Series or Parallel Battery Hybrid Systems, What's the difference?

The grid is your strong, silent, primary supply, but when you add new hybrid system, there are two basic layouts.  

Parallel connected - Where the inverter provides additional energy, alongside the grid, in parallel.

Series Connected - Where the grid is wired through the inverter, in series.

Examples of parallel machines are any standard grid connect solar inverter, or battery hybrid from Fronius, Franklin WH, Tesla Powerwall, Sigenergy & Solar Edge or even Sungrow*

• The inverter doesn't limit the mains supply, but can replace it if the mains fails.
• It doesn't matter if the inverter fails, grid supply is unaffected, a bypass switch isn't needed[1. For those who really want second third and fourth layers of redundancy, a bypass switch or generator inlet socket can still be installed.]
• The inverter can be wired in almost anywhere, so it's very flexible for properties with multiple buildings
• Requires a "gateway" to disconnect the grid during an outage, which must be hard wired back to the inverter
• This metering and control wiring is extra low voltage, so they're cheap cables even if trench digging isn't.

Series connected machines are the bulk of cheap and cheerful battery hybrid inverters, starting with Sungrow** GoodWe, FoxESS, SoFar, AlphaESS, Neovolt etc

• Any circuits connected to the backup port are limited by the rated capacity
• Whether the grid is available or not, the inverter is a choke point
• If the inverter fails, so does anything connected to the backup port
• You must have a bypass switch to reconnect "essential" circuits to the mains in the event of an inverter problem
• Generally, the inverter must be very near the utility meter box
• Wiring backup circuits through the inverter makes it impractical or impossible to put the system on an outbuilding
• Gateway is incorporated inside the inverter, but an external consumption meter may be required

Be Aware

Some solar industry experts gloss over critical detail while drawing up the quote, either because they’re poorly trained or just aren’t good at explaining the minutiae. Sometimes it’s just because they only have one product to offer and don’t want to confuse matters.

Conversely, problems arise when the customer has a rough handle on the concepts but doesn’t care for the fine print. We all know a little bit of knowledge can be very dangerous. If the system buyer hasn’t detailed to their significant other that there might be limitations, it can get pretty awkward when I'm the electrician explaining partial backup will NOT run the whole house on installation day.

Whether it’s your solar, air conditioning or water pump, whatever you want working during a power outage must be written on the quote.

Signing a generic contract viewed through rose tinted glasses is a recipe for disappointment.


* Sungrow are principally a series connected inverter, however they now offer a mini gateway called an "energy bridge" which allows parallel connection, remote from the main switchboard.

** So yes, Sungrow have a foot in both Series AND parallel camps