What generator set characteristics are necessary in order to work optimally with ZHERO?

The system can manage any type of generator set as long as it produces voltage of 230 V +/- 10% and frequency of 50.0 Hz. The connection is made at a frequency of between 49.0 Hz and 51.0 Hz, while disconnection occurs below 47.5 Hz and above 51.5 Hz.

What is the MPPT voltage and power operating range?

For off-grid mode the MPPT controller accepts a voltage range between 90 and 160 V (120 V is recommended for optimal efficiency of the MPPT). The maximum power output for each MPPT does not exceed 3.3 kW. For on-grid mode on the other hand, the MPPT controller accepts a voltage range of 200 to 600 V, with a recommended range from 300 to 400 V .

How are solar power strings connected to the string board?

Off grid: the 'string boards' handle parallel connection between photovoltaic strings, usually composed of 3 or 4 panels connected in series. Each string must have voltage from 90 to 160 V (120 V is recommended for optimal efficiency of the MPPT) and current no higher than 10 A (12 A with appropriate fuses). The strings must be inserted through the dedicated holes in the ZHERO case and screwed to the board terminal block, paying attention to the connection sequence.

On grid: the 'string boards' handle parallel connection between the solar panel strings, usually composed of 7 to 15 panels connected in series. Each string must have voltage between 200 and 600 V (300 - 400 V recommended for optimal MPPT performance) and current of no more than 10 A (12 A with appropriate fuses). The strings must be plugged in via dedicated connectors inside the ZHERO unit

Can the system be used in a three-phase line?

ZHERO is designed for use in single-phase residential installations. However, ZHERO can be installed in a three-phase line on one of the 3 phases on the condition that it supplies only single-phase services. This is due to the fact that in the event of an interruption of the line passing through ZHERO, the other phases of the system would not be interrupted, causing possible damage to the connected devices.

In the event of a system fault, will the lights go out in my home?

No. The system is automatically bypassed under fault conditions. If this also does not occur, the user can manually turn the main circuit breaker to position 2, which allows manual bypass of the system, restoring the power supply until the installer's intervention.

Can the ZHERO device be used only as a back-up unit?

Yes, it is possible to use ZHERO as a back-up unit, rechargeable from either a solar power system, the mains network, or a generator set. It is not certified as a UPS.

How should the solar power system and ZHERO be sized?

There are several factors that influence sizing of a solar power system with storage, such as the place of installation, exposure to the sun, maximum installable power, type of use of the system, etc.

What is the ambient temperature range of ZHERO?

The ZHERO ambient temperature range is -10 to +40 °C.

How can the system be moved?

Simply remove the protective skirt covering the feet and use a normal pallet truck. If necessary, the unit can be broken down into 3 parts: battery body, main body and cap. Also the side panels can be removed from the central body.

What maintenance does the device require?

Maintenance must be carried out by authorised personnel. The device requires only careful cleaning of the air filters on the front pockets and upper fan, to ensure the air flow is not obstructed by accumulated dust. It is also advisable to ask the maintenance technician to check the various AC and DC terminals in the unit to ensure they are properly tightened.

Where should the system be installed?

ZHERO should ideally be installed in a well-ventilated service room, although there are no binding prescriptions in this respect. In any case, rooms subject to very high temperatures should be avoided and ZHERO must not be exposed to direct sunlight. Avoid also installation sites subject to the risk of flooding. Check also that the floor is designed to withstand a load of 300 kg/m2.

What degree of protection does the system offer?

ZHERO's protection rating is IP20.

Can I use ZHERO to charge an electric car?

Yes, but there is no electric car communication protocol implemented at present. It is anyway possible to connect the 220 V power supply to ZHERO in the same way as with a normal electrical outlet.

How does the self-consumption percentage change compared to on-site exchange?

As a guideline, the energy consumed by a user with an on-site exchange contract is between 20 and 30%. With ZHERO, comparing different systems installed in the field, the figure is between 65 and 75%, with peaks of up to 90%. The apparent randomness of the values can be mitigated by smart energy usage strategies.

Is it possible to feed a priority load?

