Frequently Asked Questions

SolBox is a system that converts a standard water heater into a solar one. It receives solar energy, converts it into electrical current, regulates it, and delivers it to the water heater's heating element. In practical terms, SolBox heats the water in your boiler using solar energy.

If you are looking for a low-cost replacement for a cheap solar water heater, SolBox is not the right choice. SolBox offers considerably more than a conventional solar water heater.

SolBox provides complete hot water management, free from the boiling and maintenance issues that a classic solar thermal system typically presents.

SolBox measures 20×20×10 cm and weighs 4 kg.

• Never boils
• Requires zero maintenance
• Provides complete hot water management

SolBox heats water through an electric heating element and is an electrical energy system. This means that when required, it simply cuts off without any problem and stops transferring energy to the tank. This ensures you will never encounter boiling, tank damage, enamel cracking, or related issues.

SolBox takes solar heating technology a step further — it can reach the temperature set by the user. Through the app, you select the desired water temperature and the system will stop heat production regardless of solar intensity.

SolBox allows two separate and independent temperature setpoints. You can set a different temperature for free solar hot water production, and a different temperature for the backup source where energy is billed.

For solar production: Select the highest possible temperature (85°C). The logic is that we produce hot water when the sun is available and consume it when needed. Where limescale is a concern or there is no thermostatic mixing valve (risking 85°C water reaching the tap), choose a lower temperature.

For the backup source: Since energy is billed, there is no reason to heat the entire tank to a high temperature. Top up only enough energy to reach an adequate temperature, typically 45–50°C.

Scale begins to form when water exceeds 43–50°C, depending on the area and water hardness. With SolBox you can choose a water temperature that reduces the likelihood of scale accumulation in hard-water areas.

We cannot guarantee zero limescale on the element. What we can guarantee is that because the element operates at a much lower temperature and for a much longer time to deliver the same energy, scale accumulation will be orders of magnitude lower than with a classic solar thermal system or a mains-powered electric element.

SolBox can operate in self-powered mode with up to two panels. With an external power source it can operate up to 210V DC.

SolBox can self-power from the panels themselves when up to two panels are connected in series. You can also connect 2+2 panels in parallel. For more panels, an external 12V 3W power supply is required.

To switch from self-powered to external supply, remove the jumper located on the power input, under the main cover.

External power is only required when SolBox needs to command an external heating source. This is necessary so it can access the internet when there is no sunlight at all, in order to trigger its relay. If no backup heating source is used, there is no need to connect the device to mains power.

The self-powered design of SolBox was based on the 80/20 rule: 20% of customers create 80% of the problems. With a self-powered SolBox:

• You will never have to explain to a customer why their electricity bill was high in winter while they have "free" solar hot water.
• No customer can accuse you of the water being heated from the mains.
• A self-powered SolBox can be installed in holiday homes, caravans, mountain shelters, or any application requiring hot water without a grid connection.

Electric shock from the mains grid occurs when current passes through the human body to ground — possible because the mains neutral is earthed.

In SolBox, the two PV cables are not connected to ground, so there is practically no risk of electric shock. For the same reason, no residual current device (RCD) is installed on the DC side of any PV system.

Installing SolBox without a safety thermostat is not acceptable. This thermostat, upon reaching the preset temperature, activates and cuts the power supply. Manual reset is required to restore operation.

SolBox has its own temperature sensor with which it determines whether to send energy to the boiler. Commercial water heater thermostats are designed for AC operation and are not certified for DC voltage.

Such a thermostat could be installed as an additional safety measure, set to a higher temperature than SolBox's electronic system.

Important: Under no circumstances can SolBox replace the function of the safety thermostat. Equally, the safety thermostat function can never be replaced by an operating thermostat.

SolBox is delivered ready to use, complete with a surge arrester and a 20A DC fuse. As a rule, these are sufficient for the electrical installation. In any case, consult current regulations and your installer.

On the DC side, SolBox does not exceed 20A. Cable cross-section is typically 4mm², while 6mm² cable achieves significantly lower losses. The choice is at the installer's discretion, in accordance with common practice and knowledge.

In practice, many metres of cable can be run on the panel side. This is a technique applied for years in rooftop and ground-mount PV systems. There are installations where the cable run was nearly 100 metres.
Indicative losses at full sun:

• 6mm² cable: 0.3% per 10 metres
• 4mm² cable: 0.68% per 10 metres — if this is the only viable installation route, these losses are acceptable.

Cables can be routed virtually anywhere, provided solar-rated DC/UV-resistant cable is used. They can run under roof tiles, through conduits, through air ducts, or alongside mains cables.

In one installation featured in a video, the cable was run through the Ø16 pipe from a decommissioned solar thermal system. The cable route is limited only by the installer's imagination.

On the output side, SolBox is delivered with approximately 1.5 metres of pre-installed cable, plus a temperature sensor cable of approximately 1.5 metres. Therefore, SolBox must be located no more than 1.5 metres from the water tank.

