I have 3 kW of Grid Tie solar for my home (2+ years now)... I agree with the feeling of having all of that RE power available and to be dead if the utility lines go down--seems like a waste.

However, I have only had very occasional power outages over my past 50+ years, and none have lasted over a few hours. To install and maintain inverters and batteries for what would be a once in a lifetime event (earthquakes for me near SF Ca), a small 2kW Honda gnerator with 20 gallons of gas just made a bunch more sense--and was portable in case I needed to leave/live outside (ain't go'in to take 3.5 kW of solar panels and a couple of tons of batteries anywhere)... Plus that 20 gallons of gas would be very handy if I did have to leave in an emergency with my family.

At this point, if I was going to plan for multiple (non-earthquake) power outages, I would be looking at an RV type generator (hopefully converted to run on natural gas). The problem for me is that the typical "whole home" setups start at ~10kW--about 5x the amount of power I would need (and fuel consumption). A small RV genset seems to be better sized (and probably better built) than those others.

I know that Solar Guppy and others in the south/east with hurricanes have had made good use of solar RE off-grid power where it can take weeks (or longer) to get power back after those huge storms.

-Bill

I am thinking along the same lines as BB, the grid in my area has been very reliable until about 3 years ago when occasional blackouts began to hit (usually during heat wave conditions). It is still infrequent, but last summer we had 2 12-hour outage events that really got me thinking about some kind of backup power. I looked at a battery backup system to tie in to my PV system, but it is really expensive. A small generator seems like a better idea. But, I want to connect to my house with the generator safely and selectively use circuits as we need. I don't want to install a new isolation panel...I found this device that seems to fit the bill:
http://www.generlink.com/about_generlink.cfm

Has anyone tried this?

They don't list any details about the meter connection... Looks like it might be OK to install... For me, it makes the meter stick out another 5"--don't want to do that where it is installed now.

I installed a manual 6 circuit breaker panel that only cost about $120.00... But I have not seen anything that cheap for years.

If I was going to do it again, a 10 circuit would have been nicer (around $290 each), but for a 2 kW Honda--that would probably be overkill (just power a fridge/freezer, couple of lights, TV, and sump pumps).

I still have not even fired up any of the generators I have purchased over the last 10 years--power has not been off long enough to even pull one out and pour gas in it yet...

-Bill

Well here in Maine we are all very rural, grid outages are common, and happen on average once every 2 months probably, sometimes more often. Its slightly more rare but not unheard of for us to lose electricity for a week, sometime up to 3 weeks like we did in 98 during the big Ice storm that froze everything and brought down trees and hi-voltage transmission lines everywhere. Electricity being available offline is a must for us....

Also, on the windmill thing I mentioned earlier. Some websites advertising the skystream say this.
"Skystream can be used in off-grid battery charging applications that include a bidirectional inverter such as a Xantrex SW or SW Plus or OutBack FX or VFX inverter."

I understand the Ice Storms--never seen one--but I understand them

Something like 2 decades ago I knew somebody that moved from the NE and brought a natural gas powered genset with them (for emergency home power)...

When they moved to in the SF Bay Area (I think it was up in the hills--lots of trees and small landslides)--they used the generator more here then they ever did in the NE.

If your power is out that long at a time--and if your power needs are relatively small (like 100kWhrs per month, not 1,000+ kWhrs per month)--having an off grid capable RE system sure can be nice and relatively worth the initial costs.

Just as a comparison--here is a link to a comparisons of common emergency genset from 10kW to 45kW... Look at those fuel flows (gph and cubic feet per hour of natural gas--100 CF ~ 1 THERM or ~$1.15 to $1.37 per CCF/THERM)...

http://www.costco.com/images/content/misc/pdf/11195724_comparison402.pdf

Even the smallest one (10kW) at ~2.5kW flows 72 CF/H (NatGas) or 1 gph (gasoline)... My portable generator runs about 0.25 gph at 1,600 watts--much closer to my average load (which is more towards the 400-700 watt range--which is 1/15 to 1/8 gph for the small generator).

That fixed install 10kW genset would cost me ~$24 to $100+ per day to run... Not sure that I want electricity at that price...

-Bill

A key point for me is that we already have 16 "US Batteries" Deep Cycle Batteries and I feel it would be smart to make good use of them. If we got a small generator and hooked it up to something like an Outback Inverter and batteries. Then (if the grid failed) on cloudy non-windy days the outback would automatically start a small gas generator. You could hook the generator up to a large gas tank, say 50 gal for use in case of emergency and could be used for cars or for generator. A small generator could be efficient enough to run for one hour and generate enough storable electricity to run the system house for several hours. Thus getting several hours of power from a smaller amount of gas. This seems like a better Idea then a 10kw generator running all day when all you needed was 0.6 kw.