Yes. The unit is configured for this function. The priority load is programmable according to the user's needs. Priority loads are currently selected by closing a voltage-free contact.

Can an alarm signal be remotized?

Yes. The CPU board is already configured for connection via a voltage free contact that can be remotized from ZHERO.

Can energy be exchanged with other systems?

Yes, the exchange system is called Owner Grid.

Can the customer carry out repairs independently?

Absolutely not. All work must be approved by UNE and carried out only by authorised personnel.

Is there a risk of electric shock from the sheet-metal enclosure?

No, the entire system is grounded and completely safe. In the event of an insulation fault, the system will automatically assume safety status.

Can the system be anchored to prevent it from tipping over?

Yes, the eyebolts on ZHERO's cap can be used for this purpose. In addition, the system feet have holes for fixing to the floor to provide additional stability.

Is the system protected against lightning strikes?

Yes, ZHERO is equipped with specifically designed surge arresters (OPT). In addition, there are numerous fuses that limit the potential for the propagation of lightning discharges.

Can the boards parallel be remotized from outside ZHERO?

Yes, but UNE's prescriptions concerning the enclosure and connection methods given in the installation manual must be followed.

How many kWh of storage should be installed?

This value depends greatly on the type of consumer. Consumption of the home can be assessed along with the necessary investment.

Can a ZHERO system be integrated in an existing installation (retrofit)?

It depends. The solar power system can be maintained, checking however that the strings have maximum voltage between 80 - 180 V and current not exceeding 10 - 12 A each. In addition, the original inverter becomes completely obsolete as everything is and must be managed by ZHERO.

What is the tax deduction on the product?

In the case of an existing home, there is a 50% deduction on the total amount spent, reimbursed over a period of 10 years. If combined with a heat pump or heating system, the deduction is 65%.

Can complete independence from the grid be achieved?

With correct plant sizing and careful use of the energy produced, long periods of complete independence from the grid are possible. Total energy independence requires an external generator set to compensate for periods of low solar power generation.

Can the system be used with different batteries?

No. ZHERO is designed to work with its own salt batteries.

In what circumstances might ZHERO experience problems attempting to connect to a generator set?

If the generator set is an older legacy system or of low quality, able to generate only irregular frequency or frequency outside the acceptable range, connection becomes difficult. In such cases, it is preferable to replace your original generator set with a new state-of-the-art model.

Can ZHERO be lifted from the eyebolts?

No, the eyebolts are provided to secure the unit to the wall.

Can a battery be added at a later date?

Yes, the storage capacity can be upgraded by requesting the provision for second battery immediately, or the complete upgrade can be carried out at a later date.

Can the system operate completely off-grid?

Yes, the system is designed also to provide this function, even without a generator set.

How is ZHERO shipped?

ZHERO is shipped on a pallet, fully assembled and ready for commissioning. For special installation cases, the system can be shipped in disassembled condition.

Is it necessary to install the solar power generation meter outside the unit?

Yes, as with a normal connection of a solar power system to the electricity grid, an external generation meter is required. In case of an off-grid situation, this will not be necessary.

Is it also necessary to install a residual current device upstream of the system? What type?

Yes, a residual current device must be installed at the start of the line, ideally using a class A, 300 mA selective device.

Is there space in the system to accommodate the production meter circuit breakers?

Although there is sufficient space, it is preferable to keep the circuit breakers outside the unit near the generation meter.

How many contacts are available for the customer to use preferential loads?

Currently 1, but UNE can provide customised solutions on request.

How is the inside of the system accessed in order to connect the string and grid cables?

The DC and AC terminal blocks are accessible via knock-out holes on the box. In fact, 4 knock-outs have been created to be removed according to wiring needs, to be fitted with cable glands (PG36) or conduit box fittings.

Is it useful to propose an increase in meter power from 3 to 6 kW?

It is certainly necessary to upgrade from a 3 kW to a 6 kW meter to take full advantage of ZHERO's potential. Using more power than your installed meter power is inadvisable for reasons of electrical safety and regulatory constraints.

With 6 kW solar panels, is ZHERO well balanced and can a connection be made to the Enel / Hera power grid with a 3 kW single-phase line?

