Questions and answers

Find answers to frequently asked questions


Do you have questions about RCT Power Storage System? Here you will find answers to frequently asked questions.

Instructions, technical documentation and certificates can also be found in our download area.


RCT Power Storage System

1. Can I expand the RCT Power Battery retrospectively?

Yes, our flexible battery storage system is available with gross capacities of 5.7, 7.6, 9.6 and 11.5 kWh. The system is designed for plug and play operation. At any time within the first 18 month of operation you can expand capacity in steps of 1.9 kWh up to maximum capacity of 11.5 kWh. You can utilise 90%  of your system's gross capacity at any time.


2. Can I also control my domestic hot water heat pump?

With our multifunctional relay we offer you the possibility to individually control additional consumers. Look out for the SG-ready label on heat pumps! You can control switch-on or switch-off conditions via our RCT Power App.


3. Does the storage system provide back-up power supply?

Our system is fully certified under the terms of VDE-2510. The RCT Power Switch can be retrofitted the RCT Power DC coupled storage system at any time. Your photovoltaic installation is fully functional in case of power outage - either your batteries will be charged or you use the generated energy for your private consumption.


4.What are the benefits of predictive load management?

Battery Storage systems operate within a framework of pre-defined conditions. These conditions require that only a set a percentage (e.g. 30%, 50% or 70%) of the generated solar energy is fed in. This load regulation can lead to losses in the region of 10% depending on system layout. Predictive load management will reduce these losses to a minimum while at the same time it will optimise your own consumption. Using pre-defined demand and yield predictions the batteries are only loaded when it is beneficial for the network and your yield. This approach delivers higher specific yield and lower losses caused by load factor regulation. Increased battery lifetime is another positive side effect of predictive load management.


5. Do I need Internet access?

No, in cooperation with the Fraunhofer Institute for Solar Energy Systems in Freiburg we have developed a method that does not require external weather data. No chargeable third party weather data and no Internet connectivity is required for our predictive load management system. Data is stored internally in the inverter.


6. What are the benefits of Max Power Control when solar panels are shaded?

Partial shading of photovoltaic installations generally results in reduced yield. Costly solar module optimisers can reduce this decrease in yield to a minimum. Max Power Control is based on an internal control strategy at string level that always adjusts modules to the maximum power point (Global MPP) during partial shading conditions. Similar to the module optimisers the decrease in yield is minimised for the affected solar panels. Max Power Control optimises the yield from your system - just very smart and without the added costs!


7. What does "black start" actually mean?

The term "black start" originates in the field of conventional power plant technology. It refers to the capability of starting a power plant unit independently of the power grid. Your RCT Power Storage System with Power Storage DC and Power Switch also can perform a "black start". It only needs sufficient solar energy to start operation.

8. How does RCT Power implement a "black start"?

The RCT Power Storage System will power off automatically only in exceptional conditions: i.e. the PV system has not provided power for a prolonged time, and trickle charging for the battery from the grid (grid failure) is not available. Switching off the system will protect the battery from a deep discharge. As soon as the sun shines again, the system automatically switches on (even without being connected to grid power). At first, the battery is charged up to Min. SOC target (island) +3% before the backup power operation starts.

9. Why is the "black start" not working?

If the last attempt to establish a backup power supply failed consecutively three times (e.g. due to the house load being too high), the applicable installation standard mandates that before a further attempt, at least one successful connection to the grid supply must have been established.

10. What is often confused with a „black start“?

A "black start" is often understood as starting the storage system without PV power connected, i.e. only from the battery. This is currently not implemented for the RCT Power Storage System. It is designed to provide a backup power supply and not as a standalone off-grid system.

RCT Power Battery

1. Which type of lithium-ion batteries are used in RCT Power storage systems?

Our customers attach great importance to battery lifetime and safety. For this reason we exclusively use Lithium-iron-phosphate (LiFePO4) battery cells.

2. What is so special about these LiFePO4 battery cells?

LiFePO4 battery cells are among the safest Lithium-ion batteries on the market. The cell chemistry makes a thermal runaway overheating almost impossible. The cells are inherently safe even under extreme conditions and therefore they don't pose a fire risk.

LiFePO4 battery are characterised by a high cycle stability which translates into a a long lifetime even under intensive load conditions. The very high current carrying capacity of the LiFePO4 battery cells is especially useful when you want to charge your battery quickly. It is also of an advantage when you are thinking of acquiring an electric car. They will help you to securely supply your home and connected appliances in the event of power failure.

3. Why do you co-operate with the Karlsruhe Institute of Technology (KIT)?

The cooperation with Karlsruhe Institute of Technology enables us to offer a bespoke battery management system. The load management system is fine tuned by precise measuring of the battery conditions. It guarantees highest efficiency, long battery lifetime and an ultimate in battery safety.


