School me in grid tied terminology

[andrewgh]

Hey Folks,

Ive been using offgrid only solar + battery setups for trailer/campers so have some simple experience with small systems (400 AH + solar+ 3k inverter 12 v). Ive also used a sub panel generator setup to connect a 30 amp 240v split phase to, so have some basics down.

Ive had a hell of a time sifting through some of the terminology for a grid tied system. Ive read a bunch of lingo epressing the same thing, but then go on another forum thread and it gets explained another way.

What im trying to learn about: Grid tied systems that do not backfeed the grid, with emphasis on circuit breaker connection, rather than between the meter and load center or using an essential load sub panel. I want to start small, maybe a 30 amp, with maybe a 6k inverter and a small solar setup to suppliment the grid, then graduate to a bigger setup + battery storage.

Ive read very conflicting information about this type of connection, with terms such as zero net metering, power blending and a whole lot of other terms. Ive read that people dont trust zero export inverters with CTs as there are issues with backfeed, and that offgrid inverters are better, but dont provide information on how to incorporate that into the system.

I want to do the legwork and learn, so if folks have some specific videos/blogs/writeups for this, or if you can definitively let me know what i am asking for, that would be great. Ive searched a bunch of this site and unfortunately, where some of the confusion is coming from.

 

[SparkyJJO]

I don't know what exactly is the correct term, but anytime I see grid-tied I think of sell back capability and all that. Grid connected to me is all self consumption, no feedback to the grid, only can pull from grid when solar and batteries are not enough.

 

[andrewgh]

I don't know what exactly is the correct term, but anytime I see grid-tied I think of sell back capability and all that. Grid connected to me is all self consumption, no feedback to the grid, only can pull from grid when solar and batteries are not enough.

Thanks, tahts what im shooting for, pulling from grid when solar and batteries are not enough. But starting with it being connected through a circuit breaker for now, as there is a ton of red tape for a mains tap type setup

 

[Mattb4]

It all comes down to if your equipment parallels with the grid or not. If it parallels it is a grid tie. It might have zero export, or it might be a micro grid forming setup that allows your grid tie panels to operate without grid, but it all means that the electric company and you must have an agreement for you to operate in parallel.

Confusing comes in because AC parallel operations to carry loads is a bit foreign to people. Somehow DC parallel is no problem at all to grasp. If you parallel with the grid and pick up load (your house or miles away does not matter) the generator supplying the grid now has less load to carry. This is different than isolating your house loads from the grid by powering them from a non paralleled source. In that case the grid never knows about it.

In order for the grid to assist in picking up some of your load beyond PV/batteries/inverter it can only be in parallel.

 

[andrewgh]

It all comes down to if your equipment parallels with the grid or not. If it parallels it is a grid tie. It might have zero export, or it might be a micro grid forming setup that allows your grid tie panels to operate without grid, but it all means that the electric company and you must have an agreement for you to operate in parallel.

Confusing comes in because AC parallel operations to carry loads is a bit foreign to people. Somehow DC parallel is no problem at all to grasp. If you parallel with the grid and pick up load (your house or miles away does not matter) the generator supplying the grid now has less load to carry. This is different than isolating your house loads from the grid by powering them from a non paralleled source. In that case the grid never knows about it.

In order for the grid to assist in picking up some of your load beyond PV/batteries/inverter it can only be in parallel.

Right, i think i understand that one. Grid assist is another term ive seen thrown around. Grid assist through a circuit breaker is a term i have not had good results with in this forum or on the googles.

 

[Mattb4]

Right, i think i understand that one. Grid assist is another term ive seen thrown around. Grid assist through a circuit breaker is a term i have not had good results with in this forum or on the googles.

Grid assist is one of those terms not well defined. I take it to mean a grid paralleled setup that allows grid to directly add to the AC output of a inverter setup. It often is implemented such that it restricts to no output on the "AC in" wiring, in effect a zero export condition. However some folks take the UPS style off grid inverters, that allow GAB (grid as backup), as a form of grid assist.

PV setups and terms are an evolving thing. Not everyone agrees on meanings.

 

[WorldwideDave]

I had this same question, so thank you for posting.

All-In-One Systems seem to have a few things in common:

• Solar Charge Controller: Take power from the sun, and get it to your DC batteries.
• Inverter: Take power from the DC batteries and turn it into AC that you can either plug things into, connect a panel, add an extension cord to, etc.
• AC to DC charger: Take electricity from an outlet or panel and charge the batteries if you are consuming more than the batteries have. This might happen if there is no sun, a storm, clouds for days, or you are drawing out more from the batteries than you are storing in the batteries, or storing in the batteries plus adding to the batteries from the sun.

I think this is commonly referred to as an off-grid all-in-one.

My understanding - maybe wrong - is that when it is a grid-tie system, there is a way to send power generated, or generated and excess stored in the batteries back to the utility provider AKA grid.

Again, not an expert.

Imagine you had 10,000 watts of solar panels (large array with 25 panels at 400 watts each). Now imagine that you go out of town for a week, only running small DC security cameras while you're gone. Now picture your batteries being topped off the moment you leave town...where is the extra power coming in from the panels going to go? Send some of the power to the utility from your batteries and recharge the batteries at the same time. To me that is a grid-tie system, but maybe I'm wrong.

The net metering piece has to do with places like us here in california. The utility somehow someway is allowed to charge one price from 8 AM to 4 PM, another price from 4 PM to 9 PM, and another price from 9 PM to 8 AM. Now also imagine that there are two pricing structures - one for winter (cheaper) and one for summer (more expensive). Electricity is cheapest during the 8 AM to 4 PM when people have left for work and their houses are usually empty. When you get home from work and fire up the A/C, shower, etc, it goes up. How net meter or NEM ties into this is that I believe some devices can allow you to use your grid electricity during the 8 AM - 4 PM as needed, but after 4 PM when presumably the sun has already recharged the batteries most of the sunlight hours, the system will switch to the batteries only and not use the grid. This way you will still have an electric bill - maybe half what you used to pay? - but for the usage after 4 PM it is all from the batteries. Of course these can be configured that if the batteries get too low running all those inductive loads (electric hot water heaters, electric lights, electric stove, electric air conditioning compressors), it will switch over to the grid for power to recharge the batteries or supply power directly to those loads bypassing the batteries (maybe - I really don't know how this works).