Yes. Input power and withdrawal power need not necessarily to be identical. It is permissible to have input power of 6 kW due to the presence of the ZHERO and (contractual) withdrawal power of 3 kW. However, the 6 kW of input power can only be used if the system has sufficient energy in the battery and, hypothetically, only in months with high levels of sunlight. In winter, for example, the system will be frequently connected to the public grid due to absent or low levels of sunlight, so the withdrawal power value frequently approaches 3 kW, disruptions may occur due to tripping of the electricity company's meter circuit breaker. Users who are attentive to this aspect can do this, but those who are less informed of such conditions may interpret such interruptions as system faults.

Thanks to the ZHERO system, is it possible to establish a power supply contract with the operator for a power rating lower than the nominal power capacity of the solar system?

There is no obligation to switch to a three-phase supply. In terms of the relationship with the grid, the important parameter is the inverter output power.


How much does heater consumption affect battery life?

It depends. If the battery is not supplying power, self-consumption is around 100 Wh and around 50 Wh during residential use. When the battery supplies more than 800 W the PWMs are disconnected.

Is there a danger of the batteries exploding?

Absolutely not. The batteries are 100% safe: they withstand extreme temperature changes, do not produce harmful vapours and even withstand immersion in salt water with no risks for property or people.


Can ZHERO be monitored or controlled remotely?

It is currently possible to monitor the system remotely using the web app developed by UNE, available at: . This web app, accessible from a desktop PC and mobile devices, allows the user to view the operating status, the presence of faults and all the energy flows in the home. While remote controls have been implemented, they have not been made available to the user to avoid the risk of causing malfunctions of ZHERO if they are used incorrectly.

What are the "working modes"?

Working modes are the unit's operating modes, depending on the use (off-grid, on-grid, grid feeding, etc.). The working modes are set, to allow the unit to adapt to the end user's needs.

How can in-depth data management be carried out?

A USB output can be configured to which to connect and, using the dedicated UneSrlComunication software, all the device data can be viewed and downloaded in 1s steps

How much does a ZHERO system weigh?

The weight of the system is around 240 kg for the single-battery model and around 340 kg for the dual-battery model

What is the inverter power rating?

The maximum inverter output power is 6 kW. In the case of users with a lower power connection contract, power may be limited to match the grid supply.

How long is the ZHERO warranty?

The ZHERO battery is guaranteed for 10 years, while the inverter is guaranteed for 5 years. It also has a lifetime guarantee against risks of explosion, gas emissions and flammability.

What is the life expectancy of the battery?

The life expectancy of the battery, used in the ZHERO system, is 20 years.

Can product customisations be requested?

Yes, ZHERO is anything but a closed system. A large number of functions can be implemented to match the customer's needs.

Where is ZHERO made?

ZHERO and all its components (with the exception of the battery, which is manufactured in Switzerland by an Italian company) are entirely designed, manufactured and assembled in Italy

How are ZHERO updates applied?

ZHERO firmware updates will be carried out remotely via an internet connection, without requiring an external intervention.

Is the battery susceptible to heat or cold?

In general, the battery offers good thermal inertia against both cold and heat, thanks to its insulation and smart management of the heaters. In fact, the battery can operate correctly in an ambient temperature range of -40 to +60 °C. Since the internal temperature is kept almost constant, the ambient temperature only affects the activation frequency of the internal heaters.

To what extent does the battery retain its properties after long periods of disuse?

The battery retains its properties perfectly. In fact, once it has been switched off, it cools and solidifies the internal molten salts, also fossilising its state of charge; therefore, even years later the classic phenomena associated with conventional batteries, such as deterioration, loss of charge, memory effect, etc., are absent.

What is battery capacity? The C-class? The DOD?

The battery capacity can be 5.7 kWh, 7.6 kWh, or 9.6 kWh. It is classified as C4. DOD is up to 90%.

How noisy is the system?

During normal operation noise levels do not exceed 25 dB. When forced ventilation switches on, which generally only occurs during the hottest summer days, noise levels can reach 30 dB.

Why is it called All-In-One?

ZHERO contains all the necessary devices and components for a system with storage.

