Solar Water Heating Pump Controller for Distant Pool

Pictured below is our standard 2016 Solar Water Heating Pump Controller with Datalogger. We recently made a modified version of this controller for use in a particular situation where the standard unit would not be very efficient.

2016 SOLAR PUMP CONTROLLER WITH LCD DISPLAY AND DATALOGGER. Solar water heating pump controller with backlit display to show temperatures and system status information and a dataloggerIn this case, the controller was to be used to heat a swimming pool. The problem was that this pool was located 30 metres away from a garage where the controller would be fitted, with 50mm water pipes already installed running underground to and from the pool from the garage (on the roof of which were installed solar water heating panels). There was therefore no easy way to retro fit a temperature sensor at the pool – that would necessitate digging a new 30 metre long trench, fitting sensor cable into an armoured tube, and burying it.

It was however possible to fit a temperature sensor to the return water pipe where it emerged in the garage, but the contents of that pipe would cool down much faster than the large volume of water in the pool, and this would result in the pump being turned on frequently unnecessarily, often cooling the pool instead of heating it.

To get around this problem, the controller was modified to provide additional features. The key feature was that the pump would not be turned on until the temperature of the solar panel exceeded a user programmable value. When this threshold is reached, the pump is run for a user programmable number of seconds (TD) which circulates the water through the system sufficiently to get an accurate measurement of the temperature of the pool water. When TD seconds have elapsed, if the temperature differential between the solar panel and pool exceeds the user programmed differential (diffOFF), the pump will continue to run until the differential falls below diffOFF – standard operation for the 2016 controller.

If however after the test run of the pump, the differential is not high enough, the pump will be turned off, and the temperature of the pool sensor will be saved. For up to the next four hours this saved value of the pool temperature will be used rather than the sensor temperature (which will rapidly fall when the pump is turned off). The pool temperature over the course of 4 hours will not fall by more than a degree or two, so using this saved value is acceptable for efficiency. During the 4 hours, if the temperature differential exceeds the second user programmed differential (diffON), the pump will be run as per standard operation and after TD seconds the controller will start to use the current pool temperature sensor measurement instead of the previously saved value as the pipe in the garage will now be at pool temperature. The pump will continue to run until the differential falls below diffOFF.

If during the 4 hours, diffON is not achieved, the controller will wait until the solar panel temperature exceeds the user programmed temperature before running the pump for TD seconds again and repeating the above processes.

Overall these modifications (together with a few additional features not described above) will result in a far more efficient system than our standard controller would have given and less wear on the pump.

If you have any special requirements which are not met by our standard controllers, please email with details.

Five Channel Digital Thermometer

Pictured below is a five channel thermometer which is destined to be used as a part of a ground source heat pump heated underfloor heating system in Cyprus.

five channel thermometer for ground source heatpump

display for five channel digital thermometer

This system has an 11kw ground source heat pump with a 160 litre hot water cylinder (HWC). Soon 4 square metres of solar thermal panels will be added to heat a 300 litre thermal store (TS). The whole system has been put together by an experienced plumber using tapstats to control the flow of heated water depending on its temperature – no electronic controllers at all. He did however have the need for a way to easily monitor the temperature of the water in the two large vessels.

The two vessels have been made with pockets in them for temperature sensors – two for the hot water cylinder (one at the top and one at the bottom), and three for the thermal store (for sensors at the top, middle, and bottom).

We used our usual waterproof DS18B20 temperature sensors for this thermometer as they have proven to be accurate and very reliable.

If you need any kind of digital thermometer, thermostat, or data monitoring / datalogging device, email with details of your requirements.

Solar Swimming Pool Heating Controller with Datalogger and Display

Our 2016 Solar Water Heating Pump Controller is one of our most popular products. Pictured below is a derivative recently requested by one of our pump controller for swimming pool heating with datalogger and lcd displayThis controller will be used to control the operation of a pump circulating water through a solar thermal panel. Our standard controllers have at least two sensors – one for the pool/tank and one for the solar panel – but for this particular project only one sensor could be used: at the solar panel.

Therefore, instead of using the temperature differential between the solar panel and the pool to decide when the pump should be turned on or off, the user sets a high temperature threshold above which the pump will turn on, and a low temperature threshold below which it will subsequently turn off.

Sensible starter values would be 70 degrees C at the panel to turn on the pump, and around below 35-40 degrees at the panel to turn off the pump. With experimentation and analysis (this device has a built in datalogger) it will be possible to refine these thresholds to maximise efficiency. The pump should not be turning on and off too frequently and running for very short times, but the panel should also not be left at very high temperatures for a long time or it will radiate heat away before it can be transferred to the water.

If this device was to be used in a small pool or hot tub, and if the arriving hot water from the panel is pumped straight in without pre-mixing, a lower pump turn on temperature would be essential so that no-one gets burned on the incoming hot water.

If you need any kind of pump controller, email with details of your specific requirements.

Solar Water Heating Pump Controller with SD Card Datalogger

Pictured below is a controller we recently made for a solar water heating system including a full datalogger.

solar water heating pump controller with sd card datalogger

This controller is based closely around our 2016 Solar Water Heating Pump Controller which already has basic datalogging functionality – minimum, maximum, and average temperature sensor readings displayed on the LCD.

