6/1 hybrid system advice and feasibility.

[Horsepoor]

For a couple of years, I've been thinking about the feasibility and associated cost factors related to building the following system out over a period of years. Known / constant factors:

1.   Xantrex 6048 inverter – price about $3,100 (new) – Will be integrated into a future system.
2.   6/1 listeroid – already own (runs at 650 or 800 rpm into ST 7.5) – output 3.3 Kw or 4.3 Kw
3.   48 volt battery string, 1100 Ah, to be increased/replaced years from now when solar is added.

Objective: During prolonged power outages, manmade or natural disasters, operate 6/1 in its most efficient zone (about 650 rpm) with 80% load supplemented by 6048 inverter to address short term (30 minutes or less) power spikes of 2 to 4 kW.

Observations: When configuring my house for reduced power consumption and taking frequent measurements with a remote senor Cent-a-Meter, I have determined 89% of the time my reduced evening and night time power needs are at or below 3.3 kW: Sometimes below 1 kW but not for more than 10 minutes. To get this low while still maintaining a normal life style, I replaced both 4,500 W hot water heater elements in the 80 gallon tank with a 1,500 W (top) and 1250 W (lower). Also shutting down one my two 2 ½ ton Seer 18i air conditioners allows us to comfortable inhabit either the upstairs or the downstairs, but not both at the same time. The 2 to 4 kW power spikes, on top of the 3.3 kW 6/1 650 rpm output, come from the random engagements of the following: five (5) freezers and refrigerators (various sizes from an office refrigerator to full size kitchen), 1 ½ HP well pump, microwave, various small appliances, TV, etc. Yes, I know I could force the wife to cram more things into one or two units and throw the rest out, but this is not desired due to all the STUFF she has frozen. Under absolute emergency conditions, choices would have to be made but this scenario is beyond the scope of my question and objectives.  

Questions & cost factors: Can I integrate a Xantrex 6048 into a basic 6/1 system that can be expanded over a period of years into a true grid tied backup with solar capabilities? Right now, is it feasible to build a "power assist" capability when running off grid (say hurricane prolonged power outages) to cover the power spike shortfalls of my 6/1? What would be the minimum required equipment needed to charge this small 48 V battery bank and the associated estimated costs? The cost factors are very important in all answers.

Notes: I've read many posts for those of you running off grid, always thinking about the feasibility and costs of the above described system. So I figured I would just ask for advice. Please indicate the associated estimated costs with any comments, so I can weigh the cost feasibility. I own a 20/2 that can handle anything the wife wants to turn on with both air conditions engaged (except electric dryer) but I like the idea of properly loading a 6/1 running for most of a 24 hour period as the battery bank is replaced / upgraded over a period of years. I figure, an undamaged, 6048 can later form the core of any future system as I build it out with solar and perhaps one day achieve true off grid status or at least reduced dependency on the power grid.

Advice and suggestions solicited.

Bruce      

[Tom Reed]

Hi Bruce, the inverter/charger and 6/1 should play well together. With an inverter genny combo you will be running the house primarily of the generator. The 6048 inverter will switch to charger mode and charge batteries if there is excess power from the 6/1 or the inverter will sync to the generator and added additional power when demand rises above what your set for the generator.

[LowGear]

Hi Guys,

I'm pretty sure you have to turn the grid off to power the house wiring via the generator.  I don't believe it is grid tie when in generator mode. 

Casey

[Horsepoor]

Until I learn more, a lot more, assume the house and generator are isolated from the grid. Long process in the future for permits, these are brifges I'll cross years from now. At this point, I would disconnect from the grid (hurricane power outage) when in use. Also, error on the anticipated size of the battery bank. Should have been 550 Ah which leaves about 250 Ah of useful power (48V). I believe I read somewhere that this particular inverter needs at least a 1000 Ah battery bank. So thinking about cost, what other equipment (minumim) might I need to acquire other than a $3,000 inverter to make a system like this function?

[mike90045]

The XW048 has a narrow generator frequency acceptance window, so you have to keep the genset running at 60hz, to keep the charger running.  It is a wider window than the AC1 (Grid) window of 60.01 -+.01 hz, I think it's about -+7 hz

[Tom Reed]

Hi Guys,

I'm pretty sure you have to turn the grid off to power the house wiring via the generator.  I don't believe it is grid tie when in generator mode. 

Casey

Casey, I'm not I understanding what you're saying here, but the inverter has an internal transfer switch. The grid power is disconnected by the inverter/charger automatically when it detects power on the AC2/gen input.

[LowGear]

I'm not I understanding what you're saying here, but the inverter has an internal transfer switch. The grid power is disconnected by the inverter/charger automatically when it detects power on the AC2/gen input.

That's nice to know Tom.  I have had numerous people try to tell me that the 6048 will grid tie a generator and when I speak with knowledgeable Xantrex folks it always turns out that the generator is for charging the batteries.  I was heart-sick for a month when I labored under that misinformation because I had my Sunny Boy installed and it is strictly a grid tie inverter by design.  I suspect that it can be tricked into "islanding" if a good strong 240 volt source is supplied to the local system (grid disconnected) but I don't know how big.  I'd be surprised if one of these 6048s couldn't accomplish that task.  (Any body know?)

Casey

[Tom Reed]

Actually I've read articles about the Sunny inverters and yes, you can island them. In the article it was all Sunnyboy products. Check Home Power Mag about 9 or so months ago.

[Carlb]

Take a look at the link below it is for the sunny island

http://www.sma-america.com/en_US/products/off-grid-inverters/sunny-island-5048-5048-us.html

[cujet]

I've given this subject much thought. The battery bank is the real problem here. Specifically due to the expenses involved. Due to both initial cost, and the short life.

With that in mind, I'd rather engineer a hybrid system with "generator boost" as the goal. In other words, a 4000 watt genset can carry a 10,000 watt surge load for a short time via the battery/inverter tie in. This accomplishes a few things. It significantly reduces costs on both the battery bank and inverter, as there is no need for extended battery power. It allows fuel savings via the use of a smaller generator. It prevents generator overload during any motor startup. It allows for significant fuel savings via a modest array solar "tie in".

[LowGear]

Sunny Islands are nice looking equipment and I'm sure they're built to the really great standards of SMA.  But they're 120 Volt.  So if you score 2 you can have 240 volt islanding power for only about $5000.  What's the number for Xantrex?

I'll look for the "Home Power Mag about 9...." but if you have a link I won't complain.

Casey