Inverters?

rick3x22rick3x22 Registered Users Posts: 5
I am a do it yourselfer and I want to get a Grid-Tie system set up here. My biggest obstacle right now is the inverter. What size do I need? I want to do this whole project in stages (possibly 100 panels). Do I use micro inverters for each panel? I want to make the panels too? Does the inverter have to be sized accurately to the panel output?

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Inverters?

    Welcome to the forum.

    Grid tie is probably not the best thing for the inexperience DIY guy to tackle. It has to be done with the co-operation of the utility and local inspectors to make sure everything is safe and the back-feed will actually sell to grid instead of running your meter up even more. It does not lend itself to stage increases for that reason: permits are given for a plan of a fixed size.

    There are three different types of GT solar inverter. The standard "central" inverter which runs off a single array of panels and feeds their output to the house wiring and/or grid; the micro-inverter systems where each panel has its own inverter (around 200 Watts) and their output goes to the house/grid; the hybrid system which has batteries for emergency power back-up in case the grid goes down. In all cases the solar GT Watts is limited by your service panel's capacity. The total panel amount will be determined by the size of the inverter; obviously you need 3kW+ of panel to get full power from a 3kW inverter.

    And the big question is: why do you want to do this?
    By itself, solar electric is nearly always more expensive than utility power. With proper incentives from government and/or utilities it can be viable (check local terms). Otherwise it will lower your electric bill without actually saving you money. Think $0.50 per kW hour vs. what your utility charges.

    Does that help?
  • vtmapsvtmaps Solar Expert Posts: 3,739 ✭✭✭✭
    Re: Inverters?
    rick3x22 wrote: »
    I am a do it yourselfer and <snip> I want to make the panels too?

    No way. Even if you could (and you can't) make a safe reliable efficient panel as cheap as you could buy one, it would not be legal or permitted because it lacks UL certification. Your insurance company can deny a claim if you have an electrical fire with unlisted equipment.
    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • rick3x22rick3x22 Registered Users Posts: 5
    Re: Inverters?

    Are you saying that once an array is installed that I will never be able to add another to increase production?

    I don't understand your last comment about cost effectiveness of solar electric. Could you clarify because I am really excited about getting this going. I am finding out that over half of the cost for solar installations is labor cost and material mark up. Last night I did some more searching and buying thee equipment would be easier and UL approved. The county inspectors out here are great to work with and are very helpful. I have no problem installing a system, it's the technical stuff that I need to find out about.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Inverters?

    you can probably add commercial pvs to commercial pvs that are already there and inspected, but no homemade pvs. the cost effective thing is that you can't make a pv with the same quality for the money as you get with a commercially made pv. to get them certified you would need to spend a huge amount for them to go through the wringer and you'd probably sacrifice a pv or 2 in that process. search the forums for diy threads.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Inverters?
    rick3x22 wrote: »
    Are you saying that once an array is installed that I will never be able to add another to increase production?

    That would depend on the size of the initial install. The NEC basically allows 20% back-feed maximum. In short form, a 200 Amp service would have the ability to handle 40 Amps from a GT solar power system - about 9.6 kW max (not precisely, but close enough for explanatory purposes). If you put 4kW in now, you could add 4kW later for example. But the permit will be for the install now, and another would be required for the next install to make sure the wiring isn't overloaded. The total will depend on what your utility feed capacity is (especially the bus bars in the main panel box).
    I don't understand your last comment about cost effectiveness of solar electric. Could you clarify because I am really excited about getting this going. I am finding out that over half of the cost for solar installations is labor cost and material mark up. Last night I did some more searching and buying thee equipment would be easier and UL approved. The county inspectors out here are great to work with and are very helpful. I have no problem installing a system, it's the technical stuff that I need to find out about.

    Solar comes with a price. That price is a capital investment cost. Amortized over the expected lifespan of the equipment and its anticipated power production this works out to a a certain amount per kW hour. Although panel prices have come down, the whole install cost may still be, say, $6 per Watt. So a 4kW system costs $24,000 to install. It will then produce certain amount of kW hours per day. Perhaps 12 on average (big variations here depending on location). That's 4380 kW hours per year. The equipment is expected to last 20 years, so its amortized value is roughly $1,200 per year. Divide that by the yearly power production and you get a cost of $0.27 per kW hour. Again, just an example not precise numbers. If you compare that (or better a real figure) to the rate the utility charges for power you'll see that it's not always economically feasible.

    To really get an idea of what you could expect, use the PV Watts http://www.nrel.gov/rredc/pvwatts/ program to run a few scenarios for your area. It will give you a fairly good idea of how much you can expect for different size arrays and orientations and what the value would be (with year-round data).

    If you can do the install yourself you will save substantially on the install. It must pass inspection and it's not the simplest thing in the world to do. That does not mean you wouldn't be able to do it! But be advised that the "technical stuff" is technical and encompasses more than just standard electrical wiring.