And getting back to My Question about hooking up a skystream to the Output side of the Outback or Xantrex inverter. I found on the ouback forums that they (and Xantrex inverters) can do this. It is called Bidirectional operation or AC-Coupling. It is an un-documented feature of the inverters that while inverting they can also charge if a generating device is hooked up to the output side of the inverter. It is undocumented though because it most situations there is not was for the incomming power to be regulated and the batteries can become overcharged easily if not monitored continuously. In this configuration, the Outback FX series or Xantrex SW series will generate power until another device on its output side generates enough power to exceed the loads, then it uses the excess power to charge batteries, but does not monitor the voltage. In the case of the Skystream 3.7, the windmill is enabled to communicate with a battery voltage sensor which senses the voltage of the batteries and shuts down the windmill at a pre-determined battery voltage. Pretty interesting stuff. In this way, you could also figure out a way to hook a grid-tie inverter like a sunny-boy or windy boy to the aux-output port on the outback inverter and use it to send a shutdown signal to a grid tie inverter for wind or solar so that you could essentially use the Grid Tie inverter as a charge controller that would run at high voltage on the PV side. Be warned though that this can also cause power irregulaties durring grid outages in your AC current due to the Anti-Islanding feature of most Grid-Tie inverters..... Pretty interesting concept.

iboc,

I always wondered if somebody could back drive an inverter and have it charge the batteries... Many things are bi-directional but since nobody ever used it that way before, nobody really had any experiences with how well it worked (or not).... For example, you can take a regular induction motor, spin it up to speed with 120 VAC--just like normal. Then connect something else too it (say a water turbine) and start trying to drive it faster--the motor will now behave like a "Grid Tied" alternator and actually drive energy back into the grid.

So, to a degree, the SkyStream system can make sense--but because the "charge controller" is a single state controller, a separate charge controller (for float and equalization charging) would still be nice to have.

I wonder if all of this is UL/NRTL approved... Typically, something like this would need redundant protection against overcharging (if regulator and/or wind turbine regulator/radio link failed).

-Bill

And, like you state, we can hook up our grid tie solar system to a equivalent rated Outback inverter, connect a cheap dump controller on the batteries and have ourselves a cheap and dirty off-grid system.

Have to think about this for awhile...

Hmmm. Connect your Outback Inverter/Charger to Grid through AC1 (line in). Connect loads and Grid tied power to AC Out. When we have AC1 line power, inverter is off, battery charger is on, AC1 is connected to AC Out, Grid Tie Solar Inverter is back driving power to Grid--everything is fine.

AC Mains fail, failover switches to inverter, inverter charger off, AC OUT to Grid Tied Inverter is running OK, little solar power, inverter+grid tie power load, Lots of Solar--Grid Tie backdrives inverter and charges battery--diversion controller keeps things from getting to much charge voltage. Solar dies, Grid Tie goes into stand-by mode, Outback inverter operates normally. Sun comes back up and the whole process starts over again. When AC1 Line In comes back, Outback switches back to AC Mains, battery charger kicks in, all is OK...

The only thing that may need a bit of modification is the diversion controller... Basically, when the AC Main fails, enable the diversion controller as the Outback Inverter Charger is not functional.

Only thing that may not work--generator backup... Generally, don't want to back drive a generator as it has no way to "consume power" from its output (try to drive gas/diesel motor faster?). In that case, it may be better to simply use the AC generator with a DC battery charger to get the bank voltage backup...

Sweet!

-BB

Well, the reason the skystream works is because it has its own voltage sensor for the batteries taht you buy seperate. When the batteries reach full charge, the windmill receives signal to power down and put on the brakes. Thats why the skystream system works.

When researching this concept I found 2 other things that may interest you guys.
#1) the Sunny Island system works exactly like this through AC Coupling, in essance allowing you to use Grid Tied 600v inverters instead of 120v charge controllers. The sunny island ties in directly to SunnyBoy WindyBoy grid tie inverters using them as charge contollers when the grid is not functioning.
#2) I also found an AC Coupling diagram for Xantrex XW inverters that showed a feature I was not able to find any info on. Apparently you can take a Xantrex GT inverter, connect it to an XW Inverter on the AC out side. And connect the two together with a communcation cable allowing the XW system to shut down the GT in the event that the Batteries reach a full state of charge.

Both concepts are probably worth further investingation. It would seem to me that this method of setting up a solar power system, grid tied with backup, is likely much simpler than using charge controllers and would effectively eliminate charge controllers from the setup. Even though, apparently, you can still use them if you want to. Also I think I can use this setup to have a negative ground battery based backup connected to a positive ground solar array and not lose any efficiency in panels manufactured like my "Sunpower" solar panels.

Cross posted this thread and post from IBOC over at this Wind-Sun thread.

http://www.wind-sun.com/ForumVB/showthread.php?p=11848#post11848

This sounds like a neat solution for those of us with Gird Tie Inverters to make a nice off-grid backup system.

-Bill

The Xantrex drawing can be found on Xantrex's website here.
http://www.xantrex.com/web/id/1797/docserve.asp

If it doesn't open directly, click the one that says AC-Coupling Diagram