Does your hybrid solar system really need to be blackout proof?

The holy grail of affordable on-grid energy storage has finally arrived! Well, it’s almost arrived. Actually, it might be a couple of years before it really arrives and most Australians can get their hands on low cost energy storage systems such as the Tesla Powerwall, but they are coming and they will eventually be here. Adding batteries to your home means that you will no longer be forced to sell electricity for 6-8c and buy it back, at night for 30c. Hurrah!
But when the holy grail does arrive you will have a choice, so take care that you do not choose poorly.

While a bad choice is unlikely to cause you to crumble into dust like the Nazi villain at the end of the second worst Indiana Jones movie*, if you what you decide is wrong for your particular circumstances you may live to regret it. Actually, I can almost guarantee that you will live to regret it, as it is really not a life and death decision. Unless you go about it in an astoundingly bad way, such as cutting power cables with an axe and then licking them to see if they’re live, I can pretty much guarantee you will still be around to either rue or feel chuffed about your choice.
The decision to which I am referring is this: when you get your home energy storage system, are you going to choose to save money by using a common-or-garden anti-islanding inverterthat only works when the grid is working (so won’t give you a single erg of energy to use during a blackout even if your batteries are charged)? Or are you going to pay extra for a specialist islanding inverter? These more expensive inverters will give you the ability to draw upon your battery power when the grid is down and laugh at the sound of your neighbours swearing as they bang their shins in the dark.

Anti-Islanding

If you are lucky enough to own a grid-connected rooftop solar system, then there is an excellent chance you’re already aware that if the grid goes down you can’t get electricity from your solar panels . If you are not aware of this, then I’m sorry to have to break the bad news to you. Them solar panels, they ain’t gonna work in a blackout.
The reason we are usually given for why solar inverters need to prevent islands forming is safety.
A line worker could come along and touch a cable they think is dead and go, “GHHHARRRRRRHHHHHHH!!!” as they do the crispy meat resistor dance.
And this is not a good thing. It never results in super powers. Some electrical accidents have resulted in people becoming bionic, but it’s not worth it. It appears that Steve Austin lied to us.
So anti-islanding inverters can potentially save lives.  And there are other reasons why it is useful, so anti-islanding is going to stay compulsory. No exceptions, not even if you bake the grid operators a chocolate koala.

Islanding Inverters

 
If you want to be able to use electricity from your batteries and/or solar panels during a grid outage, you are going to need an islanding inverter, which is a completely different kettle of fish. Or preferably electronic components. If it’s full of fish you should probably ask for your money back.
An islanding inverter, or off-grid inverter, will isolate the house and send no electricity into the grid during a power failure. It will let the house run off battery storage and/or solar panels. A generator can also be made part of the system. When done right, it can allow a household to completely ignore a power failure. Unfortunately getting a house ‘blackout proof’ like this costs a lot of money. Even a system that is just made to run lights, laptops, and refrigeration will cost a lot more than a simple anti-islanding inverter set up.
And if you are not keen on installing a dirty diesel a generator but still want self sufficiency when the grid goes down then things really start to get expensive. To completely ignore power failures an energy storage system will always need to have enough energy to get through the night. There must be enough solar on the roof to charge the batteries during the day even if it is overcast, and the batteries need to put out enough power to run household appliances normally. This can quickly add up to tens of thousands of dollars,  a huge amount of money to pay just to waltz through power failures. Sure, it becomes a lot cheaper if you include a generator, but if you have a generator why do you need an islanding inverter? Having to plug your appliances into a generator when the grid is down is less convenient, but foregoing a vacation to afford an islanding inverter isn’t exactly convenient either.

The Middle Way

There is a third choice for inverters that lies between anti-islanding and islanding. I presume this would make it an archipelagoing inverter. This is one that, when enough solar electricity is being produced, lets you plug appliances into a power point on the inverter and use it like a silent, non-polluting generator. However, the model I saw with this feature cost so much it was up in the islanding inverter price range. But they may not always carry such a hefty premium and so are an option that could be considered. They will of course utterly fail to produce electricity at night unless your neighbour has excessively bright outside lights.

Dollars And Cents. Or Probably Just Dollars.

The UBS investment bank thinks $1,025 is sufficient to pay for an anti-islanding inverter that is compatible with the 7 kilowatt-hour Tesla Powerwall (or perhaps you can use your existing solar inverter for free ). And an Australian expert says that, as a wild ass guess, a suitable islanding inverter might cost $4,000. While I have no idea what feral donkeys have to do with his estimate, that sounds about right to me. Of course, it is possible to go cheaper than this. For example, last night in one of the dark, clammy, recesses of the internet; I discovered I could mail order an off-grid inverter for under $1,000. I assume it was made in international waters, as no country of manufacture was given. The company name looked like the output of a random password generator. And its warranty was for a single year. Sometimes choosing the cheapest product makes economic sense. This is not one of those times. I recommend it about as highly as I do licking a male platypus’s venom spur.
I am confident that islanding inverters will come down in price. This includes ones that are compatible with the Powerwall, as Tesla’s strategy is not to make money by charging licensing fees, but to make its patents available for free and allow competition bring down inverter costs and so enable Tesla to sell more energy storage. By the time Powerwalls or similar products are available in Australia, without significant delay I hope that suitable islanding inverters will be available for $2,500 or less. But hope is not a game plan. It is instead an emotional state characterised by optimism about either current or future events.

My Recommendation

Grid electricity works in Australia 99.9% of the time. That’s an average of about one day of power failure every three years. So I suggest that, unless islanding inverters really come down in price, the average Australian installing on-grid energy storage will better off with a lower cost anti-islanding inverter than paying extra for an islanding inverter and the ability to use energy storage independently of what’s going on with the grid. It may seem weird, or even just plain stupid, that during a blackout energy you can’t use storage sitting in your own home, and some old-school off-grid solar installers seem to think it is heresy. But it does save money and it should make better financial sense for most people to simply buy a small generator.
And if you don’t own a generator, that’s a good indicator that you don’t find power failures annoying enough to make the cost of an islanding inverter worthwhile. I would say that it is like Catch-22 because if an islanding inverter is worth it you’ll already have a generator and so won’t need an islanding inverter.
* If you do crumble into dust, I accept no responsibility.
This article was first published at Solar Quotes. Reproduced with permission.