Energy efficiency is one of the most important factors in a home battery system. Some energy is lost as heat whenever electricity is converted from one form to another through an inverter. We’ll get into that shortly.
You can install each energy system as either AC-coupled or DC-coupled. If you don’t want to get too technical, don’t worry. We’ll simplify it a bit for you.
Understanding AC and DC Coupling
DC coupling means solar panels send electricity directly to the battery in DC form before being converted into AC for home use. Both systems, when DC-coupled, have direct inputs from the solar system on the roof, so energy loss is minimised. They each have around 98% efficiency when installed this way.
Once energy is needed from the battery or directly from the panels on the roof, the energy is converted back to AC electricity. It’s a minimal conversion loss.
AC coupling means solar panels send DC electricity to the hybrid inverter. The hybrid inverter converts the DC power to AC power, which is what the home uses. The power is sent to the home. Leftover power goes to the battery.
However, batteries only store energy in DC form. It’s how batteries work; there’s a positive end, a negative end, and a direct current between them. So, the AC electricity must be converted again into DC power for storage.
And if the home needs power again, that electricity once again needs to be converted back to AC electricity for the home to use.
Every time electricity changes from DC to AC, energy is lost, reducing efficiency.
For batteries in their class, AC-coupled round-trip efficiency is usually around 90%.
Powerwall 3 Efficiency
- Powerwall 3 uses DC coupling when installed with a new solar system, which keeps efficiency high. The direct-from solar efficiency is 97.5%.
SigenStor Efficiency
- In a DC-coupled setup, it has an estimated 98% round-trip efficiency, slightly higher than Powerwall 3.
While the efficiencies are similar, SigenStor is slightly more efficient and the winner in this comparison.