How can the point of failure be identified in the case of malfunctions?

The alarm is shown by the red alarm lamp and an error code shown on the display. The type of problem is signalled by means of an email detailing the malfunction sent to both the user and the installer. The user and installer can then agree on the corrective action required.

What is Owner grid?

Owner grid is a 230 V single-phase AC power network that can be installed between 2 or more ZHERO systems. Through this network, special rules can be followed to transfer surplus solar power production to the other system or to receive it when needed. This exchange of surplus energy is set up as a priority channel with respect to transfer back to the grid to aid energy independence. Currently, this exchange is only permitted in Italy on the condition that a smart grid is created that is completely separate from the national grid, while in various other countries it is already permitted.

What are the dimensions of ZHERO?

The dimensions of ZHERO are approximately 600 cm wide, 600 cm deep and 1360 cm high.

What is the purpose of the skirt covering the feet of the ZHERO unit?

The main purpose is to protect the unit's feet from accidental impact. It also reduces heat loss and creates aesthetic uniformity.

Who owns all the technology contained in ZHERO?

The entire technology and know-how are the property of UNE.

How long do the batteries take to charge up the first time? How much energy do they require?

At the first start-up, with a cold battery, it will take between 10 - 12 hours with total consumption of 3 - 4 kWh.

What happens if the system enters overload status?

The recommended action in the case of overloads is to disconnect the loads responsible for the condition and press the red overload lamp on the ZHERO AC panel: the system will resume normal operation.

Can a solar power system be expanded at a later date and connected to ZHERO?

Yes, up to a maximum of 18 kWp of solar power.

When were the first systems installed?

The first installations date back to 2013.

How long has salt battery technology existed?

Salt battery technology has existed since the 1980s and has been mainly used for telecommunications, transport, green areas, etc. ZHERO introduces salt batteries also to residential applications.

Can the battery be purchased separately?

No, the battery is sold exclusively with the ZHERO system.

Can a battery be added at a later date?

No, the battery is sold exclusively with the ZHERO system.

Can the working mode be changed?

Yes, but this must be done by the installer.

Has the system gained any certifications and/or recognitions?

The system is certified CE, CEI-021, residential and light industry, and has passed all the tests carried out by the EUROFINS certification network. You can view and download copies of the certificates directly on our site. The remaining documentation can be requested directly from


Do the controllers use PWM or MPPT technology?

They use MPPT technology. The controllers always seek the maximum efficiency point to optimise solar power generation.

What is the system efficiency?

Since the system is extremely complex and unique, with many different modes of operation, no specific standards exist to evaluate this aspect. By considering the individual components however, efficiency is very high, with levels in excess of 97%.

What happens if the battery is fully charged and there is no power draw in the home?

It depends on the operating mode. For on-grid mode, the surplus production is sold back to the grid operator. For off-grid mode, this energy can be fed to a privileged CP1 line, to which loads can be connected. In the case of Owner grid, this energy will be exchanged with other systems that need it at that particular time.

Is battery charging and discharging power symmetrical or is there a difference between the two phases?

The battery can absorb a maximum of 2.16 kW when charging, and transfer up to 6 kW when discharging. Therefore, for dual-battery systems, the maximum power absorption is 4.32 kW, while the power output remains unchanged.

What indications are supplied by the app?

There is an app on which the essential parameters can be viewed, including battery charge status, power output, power drawn from the grid, solar power production and alarms.

How is the battery charge status calculated?

Charge status is calculated by the CPU by averaging the SOC values of the connected batteries. This data is extrapolated from the batteries through constant communication between the battery BMS and the CPU board.

How can I find out how much surplus energy I have in an off-grid system with charged batteries?

Thanks to a radiation sensor, the difference is calculated between the actual power generated by the MPPT and the measurement detected by the sensor. This makes it possible to calculate the surplus power to allocate to priority loads.

Is communication possible with third party home automation systems via the Modbus RTU rs485 protocol?

The system already has an additional module on our Modbus RTU rs485 motherboard ready to communicate externally with other devices. The communication protocol with these devices must be individually implemented because each one uses a proprietary protocol.