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Thread: Solar questions

  1. #1
    LHBA Member dustinfife's Avatar
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    Solar questions

    Howdy!

    I'm looking to DIY some solar stuff for the house and had a bunch of questions. Based on what I've researched, it seems I'll need about 20 300W panels if I want to produce all my own power (24.39 kwh/day, 5 hours of sunlight/day assuming 80% efficiency). Now for the questions:

    1. I assume I need to have an inverted capable of handling that much solar. I'm seeing a lot of inverters with 1000W, but not much higher than that. I'm assuming if I tie a 2400 W solar system into a 1000W inverter, I'll start seeing things turn to smoke. Am I right? If so, do I just wire the inverters in series as I would with the solar panels? Or do I just buy one mega-inverter capable of handling 2400W?

    2. I'd like to take advantage of SRECs, net metering, rebates, and the like, but I'd also like to have a system that keeps my home electrified if the SHTF. Is it possible to have a grid-tied system that I can switch to off-grid in the event of a power outage (or grid failure)? If so, will that require a separate inverter?

    3. I've heard it said that DIY solar "packages" tend to be way more expensive than just buying the products separately. What is everyone else's experience with that? Just a quick perusal, I see:

    300W solar panels for around $390 (http://amzn.to/21a3aPu), or about $8K for all my solar panels
    3000W inverters for $311 (http://amzn.to/1YbKlff), or about $650 for the entire setup.
    cables and such ($100??)
    a mounting system of some sort ($300 max if I use PT posts, plywood, and concrete--totally just making this estimate up)

    So, for all that, I'd be putting in about $950. When I price out a system on wholesalesolar.com, I find an equivalent system equal to just over $9k. Of course, the advantage of buying the products separately is I can build up my solar panels over time, but I'd have to buy it all at once if I invested in wholsalesolar.

    So, am I missing something here? Were those youtubers and DIY wonks off their rockers?

    Thanks in advance!

  2. #2
    will an MTTP charge controller fit into your plan?
    hopefully Peter or Rod will chime in soon!

  3. #3
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    1.
    20 panels @ 300 watts gives 6,000 watts (or 6 KW). Multiply by 80% and you get 4,800 watts. But you might have bright sunny days when the panels are still relatively new, and not need to derate like that. I would plan on the full 6,000 watts for your usage, to be safe.

    You might be able to find a big inverter for that, but what I did was buy Outback inverters, ones that are "stackable". That means you can wire two inverters of 3,000 watts each to provide 6,000 watts. Be careful, though, you don't just connect the power wires. They have a special separate connector so the two inverters can communicate and one will "lead" while the other "follows". Instructions cover all that, but in short, you can sum inverters that are designed to do just that.

    2.
    Grid-tie brings up Outback again. They are moving all their inverters to grid-tie, as an option. It does what you describe.

    3.
    Packages do generally run higher, because someone has already done the mixing and matching to get something reasonable. I paid 25 cents per watt for my panels, plus shipping. That is a steal, but you can easily get panels for 50 cents per watt.

    Also, be careful about inverter prices. The cheapest seem to be Chinese made, and while that often is fine, in the world of inverters, that's a bad thing. Power specs are exaggerated significantly. US makers might exaggerate a little, but their numbers are realistic for design purposes. And quality is generally better here, too.

    I can't help with mounting equipment pricing.

    Also, the inverters are going to expect 12, 24, or 48 volts input, and the panels alone will vary widely throughout the day. It's more efficient to feed solar panel power into a MPPT charge controller to charge a battery bank, and have the bank supply the inverters. And that comment opens up a can of worms about your intended usage. Batteries can be the most expensive part of a system, but if you're only operating during the day, you could get away with a small bank. But that's a pretty restrictive (unrealistic) scenario for most people.

    There is another thread around here someplace which covers solar options in great detail, maybe within the last year or two. Sorry, I don't have the link handy.


    Peter
    Last edited by donjuedo; 10-09-2016 at 05:52 PM. Reason: spelling fix

  4. #4
    LHBA Member rreidnauer's Avatar
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    1.) You need to go with higher voltages to find higher wattage inverters. Think 48v. (yes, those solar panels you linked will work with 48v inverters) Second half of question, no, a lower wattage inverter tied to higher capacity will not burn it out. The charge controller will simply regulate power into the battery bank, (and yes, that should be an MPPT type charge controller) and the inverter will pull what it needs from the battery bank.

    2.) I believe there are dual system inverters already available, that are grid-tie with battery bank. (truly the best use of solar panels) You could install two separate systems, but gets pretty complicated tying in the panels.

    3.) Yea, most the time, you're going to be able to do better sourcing components yourself, than those online package deals. However, having a local distributor/installer may be able to offer a better value. Just watch out for being talked into more than you want.

    Sent from my Galaxy Edge+ using Tapatalk
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  5. #5
    LHBA Member badsign's Avatar
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    do microinvertors(enphase), each panel to have its own @ about 140 bucks an invertor
    315 watt solar panel around 330 bucks each.

  6. #6
    LHBA Member loghousenut's Avatar
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    OK, Badsign... say it again, real slowly, and I will try and figure out an answer.
    And you thought he was unteachable!

    Every time I have strayed from the teachings of Skip Ellsworth it has cost me money.

  7. #7
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    LHN, there is a company, Enphase (https://enphase.com/en-us/homeowners) that manufacturers a different type of power inverter, called "micro-inverter". Two things make it different, as I recall. One is that only one solar panel supplies input power to the inverter (or maybe one string). The second is that many inverters can have their 120 Volts AC connected to each other, and to the grid. Somehow, they magically know about each other, so that when the grid goes down, they all go down, and no electric company lineman gets killed by the inverters.

    My brother has 49 of these hooked up like this, with no batteries. In effect, it's like the grid is his battery, infinite in size. He stores all the energy he wants in the grid, and uses from the grid when use exceeds solar production. Naturally, the electric company buys at a low rate, and sells at a high rate, but that is the classic formula for profit, and also a different subject.

    I steered clear of these largely because the cost per watt was just too high for me to pry open my wallet. Instead, I paid a small fortune for NiFe batteries, at half the rate of US sellers. More on that later.


    Peter

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