Grid Tied with generator backup - will solar provide any power if grid is down?

[HappyInMa]

Ok - first what I do understand (or perhaps my assumed facts you can correct if I'm wrong)
1) Gridtied Solar won't function if the grid is down - it 'senses' the power from the grid and shuts down the inverters
2) Cost of putting batteries for backup power on a grid-tied system is basically crazy-expensive and doesn't make sense (whole house UPS, just don't bother).

So - if I want to have power in the case of an extended power failure (like recently happened around here - some folks had a week without power) the most economical option is likely to be a generator. I get that part.

However, my question is this - IF I hook up a generator to the house after my grid-tied array is functional, will I be able to draw any power from the PV array when the sun comes out? What I'm picturing is the grid goes down - a transfer switch cuts the house from the grid and the generator kicks in powering up the house which is now isolated. Now the inverter 'sees' power from the generator much like what the grid used to provide so the generator will run along reving up as demand increases, but perhaps if the sun comes out the PV array could provide power and the generator could then not burn as much fuel.

Does it work this way? If it CAN work this way, does it require special inverters or other equipment/wiring/planning to make it work like this? If it doesn't/can't work this way, can someone explain why not?

Thanks in advance....

[Sunking]

However, my question is this - IF I hook up a generator to the house after my grid-tied array is functional, will I be able to draw any power from the PV array when the sun comes out?

Does it work this way?

Will not work. The GTI's are current sources, not voltage and must see the ultra LOW impedance of the grid to operate.

What you can do is cycle the generator to conserve fuel, say 20 minutes of every hour to keep refrigerators cold, and the home tolerable in summer.

[HappyInMa]

That was fast - Thanks.

I figured there was a simple answer, even if it wasn't the answer I wanted.

So - then is there ANY way to get use of the array in an extended power outage?

[Sunking]

That was fast - Thanks.

I figured there was a simple answer, even if it wasn't the answer I wanted.

So - then is there ANY way to get use of the array in an extended power outage?

Not unless you have a hybrid GTI system using batteries, which requires a generator.

[Naptown]

Not unless you have a hybrid GTI system using batteries, which requires a generator.

And add about 12K to the cost plus the generator

[HappyInMa]

And add about 12K to the cost plus the generator

Would take one heck of a power failure to cost justify that differential - or a very unstable grid (thank goodness we aren't there yet!).

Ok - so last question on this line of thinking...

If I do choose to put a generator at the house, I put a cut-over switch to isolate the house from the grid on failure when the generator kicks in... now do I need to do anything special to isolate the PV inverters at the same time since I won't be using them or do I just ignore them?

[Naptown]

Most generator set ups use a separate panel for the essential circuits and either an automatic or manual transfer switch. If the PV input is not put on this panel then there is no conflict or problem. But be aware that some of the newer GE generators will run the entire house using a load management system that rotates through the higher load items to limit the load on the generator. These may keep the circuits alive to the inverters which will destroy it or them. This is something that needs to be addressed by the generator installer to make sure the PV is shut down. Not a problem other than to make sure it is done correctly.

[Sunking]

You have to install an Automatic or Manual Transfer Switch which isolates the grid and inverter. Your electrician will know what to do. It is beyond DIY.

[HappyInMa]

You have to install an Automatic or Manual Transfer Switch which isolates the grid and inverter. Your electrician will know what to do. It is beyond DIY.

Thanks - I'm not considering this a DIY project. I'm just trying to visualize the components so I have a clue of what is required and why. It helps for me to have reasonable expectations of what can and cannot be done and the order of magnitude of costs that may be involved before I go asking someone for an estimate.

The other thing I think I've learned here is that IF there were a power failure for some period of time and I were hooking up a generator to the house on a temp/emergency basis, I would want to be careful to isolate the PV system - or at least be sure whoever was helping do the work actually knew what he was doing with regard to it.

[Mike90250]

Xantrex has just come out with a high voltage input (600VDC) 48V battery charger. That can be used to charge batteries, and with an XW hybrid inverter, can work WITH your generator to keep house powered for about $5K.

What is your GT array size ?

[HappyInMa]

Xantrex has just come out with a high voltage input (600VDC) 48V battery charger. That can be used to charge batteries, and with an XW hybrid inverter, can work WITH your generator to keep house powered for about $5K.

What is your GT array size ?

My array isn't up yet - it is/was supposed to go up this week. Apparently the panels were delayed... Something going on there it seems... Anyway, it is to be about 6.4Kw composed of 35 Suntech 185s. We are discussing a swap out to 190s due to better availability at the moment. Will see.

Anyway, I'm not THAT interested in continuous power - I don't have a generator now as we don't experience failures all that often and don't have anything that is all that critical if we do (our heat is wood and doesn't require electricity, no medical problems etc). So, we can survive without the electric for a day or two if necessary and save the $'s for a generator, never mind another $5K extra on top of that to make use of the panels in the meantime for a couple days that may or may not ever happen!

My question initially was more to clarify the situation. If someone came back with at "well for $100 you can install a xyzWidgit and then you will have power anytime the sun is shining if the grid is down" then I'd have been interested. Seems I wouldn't be alone in that eh?

[Naptown]

My array isn't up yet - it is/was supposed to go up this week. Apparently the panels were delayed... Something going on there it seems... Anyway, it is to be about 6.4Kw composed of 35 Suntech 185s. We are discussing a swap out to 190s due to better availability at the moment. Will see.

Anyway, I'm not THAT interested in continuous power - I don't have a generator now as we don't experience failures all that often and don't have anything that is all that critical if we do (our heat is wood and doesn't require electricity, no medical problems etc). So, we can survive without the electric for a day or two if necessary and save the $'s for a generator, never mind another $5K extra on top of that to make use of the panels in the meantime for a couple days that may or may not ever happen!

My question initially was more to clarify the situation. If someone came back with at "well for $100 you can install a xyzWidgit and then you will have power anytime the sun is shining if the grid is down" then I'd have been interested. Seems I wouldn't be alone in that eh?

If it were that simple and inexpensive everyone would have one. Including me.
Your question is one that I hear almost every day. And the answer is always the same. Doesn't mean you can't ask though.

[HappyInMa]

If it were that simple and inexpensive everyone would have one. Including me.
Your question is one that I hear almost every day. And the answer is always the same. Doesn't mean you can't ask though.

Well, on the surface it SEEMS like it should be simple. Then of course the devil is always in the details isn't it?

We spend a ton of $'s on the capacity to collect energy and turn it into electricity, then if the grid fails it would seem like we would be able to make use of that.. then we are just as helpless as our neighbors. Just doesn't seem right somehow. But as I tell my kids every day - life isn't fair.

[russ]

One could also use a large bulldozer as a family car -

A better comparison would be to buy a TV but have no reception due to the lack of an antennae/sat dish/cable.

Installing part of the equipment required for most anything rarely does the job.

[HappyInMa]

One could also use a large bulldozer as a family car -

A better comparison would be to buy a TV but have no reception due to the lack of an antennae/sat dish/cable.

Installing part of the equipment required for most anything rarely does the job.

I suppose that is one way to look at it, but I'd rather think of it more like having an oil well in the back yard doesn't mean I don't have to buy gas for the car anymore