A different approach for solar grid-tie with battery backup?

[DSinOR]

Greetings.  I found your board while searching for "outside the box" ideas for using batteries and inverters in a residential power system.

Check out my drawing. 



I want a solar grid-tie with battery-backup system.  I want to obtain the tax credits, so I'll be using UL Listed components and following code and obtaining permits and inspections. 

I don't like the Xantrex XW solution because it restricts backup power only to a selection of dedicated circuits in a subpanel.  Plus it's all automated.  Plus it's $3500. 

My family uses 50kwh on a normal day.  We can cut that to 10kwh pretty easily.  Therefore I don't need to restrict my backup power to a handful of dedicated circuits.  I want the capability to access backup power on any circuit in my main panel, excepting obvious hogs like water heaters and cookstoves.

In the style of typical grid-tie (no-battery) systems, I'm okay with losing all power when the grid goes down.  In power outages, I'd take this opportunity to turn off computers, UPS's, light switches, and the breakers for cookstove, water heater, and clothes dryer, thereby transforming my 100-amp service household into a 30-amp service household.  The only things left on are fridge, freezer, and water well.  At that point, I could then actuate a DPDT manual transfer switch that isolates me from the grid while simultaneously connecting my backup power sources to my inverter and main panel. 

I think of it as an off-grid system with a grid-tie capability. 

My questions for you guys:
Is this feasible? 
Can it be done in compliance with code?
Is there a synchronizing, auto-shut-off grid-tie inverter on the market that allows a workaround so that it will serve as a basic off-grid type of inverter when I actuate my manual DPDT transfer switch?  Or something equivalent, perhaps an off-grid inverter with add-on synchroniser and auto-shut-off accessories?  Or something totally different? 

I'm not an electrician.  I need ideas on how to bring something like this to fruition in a way that will satisfy my inspector and meet code requirements and use UL Listed components. 

I asked on other boards, but I keep getting the same answer: buy the Xantrex.  I'm hoping for some discussion here. 

Thanks!  By the way, great board!

[mike90045]

if you have any need of 240Vac,  the XW series is your only UL choice.  Next is a pair of outbacks with a 240V transformer.  Not sure where you think "restricts backup power only to a selection of dedicated circuits in a subpanel".  I'm off grid, and have no restrictions, I just feed everything from it. Shop tools, fridge, well pump.   I've installed 3 sub-panels, with a bunch of stuff on each, just have to stay within the power limits - I've got 300A worth of breakers, but only 30A (x2) worth of source.

[DSinOR]

Hey - thanks for the replies!

Mike - If I proceed with a grid-tie, I obviously have to comply with code, etc and pass inspection.  The XW is rated to a max of 60amp output on backup power.  To pass inspection, my subpanel must have a max rating of 60amp.  My main panel is 100 amp.  Therefore I have to get rid of 40.  Plus I have to install a subpanel.  That's what i mean be restrictive.  It restricts me to a certain course of action.  PITA really.  I would much rather have a less automated and less restrictive system that fed backup power to my existing main panel and allowed me to ration power to any destination I choose, much as you already are doing in your off-grid system. 

The point is: it is very possible to have less automation and less restriction in a safe reliable transfer system.  To boot, in my experience, less automation = less cost and increased reliability.

I understand that the market is currently driven by big-dollar customers who prefer total automation.  But i also feel there's a large market out there who would be satisfied with less automation at a lower price point. 

The 240 part is a bummer.  I've read a bit about stacking, but to be honest, I struggle with paying high prices for two inverters just so I can to stack them.  Correct me if I'm mistaken, but 2 outbacks will far exceed the cost of 1 XW?

I didn't know that using the same inverter for both grid-tie and off-grid application was completely out of the question.  That's also a bummer. 

The primary concern from a design and inspection standpoint is to assure safety for both the homeowner and the grid operators.  That's what 'safe transfer' is all about.  Jens suggests that dual service is feasible, but not legal.  If multi-pole switches can be applied to ensure isolation, what other reason exists for prohibiting dual service from an inverter?  My reason for asking is not to be objectionable, but rather because I'm really interesting in learning why or why not. 

Jens - thanks for the suggestions and ideas.  I intend to give them some study as time permits. 

[LowGear]

To pass inspection, my subpanel must have a max rating of 60amp.  My main panel is 100 amp.  Therefore I have to get rid of 40.  Plus I have to install a subpanel.

60 Amp minimum or maximum?  I think you need a certified electrician.

My main panel is rated at 200 Amps but the main breaker and meter base are rated at 125 Amp.  Look at any main breaker box and add up the breaker potential.

Casey

[mike90045]

Actually, I have mis-spoke.   A single 120V inverter can power a step-up transformer, which can power the 240V devices.  But, 2 stacked inverters is a more elegant way to do it.

The auto-transfer is a UL/Utility/Code requirement, to prevent linemen from getting electrocuted, not a rich fop's brainless work-a-round.

There is no other inverter than the XW6048, that can power as much, and their pass through
capability is the highest around. Correct me if you find I'm wrong on that.

The XW line, some Outbacks, and likely Sunny* can all be used as battery/grid tie.  Most end up being fairly complicated though, and only 120V.

[Lloyd]

I know a couple of dealers that quit carrying Xantrex bc of the number of failures, and repair is almost impossible unless you want to send it back to the factory.

I think the failures may be related to trying to cram to much in to small of a package at a consumer driven price.

I have installed at least a dozen Xantrex's, about 2 dozen outbacks, and about 8 Victrons...first install was a Xantrex about 9 years ago... To date I have not had one of my inverter installs fail, of any brand.

But I just replaced three Xantrex's in one Yacht. I believe they failed bc of a poor installation, they were in an heavy duty cycle, and all of the cables were were undersized...I figger the voltage drop was in excess of 18%...which I believe caused heating on the boards. I tested all of the transformers they were all ok...I've got say that those transformers are very heavy duty and well built.

What I like about the Outback's is they are completely modular...if there's a problem just pop a board, install a new one and you're up and running..they pretty easy to self diagnose.

I think the Victron's are the best built..and will be the most robust in the long haul...I just wished they made a sealed unit like the Outback option.

My guess is for 220 stacking is a better option for long term if the duty cycle is going to be anything but intermittent.

Lloyd

[elnav]

LLoyd the downside to stacking lies in the fact  if one goes down  then your whole system goes down  due to the fault signal  from one shutting down the other as  a safety. 
In my systems I use victron 230V output to drive the heavy loads including air conditioning, then step down th 230V to 115V for light utility circuits. As you know  Victron can be selected for either 50Hz or 60Hz and they can be  paralleled up to 5 units together; provided you can deliver that much DC. 

Hyperion had  about 30 Victrons installed because  the 230V AC power was actually 3 phase. 

[Lloyd]

Enlav,

Not disputing...but it also seems to me if you have one 220 unit when it goes down then you're also out of power. But for 220 I would also go with the Victron, bc they are so well built...and it's def more efficient then the 120 units....But then you have the step down transformer so if most of your loads are 120 then the efficiency hit washes the 220 beni.

It's also is going to take a damn big bat bank to run 220 getting over the Pukert trap...maybe a nice little DC gen(3-4kw DC) to run when the big 220 loads are on.

Glad to see you posting. I always look forward to your insight.

Lloyd