# Solar Power System Write-Up (Grid-Tie with Battery Backup)



## Dan in Ohio (Jul 16, 2005)

I promised TNAndy (who gave me lots and lots of advice over the last nine months or so) that I would write up my system and post some pictures. My system just went active on Saturday, so now I can do that without jinxing myself so here it is . . . 

Iâve been thinking about doing a solar power system for 5-10 years, but every time I looked into, I just didnât see the payoff. To be frank, unless your state has great incentives, I still donât think the economic payoff is very good . . . although it is a lot better than it used to be since the price of panels has come down so far.

The first thing to decide is whether you want a grid-tied, off-grid or battery backup system. For me a grid-tied only system was a non-starter since you have no power in an emergency . . . and an off-grid wouldnât really let me âuseâ my generated power as easily and would put more wear and tear on the batteries, so I decided on a grid-tied with battery backup so I can easily dump/sell the power back into the grid and have a pristine battery ready for emergencies.

Having decided that, the next thing is to figure out the size of the system. I got one of those Kill-a-watt devices and plugged it into the main appliances in the house to figure out what I was using. My goal isnât to replace all of my power, it is primarily to power certain things during an emergency. My lowest level of emergency power required would be 1.5kW for my freezer and woodstove insert fan (I can stay warm and keep my food cold), but I just doubled that for some lights, computer usage, charging devices, etc. So I figured a minimum of 3Kw daily usage (in normal use with cheap power we -- large family -- use about 30Kw/day). Long story short I looked at what I could fit on my garage roof (best southern exposure I have) and I put on a 3.7kW system (15 panels x 245 W). Charts show average solar exposure for my area is 3.5 hours, so I just figured 3 hours/day average, so overall I should average 11.1 kWH/day (but my placement is not ideal, so maybe a little less than that frankly). Anyway, this will produce about 35% or so of our power needs. Why not bigger? I would have had a hard time fitting more on the garage roof and above 4kW I would have needed to step up to a 240V inverter system which would have boosted the cost another $2k or so right there. So that was a good stopping point for me. If I add in the future the power system I used can be stacked with multiple units as master/slave, so I could expand possibly.


Equipment wise, I found I was able to go with all main components being made in USA with very little extra cost. The main components of the system were racking (Iron Ridge), panels (Suniva poly 245W), combiner, disconnects (inspectors required two separate ones on garage and house), and power system which has the charge controller and inverter and all cutoffs and surge protectors (Outback FlexPower One GVFX3648 system) and finally a 48V 600A forklift battery.

I donât want to bore you with all the details, but I put the racking and panels up myself and wired them into the combiner box. With those 15 panels, there are five strings of three panels going into the combiner box, so each string of three panels has about 105VAC coming out at 8.5A -- when combined then they are 105VAC at about 42A. I hung the Outback power system myself and installed the interlock kit on the service panel. And I hired out the trenching and wiring from the combiner box to the Outback panel to an electrician. The racking took me the better part of a whole weekend to install (long story short, I ran cross supports between my garage attic trusses since I couldnât reliably find and drill into the trusses themselves). Fastening the panels on the rails and wiring to the combiner took me a few nights after work . . . easy work except that those panels are bigger and more awkward than you might think when you are standing on a roof! (3x5 and 40 pounds I think) This was an easy low roof . . . God bless you if you are doing this on a second story roof (personally, I wouldn't do it myself and I am a big time DIY guy). 


The Outback system is great, it saves so much time from selecting compatible components and wiring it all together and it makes a nice compact package. This one is a GVFX3648, so a 3600W inverter using a 48V battery bank. It doesnât cost much more than buying everything separately, so I would definitely do that again. Once the wire is run from the combiner (on the roof) to the Outback system, the only other connections are to the battery bank (a 48V forklift battery for me), an AC interconnection with a circuit breaker on the panel (that is a 120V breaker, as is the inverter obviously) and an emergency connection to the panel . . . for the emergency connection (they call it AC output) you wire in an interlock kit so that you have to switch off the main switch before you can turn on the backup power (which runs from the battery). Interlocks are generally used for tying generators into service panels. I tied the emergency power into a 240V breaker and divided the 120V power onto it so I can run both sides of the circuit breaker panel (I just have to turn off the 240V breakers first). So I can pick and choose which circuits I want to use rather than being limited to using just a few pre-selected ones via a transfer switch/box. We tested it out and it easily carried the whole house load during the test (makes sense, this is a 3.6kW inverter).

So, this weekend was partly cloudy Saturday and flat out gray and cloudy on Sunday and it generated 8.2kWH Sat and 3.1 kWH Sun. That might seem disappointing but the days are short now, the weather was bad and . . . going back to the beginning . . . even on a cloudy, lousy day it generates enough to run my woodstove fan, freezer and some other things, so I am satisfied. And that battery has at least 24kWH of usable, dischargeable storage in it, so I've got 8 days of baseline emergency use even with *no* solar recharging taking place. And in ordinary times I should be able to add about 10-12kWH/day back into the battery.



I could go on and on about the project, but I'll just leave it there for now . . . just let me know if you have any questions. And many thanks to TNAndy who really helped me out a lot on this project!



Picture of roof flashfooting mounts:













Picture of rails:











Ironic picture of panels one day after the utility approved the system (covered by a dusting of snow):













Interlock kit -- you have to flip the main at the top before you can flip the backup power breaker:














Forklift battery -- 1400 pounds of lead and acid sitting on top of two auto dollies with a platform on top of them. Actually not too bad to move around on those:











Picture of what the Outback system looks like. Mounted in a tight space which probably wouldn't have been possible if I had to assemble the components myself:












Readout from the first day  with 8.2kWH produced:


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## txsteele (Nov 19, 2014)

So I'll understand if you don't want to answer, but what is "ball park" price on a system like that?


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## Dan in Ohio (Jul 16, 2005)

Panels, racking, combiner, Outback power system and cables were about $8,400. Probably another $300-400 in various odds and ends. About $3,800 for the forklift battery and then $2,200 for the electrician who provided the intermediate cabling and grounding materials and did the trenching and wiring. So, I think I ended up paying him somewhere between $1,000 and $1,500 for his labor. All in, just under $15k for the system, so about $10k after the federal tax credits. Could save maybe $2-3k if doing all the electrical work yourself and settling for a L-16 based battery bank. Otherwise, I don't think it could be done much cheaper for this type of system.

If you want solar and the best economic payback then grid-tie is the way to go since you could ditch the battery costs and some of the components can be cheaper.


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