supply the same bus, solar first

A hybrid PSk system has a single power electronics stage and a single motor. The photovoltaic array and the alternating source both reach the same direct-current bus, the one that supplies the pump controller. The smartPSUk2 data sheets describe the behaviour in one sentence: the system combines the energy continuously, so that only the quantity needed is drawn from the non-solar source.

The practical consequence comes down to three points. Photovoltaic keeps priority and supplies what it can at every moment, depending on irradiation. The second source brings the complement, instantly and to the extent of the shortfall. The flow or the pressure demanded stays held while the external contribution varies, minute by minute, in the opposite direction to the sun.

On a grid-connected site, this amounts to consuming backup kilowatt-hours only during the dips in irradiation and the hours without sun. On a site fitted with a generator, the machine runs at part load most of the time, since it only covers the gap between what the pump needs and what the array produces. It is this behaviour that allows, as the smartSolution hybrid pumping note describes, the choice of a generator markedly smaller than the one a purely thermal drive would impose.

Continuousboth sources work at the same time, the backup source mirrors the irradiation
Nightpumping continues on the alternating source when the programming calls for it
One motorthe same pump and the same controller serve both regimes
PumpScannerthe whole hybrid configuration is set from the app, sensors included
The family

The PSk3 carries its AC input, the PSk2 receives it from the smartPSUk2

Two architectures cover the range. On the PSk3, the alternating-current input is built into the controller: the three-phase cable enters the unit directly, just like the photovoltaic array. On the PSk2, the function is carried by a dedicated cabinet, the smartPSUk2, which receives the solar array and the alternating source and delivers the combined direct current to the controller.

PSk3 controllerPSk3‑7PSk3‑15
Nominal output power8.3 kVA16 kVA
Nominal motor power5.5 kW11 kW
Solar input, voltage range400 to 850 V400 to 850 V
Minimum MPPT voltage575 V575 V
AC input, nominal voltage380 to 480 V ±10%380 to 480 V ±10%
AC input, maximum current17.5 A30 A
Maximum AC fuse rating20 A35 A
Controller protection ratingIP 66IP 66

The inrush current of the alternating input reaches 42 A on both sizes, a value to keep in mind when choosing the switching devices. The frequency range accepted at the input is 45 to 60 Hz according to the technical data table, and the manual adds that the controller monitors the grid voltage before connecting to it, then throughout operation: it connects when the voltage sits within the expected range, and stops on an unstable grid.

In hybrid mode, the array voltage governs access to blending. The PSk3 rectifies the alternating voltage internally; for both sources to work together, the real Vmp of the array must stay above that rectified voltage. The manual gives the correspondence: 380 V AC call for 535 V DC at least, 400 V AC require 565 V DC, 460 V AC raise the threshold to 650 V DC and 480 V AC to 680 V DC. The same chapter sets a short and firm installation rule: in hybrid mode, the photovoltaic array must not be earthed.
PSk2 controllerSolar inputMotorOutput currentMax. AC input per phase
PSk2‑2121 kWp15 kW3 × 33 A38 A
PSk2‑2525 kWp18.5 kW3 × 40 A45 A
PSk2‑4040 kWp30 kW3 × 65 A70 A
PSk2‑100100 kWp75 kW3 × 160 A170 A

Two cabinets cover this range. The smartPSUk2‑40 pairs with the PSk2‑21 to PSk2‑40 controllers: its alternating input accepts 3 × 380 to 415 V ±10% at 50 or 60 Hz, within a limit of 38 kW and 48 kVA, and its direct output is rated for 850 V maximum and 70 A. The smartPSUk2‑100 serves the PSk2 units above the PSk2‑40, up to the PSk2‑100, with the same input voltage range, a maximum power of 95 kW and a direct output of 170 A. Both cabinets accept an array open-circuit voltage of 850 V, are protected to IP 54 in a powder-coated stainless steel enclosure, operate from −10 to 50 °C ambient and carry protection against overheating as well as active cooling.

The smartPSUk2‑100 requires 380 alternating volts at least. Its data sheet flags this as a warning: below that threshold, the available motor power is limited. On a weak grid or one subject to voltage variations, LORENTZ points to two answers, reducing the power limit in the PSk2 controller from the operating parameters of PumpScanner, or installing a transformer, preferably with multiple outputs between 400 and 460 V to suit local conditions.

On the compatibility side, the knowledge base article is clear: the smartSolution, smartPSUk2 and smartStart components work with the current-generation PSk2‑x systems, recognisable by their blue enclosure. These systems replace the grey-enclosure PSxk2 units, but no electronic board is common to the two generations.
The smartStart

The generator starts and stops at the pump's request

The smartStart is the box that gives the system control over the generator. It connects to the controller through a prepared cable, which carries both the supply and the dialogue between the two units. Depending on the programming chosen, the system starts the machine and shuts it down, with no visit by the operator to the site.

