A solar inverter cannot see what happens at the household's grid connection point. The smart meter fills that gap: it measures power and energy at the main supply point and feeds the data to the inverter.
Types
- DDSU666: single-phase meter for smaller residential systems and single-phase Huawei and similar inverters.
- DTSU666: three-phase meter, the right choice for most Hungarian family homes. Available in direct or CT (current transformer) versions, the latter for higher currents.
The CT version is common in larger setups such as commercial systems, where current exceeds the direct meter's limit. Other brands (Fronius Smart Meter, Deye, SOFAR, Solis) use their own compatible meters; always choose the one approved by the inverter manufacturer.
What can the meter do?
Export limitation
If the utility's connection conditions allow, for example, 0 kW or less feed-in than the system capacity, the inverter reduces production based on the meter data and stays under the permitted value toward the grid.
Zero export
The inverter produces only as much as the house is using at that moment. This is useful when the grid will not accept more feed-in, or when exported energy has little value. Keep in mind that with zero export some production is lost, so pairing it with storage makes sense.
Hybrid system control
In a hybrid system the meter tells the inverter when to charge the battery (surplus) and when to discharge it (deficit). Without it the battery cannot follow the house's consumption.
Accurate monitoring
Without a meter the app only shows generation. With it you can see consumption, the self-consumption ratio, and energy imported and exported.
Where is it installed?
At the grid connection point, behind the utility meter (on the house side), where it measures the current of all loads. If it is placed in the wrong spot, for instance after the solar branch, it gives wrong data. It needs an RS485 communication cable to the inverter, and with CT versions the direction of the clamp-on transformers matters.
Common mistakes
- Reversed CT direction: the system reads consumption as generation.
- Wrong phase order: inaccurate power data.
- Several consumption points but a meter on only one.
- Export limit setting forgotten at commissioning.
When can you do without it?
With full feed-in, unrestricted, simple string systems, where there is no hybrid and no grid limit. Today, though, most systems need one: because of utility conditions, batteries and monitoring. They are cheap and highly useful.
SolarBay fits the correct meter to every hybrid and export-limited system and checks direction and phase at commissioning.
Setup and verification
At commissioning, meter communication and measurement direction must be verified. A simple test: switch on a large load, such as a kettle, and check in the app that consumption rises and grid import changes in the expected direction. If the sign is opposite, the meter or current transformer is wired backwards. Accurate meter data is critical because battery charging, the export limit and self-consumption statistics all rely on it. A wrongly wired meter can go unnoticed for months, so the handover report should record this check.