To this we have added a micro SD card reader and a high accuracy DS3231 Real Time Clock (RTC). Every 15 seconds, the temperature of each of the sensors, the status of the controller, and the date and time are appended to a logging text file on the micro SD card.

arduino data log file from sd cardThe collected data can then be copied over from the SD card to a computer for detailed analysis, graph plotting, and so on.

This controller is based around an Arduino Pro Mini coupled with an LCD module, DS3231 RTC module, micro SD card module, and DS18B20 temperature sensors – all of which are readily available and economically priced. The only difficulties with this project came from the limitations of having only 32KB of flash memory (program space) on the Arduino Pro Mini – not a lot when including so many code libraries for the various modules and sensors as well as 750 lines of of project specific code for this complex datalogging controller.

running out of sram arduino

If you need any kind of datalogger, please email with details of your exact requirements.

LED on Import Electricity Meter Used to Turn on Immersion with Exporting

In our article Flashing LED on Electricity Meter we looked at how the status of the LED on an electricity meter in a grid tied solar PV system can be used to decide when to turn on a water heating immersion heater to use surplus solar generated electricity rather than exporting it.

When there is a dedicated export meter with an LED which flashes at a rate proportional to the power currently being exported, things are relatively simple, but for one client recently we had to deal with a system including only a standard domestic import meter. This has an LED which flashes at a rate proportional to the amount of electricity currently being imported (i.e. purchased from the National Grid), and which is permanently on while electricity is being exported.

Export meter for solar PV system LED detection circuit to power immersion with surplus power

The client wanted a device which would turn on his immersion (standard 3kW element, but powered via a power reducer which halves the power consumption to 1.5kW), after a user programmable number of minutes of continuous electricity export. The exact number of minutes desired for efficient operation was unknown, so we made the device programmable – i.e. the user could themselves set the number of minutes of continuous export required before the immersion would be turned on.

The immersion would then remain on until 5 seconds of the import meter LED flashing. Therefore, if turning on the immersion results in electricity being imported, the immersion would be turned off within 5 seconds, so very little electricity would be imported to power it. While the amount of electricity taken by the immersion is insufficient to use up the full export surplus, the immersion would stay on, heating water.

Surplus solar PV immersion controller using export meter LED to decide when to turn on immersion

Obviously this is not the most efficient system possible – something with a current sensing clamp to detect the exact level of import or export power is better, but the commercial options with this feature start at around £130.

This simple and easy to install system ensures that on a sunny day when no-one is at home using a high powered appliance such as a kettle or washing machine, surplus electricity from the solar panels will always be used to heat water rather than being exported (for which just a few pence would be paid), resulting in a payback period measurable in months.

The status of the LED on the meter (on or off) is detected using a simple light detecting resistor (LDR).

If you would like something like this device, please email with details of your requirements.

Double Controller for De-Stratification

Pictured below is a controller we recently made to de-stratify hot water cylinders. Stratification is the layering of water of different temperatures within a tank or cylinder. It leads to the problem of having a thin layer of extremely hot water at the top sitting above a quantity of much cooler water. Therefore any thermostats or temperature sensors on the cylinder will only see cool water (making the system inefficient), while dangerously hot water comes out of the hot tap.

Double de-stratifying Circuit for hot water cylindersThis double controller is basically two of our 2013 solar water heating pump controllers put onto one board with a single power input. There is a top sensor and a bottom sensor for each cylinder to be de-stratified. (We used precision LM335Z temperature sensors for this project)

When the top sensor is measured to be a user set number of degrees (diffON) hotter than the bottom sensor, a circulation pump is turned on via the relay to mix the top layer of hot water into the cooler water below. This heats up the cooler water and cools down the hotter water giving a more consistent temperature throughout. The pump stays on until the difference between the top and bottom sensors has fallen below a second user set number of degrees (diffOFF).

With this particular controller diffON is set in steps of five degrees whereas diffOFF is set in steps of single degrees.

If you need any kind of temperature sensing relay controller or similar, email with details of your exact requirements.

Solar Water Heating Pump Controller with Maximum Pump Run Time

Our 2014 Solar Water Heating Pump Controller with LCD is one of our best selling products. We recently receive an original request for a modified version of this controller for use with a solar heated swimming pool in France. This particular system has a 12V powered submersible pump which has a maximum duty cycle of 15 minutes – i.e. if the pump is run for longer than 15 minutes continuously it could be damaged.

In general the pump in such a system will not run for that long, but it is likely to happen from time to time – particularly in the spring when the pool is cool, but the panel is getting well heated in the middle of the day. Therefore something needs to be added to the controller to protect it from this eventuality. Also, this controller has a manual override to force the pump to run, and this could be forgotten and left on for hours burning out a vulnerable pump if there is no protection.

solar water heating pump controller with maximum pump run time

Pictured above is controller board we made – this time with a relay to switch the current to the pump rather than the standard MOSFET 2A 12V output. We also added waterproof temperature sensors to make the device suitable for pool use.