The condition of use concerns the generator itself, which must have a two-wire automatic remote start. The smartStart then provides a potential-free switching contact, closed when the start request is triggered. The PSk2 and PSk3 manuals give the same maximum rating for this relay contact: 250 alternating volts or 30 direct volts, 2 A. As for the characteristics accepted for the machine, the PSk2 smartSolution documentation lists 380, 400 or 415 V three-phase at 50 or 60 Hz; the PSk3 manual widens this list to voltages of 440, 460 and 480 V.

A battery sits inside the enclosure, a 12 V lead AGM of 7 Ah at least, of the Genesis NP‑12 type or similar. The controller recharges it during solar or grid operation. It serves precisely for the hours when nothing is producing any more: without it, a system whose pumping must start at two in the morning would have nothing to supply its logic boards to command the start. The box is installed less than a metre from the controller, with a clearance of 250 mm above and below.

A second smartStart output controls neighbouring equipment. The ancillary equipment switching note gives the uses and the triggers: starting a fertiliser injection pump when the LORENTZ pump is running, launching an irrigation pivot when the available power is enough for the target flow, or starting a second pumping system when the borehole probe trips or when the first system receives its run command.
The generator

A sizing that starts from the power at the operating point

The application note devoted to the design of PSk2 and smartPSUk2 hybrid systems sets a simple rule and demonstrates it on two cases. The power to be used for the generator is the one drawn by the motor at the target operating point, multiplied by a safety factor of 1.5, and it is understood as continuous power, the power the machine holds without interruption.

First example from the note: an installation that must produce 25 m³/h against 50 m of total dynamic head. The power drawn by the motor at that point is 6 kW, which leads to a 9 kW generator in continuous power. This machine remains smaller than the pump motor, and the document draws the consequence without hedging: it does not hold the pump at full power without the help of the photovoltaic array. Second example, the same installation taken to full power draws 12.5 kW at the motor, that is 18.75 kW of generator, and there full autonomy is secured.

The choice between these two logics belongs to the project. The smartSolution hybrid pumping note documents the case of the deliberately compact generator: a speed limit, set in PumpScanner under the heading PSU speed limit, caps the pump speed in hybrid mode and allows a generator of continuous power lower than that of the motor to run the whole set. The PSk2 manual mentions the same setting for a low-yield borehole or for a smaller generator. Finally, the behaviour of thermal machines varies from one model to another: if unusual oscillations or vibrations appear when the hybrid system starts, the note advises reducing the pump speed until steady operation is restored.

× 1.5factor applied to the motor power to obtain the continuous power of the generator
6 → 9 kWthe example from the note for 25 m³/h against 50 m of total dynamic head
Part loadthe normal regime of the generator, since it only covers the gap left by the sun
Start delaythe delay avoids stalling the engine when the hybrid system starts

This delay, also set in PumpScanner, comes back in every application note as soon as a generator is involved. It gives the machine time to reach its speed before the pump asks it for its power.

The control modes

Four documented ways of running a hybrid system

The LORENTZ application notes describe four control modes, each with its sensors, its PumpScanner settings and its use case. They are chosen at commissioning and can then be changed remotely, by season or according to the needs of the crop.

Constant pressure

A LORENTZ pressure sensor connects to an analogue input of the controller and is configured in PumpScanner; on the CS‑F and CS‑G surface pumps, the documentation indicates the mounting positions provided on the pump body and on the flanges.

The system adjusts the speed to hold the setpoint, and the alternating contribution fills what the irradiation does not supply. The PSk2 manual explicitly lists constant-pressure demand among the reasons for using the smartPSUk2. The Spanish case published by LORENTZ thus uses a setpoint of 2.5 bar for an irrigation network.

PSk2 manual, chapters 10.5 and 15.2.1; Hybrid irrigation in Spain case study.

Constant flow

A water meter with a pulse output measures the flow and the system adjusts the pump speed to hold the programmed value. Alternating power is only called on when it becomes necessary to hold that setpoint.

The note takes as its example a sugar mill that requires 130 m³/h continuously over sixteen hours, from 04:30 to 20:30. The automatic start happens at the chosen time, before or after daybreak, and the installation in a diesel-hybrid system also receives the start delay.

Application note automatic flow control.

Programmed daily volume

LORENTZ documents this control mode under the name “daily flow”, set in PumpScanner under the heading “daily amount”. It describes a programming of the system, not a guarantee of result carried by LE LAB. The water meter serves as a totaliser: the programming sets the quantity to be pumped and the system stops as soon as it is reached. If the solar day has not been enough, the machine switches to the alternating source and continues pumping at night until the required volume is reached.

The reset of the meter can be programmed at the desired hour, which allows the backup source to be aligned with a chosen window: the note illustrates a range from 22:30 to 04:00 and a meter reset at 04:00. The water need of a crop varies over the year, and the setting is revisited season by season.

