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.
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I am rather new to this fancy solar power magic.
My system produces power when the sun shines and does nothing when the sun doesn’t shine. I expect most do.
My question is this: how does adding batteries to the system make it work at night as all excess power is fed into the grid ?
Would I need a fancy inverter that knows what I am doing. Eg my system is 4.5kW. Does it knows I am using 3kWh and if I am producing 3.5 kWh will feed the 0.5 kWh to the batteries ?
Then if the batteries are full does it feed the rest to the grid or burn it off?
If run in winter an I charge the batteries off peak to use on peak ?
Does this happen automatically? However I feel I would want control over it.
Hi Neil, I’m an electronics technician not a solar installer. It sounds like you have a grid-connect inverter which effectively uses the grid as your batteries, so when the sun isn’t shining the inverter grabs the power you need from the grid. During the daytime, if your solar panels are producing less power than the appliances you are using, the inverter also grabs the shortfall from the grid.
You are correct that the average grid-connect inverter is not intelligent enough to manage batteries. I personally don’t understand how Tesla is going to make their powerwall compatible with certain new generation grid-connect (like) inverters. If your grid-connect inverter isn’t compatible with the Powerwall or anyone elses brand, then yes you will need a new inverter/charger designed to know when to charge batteries and when to use your batteries to save you paying peak electricity rates. This is the chief problem, the inverter/charger is the brains of your solar system and that intelligence to manage multiple power sources – solar panels, batteries, grid, generator – costs extra money. Like yourself, I too would like to see more attention on this site on inverters and this article is a fantastic one.
I thank you very much for trying to help me understand.
Yes I do have a grid connected solar setup.
I have a few things on my wish list.
I would like to use all the power I make and if I can’t then I am happy to let someone have it that needs it.
I see 2 ways I can do this in the future.
1: be on the grid as I am and be on a 1 for 1 deal effectively using the grid as a battery so to speak.
2: have a much smarter setup than what I have now with batteries to store power I have made for when I need it.
In the end I don’t really need to know how it does this and don’t really think I can understand how to make this happen but someone will know about the time it is affordable to do it and I expect they will knock on my door one day and offer it to me.
I love the Internet as I can learn as I go.
Thanks again
unfortunately its unlikely solar families will get a one for one as solar families sell for rates more comparable to the cost of generation and then buy back for the regular retail rate (after everyone takes their cut to get it there). what this means to me is accepting we will never get a comparable import and export rate, and instead getting our solar installer to gear our solar system for self-consumption, meaning we consume the energy we generate. Presently your best strategy is use as much power during the daytime, invest in low wattage appliances when every one breaks (so your solar panels have more chance of keeping up with the power your appliances use at any time, and probably one day get a few batteries, so you can store all the power your solar panels generate until you can get to using it.
A high quality grid interactive inverter with a decent amount of storage (10kWhr) that can supply power in a blackout would set you back around $15K installed. Perhaps not compelling if you just look at the payback period but if you are on the fringe of grid where every time there is a storm you loose power then that is a different matter.
Great article. The following islanding inverters cost:
Selectronic SP Pro 3kW continuous output when operating in island mode (with 15kW grid transfer ability when the grid is working) is $4.6k on eBay. Selectronic are founded in 1964 (making transformers and inductors), 1981 they begin making power conversion products for the renewable energy sector, 1994 they make their first sine wave inverter, Australian company, highly engineered, perhaps an industry leader. I think its a 5 year warrantee and 7 years if installed by a Selectronic qualified installer.
Victron MultiPlus 2.5kW continuous output when operating in island mode (50A model has over 11kW grid transfer ability when the grid is working) was $2.2k when I bought one a few months ago from http://www.springers.com.au. This inverter/charger is classified as a remote inverter with charger capability. In the coming months the inverter will meet new Australian requirements for grid feed in ability. Victron Energy was founded in 1975, is located on the coast of the Netherlands, has been exclusively producing power conversion products since its beginning, in the most varied and extreme conditions, including developing countries, automotive, marine, off-grid and backup applications. On one hand engine rooms of boats are often extremely hot and on the other hand the inverter/charger is used in the base camp of Mt Everest. In Australia we use the inverter/charger in Australian Navy and Australian Customs Patrol boats. They are also used in the signalling equipment on Rio Tinto’s iron ore train lines in Karratha. So that’s an inverter with one of the longest and toughest track records in the world. 5 year warranty.
The prime reason I would never recommend an anti-islanding inverter, is it makes solar families an ineffective lobby group. If we wish to be taken seriously, we need an inverter that can stand on its own feet and an inverter that has real choices around if and when we consume from the grid. People who buy grid-connect systems and anti-islanding inverters, make us all weaker in our collective plight for fair relations with the grid.
I’d still like to run my fridge and make the neighbours jealous during blackout … so islanding here we come. A proud decision based not on good economic sense, but ‘coz we want to.
Being blackout proof is an advantage. Any other strategy will therefore be a short term cost benefit, until fully functional solar systems evolve.