A typical installation takes approximately 40% less time compared to a conventional solar thermal system. SolBox has no fluids, no heavy tank to hoist onto the roof, and no pipework. Cabling is considerably easier and faster than pipework.

SolBox must be installed in a location that is dry and protected from moisture.

Yes, it can be installed anywhere where humidity does not exceed 90%.

The lower temperature limit is dictated by the need to avoid condensation. If the upper temperature exceeds 35°C, system output may be reduced due to overheating.

SolBox can operate with any PV panel rated between 450W and 720W, with no restriction on manufacturer or type.

SolBox is compatible with any water heater. Tanks of 150 litres or more are recommended, following the same logic as a conventional solar system: water is heated when the sun is available, stored, and consumed when needed.

2 panels in series: Self-powered; covers 150 litres in summer.

2+2 panels (2 series, 2 parallel): Self-powered; covers 200 litres with an extended operating season (beyond summer, into autumn and spring), or 150 litres in partial cloud.

3 panels in series: Comfortably covers 150 and 200 litres in summer.

6 panels (3+3 in series): Maximum SolBox output; covers 300 litres in partial cloud with a maximised operating season.

A key difference from conventional solar thermal is that SolBox does not define the number of panels based on tank size. In conventional systems this restriction exists to prevent summer boiling. SolBox is an electrical system: when it should not produce, it simply switches off. You can connect 6 panels to an 80-litre tank and have hot water even on moonlit nights.

Axinar offers dedicated heating elements designed with the exact electrical properties required for optimum SolBox performance.

No. We have no intention of locking technicians to our parts or delaying any service. Alternatively, a 3-phase 9kW or 12kW element can be used with all 3 windings connected in parallel, so the resistance drops to 1/3 of a single winding and becomes compatible with SolBox voltage.

It works with an existing element unless it does not match SolBox requirements. With the wrong element there will be reduced performance, but it will suffice until the correct one is fitted.

A heating element has no active role — it simply converts electrical flow into heat. If the element were a light bulb, on a cloudy day you would see it varying in brightness like a Christmas fairy light. But an element submerged in water has no problem at all with these variations.

SolBox has a built-in relay with a dry contact rated at 250V / 3A. This contact is sufficient to command another heat source.

Any source that requires only a low-current signal. If a mains electric element needs to be connected for domestic hot water production, an external power relay is required.

SolBox can command hot water production in two ways:

Scheduled time: A specific time is set and, if necessary, the backup source activates to heat the water to the desired temperature, after which the system returns to standby.

Time window: A time range is defined and SolBox can issue commands as many times as needed within that window.

This is where SolBox's major energy advantage lies. The system delivers as much energy as it can, and the remainder is automatically topped up by the backup energy source. The share produced by SolBox is always the maximum possible and is unaffected — no valve changes or manual adjustments are needed.

SolBox starts at first light, producing energy from as little as 10W up to maximum. 10W obviously does not heat the water, but the system can harvest the very last joule of energy.

A major SolBox advantage that no other solar energy source can match is that it adapts to changing irradiance within 10 seconds. Even if the clouds part for just a few minutes, SolBox produces the maximum possible energy in that window, filling the tank with as much free energy as it can.

SolBox's MPPT finds the optimum operating point twice per second. Its response to irradiance changes is essentially instantaneous and incomparably faster than conventional solar systems.

Depending on conditions — especially on partially cloudy days — SolBox can deliver up to 10% more energy. This is not a marketing claim; it is reality. SolBox follows no charging curves or grid-synchronisation profiles. It can literally vary output from maximum to minimum in seconds, because the energy goes into a resistive element rather than a conventional electrical load.

It can be powered from batteries in an off-grid system, but it has a constant 3W draw. In an off-grid system without a backup energy source for hot water, it is more efficient to set it to self-powered mode to avoid draining battery autonomy.

No, for two reasons:

Uneconomical: If 2 kWh of energy is surplus, simply increase the tank capacity. Energy stored in water is approximately 140 times cheaper per kWh than energy stored in batteries.

Technical limitation: SolBox does not produce charging-compatible current — only PWM optimised for use with a resistive element.

No. SolBox does not output 220V AC. It outputs a DC pulse. Any device connected that is not a simple resistive element will be destroyed immediately — either the device or SolBox.

No. SolBox has MPPT on the input, but on the output it follows no charging curve. It produces PWM suitable only for a resistive element. The most likely outcome is immediate destruction of either the battery or SolBox. It is not designed to have any energy source in any form on its output.

SolBox carries a 5-year warranty and its expected service life is 25 years.

SolBox is designed and manufactured 100% in Greece, by us. This means we are able to repair anything that may occur on its PCB.

No. SolBox has no connection whatsoever with the grid to which the home is connected, so it cannot affect or interact with net metering or net billing in any way.

With an end-user licence, the app displays the key measurements, device status, and control and status of the backup heating source. It does not overwhelm the end user with unnecessary technical information.

