Home / Intelligent excess function - 1 kW solar heating element

Surplus function

What is the advantage?:
 The surplus function enables the easy use of excess photovoltaic energy for electricity generation (grid feed-in) or hot water generation (cascade circuit).

Why is that useful?
Especially during the summer months, it often happens that more photovoltaic energy is available than can be converted into hot water. When the maximum water temperature is reached, the solar heating element automatically stops the heating process. Therefore, no more photovoltaic energy can be converted into hot water.

800 W mains power supply

Cascade circuit

Grid feed-in

First, your hot water is heated with solar power, and as soon as the hot water storage tank is fully heated, excess energy is automatically fed into your own home network via the output of the solar heating element using a micro-PV inverter.

Easy assembly
The micro-PV inverter is connected directly to the output of the solar heating element using a standard solar extension cable (see image below). To feed up to 800 W of excess power into the grid, the two inputs (2 x 400 W) of the TSUN micro-PV inverter are connected in parallel using a parallel connector (Y-connector) .

800 W mains power supply
The micro-inverter converts excess direct current into standard household alternating current (230 V AC). This current can be used directly in your home's electrical system.
fothermo cooperates with TSUN, a micro-PV inverter.

Compatibility note:
Only products approved by fothermo may be connected to the output of the solar heating element. A list can be found in the whitelist at the bottom of this page in the download area. fothermo has received permission from TSUN to connect the two solar module inputs in parallel and to connect more than two photovoltaic modules to the micro-PV inverters.

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Cascade circuit

Energy-efficient stratification of hot water:
Two solar heating elements can be connected in series. This enables energy-efficient stratification of the hot water in the storage tank.

Automatic switching:
As soon as the upper heating element reaches the maximum temperature, the system switches to the second heating element, which is screwed into the storage tank further down.

Assembly :
A simple solar extension cable (min. 6mm²) is used to connect the two solar heating elements.

Frequently Asked Questions (FAQ)

No, parallel operation is unfortunately not possible.

Example:
When 2,000 watts of photovoltaic power are applied to the heating element, the hot water is initially heated using 1,000 watts. The heating process continues until the set water temperature (5 °C to a maximum of 85 °C) is reached. Only then does the system automatically switch to the inverter or a second solar heating element.

No switchover occurs. The heating process ends when the set target water temperature (5 °C to max. 85 °C, adjustable in 5 °C increments) is reached.

It's very simple! The switchover always happens automatically as soon as the maximum water temperature is reached.

You don't need to adjust anything.

We recommend a cable cross-section of 6 mm².

Both for the solar extension cable from the photovoltaic module to the heating element and at the OUTPUT of the solar heating element.

fothermo only permits the connection of products approved for use with the solar heating element. A complete and continuously updated list can be found in the download area under "Whitelist".

fothermo System AG assumes no liability for the use of other micro-PV inverters and other solar products that are not listed in the whitelist.

If grid feed-in is done via a micro-PV inverter, then it must be registered like a balcony power plant.

The TSUN brand inverter, approved for use with the fothermo solar heating element, limits the maximum feed-in power to 800 watts. As soon as the photovoltaic modules generate more than 800 watts of power, the inverter automatically limits the input current.

Therefore, no more than 800 W will flow from the OUTPUT of the solar heating element.

Download

A list of recommended compatible solar devices/inverters can be downloaded here.