How does a solar inverter work?


I’ve heard about three types of DC to AC converters used in the solar power business.

Microinverters, String inverters, Grid-Scale Inverters

Please how they work.

In: Technology

Solar panels provide DC current. So there is one positive wire and one negative wire and the current flows through it only one direction. However the power grid uses AC current where the current changes direction back and forth 50-60 times a second. The main component in an inverter is a row of switches which is used to invert the connections according to the current direction in the grid. It is of course more complicated then that with components to transform the voltages correctly and make sure to always collect all the current from the solar panels and that the output is a nice sine curve and so forth. This is also how some inverters are better then other and how some need a connection to the grid and some can work off-grid.

A control circuit generates a stable 60Hz signal. That signal is used to control power transistors that switch the DC from the batteries/panels and make an AC signal. The AC is then filtered, and used to power devices designed for wall power. It’s not synchronized with the local power grid, most of the time, requiring switchgear to disconnect your house from the grid to connect it to the solar system. Some solar inverters are grid synced, when the grid power is available, though regaining sync when the grid comes back sometimes requires a switching glitch.

All the inverters you listed are fundamentally the same types of devices with the exception of scale (power rating).

Inverters can be pure sine wave (best) or modified sine wave (meh).

Inverters can be grid-tied or grid-isolated. Grid-tied inverters require a mechanism so the power they produce is in synchronization with the grid power or havoc will result. Grid isolated inverters have no need for synchronization so they have some internal frequency source that produces either 50/60 Hz AC. Those frequency sources are usually not as accurate as the grid frequency over the long run.

Grid-scale inverters are massive inverters used to provide transient power to grids in case of need. They are usually limited in capacity to an hour or so, usually plenty of time to get older, steam-based generators online and synched. Grid inverters can be used to convert between different grids, for example between a 50 Hz grid and a 60 Hz grid though that function is usually performed by massive rotary converters.