I’m considering expanding my solar system. Thailand is getting hotter, my EV needs more energy than my current solar system can provide. However my existing PEA export contract does not allow me to expand it. So an additional off-grid system seems to be my only option. While sizing the extra solar, inverter and home battery, I had a simple thought: Why buy a home battery when my EV already has a much larger one? That led me to look for V2H (Vehicle-to-Home) systems currently available in Thailand. So far, I found two real-world solutions. Sigenergy EVDC: A highly integrated approach. As part of the SigenStor ecosystem, it uses a 12.5/25 kW module to create a unified DC bus. It’s elegant, as it doesn't strictly require a separate home battery, but it’s a premium, "all-in" investment. https://www.sigenergy.com/en/products/dc-charger, https://www.facebook.com/groups/1233045914820186 Bitidea: The modular DIY alternative. These 10/20 kW bidirectional DC chargers connect directly to the PV input of an inverter. It’s a clever, relatively affordable "hack" that tricks the inverter into seeing the car as a solar string. https://www.facebook.com/share/v/1HtpbXfX8P/, https://youtu.be/9URhDCrIcpU?si=nHI55cUK_ZFsvkrK How does it work? Both systems are essentially bidirectional DC/DC converters. They do not convert the EV battery directly to household AC. Instead, they connect the EV to a high-voltage DC bus. After the CCS communication handshake, the charger can either charge or discharge the EV. Bitidea states support for ISO 15118-2. However, bidirectional V2X power transfer is associated with ISO 15118-20. Sigenergy does not clearly state which ISO 15118 version its EVDC module uses. The Bitidea charger is connected to the PV DC input of an inverter. The PV voltage must be sufficiently higher than the EV battery voltage for the EV to charge. When the PV voltage drops sufficiently below the EV battery voltage, the EV can discharge into the inverter. This makes the system relatively simple, but also somewhat dependent on the inverter and PV voltage. I measured my EV charging at 7 kW and found a working voltage of approximately 383 V at 80% SOC. After allowing for cable losses and a blocking diode, I would probably need an inverter with a PV operating voltage around 600 V, as the string voltage must be at least 440 Vmp. Unfortunately, there are only a few single-phase inverters like Goodwe in this voltage range. Owners of EVs operating around 340V are lucky. They can do with a 500V inverter. Sigenergy is a more integrated solution. The EVDC module connects to a high-voltage DC bus shared with the inverter and, if installed, a stationary battery. The system can therefore combine: solar + grid + stationary battery + EV battery. The major advantage is that Sigenergy does not require a home battery to use the EV as an energy source. How to use? The average car is parked for roughly 95% of the time. In my case, I could plug the EV into the DC charger and leave it connected for several days. During the day the EV is being charged and it dispenses the charge in the evening. With Bitidea, the main control is the EV's operating SOC range. I would let my EV cycle between 30-70%, thus having a buffer of 24 kwh. Sigenergy offers more advanced time-based control, allowing you to schedule when the EV charges or discharges. Can it work without a home battery? For on-grid and hybrid systems: yes. For off-grid systems, it depends more heavily on the solar capacity, inverter and load profile. With Bitidea, for example, the EV only starts discharging when the PV voltage drops sufficiently below the EV battery voltage. Sigenergy is primarily designed as part of an integrated hybrid system. Will it work with my EV? Sofar Bitidea has been tested with more EV models than Sigenergy. https://aseannow.com/topic/1257405-electric-vehicles-in-thailand/page/411/#findComment-20665594. Based on the available compatibility data, if an EV works with Bitidea only with limitations—or does not work at all—it is likely to face similar limitations with Sigenergy. But compatibility today does not guarantee compatibility tomorrow. Unlike V2L, EV manufacturers have not yet fully committed to supporting V2H. A future software update could potentially disable or restrict bidirectional charging. The upcoming V2H trials in Australia will be particularly interesting. It will be important to see how manufacturers such as BYD respond once V2H becomes a real market requirement. Battery and EV degradation For a typical home, V2H discharge rates are relatively low. In my case, the discharge rate would be comparable to driving the car at around 50 km/h, The additional cycle degradation should be limited. Temperature-related degradation should also be relatively small. These have all been backed up by several scientific studies. V2L is potentially harder on the vehicle electronics because it uses the EV's internal inverter and onboard charging hardware. https://www.sciencedirect.com/science/article/abs/pii/S2590116824000067 https://www.sciencedirect.com/science/article/pii/S0378775325023183 https://arxiv.org/abs/2605.03844 Is it worth the investment? It depends. If you do not have solar yet, a relatively affordable solution could be an on-grid inverter combined with Bitidea and zero export. A 10 kW Bitidea charger costs around 50k baht and has been tested with inverters such as Huawei and Deye. The higher your evening load is, the lower your ROI. If you already have an on grid system, you may consider adding a Bitidea charger. A complete Sigenergy system, however, can easily exceed 300-400k baht when a stationary battery is included. For my off-grid application, I could build: 10 kW inverter + 15 kWh IP6x home battery: around 260k baht same inverter, a smaller 5 kWh home battery + 10 kW V2H Bitidea: around 280k baht The second option gives me access to the much larger EV battery, but the smaller battery would need to be installed indoors because it does not have the same IP6x protection. Since I still have a grid connection, I do not necessarily need the much larger V2H EV buffer during rainy weather. Without a grid connection, however, the extra 20k baht could make V2H much more attractive. Conclusion For now, waiting may be the smartest option. The technology is already here, but the biggest uncertainty is the EV manufacturer. Will manufacturers officially cover V2H under warranty, and if so, how will they limit these e.g. certified chargers and account for cycle-based degradation due to V2H? Australia may provide some of the answers through its V2H trials and where there is a push from the biggest Sigenergy installed base. China is also pushing V2G, as most of the people live in apartments. Fleet owners and local grid operators are doing trials in major cities.
