Controller for boiler supplying from solar panels - building kit.

Want to save money on water heating or heating? Read on. Are you a cottage owner and need to heat water in a boiler in summer and temper the building with a conventional direct-fired heater in winter? And not pay for energy? The controller is for you too. But beware, the connected device must be purely resistive without additional electronics (display, electronic thermostat, fan etc.) and must be switched off by a mechanical thermostat.

A kit (board + components, see instructions in the Downloads section) for those interested in electronics. Plastic box or panels with holes for good cooling (see Related tab) can be ordered.

Description of operation, software version 9

What's new in version 9? The waiting time for the appliance to connect to the DC output has been extended to 2 minutes, it is possible to set the output voltage up to 320 V (for those who want to take advantage of the maximum supply voltage and have a custom heating coil wound.), the maintenance of optimum power between panel tests has been improved and it is possible to have the current controller settings indicated by LEDs.

The MPPS controller is a 1st generation controller and optimizes the matching of the resistance of the boiler heating coil and PV panels to maximize the energy recovered from the panels. It is connected between the solar panel and the boiler heating coil. It is designed to be built into the switchboard with other devices such as disconnectors, surge protectors, contactors, etc.

The output voltage at the output is AC, so the controller can also be used with a conventional boiler with an AC heating coil.

A boiler with an input power of up to 3 kW (up to 4 kW with active cooling) can be connected to the output. The input voltage can be from 60 to 430 V and the input current up to 16 A. The controller uses a new method of active Maximum Power Point Searching (MPPS) when powering the boiler. This method eliminates power losses compared to the MPPT method when the PV panels do not have the same characteristics, power rating, temperature changes or are not evenly illuminated. The 6 LEDs on the front panel are used to indicate power and current output. The controller has a second DC output to which power is automatically diverted (without any other intervention) from the panels in the event that the boiler is disconnected at the AC output. The controller can operate in four modes of operation, which are described in the following text. Using a button on the controller board, eight parameters can be stored in the processor memory: nominal output voltage, panel test period, boiler output connection test period, mode of operation, nominal load input, heated water volume, minimum heating temperature, and minimum panel voltage.

Modes of operation of the controller:

1) priority AC output, secondary DC output: as long as a load is connected to the AC output (tested periodically), the DC output will never turn on. If the load on the AC output is disconnected, the DC output turns on (i.e. there is panel voltage on the DC output, but the controller does not regulate this voltage in any way). After a set period of time, the controller turns off the DC output and tries to test if the primary load on the AC output has reconnected. If so, it leaves the AC output on, if not, it turns the DC output back on.

2) Priority DC output, secondary AC output: as long as a load is connected to the DC output (tested periodically), the AC output will never turn on. If the load on the DC output is disconnected, the AC output turns on (i.e., the AC output is voltage regulated (MPPT). After a set period of time, the controller turns the AC output off and tries to test if the primary load on the DC output has reconnected. If so, it leaves the DC output on, if not it turns the AC output back on.
3) The AC output always has priority, the DC output is used to switch the two loads using an external contactor: as long as load 1 is connected on the AC output (tested periodically), the DC output is off. If load 1 is disconnected on the AC output, the DC output is switched on (i.e. the panel voltage appears on the DC output). This voltage supplies an external 24VDC switching power supply* to which the coil of the external contactor* is connected. The contactor switches the AC output to load 2 and the controller five regulates the output voltage (MPPT). After a set time, the controller turns off the DC output, the contactor drops out and load 1 is connected to the AC output. The controller then tries to test if load 1 is connected. If it does, it starts regulating the voltage on load 1, if not it turns on the DC output, this turns on the contactor, load 2 is connected and the controller starts regulating the voltage on load 2. Should neither load be connected, the controller uses the DC output to switch the contactor back and forth until it finds a connected load. In this mode, the DC output is only used to switch loads on the AC output.

4) A boiler on the AC output, which the controller connects with an external PN4316 switch (using the DC output) to the 230 V mains voltage when there is not enough solar energy: the aim is to have the water heated to the minimum selected temperature in the evening, even on days when solar energy is scarce. In each test, the controller assesses whether the energy supplied by the panels is sufficient to heat the water in the boiler to the selected temperature in the evening. The user sets the nominal power and volume of the boiler and the minimum required water temperature. From the values entered, the controller calculates the amount of energy required. If, during the panel test, the controller considers that the solar energy is insufficient, it switches on the DC output. An external switch connected to this output disconnects the boiler from the AC output of the controller and connects it to the 230 V mains voltage.

* The power supply and switches are not included in the price of the controller, but we can supply them.
Note: The controller uses pulse-width modulation, which may cause a slight humming noise from the heating coil in the boiler, which could disturb the quietness of the room in which the boiler is located.

Basic technical data:

Supply voltage: 60 to 430 V

Input current: maximum 16 A

Nominal boiler voltage: adjustable from 10 to 320 V

Minimum panel voltage: adjustable from 60 to 250 V

Panel test period: adjustable from 10 s to 34 minutes

Thermostat test period: adjustable from 10 s to 34 minutes

Control frequency: 122 Hz

Outputs: output 1 (AC) for connection of a conventional AC boiler, output 2 (DC) for connecting another appliance

Power indicator: five white LEDs, range 0 to 100% with 5% resolution

Dimensions: 180 x 120 x 45 mm

Optimal power supply for the controller:

Panel voltage must be neither too low nor too high. If the voltage is too low, the power of the panels cannot be pushed into the load, too high a voltage will force the controller to operate in a disadvantageous position or could even damage it. The optimum supply voltage should be between 100 and 115% of the nominal load voltage (this is usually 230 V). The supply voltage is calculated as the product of the number of panels in series and their voltage at the operating point (the lower voltage value in the panel documentation). The optimum peak power of the panels (again see panel documentation) should be between 100 and 125 % of the load power. Compliance with these conditions will give the most favourable cost/energy ratio. If you are using an appliance for higher voltages than 230 V, the supply voltage can be higher (it is still recommended that the supply voltage should be 100 to 115 % of the nominal load voltage). But even in this case, the maximum number of panels in series can only be such that their no-load voltage never exceeds 430 V. The control is easy. In the panel documentation you can find the no-load voltage (this is the highest value given), multiply this by 1.15 to calculate the voltage of the panels at an outdoor temperature of -25 deg. C. Multiply the resulting voltage by the number of panels in the series. The calculated voltage must always be less than 430 V! If it is not, the number of panels must be reduced!