I am considering installing a PV plant (1 - 1.5 Kw) and am interested in the pros/cons of using a SB 2500 vs the 1700. Aside from choosing the panels for the proper input voltage ranges - I am conserned about the Pros/Cons of feeding one phase (as 1700 does) versus two phases (as the 2500 does). I ***ume that the meter takes care of it all and if all my consumption is on one phase while all the generation is on another it will all balance out -- but please correct me if I am wrong.

Now the tough part -- In the event of loss of the grid the SB goes into isolation and will not feed power for safety reasons that I understand well.. But If the grid is down and I want to take advantage of my generating capacity what can I do?

Would it be possible to Isolate myself from the grid and then use a battery and inverter as an "reference exciter" to stimulate the SB into providing whatever the PVs are producing?

If this works what about the pros/cons of the two vs one phase units?

If not any any other ways other than another inverter for non grid-tie operations?

Thanks Vetro

As an owner of a similar brand X grid-tie inverter, I've looked into what happens with grid failure. The only inverter that I'm aware of that will maintain AC power during grid failure is the Vanner. It maintains AC power on a "backup" circuit so long as there is sufficient solar input. While batteries can be used, they are not required.

The problem with SMA/Trace ST/Advanced Energy GC1000 grid tie inverters is that they only provide one output - to the grid. Safety requires that if the grid fails, the unit shuts down. Spoofing the unit into thinking that the grid is still there would be very difficult, since these units carefully analyze the grid power quality. If the frequency or voltage go out of spec (such as would probably happen with a generator), then they are required to shut down.

Battery based inverters (plus the Vanner with solar only) take power from the grid, mix it with solar and/or battery power, and output AC on a separate output. If the input fails, the solar/battery takes over, but the grid connection is left at zero volts.

You need a separate inverter to use the panel power during grid outage. All of the inverters that I'm aware of (except the Vanner) require a stable 12, 24, or 48 volts DC. This means not only an inverter but also a charge controller and a battery.

If any inverter manufacturers are reading this, there is money being left on the table on this issue. It is easily worth an extra $1000 to provide critical circuit backup during grid outage. Just don't make me deal with batteries, because they are dangerous objects that I just don't need to worry about. The power outage that I want to back up is a rolling California outage. It happens in the middle of the afternoon on very hot sunny days. It is a proven tool for extracting higher electricity rates, and we can expect it to be used more in the future.

I agree that managing expectations is extremely important with regard to what a solar power system can produce. One of the rude awakenings that I got was that the system shut down when grid power failed. After all that money, 2.8 KW of panels on a sunny day, and the thing turned itself off exactly when it could be expected to fill in for the grid failure. I understand the technology now, but I still have trouble accepting that the panels are useless during grid failure. I should be able to continue operating the refrigerator, TV, computer, maybe a few lights. The air conditioner would be nice, but I understand that it may be too large a load. Obviously, the electric range is out of the question. The microwave seems like a borderline load.

Perhaps a super capacitor (like they use to run automotive boom boxes) would provide enough surge power to start motors like the refrigerator. For full backup, batteries are obviously necessary. But batteries large enough to run a kilowatt load are dangerous objects that need proper management far beyond what most grid-tie installations have available. The technical expertise required for an off-grid battery installation is simply not to be expected at the vast majority of grid-tie installations.

SMA America has been award a contract from the State of CA to develop a low cost grid feeding inverter with batteries. Providing backup power directly from the solar array without batteries is harder than it seems. You have to limit the backup to a few hunderd watts and have essentially no surge capability for motor starting. Technically there is no real barrier for us to do this but we want to make sure there is a market for it. I am not sure all the trasde off's are well understood by end users and we do not want to dissapoint customers by developing the wrong product.

When I specified my system I wanted to have power when the grid was down so I went with a battery system. I didn't want any maintenance so the system was designed with AGM batteries (from Concorde). I can certainly start a kilowatt load. I don't consider the batteries any more dangerous than the other things in my garage (water heater) or around the house (gas furnace).

BTW Vanner appears to have something is close to what you want:
http://www.vanner.com/htm/pro_01.htm?series_sku=3206710345182912&a=a&pt=3

I know nothing about except what is on the web page.

arnold

The Vanner is everything I want, except that it's double the capacity I need and 2-3 times the price. Maybe Vanner can offer a lower end product for the 2.5 Kw grid-tie market. I'd pay maybe $2600 street price for the inverter (I already paid $2000 for an ST2500, currently on the dump it as soon as possible list).

I agree that AGM batteries are the best choice among batteries, but they still can offgas hydrogen if they are overcharged. Hydrogen plus the pilot light of a water heater is not something I want in my garage. I'm not willing to bet an explosion that the batteries will always be properly maintained. They belong in an area p***ively isolated from any source of combustion. That's either outside, or perhaps in a battery box with outside (only) venting.

Apparently the word p_a_s_s_i_v_e_l_y got censored to p***ively. Gotta watch out for those dirty words! [img]images/smiles/icon_rolleyes.gif[/img]

Well I always make sure that there are reasonable provisions with regard to venting. They should postively be in a battery box for other reasons too like protecting them from abuse, keeping the terminals protected, etc.

OTOH I personally wouldn't lose sleep over the risk of an AGM battery getting overcharged in a garage with gas heater(unless I was dumb enough to put the batteries and the water heater together in a tiny closet with no vents). I would sooner expect to die from getting hit by lightning versus having enough hydrogen gas be vented in a garage that can be ignited by the water heater pilot. Hydrogen will rise so getting it in enough concentration near the water heater pilot would be a tough challenge.

I would expect that a gasoline lawn mower parked in a garage is a bigger risk.

arnold

John,

Is the Sunny Island product in the works for the USA?

We are working on a version of the Sunny Island for the US market but it will be different that the Sunny Island we sell in Europe. The Sunny Island is very sophisticated and targeted at the remote viullage electrification market. IMHO, it is too expensive for the US backup power market. The new Sunny Island Light will be a lower cost option that provides you with backup power during an outage. UL requires us to disconnect from the grid and then the SIL "fools" the Sunny Boys by giving them a grid to work into. They then come back online and provde PV power plus anything extra comes from the battery. IF there is too much PV power available the SIL commands the Sunny Boys to reduce the power. We think the system should be available late in 2003