From pv magazine France
DIY enthusiasts equipped with a photovoltaic system can now build their own management system to optimize their self-consumption. French electronics and telecommunications engineer André Buhart, now retired, designed a “solar router” to direct excess solar power to electrical devices. The plans and software for building the system are available for free online, as open source.
Dubbed F1ATB, the system is built from a shopping list, available on the designer's website, which details all the necessary components according to the desired system configuration. The manufacturing steps are explained step by step, and safety rules are clearly outlined. “DIYers will have no problem,” André Buhart told pv magazine France. “You only need to do proper electrical wiring and assembly, without being an expert electrician.”
Modular structure
The router connects to the electricity meter to be split into two, or even three, separate modules according to the homeowners' needs. This architecture allows the measurement part to be installed close to the meter, while the control modules can be placed next to the equipment to be powered, regardless of their location or distance from the meter, thanks to Wi-Fi communication.
“This modular structure is very successful,” said Buhart, noting that he regularly interacts with users online. “A large community has grown around the system over the years, as is often the case with open-source projects.”
According to the engineer, the F1ATB system now has some 4,400 members in a Facebook group, 20,000 subscribers on YouTube, and 1,700 participants on the site's forum, which lists more than 10,000 messages related to installation and usage questions, and on which André Buhart contributes.
No authorization is required in France to install the system, which is built from standard parts that can be ordered online. For a simple assembly accessible to non-technical users, the kit consists of a Shelly module, an ESP32 microcontroller mounted on a card, a heatsink, and the appropriate cables, for a total cost of around €100 ($117.7). The most experienced users can reduce the bill to around €30.
Once the measurement is complete, the data is transmitted to an ESP32 microcontroller, an inexpensive component costing around €10, which is often used in home automation. Buhart has installed a web server on this microcontroller to record historical data.
The equipment is controlled by small electrical components such as triacs or solid-state relays (SSRs), used as very fast switches. The choice of component depends directly on the power of the device to be controlled – generally between 2 and 3 kW for a water heater, but there is no specific upper limit. “It's essential to select the right amperage and to oversize it to integrate a good cooler,” explained Buhart. For example, for a 3 kW water heater, it's recommended to use a 60-amp SSR and adapt the power accordingly. All of these recommendations, including component selection, assembly precautions, and concrete examples, are clearly detailed on the project website.
For control, Buhart preferred to use the “multi-sine” and “sine train” approaches rather than traditional sinusoidal slicing, which tends to create interference on the network. The former involves sending only a limited number of complete sinusoids per second, for example one in five to transmit 20% power), and the latter relies on sending continuous sequences over a given period. The details are also described and available online.
Energy management
To access the data, there is no smartphone app, just a web interface accessible from a phone or computer. Key information is available in real time, including injected power, consumption, and history, among other things.
The French engineer also developed a device for live local display based on a small, 3D-printable box in the shape of a small house, which displays available power in real time. A color code allows for quick reading: red when consumption exceeds production, green when solar production is in excess.
The router's management software can be downloaded directly from the F1ATB website, with the user connecting the router to their computer via a USB port and installing the program.
How did the idea of developing this DIY router come about? “After installing solar panels at home, I looked at the technical constraints, and, like others before me, the question quickly arose of how to improve my self-consumption,” said Buhart. “The water heater is, in itself, a super battery. The router allows it to be used during the day and not just during off-peak hours at night.” User requests and the engineer's needs then dictated the device's development
Going forward, Buhart said he is working on new developments and configurations for the solar router. If the device were to enter industrial production, a certification process would be required. Certification is not planned at the moment.
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I did a similar build for my off grid system, monitoring the 230V frequency and using a SSR to control my hotwater system, it’s built around an arduino and has been reliably working for almost 9 years now, the frequency is monitored via a transformer, bridge rectifier and optocoupler, giving a 100hz output at normal mains frequency of 50hz , as the frequency rises past 100.4 hz/50.2hz, the element is turned on for 30 seconds, if the frequency continues to rise the element remains on for several minutes or until the frequency drops, the cycle continues until the frequency drops below 100hz/50hz.
Is this not a regular solar hot water cylinder diverted?
In my opinion, this is a rather outdated approach. Nowadays, logic is left to software.
So, on one side, you would only have a sensor part that would report measurements to, for example, Home Assistant. On the other side, you would have actuators that receive commands from Home Assistant and turn on consumers.
Then you program the operating logic in Home Assistant.