Hybrid inverter advice please.

[Marvo]

I was hoping a few of the solar veterans would cast a beady eye over a product I'm considering importing.

It's what I would call a hybrid inverter. It's basically a large UPS which combines DNO power and standby battery power into a unit with an automatic 10ms switch when power fails. It has a built in charger and also can accommodate other alternative power sources such as genny and PV panels etc.

What I'm tying to achieve is to offer customers a reasonably priced but reliable option for short term power back-up during blackouts. At the moment we're on a national load shedding schedule which involves 2-3 hour scheduled rolling blackouts each day so this solution would be for essential items which is mainly commercial IT equipment and possibly emergency lighting etc.

Load shedding has been in place since November last year and it's likely to persist for at least six months and possibly a lot longer so interest in any kind of off-grid systems is very high here at the moment.

There is no option to export power on our national grid and there's no FIT structure so any solar installation will have little return. I'm looking at installing these as a UPS with a bank of deep cycle batteries with the option for PV panels to be added at a later date.

The item is called an 'Axpert KS inverter' and there's downloadable datasheets on the site I linked. They're a Taiwanese unit and I can land them in SA at around ZAR4600.00 each for a 3000VA. To put it in perspective the other options locally include the Victron Multiplus which seems similar in functionality but it's 'dealer' priced locally at ZAR19000.00.



Any suggestions, advice or even general observations greatly appreciated.

**edit** There's around 18 or 19 South African Rands to one of your UK Pounds.

 

[Gavin A]

well, on paper it looks like it should do the job, but its' cheap as chips so I'd query how long it will last, maybe worth bringing 2 in so you have a back up as it's probably a long lead time for replacements.

I'm a bit concerned at why it says it's 1kVA, but 0.8kW. does that mean it has a power factor of 0.8? Is that an issue for you?

The surge capacity trip time looks very low at 5 seconds, that'll trip any time anything like a fridge kicked in with start up surge current.

Efficiency ain't brilliant, and I'd be pretty concerned for the lifetime of the batteries if you can't change those settings if in daily use, as the low voltage cut out settings look very low.

Word of warning on the batteries, you really want to size them on 50% rated capacity at most, and ensure they don't need to draw power off at more than the C10 rate (10% of the nominal capacity / 10 hours to discharge in full - not that you ever would) otherwise the storage capacity and discharge cycle efficiency will be really bad.

But yeah at that price it looks with giving it a go, as long as the customer is aware they're buying something relatively cheap that might not last too long (or might, who knows).

 

[Marvo]

Thanks for the adivce Gavin, much appreciated.

As you rightly point out the reliability is the big unknown. I've been doing some due diligence and I spoke to a company in New Zealand who are offering the same item rebranded as a different name to try get some feedback. It appears they've been installing them for over a year and didn't have any complaints about failure rates etc. I also spoke to our export agent we've used several times on the China mainland and he holds the manufacturer in high regard and says he's dealt with them previously for orders of regulators etc.

I already landed 3 of these units as samples just before the new year, it took me less than an hour to sell all 3 at what will be our dealer pricing with an agreement we have rights to monitor and site trial them for 3 years. I've used 6v deep cycle lead acid batteries which are of known quality and are imported by a friend of mine for his electric vehicle business. They've been running since earlier this month....so far without issues. One logged an over temperature condition on a day that was over 40 degrees but it wasn't sufficient for it to shut down. We've since louvred the door of the small broom cupboard it was installed in and there's been no repetition since. Only one of the installs is running at close to full specified capacity with a battery cycle of closer to a C7 cycle rather than the C10 rating so I'm interested to see deterioration rates on that one. I'm going again to all 3 sites at the end of next month to do a full check-up including battery condition etc so I should know more then.

 

[Marvo]

I didn't get much feedback on these but I thought I'd give an update for anyone interested.

I now have 13 of these units running, 12 are on clients sites (3x 2kW and 9x 3kW units), the last two of which I completed the installation last week. I was going to keep one 3kW unit for shelf stock in case of any failures but I had second thoughts last week after 2 days of rolling blackouts, several lost quotations that I was busy with and making dinner by headlight one evening I decided to use the shelf stock unit in my house.

So far no failures whatsoever. I spent an evening pushing the one at home to the limit to see how it behaved and to be honest it was lacking in surprises.

I ran it to a minor 5% overload which caused it to alarm and shut down after a minute, a 10% overload had similar results after 15 seconds which was all as per spec. I ran it to 10 simultaneous 10% overload faults with no time between resets and it behaved as it should with little variation in the temp of the air coming from the exhaust vent. I played around with several other faults such as adding an extra battery to make it alarm on battery overvoltage and removing a battery to test the undervoltage alarm. I also created a couple of short circuit faults with a 15m length of 1.5 flat twin to check its disconnect times and both were as per spec. I didn't have the heart to attempt a direct short at the output terminals because I don't have a replacement unit if it doesn't survive but I may try it when my next order arrives.