Application note daily flow.

Solar by default

This control mode addresses sites that already have a generator and want to keep it as a backup, without changing the operator's habits. The equipment comes down to the PSk2 controller and the smartPSUk2; PSU mode is enabled in PumpScanner, with a speed limit if needed to allow for a generator of continuous power lower than that of the motor.

After that, use comes down to one action: the operator starts the generator by hand and the system goes into hybrid mode; the operator stops it, and the return to solar alone happens on its own. The note keeps this control mode for the simplicity and the operating safety it brings to a site that is already equipped.

Application note solar by default operation.
The installation point

A non-sinusoidal current, and components sized on the maximum

This is the technical point the manuals treat with the most insistence, and it deserves to be set out from the study onwards. The alternating-current input works as a rectifier: it draws from the source a non-sinusoidal current, loaded with harmonics, whose maximum value slightly exceeds that of a purely sinusoidal current.

The current actually drawn depends on the impedance and on the voltage of the source. The published values correspond to the most demanding case, that of an oversized generator or a strong grid, when the system runs at full power. The PSk3 manual states up to 30 A rms per phase for an 11 kW motor taken to full power, its technical data being established on a three-phase 400 V grid of low impedance. For the PSk2, the table of cable cross-sections and alternating input currents rises from 38 A per phase on the PSk2‑21 to 170 A on the PSk2‑100, passing through 70 A on the PSk2‑40. The instruction is identical in both manuals: all the components of the installation are sized on this maximum current value.

The public grid sometimes imposes a further constraint. Where local requirements govern harmonic distortion, the documentation provides for filters to be installed at the alternating input. The PSk3 manual adds a useful effect: these filters also reduce the rms current drawn from the source. The other items fall to the installer, namely the cable, the alternating disconnector or circuit breaker and the fuses, with neither AC fuse nor AC circuit breaker built into the controller. On the PSk3, the recommended fuses are of type gR or gS, rated at 20 A for the PSk3‑7 and 35 A for the PSk3‑15. As for residual current protection, the documentation is explicit: this product can generate a current with a direct component, and only a type B device is accepted upstream.
In the application

PSk systems in LE LAB

PSk systems appear in the application catalogue, with their curves and their limits of use: the PSk3‑7 and PSk3‑15 for compact powers, then the PSk2‑21, PSk2‑25, PSk2‑40 and PSk2‑100 above them. The calculation calls on them where constant-pressure control and the use of a backup source make sense, that is on irrigation networks that require a setpoint held whatever the light of the day.

LE LAB results screen in constant pressure: histogram of the volume pumped month by month, with the share held by the sun and the share supplied by the backup source, followed by the table of monthly values.
The split between the sun and the backup source, month by month, as the application renders it at the results step. The annual solar share and the months where the backup source works appear directly, with the table of values under the chart.

The report repeats this split for the project studied: the volume pumped month by month, the share held by the photovoltaic array, the share supplied by the second source, and the power the generator must hold at continuous load. These three elements make it possible to assess the continuity of operation foreseen by the study and the regime of the thermal machine.

Size my project Constant-pressure pumping
Sources

Where this information comes from

  • PSk3 pumping systems manual, LORENTZ: technical data of the controller, solar and alternating inputs, wiring of hybrid operation, voltage correspondence, input current and harmonics, fuses, smartStart and generator compatibility.
  • PSk2 pumping systems manual, 2023 edition, LORENTZ: technical data of the PSk2‑21 to PSk2‑100 controllers, smartSolution chapter, installation and operation of the smartPSUk2, table of cable cross-sections and alternating input currents, smartStart, volt-free contact of 250 VAC or 30 VDC at 2 A, and battery.
  • smartPSUk2‑40 data sheet, LORENTZ: compatibility, alternating input, direct output, protection rating, temperature range, dimensions and connection to the controller.
  • smartPSUk2‑100 data sheet, LORENTZ: compatibility, alternating input, direct output, warning on the minimum voltage and the available motor power.
  • Application note PSk2, smartPSUk2 hybrid system layout and design, LORENTZ: safety factor, generator sizing examples, generator specifications.
  • Application notes smartSolution hybrid pumping, automatic flow control, daily flow, solar by default operation and ancillary equipment switching, LORENTZ: documented control modes, required equipment, PumpScanner settings and operation.
  • Knowledge base article Compatibility of PSk2 versions, smartPSU, smartSolution components, LORENTZ: controller generations and compatibility of the smartSolution components.
  • Case study Hybrid irrigation in Spain, LORENTZ: configuration of a PSk2‑40 system with smartPSUk2, smartStart, pressure sensor and water meter.
  • To go further: constant-pressure solar pumping, solar and the generator on the same installation and the case study of a kiwi orchard in South-West France.