Home batteries used to be a niche market for tech enthusiasts and those needing emergency power. But as battery-backed hybrid solar systems proliferate, the solar industry is learning that even the best plans can go awry.
Most hybrid solar power systems have limited capacity, so you invariably choose only the most important home circuits for backup. If the hybrid inverter fails, it can prevent grid electricity getting to those essential circuits. They’ll lose power. And you don’t want to be calling an electrician to come and rewire the switchboard at the drop of a hat.
If your essential circuits stop working, the lights go out and the fridge goes warm, you need a simple switch to restore ordinary grid power until the system can be diagnosed a repaired.
The grid is legislated to be 99.998% reliable, (you’re entitled to get upset if you lose power for more than 10.5 seconds per year?). Many Australians go years without electricity interruption, especially in newer suburbs where the infrastructure is buried, safe from storms and kamikaze car drivers.
So for many customers the idea of battery backup is much more important than the actual capability. It becomes a somewhat emotional decision to buy a security blanket economically justified as stored energy saving a few dollars every night. Things come unstuck if that costly insurance policy fails to kick in, or even worse, ends up costing even more money and causing further inconvenience or losses.
What Are The Risks?
I’ve seen someone inadvertently unplug a deep freezer full of fish. A fortnight later, that wasn’t pretty.
From a solar installer’s perspective, if there’s no bypass switch and something goes wrong in the inverter, the reputational damage to your business can be dreadful, as you’re the crowd who sold this lemon that doesn’t work. It creates emergency call-out work that wrecks operational calendars and overtime budgets.
From a customer perspective, you’re entitled to expect a reliable product. If you have to call and demand out-of-hours service to restore power to your most important electrical essentials, it can ruin the relationship you have with the people who are there to provide warranty and technical support.
How Much Does A Bypass Switch Cost?
Included on install day, a bypass switch for a single-phase house might be an extra $100. Even on a three-phase install, the hardware and labour won’t exceed an electrician’s basic call-out fee. It’s one of those things that hopefully you’ll never need, but when you do, it pays for itself immediately.
If You’re Struggling For Switchboard Space
If your switchboard is jam-packed, especially a 3-phase one, you may need a complete overhaul or an additional load centre added inside or next to your main switchboard – especially if you’re backing up more than a couple of circuits. As we’ve written previously, adding solar panels can be an excellent time to upgrade your switchboard and add hot water control, because it’s often a good deal more expensive to do after the fact.
Labels, Labels, Labels.
Meeting the letter of the law means you should have a completely separate switchboard for loads running off an alternate supply. Pragmatically, this often doesn’t happen. Most places simply have a few labels in the meter box.
In any case, you should have comprehensive and easy-to-read labels so any householder, plumber or ordinary domestic electrician (we call them roof possums) can understand that a home battery is present, and how to isolate and bypass it.
When workplace safety laws dictate anyone entering the roof space must first turn the power off, those working on the house must be aware the hot water may turn on automatically or that switching the grid supply off doesn’t mean the whole house is dead.
Of Course, There Are Exceptions
Fanbois unite! If you have a Fronius Gen24, or some other parallel connected hybrid inverter (like SolarEdge), then there’s no need for a bypass switch.
Systems using a contactor or a “backup box” don’t have the essential circuits passing through the inverter, so if anything goes awry with the hybrid, the backup supply isn’t affected.
Fat Supply Cables Are Also Essential
Many experienced solar electricians have been caught out by the fact that hybrid inverters can impose really big loads on the grid connection. After a decade of connecting 5kW solar inverters on 6mm² cable with a 32amp breaker, they haven’t realised that when you have backup loads running and force charge a battery at the same time, there could be a sustained 55amps or more drawn over the inverter circuit.
So, when your average house supply will deliver 63amp (~14kW) via a 16mm² cable, you need exactly the same supply to the nominally rated 5kW hybrid inverter. In fact, if the hybrid goes in your garage 35 metres away, you’ll need an even bigger cable to fight voltage drop.
Insist On Reliability
For series-connected hybrid inverters, the essential circuits are powered through the inverter. If it falls over or needs servicing, you need a bypass switch to keep everything online. For less than $100, both the solar installer and the customer will sleep easier. It’s a bargain.