To the standard user programming options we added the ability to set the maximum number of minutes the pump may run continuously, and the number of minutes the pump must then be left off before it can be turned on again. These values can be set to anything from 1-60 minutes each to give flexibility should the pump need to be changed in the future. The user of this controller intends to set a 12 minute maximum run time and a 3 minute forced off time. (As the 2014 controller is Arduino based, we used the millis() function to keep track of time while the pump is running).

If you need any kind of solar water heating pump controller, please email details of your exact requirements to

Solar Pool Pump Controller with Overheat Diversion

Pictured below is a controller we recently made based around our standard 2014 Solar Pump Controller. The modifications and additions have been made so that this device can be used to safely control the pump for a small solar heated pool located in sunny Egypt, ensuring that neither the pool nor the solar panel will overheat in the extreme weather conditions found there.

Solar water heating pump controller with automatic diversion overheat protectionWith our standard controller, the pool temperature could become unpleasantly or dangerously hot in very sunny climates. We have made many controllers which automatically turn off the pump if the pool temperature exceeds a user set threshold (such as this simple solar hot tub pump controller). However, just turning off the pump in the middle of summer in Egypt could easily result in the the contents of the solar collector boiling which could also be dangerous and damaging.

Therefore this particular controller can be set up by the user (via the on board buttons and provided LCD display) with a maximum pool temperature. If the pump is running (because the solar collector is hot) and the pool reaches the maximum temperature, a relay closes which turn energises a solenoid valve. This valve will divert the solar heated water away from the pool and through a copper coil into a vented tank or barrel where it can boil/evaporate off safely. A float valve at the top of this container will top it up with cool water to replace evaporative losses. When the pool temperature falls by two degrees, the solenoid valve will be de-energised and the solar heating of the pool will start again.

If you need any kind of solar water heating pump controller, have a look at our range of off the shelf products here: Solar Water Heating, and if you cannot find something suitable, email with details of your exact requirements so that we can design and build you something.

East West Solar Water Heating Pump Controller

We have recently finished work on a new solar water heating pump controller to be used where the array of solar water heating panels is split between an East and a West facing roof instead of the more typical single South-facing (in the Northern Hemisphere) solar array. This controller has been based around our 2014 Solar Water Heating Pump Controller with Display with some additions and changes.

Solar water heating pump controller for use with an East / West solar arrayThis controller has connections for three waterproof digital temperature sensors – one for the East array, one for the West array, and one for the hot water tank (or pool).

The customer for this controller did not want to have the water flowing through both solar arrays at the same time to prevent heat collected on the hotter sunny side of the roof from being immediately radiated away from the cooler side. Therefore his system features two solenoid water valves which, when the pump is turned on, will ensure that water only flows through the hotter of the two solar heating arrays.

Display for East / West solar water heating pump controller

The display (LCD) for this controller shows the three measured temperatures on the top line, the temperature difference between each solar array and the hot water tank (or pool), which if either of the valves is open (therefore also indicating that the pump is running), and the temperature difference (diffON or diffOFF) required for the system to change state (i.e. for the pump to turn on or off).

In the above photograph, the valve on the West side is open, and the west solar array is +5.8 degrees Celcius hotter than the hot water tank. When this temperature difference falls below 4 degrees (diffOFF), as the East array is relatively cool (just +1.2 degees hotter than the tank) the West valve will close, the pump will turn off, and the display will now show diffON – the temperature difference required before the pump can be turned on again. (If the East array had been hotter than the tank by more than diffON at this time then the pump would keep going, the East valve would open and the West valve would close).

This controller also has a manual override facility which lets the user force the pump to run with the East valve open, the West valve open, or even both valves open at the same time – for example while testing. The values of diffON and diffOFF can be set by the user as per the standard 2014 solar water heating pump controller.

If you need a controller like this (or any other solar water heating pump controller), please email with details of your exact requirements.

Solar Pump Controller with Diversion Valve

Pictured below is a solar pump controller we recently built to meet a specific requirement. A solar water heating panel is used to heat the water in a hot tub, but if the hot tub exceeds a maximum temperature for comfort, then any additional solar hot water is diverted to heat the contents of a cylinder used for domestic hot water.

Solar pump controller with diversion valveThis controller is closely based around our standard 2014 Solar Water Heating Pump Controller with LCD Display, but with the addition of a third sensor to measure the temperature of the cylinder (since we only want to send water from the solar panel to the cylinder if the solar water is hot enough to heat it up).

LCD display for solar water heating pump controller with diversion

If/when the temperature measured of the hot tub reaches or exceeds the user’s desired maximum for comfort, a three-way solenoid valve is energised automatically diverting the hot water from the solar panel to the cylinder . The pump then carries on pumping until either the hot tub’s temperature has fallen by a couple of degrees, or the solar panel cools to close to the cylinder temperature.

All sensors used are waterproof digital temperature sensors, and the display is enables the temperature of all three monitors to be constantly monitored. A solid state relay is used to switch the mains powered circulation pump on and off.

If you need a solar water heating pump controller, please take a look at the selection of units we have in the REUK Shop. If you do not find exactly what you need, please email with details of your requirements.