Questions and answers

Find answers to frequently asked questions

FAQs

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?

We offer flexible RCT Power batteries with a gross capacity of 5.7, 7.6, 9.6 or 11.5 kWh. The storage can be expanded at any time in 1.9 kWh steps up to max. 11.5 kWh using the "Plug and Play" method. The capacity of the battery expansion is based on the actual capacity in the existing battery tower. For this reason, we recommend a battery expansion within the first 18 months to make the best use of the expansion. The warranty is not affected by the battery expansion, as this is related to each individual module.

In addition, the correct procedure described in the technical documentation "TD6" must be observed when installing the extension.

 

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 Battery: Calibration and Balancing

1. What is a calibration process?

The calibration process is used to determine the capacity value of the RCT Power Battery. To do this, the battery must be fully charged once (100%) and then completely discharged (0%). This process is primarily controlled by the PV generation during charging and by the house load during discharging. To ensure that this process does not take too long, e.g. when the house load is very low, forced charging/discharging via the grid can occur. 

This figure is a representative curve. The time segments do not have a time scale.

Sequence of the calibration process:

1. Start of the calibration process with charging of the battery primarily from PV generation.

2. Start of balancing to charge all battery cells.

3. The charging phase is completed.

4. The battery discharge phase begins as soon as the house requires energy.

5. The battery is discharged via the house load. If the house load is not sufficient, active discharge to the grid may be necessary.

6. The battery returns to normal mode and is charged via PV generation.

 


2. What does balancing mean?

Balancing is a control procedure to bring all cells of an RCT Power Battery to the same state of charge and thus enables a 100% full charge of the battery in addition to an equalisation of the battery cells. Balancing ensures high availability of the battery capacity, high performance and a long service life of the RCT Power Battery.

Balancing occurs in different operating states of the system:

    • During the calibration process, the necessary balancing is evaluated and an initial balancing is performed for a limited period of time.

    • Based on this evaluation, further balancing takes place after the calibration process until the battery cells within a power battery slave are at a similar level.

    • Balancing takes place during the calibration process between the charging and discharging phases (see diagram Calibration process).

 

 

3. Will the battery be overcharged or deep discharged by the balancing or calibration process?

No, in order to protect the battery, only the usable capacity is available for charging and discharging. The 0 % and 100 % battery state of charge (SoC) displayed in the RCT Power App refer to this usable capacity.

 


4. How often does the calibration process and balancing occur?

The process is performed approximately every 30 days. As this process has been optimised as of Feb. 2022, this may initially lead to longer balancing times.

 


5. Why is charging to 100% when the battery setting SoC target is 97 %?

The RCT Power Battery is calibrated every 30 days. For this process, the battery is charged to 100 %. Afterwards, it resumes normal operation and respects the previous battery settings. This is a safe procedure and serves to optimise the performance of the RCT Power Battery.

 

6. How long does the calibration process and balancing take?

The calibration process and balancing can take different lengths of time. A period of 30 minutes to 5 hours is quite common.

 


7. Why does the RCT Power Battery discharge to SoC = 0 % during the calibration process?

To determine the capacity of the battery, it is necessary to discharge to 0 %. This is a secured process to optimise the performance and does not mean a deep discharge.

 


8. Why does the battery continue to charge even though the SoC = 100 %?

When an RCT Power Battery is in balancing, the balancing is displayed with SoC = 100 %. It is not possible to show decimal numbers on the inverter display. Balancing is displayed in the RCT Power App with a value of "SoC = 99.9 %".

 

9. Why can't the battery be discharged although SoC = 100 % is displayed?

In order to carry out the measurement completely and correctly during the calibration process, it is not possible to discharge the battery during the charging phase of the calibration process to 100 %.

 

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.

 

It will load necessary cookies, Google Fonts, Google Maps, OpenStreetMap, Youtube and Google Analytics. More details in our privacy policy and our imprint.