In today’s world, data is everywhere. Improved data logging capabilities alongside widespread options to store, access and analyse data help diagnose systems in many industries.

Why log solar thermal data?

Data logging solar thermal systems can be a great way to:

  • evaluate if a solar system is running efficiently
  • determine if and when the solar system is overheating
  • maximise the overall system efficiency. This enables you or an engineer to optimise the boiler controls for after heating.

How can I log solar thermal data?

Resol DL2 data logger
Resol DL2 solar water heating data logger

Resol are the market leaders in solar thermal controllers. The DL2 offered by Resol logs solar thermal data. This add-on unit can be connected to any of Resol’s controllers to log key system data such as

  • panel temperatures
  • cylinder temperatures
  • pump speeds
  • faults

Analysing this data can help in increasing your solar system’s efficiency as well as diagnosing any faults or anomalies.

Data logging with Resol’s vBus

In general, Resol are using a feature on nearly all of their controllers called vBus. This is a communications protocol that can be used to connect to external devices that allows monitoring and analysis of the behaviour of your solar system. To make the data provided by vBus readable, there are a number of options at various levels and costs.

For all monitoring options, it is best to have a network an Ethernet connection available ? in fact, for live monitoring this is essential, although there is a Wifi option with the KM2 module. is Resols?s offering for remote monitoring and logging of data. The allows to connect to the Internet enabled devices listed below and show live data as well as letting you export historical data in standard formats (such as CSV) for further analysis or import into other tools. Resol?s portal can be found here Generally, when purchasing a product with access, you get access to the premium version for 30 days which will be moved to the basic version if you are not interested in paying the subscription. We find that basic (free) offering is sufficient for most users.

Data logging

For controllers that are not connected/cannot be connected to a network and/or the Internet, there are devices available that allow the logging of data on an SD data storage card. This data can be extracted and analysed in software such as Excel and others.


  • full access to all data a point of convenience
  • absolute control and privacy control
  • no further costs


  • no live data/monitoring
  • manual process

Current controllers with built in data logging functionality

Resol DeltaSol SL Solar Controller
Resol SL solar controller with built in data logging facilities

As an alternative to the DL2 data logger add-on, we can install a modern. Resol Controller that has integrated data logging facilities such as Resol SL, Resol SLL, Resol SLT or Resol BS Plus.

Please also check our controllers page if you are looking for other controller models.


There are a number of Resol controllers available that include an SD card for data logging. Higher specification controllers allow for complex systems and set-ups, but the SL range is the entry level controller that includes and SD card slot. Alternatively, a DL2 data logger can be connected to a more basic Resol controller to log data. This Resol DL2 solution also includes access to, see more below.

Data (live) monitoring

To monitor live data and get a current view of your solar system, you need to have a wired or wifi network connection available. There are various options to connect your system to Resol?s

Communications module KM2
This is a simple electronics module that connects your vBus enabled controller to the Internet via Ethernet or Wifi. With this module you get access to Resol?s portal.


  • entry level connectivity to
  • Wifi enabled
  • No manual data handling
  • Can work with any vBus enabled controller


  • No access to data other than
  • No data logging away from

DL2 data logger

A more advanced option for data logging and monitoring. The DL2 has a built-in web interface to allow you to access data from your solar system. It includes a data logging for historical data and also connects to for remote monitoring.


  • Local and remote monitoring
  • Data logging in the unit and via SD card
  • No requirement for Internet connectivity if not desired, whilst allowing local network connectivity
  • Can work with any vBus enabled controller


  • No Wifi connectivity, requires Ethernet connection

Analysis of the solar thermal data

Once we have the data of your solar thermal system, we prepare the data ready to visualise it with a data package. We then host the data on one of our own servers and give you password protected access. Below you can see some of graphs that we can produce. Please The data package allows you to zoom in on individual data points and points in time. This is particularly helpful to get a deeper understanding of your system. As a result we can offer advise on changing settings of your solar controller or your boiler settings.

Hours run of a solar system during April
Hours run of a solar system during April
A solar heat exchanger data log
Sensor temperatures showing problems with heat transfer as the temperatur distances are too large.
Graph of a solar sytem with two sets of panels and an heat exchanger
Sensor temperatures showing good heat transfer
Solar Thermal system with 3 sensors
Panel temperatures during a sunny day, showing good heat transfer to the cylinder
Cylinder temperatures of a Solar Thermal system with 3 sensors
Cylinder temperatures rising during the day, water extracted in the afternoon and reheating to temperature.