such a thing as grid-interactive vs. grid-tie?

10 Posts
May 22, 2008 09:42 am
such a thing as grid-interactive vs. grid-tie?

My apologys if this has been asked before.
What I would like to do is start out small and maybe expand as time, budget, interest, success,... allow. I have a south facing porch roof with enough room for approx. 1000 watts worth of panels. Phase one I wanted to be just the panels and an inverter. Can I just suppliment my electric use this way? I'm not interested in the hastles of grid-tie. I believe I have read about inverters and/or controllers that have dump-load capability so if I'm making more electric than I'm using at any given time I'd just like to dump into a dump-load.
So is a setup like this possible?

My future thaughts involve addition of more panels, I have a west facing roof face with room for probley 2000 watts. I'd also like to maybe do something with wind. I want to at some point add a charge controller and some batteries,...
Any help/advise would be appreciated, Thank you.
462 Posts
May 22, 2008 10:58 am
Re: such a thing as grid-interactive vs. grid-tie?

Gordon, way to go! In my opinion all PV should be installed as a means to reduce your dependant load on the grid and to grow until you no longer need them. Soon the electric barons will be the same as today's oil barons!
 But do consider using batteries for storage and supply to your inverter. Sacrifice a couple hundred Watts for now and purchase some batteries. Also use a charge controller. You can use small, cheaper ones in parallel or make an investment for the future with a larger one. Diversion loads can be made or purchased when using the larger controllers.
 One other thing, panels should be installed in the location that gets the most sun over the entire day and year. Sometimes the roof is not always the best spot, for this and other reasons.
 Good luck and I'm sure the folks here will help you in getting just what you need.
10 Posts
May 22, 2008 01:09 pm
Re: such a thing as grid-interactive vs. grid-tie?

More specifically what I'm asking,
Is it possible to make a system where the inverter and grid interact without having to do a grid-tie system?
For example: say at any given moment the house needs 1200 watts, but the inverter can only deliver 1000 watts, can the inverter be used to supply the 1000 watts while the extra 200 watts come from the grid?, or would the system have to switch completely to grid power until the demand falls below what the inverter can supply?
Clear as mud?
Thank you again for anyones feedback.
163 Posts
May 22, 2008 02:19 pm
Re: such a thing as grid-interactive vs. grid-tie?


For two or more power sources to share the same load they have to be in phase. That is what grid-tie does. The best thing to do is find a small load that you can transfer to your inverter, and once you are happy with how that works then keep adding new loads until you are getting the optimum amount of power out of your inverter.

I use simple 3-way light switches with one pole connected into my main distribution panel and the other pole into a second distribution panel that is my inverter's output (mounted next to my main distribution panel on the wall). The third pole on the switch is then connected to the load (re-routed from the main distribution panel). This allows me to easily change (one load per switch!) between grid and inverter. UP for solar and DOWN for grid.

The description may sound confusing but it is really quite simple, and after a year I only need to take a glance up at the sky on any given day to know which switches I am going to throw.

If you are not going to connect your inverter to the grid then you will need a system that includes batteries.
578 Posts
May 22, 2008 03:34 pm
Re: such a thing as grid-interactive vs. grid-tie?

anytime you are feeding any circuit that is tied to your main  panel where you recieve electricity from your power company that IS a grid tied system, and must meet the regulations of UL 1741.  whether or not that system has batteries is up to you.

here are the categories of inverters that can do this.

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10 Posts
May 23, 2008 09:02 am
Re: such a thing as grid-interactive vs. grid-tie?

Okay, well then can I use a grid-tie style of inverter and just not sell power back to the utility?
I happened upon "bob's solar blog" on the net, and his system as he seems to be describing it is what I'm looking for. I make and use what power I can, and any additional power that I need above what I produce I just pull from the grid. I want it simple and automatic without any switches to have to manually control.
Thank you again for any additional info.

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