30 kw Grid Tie System

chases12

I have been doing some research and calculating our monthly consumption of electricity. I am wanting to offset 100% of my electric bill, but being tied into the grid. I am needing approximately 3500 kwh/month. From my understanding a 30-35kw solar array should be sufficent. I am using Trina Solar TSM-325PEG14 (325W) panels as I can get them for $0.38/watt (I work at a solar distribution facility). I am also wanting to use the Enphae IQ7+ microinverters. 

My biggest question is, what would the wiring set up be, do I need a combiner box? What combiner box is needed and how will I tie it into the panel correctly?

Kind of loaded questions, but I am fully aware of the smaller array's involving the microinverters, but not the larger systems. My reasoning for using Enphase is because of the support and GUI for monitoring everything is super clean. 

Any thoughts would be great.

Dave Angelini

You should learn about conserving it first !
You may require a much larger service drop from your utility for what you propose.
Before that their permission should be looked into.

A  downside of micros, is going up on the roof for repairs. They have had more than a normal amount of failures from the guys I work with who do grid installations. Much easier with a central inverter in the garage. They also have excellent monitoring! The other downside of micros is you will be up on a roof lifting panels.

My business is Offgrid and the last thing we want is electronics out in the sun or shade. The only plus for micros to me is if you have shading. We do not have that offgrid!  If we do, we deal with it by taking down the tree or building the array far from the home.
 This long distance is the same concept you should consider. I mean, the way we do this is high voltage strings that a grid tie inverter would give you. No combiner required and far easier to wire. Some grid inverters have 3  mppts and each can have 2 long strings of panels without combiners.

Good Luck! 

mike95490

Once you pass 10kw of generation, you generally move into commercial power plant territory.   Your first call should be to the utility to see what their residential inter-tie cap is.
Second call should be for an energy audit, because something is way out of line for a standard house with 2 adults and 4 kids

mcgivor

Additionally, you need know what the feed in tariff is, it's unlikely the utility will pay the selling rate so a larger array may be needed to offset the difference. The 3500 kWh per month seems excessive for residential, is this a commercial application ?

chases12

mcgivor said:

Additionally, you need know what the feed in tariff is, it's unlikely the utility will pay the selling rate so a larger array may be needed to offset the difference. The 3500 kWh per month seems excessive for residential, is this a commercial application ?

This is residential. I am basing it off of our previous built home that we just sold. We had 1200 kwh during the summer months. I am also adding more items to the electrical grid. These new items are a heat pump for primary heating added with electric radiant floor heat as a primary and having electric water heater added as well. Since my previous house had a furnace on propane, I figured the heat pump would add a significant amount of electrical consumption as well as the electric radiant floor heat. I am discussing further with the company on the electrical consumption for the radiant floor heating to get a more solid answer. 

If I did have to have a large array, 60-70+ of the 325W panels I have access to, what items would I need to keep in mind if I wanted to be grid tie and use microinverters? Is there a combiner box I need to be aware of or?

mike95490

Please consider string inverters instead of micros, especially with as many as you would be installing.  Even with just a few failures, the labor involved to open up a path in the array to the dud, will become "tiresome" with frozen bolts that break and need replacing and the big kicker, the panel map is wrong and you have changed out a good inverter, and no idea where the dud is.

Unless you have massive shade you cannot avoid, micros are a second tier choice.

chases12

mike95490 said:

Please consider string inverters instead of micros, especially with as many as you would be installing.  Even with just a few failures, the labor involved to open up a path in the array to the dud, will become "tiresome" with frozen bolts that break and need replacing and the big kicker, the panel map is wrong and you have changed out a good inverter, and no idea where the dud is.

Unless you have massive shade you cannot avoid, micros are a second tier choice.

I appreciate the honesty and consideration. I am not against string inverters, but would like the idea of micro inverters, personally. 

With doing so on the micro inverters, what combiner box would be compatible with such a system? I am projecting to have 96 panels.

mike95490

Generally, micros have combiner cables, where some number combine for the home run to the main panel breakers.
 You will need something like a 200A main house panel, filled with breakers, and each home run goes to it's own breaker.   Make sure your panel has enough breaker slots for your micro arrays.