4. What is the definition of intelligent charging behaviour, and how does RCT Power implement it?

The RCT Power Storage system records the power consumption and generated solar power values of the last ten days. It then combines these with the current irradiation values and calculates optimal setpoints for battery charging and discharging. This intelligent charging behaviour controls the power feed into the battery and also helps to avoid derating losses.


5. I have a RCT Power Storage System. Do I have to charge the battery regularly?

No, this is done automatically. Every 30 days, the RCT Power Battery is calibrated with a charge to 100% capacity.  Afterwards, regular operation resumes.


6. My RCT Power Battery automatically charges to 100 % capacity approximately every 30 days. Why?

This is a so-called "calibration charge". It is required to be able to continuously monitor the SoC (State of Charge) of the battery.


7. As soon as my RCT Power Battery reaches an SoC of 5 %, it is charged with 100 W. Is this correct? 

Yes, it is correct. At an SoC of 7 %, the energy supply from the battery to household consumers stops. Then the control electronics of the inverter and battery will continue to discharge the battery with a standby consumption of only a few watts. Especially at night, the battery can reach a threshold of 5 % SoC with this standby consumption. When this threshold is passed, a battery charging process with 100 watts is triggered to prevent further discharge. Once an SoC of 7 % is reached again, the trickle charge stops. (All  based on the default setting!)


8. Should my battery be charged to the full as quickly as possible at any given time?

Ordinary domestic power storage units switch to "charge" mode as soon as the PV system provides excess solar power. They are often fully charged before noon and then remain in this charging state for the remainder of the day. This will reduce the battery life and the long term benefit of the storage unit significantly. RCT Power uses a dedicated strategy for battery conservation: We ensure that the defined maximum state of charge is only reached in the afternoon. This will keep the stay in this state as short as possible. It is irrelevant at what time during the day the storage unit is charged to the defined full capacity to supply the required energy in the evening and at night. However, this approach is beneficial for the storage unit lifetime. Battery charging and discharging is controlled by an internal algorithm that changes dynamically based on solar radiation, power demand and battery charge.


9. Now and then, the state of charge (SoC) of my battery drops to 0% and is then charged again to 7%. Why does this happen?

The battery management system (BMS) monitors the voltage of each battery cell in the storage unit to correct inaccuracies in the SoC calculation. Occasionally, corrections will be performed during low solar irradiation. Briefly reaching the 0 % SoC threshold is not critical for the battery, as the actual voltages are still sufficiently removed from lower voltage thresholds. When the 0 % SoC is reached, the battery is charged with a 100 W trickle charge up to 7 % SoC. Then the energy is available to the system again and not lost.

10. What is a full charge cycle?

A full charge cycle can be described as a one-time charging and discharging of a power storage unit utilising its total useful capacity. A partial charge cycle refers to the charging and discharging of the storage unit with only a portion of the useful capacity.

A full charge cycle, for example, is accomplished when:

  • The battery is once discharged to 0 per cent residual capacity and then charged to 100 per cent capacity.
  • The battery is twice discharged to 50 per cent capacity and then twice charged to 100 per cent capacity.
RCT Power Storage

1. How do software updates of the RCT Power Storage work without an internet connection?

With the RCT Power App, the latest firmware is always available on your smartphone or tablet. All you have to do is select "Allow update" from the Google Play Store during the initial installation. You then simply connect to the RCT Power Storage via the RCT Power App and conveniently perform the update.

RCT Power App

1. Where can I get information about the RCT Power App?

For Android mobile phones you can download the RCT Power App in Google's Playstore. The RCT Power App includes a pre-set Power Storage installation for demonstration purposes. To load this installation select Tab “NETWORK”. Overwrite Add device line with ‘Demo’ and press the green + button. Demo Power Storage 6.0 has now been added as a new device. Under the “ONLINE” tab you will see a visualisation of the Demo Installation. Touch each symbol for more information. Touch “ONLINE” tab again to get back to visualisation screen. Select Tab “HISTORY” and touch the chart symbol. You will see the performance chart of the Demo installation. A quick double finger touch anywhere in the chart area will call up the chart display options.


2. How do I connect the RCT Power App to monitor my storage unit?

For the initial commissioning, the installer uses our RCT Power App (Android version) and connects to the Power Storage devices via WLAN. Afterwards, you also have the option of integrating our devices into your home network via LAN or WLAN connection.


3. When I tap the gear symbol in the top right corner of the RCT Power App, a LOGIN prompt screen opens. What end-user password do I need to enter?

Your end-user password is : ******** (eight times the * character)


4. Can I monitor my installation using the RCT Power App?

Yes, the RCT Power App allows you to monitor your installation in a simple manner. It includes system monitoring and comprehensive data visualisation. Together with various configuration options and a "one-click-update" function the RCT Power App provides everything the installer and the end-user expects.


5. I can see in the RCT Power App that the battery is only used in the SoC range of 7 % to 97 %. What is the reason?

We use 90% of the maximum capacity to conserve the battery. This prevents the battery from being unused when fully charged or discharged.


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