Grid-Tied with Backup - available inverters?

[Bruce Bon]

I am considering retrofitting my 1982 home with a grid-tied with battery backup solar PV system. I understand that there are a limited number of appropriate hybrid inverters available, but don't know what models they are. At the Xantrax site, I couldn't even figure out which, if any, of there devices were appropriate. From one forum message I ran across, the Xantrax XW6048 has been replaced with a different model, but the writer did not identify the new model number.

I would appreciate anyone pointing me to model numbers (any manufacturer) appropriate for my application. I can then look up the specifications and prices and try to make sense of it all.

Thanks.

[Rob Beckers]

The Xantrex XW6048 is still available (as far as I can tell). The company, Xantrex, was bought up by Schneider Electric, and the XW models are now listed on their Web site (http://www.schneider-electric.com/sites/corporate/en/products-services/renewable-energies/products-offer/range-presentation.page?c_filepath=/templatedata/Offer_Presentation/3_Range_Datasheet/data/en/shared/renewable_energies/xantrex_xw.xml).

There still is a Xantrex Web site as well, and it also lists a number of inverter (http://xantrex.com/power-products/inverter-chargers/overview.aspx)s that look to be suitable for battery backup (ie. they switch the grid through when available, and switch to inverter when the grid is down). Why the Xantrex site is no longer listing the XW series is a mystery though.

Besides Xantrex, another very well known brand for this type of inverters is Outback (http://outbackpower.com/). They too make grid-interactive inverters that can export renewable power to the grid, power loads directly from the grid when available, and switch to battery power (inverter) when the grid goes down.

-RoB-

[Rob Beckers]

There's something I would like to add: If grid power in your area is reliable, and you are not planning on major renewable energy sources (where the excess can be sold back to the grid), you are likely better off with a fossil fuel backup generator. Sad as that is, and as much as I like renewable energy, for most people it just doesn't make sense to have a large battery bank that is virtually never used. Batteries are very expensive, and they have a limited life time, even if they are never used. Cheap ones last about 5 - 8 years, the very expensive ones will get you about 20 years, but they will all need to be replaced eventually.

For most regular houses the electrical loads are so high, that even switching just some critical loads would take lots of batteries to run it for a usable amount of time. If you have an idea of what you would like to keep running during power outages, and for how long, I can calculate what that would take in batteries (and money).

-RoB-

[Bruce Bon]

We are in the situation you describe, with a 30-year-old home and a grid that has been reliable in the past. I do understand the trade-off, and if economics were the only consideration, it is pretty clear that a generator, or no backup, would be preferred to battery backup. But when you consider the possibilities of terrorism or natural disasters interrupting the flow of fossil fuels and/or disrupting the grid, then the equation looks a bit different. The extra expense and trouble becomes insurance, and how much one is willing to pay for insurance protection against risk is a very individual decision.

There's something I would like to add: If grid power in your area is reliable, and you are not planning on major renewable energy sources (where the excess can be sold back to the grid), you are likely better off with a fossil fuel backup generator. Sad as that is, and as much as I like renewable energy, for most people it just doesn't make sense to have a large battery bank that is virtually never used. Batteries are very expensive, and they have a limited life time, even if they are never used. Cheap ones last about 5 - 8 years, the very expensive ones will get you about 20 years, but they will all need to be replaced eventually.

For most regular houses the electrical loads are so high, that even switching just some critical loads would take lots of batteries to run it for a usable amount of time. If you have an idea of what you would like to keep running during power outages, and for how long, I can calculate what that would take in batteries (and money).

-RoB-

[Brian McGowan]