If I had to find fault it would be minor issues, the cable entry for the 230v supply in and supply out don't have strain relief for the cables, the termination blocks are a bit fiddly and awkward as well, it took a couple of termination attempts on one of the wires before it was satisfactory. It's located at head height in my office less that a meter away from me when I'm sitting and the fan is a bit on the noisy side. It's not a poor quality issue it's just the volume of the air movement. Thankfully it only runs during power outages and 2 or 3 hours after during battery recharging. Once the batteries are charged the fan is completely off all the time.

I don't have solar panels connected to any of my installations so far so I can't comment on that side of things. SolarPV panels are not an easy sell in a country with no feed-in tariff. Everyone is struggling to do business because of load shedding power outages so the focus at the moment is UPS's, inverters and generators. Even though the supply is off for 2 hours each day it's still cheap power when it's available at ZAR1.20 / KWh (6.6 UK pence/KWh).

 

[Gavin A]

Thanks Marvo

clarify things, does it only supply back up in the event of grid failure, or can it also run in parrallel with the grid?

ie can it be used to store excess solar geeration then use it in the evenings with the grid still connected?

 

[Marvo]

Okay, I've attempted to scan the manual because it's probably going to answer questions better than I am. Apologies for the quality, I'm not good with the office stuff and I was trying to keep the filesize small enough to attach. I'll get one of my office girls to do a better job of it on Monday.

**attachment removed, see below for better version**

 

[Marvo]

Yeah, the last scan was appalling I know, the secret seems to be to ignore the 2 gigs of bloatware that comes with the scanner and force run it from a command line.

Here's a better one.

View attachment Inverter Manual 2.PDF

Just watch the page numbers, I scanned it 2 pages at a time so it's will print and staple again as a booklet.

 

[JD6400]

Thanks Marvo , I have been trialling a similar thing on a local "off grid" landscape gardeners yard since last summer .
We have a 3.6 kW Outback flex one system in there on 4 kW of solar and a 20 plus kVA gen set for heavy use tasks , these feed in to what used to be 4 , but as from January are now 8 in total Rolls 6v batteries .
The idea is to keep a 24 hr base load going for vital services such as gates , phone , cameras and computers from the solar , with the larger loads being taken care of by the gen set and topping up the batteries if needed .
We have also incorporated an auto start into the system for periods of low / no use on the gen set and combined low solar input .
I will be now looking into your one as it is a hell of a lot cheaper than the Outback and looks smarter as well .
As for the fan noise , from the out back sounds like a hurricane !

 

[Marvo]

Thanks for the comments JD, how much does a similar Outback system run to? Is a 'Rolls' battery a tradename or is it a specific type? I'm glad to hear your fan is also noisy, it means it's probably normal which is reassuring. Whilst we deal with inverters in various commercial and industrial applications I've only got limited experience with off-grid or back-up power installations with multiple power source integration.

These inverters we've been installing are meeting our customers immediate needs without PV but there's a possibility that load shedding periods may increase so solar will be an optional addition that may reduce the need for extra batteries in the future to carry longer back-up times requirements during office hours especially. I looked at the solar compatibility of these Axpert inverters and they seem to be quite specific about the PV voltages and configurations they can handle, I'd be interested to hear from those with more PV experience if the specs outlined in the PDF I attached are a limiting factor when specifying a panel array.

These inverters also come with some monitoring software which we haven't had to set up yet, none of our customers have been interested in it. I've attached the software manual below, again any comments appreciated.


View attachment WatchPower user manual.pdf

 

[Marvo]

I realise it's not going to win any awards but here's some pictures of the 3kW unit with 4x 225Ah batteries I installed in my home office;

 

[Gavin A]

looks like they would do the job, but aren't G83/2 compliant that I can see.

 

[JD6400]

Hi Marvo

Rolls are just a trade name , but as I understand it , they are one of the best .
As for the cost , I will have to have a look on Monday as I can not remember what I did last week , let alone the cost of something last year .:wheelchair:

I know that the lads fitted a string box with fuses on the pv side , using only two strings but with the capacity to take at least four more if demand rose .
As for extended periods of use , either more battery storage is the key ( as I am sure you already know ) or if the solar input is available , this seems to easily take the slack .
The connection points on your one are a lot more accessible than the out back and we had no end of trouble with the internal GFI , and ended up removing it in the end .
You should get those battery terminals covered up , and be careful with any gasses given off as it looks like it is inside your house !?

 

[Marvo]

I'm not sure about GS83/2 compliance Gavin. Would it be required for an installation that's basically set up as a UPS and doesn't export into the grid?

Thanks for your concerns JD,the installation was a bit neater before I started playing with it to test it's capabilities. It does have a battery cover that's removed at the moment. The office is fairly well vented, it would be well over the 2 air changes per hour which the ASHRAE regs suggest.