    You can spend some time reading through the grid-tie section here and see what some of the issues are that come up. It's good to be forewarned. :D

    But the big question remains: why were you thinking of doing this?
    I can't tell you how many times people say "to reduce my electric bill" without realizing they can do better at that through conservation. Conservation should be the first action in either case. You'd be amazed how many people are willing to drop $30,000 on a solar power system but balk at spending $3,000 to replace power-hungry appliances and lights!
  • rick3x22rick3x22 Registered Users Posts: 5
    Re: Inverters?

    So true! I have done all the energy saving changes I could think of, extra insulation, replaced all windows and doors, appliances and some lights(the ones we use regulary). I work at home, I have reduced my garbage to a small bag a month, No garbage service. I am on a well, No water bill, No sewer bill. Electric and Television is all that is left. I want to eliminate as much of my electric bill as possible. I know I can never get off the grid but it would be nice when I am retired to have next to no bills.
    I realize that when the power goes out the solar won't work. I have a generator for that. I do have a spring on the property. The flow may be enough to generate power but that is harder to find information and equipment.

    I have a 3000sqft house and average 2600KWH usage per year. It shouldn't take much to put a dent in that with solar panels?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Inverters?

    Let's see ... 2600 kW hours a year ... divide by 365 is 7.1 kW hours per day average. Or about 3 times as much as the cabin uses. :D

    You sure you've done all the conservation you can? :p

    So the next questions would be: 1). Does your utility allow grid tie? Do they buy surplus power? You have to look into that carefully. 2). Have you got a budget plan? It's usually best to go whole-hog right from the start if you can. 3). Site evaluation; has it got good southerly sun exposure? Are there going to be problems with shading from trees/poles/buildings at any time of the year? 4). How is the service panel? If its got 250 Amp bus bars in it you're good. If you don't know/can't tell you'll need a good electrician to evaluate that.

    Here's some example quotes from our host NAWS for various size GT systems, just to give you some idea as to costs: http://www.solar-electric.com/grtiesyexqu.html
    That doesn't mean you have to buy from them or buy any system like that; only an example. Note the 7kW system is about $20,000, not including installation or shipping, tax, et cetera.
  • rick3x22rick3x22 Registered Users Posts: 5
    Re: Inverters?

    Yes to all your questions, great exposure, even the buildings roof pitch is almost exact to what the angle should be for this area. I will have to upgade the panel but I was going to do it anyway.

    Lets say I put in a 7kW system. my array will be approx. 175 ft from the meter and house electrical panel. Estimated guess of wire size to house panel? Are we talking 60 amp disconnect? I am trenching a water line in this weekend and I want to drop a conduit in the trench for future wiring of this project.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Inverters?

    With that size system and 175 feet run @ 240 VAC you're looking at at least 8 AWG to keep the V-drop below 3% (rough calculation). The spec'd disconnect on that system is 30 Amp (30 * 240 = 7200 Watts). Depending on the exact unit you end up with it may be more or less.

    If you're doing trenching and conduit now, make it as large as you can afford. It never hurts to have extra space to run wires through. Like I said, you'd need at least 8 AWG for that 7kW system and you might want to run other wires for other things. Put some 1/4" nylon rope in it now too; makes it easier to pull the big wires through if you've something to attach them to.
  • rick3x22rick3x22 Registered Users Posts: 5
    Re: Inverters?

    You the MAN!!!! You have been an enormous help!!!! Thank you so much. In my case it just goes to show "It's not what you know, But who you know"

    Thanks again, I am sure I will be back when it is time to install!
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Inverters?

    You're welcome. :D

    In case anyone else is reading this I'll mention that 6 AWG would be even better for the 240 run because it would reduce the V-drop to less than 2% (based on the 7kW system). This is important on GT systems because the inverter periodically checks line Voltage and frequency to make sure the grid is up. If the wire allows too much drop the inverter may decide the grid is down and shut off. There are other factors that come in to this (like the actual grid Voltage supplied), but as a rule minimizing Voltage drop is always a good idea.
  • Ralph DayRalph Day Solar Expert Posts: 953 ✭✭✭✭
    Re: Inverters?

    Hi Marc
    My experience with grid tie and wire size: microFIT install with Enphase inverters about 200 feet from meter base connection. The electrician sourced #6 wire for 3% voltage drop or less (as per electrical code). When feeding power to the grid the voltage drop is reflected as a rise in voltage. As a result the enphase inverters were dropping out from too high a voltage. For me the terminus at the array will sometimes read 255vac or higher, now the inverters are programmed for the "extended voltage" of 260vac max. No problems since.

    Lesson learned...install with as large a guage wire as permitted by chequebook and electrical code...not the minimum. This results in about 1% less harvest as identical systems close by. (close to $1000 per year on payout, depending on the year)

    Ralph
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