For what it is worth, here is my situation. I am in a 50+ year old house and we lose power occasionally. My first summer in this house we had a hurricane come through and drop a tree on the wire and break off the telephone pole in my yard. More than 350K people without power and I am one of four houses at the end of a line. We were 5 days without powerbefore they got us a new pole and transformer. My wife is from N.E. Philadelphia and was not pleased about this. I borrowed a generator from work but that was not pleasant either and it used gas and made noise. I had the material to wire it into my circuit breaker box and was able to run the house that way. I have always been interested in alternate energy since the 70's and decided now finally to do something useful and start playing with it. My objective was to learn and grow a backup system. I ran wire through the house from batteries in the garage charged by a couple of small panels and tapped off in strategic locations around the house so I could plug in some nice LED fixtures and a couple of 12V compact flourescents for emergency lighting. She was thrilled the first time the grid went down and I turned those on and they were plenty bright enough to avoid stepping on our black cat. I got a small modified sine wave inverter and started using the charged batteries to do stuff around the house like weekwacking or hedgetrimming or running my power tools while building other alternate energy projects. The next storm we lost power the night before we were supposed to go on vacation. Still no power the next morning and she wanted me to stop packing and run around and find a place with power that was selling coffee and tea and get some. I realized I could hook my one cup at a time coffee maker to my inverter and make coffee and tea. She was thrilled and so was I that I didn't have to go find this stuff. I have grown my system since then and learned a lot and now find ways to use the power I make and with a better inverter I can now run my house for maybe 6-8 hours on the batteries I have. Not all at once mind you but I can keep the house warm and the fridge cold and watch TV and the computer in a round about kind of fashion. After that I hooked a car alternator to a lawn mower engine so I could charge the batteries during a longer event. While clumsy, I have used it twice so far to keep the house going when the power goes down and was extremely happy I had it. I ran a power line through the basement with a 4 outlet box at each end and a wire out to my big inverter and when I know I am going to be down for a while I run extension cords to the important stuff from those boxes and turn on the inverter and keep the batteries charged with the solar panels or if it's windy my small windturbine or the lawnmower engine/alternator if I must. Unlike a generator, you can run the lawnmower engine at slower speeds to conserve fuel if you are not using a lot of power or even shut it off when other sources of power are generating or you are not using alot. My latest aquisition was a 6.5HP single cylinder diesel engine so I can replace the lawn mower engine and then run it on biodiesel and waste vegetable oil. In an emergency it could also run on regular diesel and heating oil which I generally have a very large quantity of for the heater. During this time I also cut the power usage of the house by 1/2 from 26-28kWh per day to 12-14kWh per day with new appliances and energy saving measures. That was key since the less power you need, the smaller your generation system needs to be and the less fuel it consumes when you are running the engine and the longer you can go without the engine when you have alternate charging equipment. At some point here I will get a grid tied PV system, I figure about 4kW, which should more than cover my needs at which point I will get a grid powered battery charger and keep my batteries up that way for emergencies while still maintaining the engine/alternator arrangement and my little windturbine.
So there you have it. I started off small and basic with emergency lighting and then reduced my power usage and grew a system until now I can actually run the house with it and when it is sunny and the batteries are already charged I will do a load of wash with the power or if I know it's going to be sunny tomorrow I run my entire computer room off of it for the night thereby making use of my "backup system" as often as possible.
Fortunately there are people here that can help you avoid the mistakes I made while "learning".
Anyway, just thought I'd ramble that out there to give you something to think about. Sorry it wasn't thought out better.
Brian

[Ralph Day]

Hi Brian
Have a look at the xw series of inverter/chargers from Xantrex. They support grid tie while also supporting generator power and batteries. The best of both worlds. Others probably do the same the Xantrex has it all in one box (except you need a solar charge controller separate from the inverter unlike straight grid tied inverters).

Ralph

Ps I have Xantrex for my domestic system, Enphase for my microFIT.

[Brian McGowan]

Ralph,
I currently have an Outback Flexmax80 for a charge controller. I am giving serious consideration to the Enphase inverters for the grid tie system. I have read a couple of interesting articles about them and I think they just retroactively upped their warranty to 15 years. I think it was here that I saw what was labeled as an AC coupled grid tied system where there were grid tied inverters for the panels but there was also a battery powered inverter to get the grid tied inverters to run when the grid was down. That way I could still charge the batteries and also possibly run some heavier equipment during the day while the sun is shining. I think that used a xantrex inverter. I will have to see if I can find that again.
Brian

[Steven Fahey]

What's old is new again!

I spent 1/2 hour perusing the Schneider website - yeah a lot has changed. Then I checked the old version of the Xantrex website, and found this:

http://www.xantrex.com/images-content/inverter-chargers/hi-res/rv-series.jpg

Now doesn't that look a lot like the SW4024's from the 1990's? A bit of re-packaging to get all the wires on one side (yay). The re-design seems to make it more suited to the Recreational Vehicle market, but I don't see a big impediment to using it for RE.

Haven't read enough to know all the specs, or how welcome such a unit would be hard-wired to the grid, but it does promise all the grid-tie, battery backup, 240V stacking, and generator start features that the SW4024's used to offer.

Here's the link: http://www.xantrex.com/power-products/inverter-chargers/rv-series-gs.aspx

Edit:
Aww it's not true. It's hard-wired to be "mobile" power, not "backup" power, and definitely not for "RE" power. It's also mod-sine wave, so no chance of hooking up as a sell-to-grid inverter. If you try to use it as a back-up inverter, it cannot be programmed to accept or prefer renewable energy sources - it will charge the batteries from the grid or fuel-powered generator.