With an installer licence, the app displays additional measurements — voltage, current, output power, operating temperature, etc. — for the devices the end user has granted access to.

The technician can know exactly what the fault is and how the system is behaving. This means they can arrive on site fully prepared to resolve any problem immediately, knowing in advance what parts are needed and what actions are required.

One account can manage an unlimited number of devices. Each device can be given a custom name for easy identification.

Yes. The technician can assign their own name to each device, independently of the name given by the customer, so they can easily identify which device belongs to which customer.

The app runs on all platforms (iOS, Android, desktop) as it is a Single Page Application (SPA).

The app is available in 4 languages and can easily be translated into any language upon request. This is a fundamental prerequisite for export growth.

Yes. The user sees the total and daily history. The technician can view every day over a 30-day period, along with averages and production graphs.

The technician can tap "Identify" in the app and watch the LEDs of that specific device flash in a distinctive pattern.

Not yet, but they are planned.

Yes. SolBox checks 15 different functions and conditions every second to monitor its own operation.

If the end user has granted permission through the app, their chosen technician can receive automatic notifications and remotely monitor the SolBox status.

Of course. The primary account holder decides who to share the device with and what permissions each user has.

Yes. Its production graph mirrors daily solar irradiance — on a clear day it appears as an ideal bell curve. If a recurring power dip occurs at a specific time, that indicates shading.

Yes. Because it always produces at maximum output and shuts off once the water reaches the target temperature, it can use linear interpolation to calculate lost kWh per day. This allows the technician to easily determine whether additional panels are needed or whether a larger tank is required.

The company collects data from internet-connected devices on an internal European server, but the data is anonymous. We see the devices, consumption, production, production curves, etc., but we cannot see which device belongs to whom or to which account.

When someone calls or emails for support, they need to provide the device serial number. This allows us to identify the specific device.

To provide reliable service and useful guidance, we retain data for 30 days. This history provides whatever information we need to resolve any issue quickly and efficiently.

Of course. The hot water production function is fully autonomous and requires no connection.

SolBox is compatible with every type of WiFi network, without any restriction.

No, Ethernet connectivity is not available.

When the backup source is configured to guarantee hot water availability at specific times, an internet connection is required. If the connection is lost, the scheduling function stops after the device reboots.

SolBox temporarily retains the scheduling function until the device reboots.

For safety reasons, we want the user to be able to interact with the device while it is running an automatic programme. The system temporarily retains scheduling for cases where the internet drops briefly, but following a reboot it does not resume the schedule automatically.

The self-powered SolBox reboots every time the day ends and power production stops. The externally powered version is programmed to reboot every evening.

Yes. SolBox checks for updates every morning. A new update adds features or resolves a potential bug and is essential for safe operation. The process runs automatically.

Yes. Even when the schedule is inactive, if a water temperature below 5°C is detected, the system automatically commands the backup source until the water reaches 8°C. This provides additional antifreeze protection for the installation.

No. It cannot be guaranteed to save an installation under all circumstances, but it acts as a supplementary measure. Additional precautions must be taken according to each specific installation.

Yes, a certification programme exists. Certification is valuable and demonstrates that the installer knows the product. However, non-certified installers are not excluded — it is the customer's choice to select the installer they prefer.

A solar router is a device used in combination with a microinverter. The microinverter converts DC from the panels to AC and feeds it into the home network. The solar router detects whether there is a surplus of energy and redirects it to the water heater's element via a dimmer (triac).

The microinverter powers the home's needs first. Only what is left over goes to the water heater. If the washing machine, oven, or air conditioners are running, nothing is left over. With SolBox, the panels are exclusively dedicated to hot water and do not compete with any other load.

In winter, panels rarely produce enough even for basic household needs. There is no surplus, so the router sends nothing to the water heater. SolBox utilises every watt the panel produces, even if it is just 10W.

Plug-and-play microinverter systems in Europe are limited by regulation to 800W AC. A water heater element operates at 2,000–4,500W. Even if all the energy went to the water heater, 800W would be entirely insufficient. SolBox accepts up to 6 panels (~3,500W) with no regulatory restriction, because it is not connected to the grid.

Yes. A microinverter cannot operate without the grid, because it must synchronise with the 50Hz frequency. If the power goes out or there is no connection, it stops. SolBox self-powers from the panels and operates wherever there is sun.

A solar router requires a microinverter, a CT clamp on the distribution board, a wireless transmitter, a grid connection, and WiFi configuration between the components — meaning an electrician must intervene in the distribution board. With SolBox, all connections are made with plugs and connectors; no board intervention is required.

Yes. The solar router's triac chops the AC sine wave, creating harmonics that can affect sensitive equipment. SolBox operates exclusively on DC and has absolutely no effect on the home's electrical network.

A microinverter connects to the grid and in many European countries requires a declaration to the distribution network operator. SolBox has no relation to the grid — no documentation or declaration is required.