{"id":7434,"date":"2016-08-25T16:30:11","date_gmt":"2016-08-25T07:00:11","guid":{"rendered":"http:\/\/www.solarquotes.com.au\/blog\/?p=7434"},"modified":"2017-04-18T17:25:18","modified_gmt":"2017-04-18T06:55:18","slug":"off-grid-with-z-cell","status":"publish","type":"post","link":"https:\/\/www.solarquotes.com.au\/blog\/off-grid-with-z-cell\/","title":{"rendered":"Going off grid with Redflow’s ZCell? Here’s how to handle the ‘maintenance purge’."},"content":{"rendered":"
\"simon

Simon Hackett with an early customer’s double Zcell off grid system.<\/p><\/div>\n

Yesterday, Aussie solar veteran Tony Smith left an interesting question at the bottom of our ZCell battery review<\/a>.\u00a0Tony asked, for an off grid application,\u00a0how to handle the fact that the ZCell battery needs to shut down so it can\u00a0perform maintenance mode every week or so:<\/p>\n

Hopefully not a too stupid question \u2026.<\/em><\/p>\n

 <\/p>\n

Ok so we use it in an off grid application. So far so good.<\/em><\/p>\n

 <\/p>\n

To avoid assumptions, off grid inverters need to be connected to the battery bank to stay alive. Disconnect the battery bank, they instantly turn into a boat anchor.<\/em><\/p>\n

 <\/p>\n

Our Redflow Wunderkind happily does its things for 2 weeks and there is great rejoicing. The owner issues a smug warning to his off grid neighbours laughing derisively at their prehistoric lead acid systems.<\/em><\/p>\n

 <\/p>\n

But then! Our redflow decides it\u2019s time for its fortnightly shut down and purge. So it shuts down\u2026.<\/em><\/p>\n

 <\/p>\n

Can you see where this is going yet?<\/em><\/p>\n

 <\/p>\n

Our smug owner now has zero power for 2 hours. The off grid inverter died at the same time the redflow started its purge cycle. Once it\u2019s dead, it can\u2019t start a generator and as far as I can tell, nothing in the redflow did either.<\/em><\/p>\n

 <\/p>\n

Now our redflow has zero power available to it because its killed the off grid inverter and the generator auto start function in one fell swoop.<\/em><\/p>\n

 <\/p>\n

So where does our redflow get the power from to do its purge cycle? Remember it\u2019s killed all potential sources of power\u2026..<\/em><\/p>\n

 <\/p>\n

As far as I can see it can\u2019t do its purge because there is no longer any power anywhere.<\/em><\/p>\n

 <\/p>\n

Maybe I\u2019m missing something?<\/em><\/p><\/blockquote>\n

It’s a good question, the maintenance mode is unique to Redflow’s Zinc Bromide technology, and is something installers have not had to think about before.<\/p>\n

So I thought a comprehensive answer would be useful and I popped the question to Redflow Executive Chairman (and Chief Geek), Simon Hackett<\/a>.<\/p>\n

Here’s Simon’s\u00a0very comprehensive reply (headings added):<\/p>\n

ZCells, Maintenance Cycles and ‘Black Starts’<\/h2>\n

The maintenance cycle timing depends on activity level. If a battery is cycling continuously 24×7 the maint happens every 4 days. If its being lightly used and mostly idle, yes, it can take as long as two weeks. The battery management system handles this automatically (and minimises it automatically).<\/p>\n

At face value you\u2019re right – but only if you don\u2019t design in one of multiple ways to resolve that. And there are multiple ways to resolve that.<\/p>\n

Most offgrid systems include a generator – because there is always one more run of bad weather days (i.e. because statistically the battery will always run out sometime, unless you had an outrageous number of them). This can also happen if you under-size the solar array or over-size the loads.<\/p>\n

So there always needs to be a way to black-start an off-grid system anyway – you\u2019re just describing another circumstance where a black start is needed.<\/p>\n

The Redflow ZBM\u2019s [AKA ZCells] aren\u2019t fussed by being allowed to run flat (or staying that way for ages) – unlike other batteries – so this doesn\u2019t damage them. Perfect for an offgrid system on a \u2018weekender\u2019 where you might only be there sometimes, and where having the batteries run flat is thus not necessarily a problem when you\u2019re away. And if a battery does go dead flat with no external power source, no harm is done, and it wakes up and finishes the maintenance cycle once power does return.<\/p>\n

Ok, so what are the ways around your scenario below? Multiple of them;<\/p>\n

Option #1: Two Batteries<\/h2>\n

Have two or more Redflow batteries (as per the system pictured). The Redflow BMS<\/a> automatically sequences maintenance so there is only ever one battery in a maintenance cycle at once. The system pictured is precisely such a system:<\/p>\n