I690.64 (B) (2008 NEC) permits connection "at any distribution equipment on the premises". Can this be a sub-panel at some distance from the service disconnect? Consider a barn with panels on the roof, can I connect (assuming other code conditions are met) to a a breaker panel in the barn, or do I need to bring the PV generated power, via a separate feeder, back to the house where the utility service disconnecting means is located?
There seems to be some ambiguity in the code which speaks of the inverter output being "connected to the load side of the service disconnecting mean" but then that connection can be "at any distribution equipment on the premises" (with some additional conditions). What is the meaning of this phrase "at any distribution ......" and why is it put in the code?
Can panels on the roof of a 9 story building connect via inverters to a breaker sub-panel on the roof, presently used solely to distribute power to the elevator motor? (assuming, of course, that requirements 1-7 of 690.64(B) are met?) That would be a dramatic saving in costs if a separate new riser for the PV system is not required.
If what they are telling me about the system I am looking at that is true. You just pop a breaker in anywhere and hook it up. The IAEI news had an article that said you should hook up to the opposite end of the panelboard bus as the main connection.
Ensure that the inverter is listed for this type of connection. This means that if the utility cuts out for any reason the inverter cannot operate. Otherwise an automatic disconnect would be required at the service to avoid back feeding the power line. This also means that when the power drops out the solar also drops out. In otherwords the solar does not act as a power backup system and this is typical for the installation as I understand the question.
#193362 - 03/29/1012:37 PMRe: Connection point for utility-interactive solar PV?
This is also how it was explained to me. I am seriously thinking about some kind of transfer equipment that would allow me to use my solars in a power failure. I am really surprised they don't offer that as an option. Since you are only transferring a fairly small supply and it could be a manual transfer, I don't see this being that big a deal. I foresee putting a few critical loads into a small sub panel, with the inverter and transfer equipment integrated there but I don't know if that is actually available. I still have not had the solar guy over here for that kind of chat.
Solar isn't practical to use during a power failure without a battery bank, which gets very expensive very quickly, and requires fairly frequent battery replacement. The more economical solution is almost certainly to leave the solar panels grid-tied, and install a generator for power failures. The inverters *may* work while the generator is running and save fuel bills; hard to say without more information on the model of generator and details on the interver.
I know my little UPS unit hates my portable generator with a passion, so there's something dirty going on that might not play nicely with the inverter(s).
I have over 600 A/H of battery storage in my golf cart. I would like to figure out how to use that. It is similar to those plans that use your electric car battery to supplement the grid in peak load situations. The trick is finding the appropriate inverter. The reality is that most of the time our long term power outages are in the summer when you should be getting 14-15 hours of usable sunlight. My fridge will hold overnight if I can get it cold in the daytime. I am also looking at a separate system for the pool pump (all DC) that will keep my pool blue. If I have food, cold beer and the pool is OK what else do you need?
There are inverters available that are specifically not for grid tie. What this means is that you would have to have two separate systems as the non-grid tie type inverter is not compatible to feed the grid meter, it will not sync thus shorting out situations and destroyed equipment possible if tied to the grid.
You will effectively double your cost for little gain.
I also recommend a generator. And the inverter "may" as Steve put it, work while the generator is operating. For small loads I recommend an inverter type generator, often called a low speed generator, where the AC output frequency is created and has nothing to do with the speed of the motor. They save on fuel as the generator can slow right down and save fuel under low and no load situations. This is again as Steve mentioned.
UPS's and generators don't like each other. The UPS sees good AC, switches the load to the generator, the voltage dips as the generator ramps up to accept the load (unless a high speed generator oversized), mean while the UPS sees the voltage dip and removes the load back to it's battery, creating an endless cycle.
#193392 - 03/30/1011:40 AMRe: Connection point for utility-interactive solar PV?
I see a generator as being a big cost for little gain too. One more engine that won't get used enough to be reliable when you need it. The last time I had an extended outage (Charley) we survived using inverters running off my car. To be honest I have been thinking about 2 or 3 systems anyway. The solar contractor says he can work the loopholes so I can get the rebates on everything as long as some of it is grid tied. The collectors are the big thing and he can diddle the numbers to get all of them on the rebate. I really like the direct drive pool pump idea. That is elegant without complication. The grid tie part in necessary for the rebates and I would also like a battery system that uses my golf cart for storage and runs the tiki bar fridge and a few outlets.
My real problem at this point is available south facing roof. I may end up with collectors in ground racks.
Then go for it with the dual systems, just ensure there is no way to interconnect accidentally and you will need approval from your power company (at least we do here) if you want a net metering situation and for the grid tie portion. You will need to take care with how you handle the non-grid tie and make sure you program the battery charger correctly for golf cart batteries.
Finally, I would like to offer up my roof for any extra space you may need for south facing (I designed it specifically for panels 15 years ago thinking someday I might be rich or panels would be really cheap but neither have happened). I have even removed the 140 foot tall poplars that provided shading.
#193413 - 03/31/1012:38 PMRe: Connection point for utility-interactive solar PV?