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Thread: Got my solar power off-grid system up and running (finally)

  1. #1
    LHBA Member kahle's Avatar
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    Got my solar power off-grid system up and running (finally)

    IMG_0651.jpgIMG_0649.jpg

    I've been working on this for a long time and I finally got my solar power system all set up and functioning. I ended up designing it myself mostly because I couldn't find anyone that was willing to do much more than just sell me a package. I made the mistake of buying my Solar Panels back in 2007 when I first started thinking about this. That turned out to be a HUGE mistake because the price of PVs has dropped considerably since then. If I had waited until this year to buy them I would have paid 1/4 of what I did back then.

    The good news is I found a 2000 Watt Pure-Sign Wave inverter on Amazon for only $340 bucks.

    Anyway, I've never seen any kind of guide that would tell you the proper ratio between you PV watt size and your battery KWh size. I ended up with only 250 watts of PV and 5.4 kWh for a battery bank. In my case, I often only use the cabin on weekends so there is a long time for recovery. That's why I figured I could get away with this particular ratio. But some of the cabin kits I saw had even worse ratios than that.

    I went with a 24v system because (1) I don't really have any need for any 12V DC takeoffs, and (2) doubling the voltage allowed me to use smaller wiring.

    I got a 2000 Watt inverter even though my lighting load is pretty small. Maybe 300 watts total. But my occasional loads, a circular saw, a hair dryer, a vacuum cleaner or a waffle iron should run without an issue there. The inverter eats up about 50 watts of power just being on and maybe a smaller one would consume less. I'm not all that familiar with inverters. Maybe that's a big energy debt to pay for the small amount of power I actually need?

    My charge controller can handle another 500 watts of PV if I want to add them later. But I'm just going to see how well this works first before I start to tinker.

    Anyway, anybody want to critique my design, feel free.

    Paul

  2. #2
    LHBA Member rreidnauer's Avatar
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    Quote Originally Posted by kahle View Post
    I've been working on this for a long time and I finally got my solar power system all set up and functioning. I ended up designing it myself mostly because I couldn't find anyone that was willing to do much more than just sell me a package. I made the mistake of buying my Solar Panels back in 2007 when I first started thinking about this. That turned out to be a HUGE mistake because the price of PVs has dropped considerably since then. If I had waited until this year to buy them I would have paid 1/4 of what I did back then.
    Yea. I made the very same mistake. Thought there was going to be a supply/demand issue when energy prices went nuts back then, and I thought I done real good at $4/watt. (LOL)

    The good news is I found a 2000 Watt Pure-Sign Wave inverter on Amazon for only $340 bucks.

    Anyway, I've never seen any kind of guide that would tell you the proper ratio between you PV watt size and your battery KWh size. I ended up with only 250 watts of PV and 5.4 kWh for a battery bank. In my case, I often only use the cabin on weekends so there is a long time for recovery. That's why I figured I could get away with this particular ratio. But some of the cabin kits I saw had even worse ratios than that.
    Really? Actually there is a standard, and I know I've even posted it on these forums several times. Anyhow, the best ratio is 20:1 (battery watt-hours to panel watts) It's basically figured by taking the top 25% of your battery bank's capacity, and figuring five hours to recharge that. However, the ratio gets smaller if you are using more power and/or figuring multiple 'non-charging' days. A lower ratio isn't harmful, just inefficient.

    I went with a 24v system because (1) I don't really have any need for any 12V DC takeoffs, and (2) doubling the voltage allowed me to use smaller wiring.

    I got a 2000 Watt inverter even though my lighting load is pretty small. Maybe 300 watts total. But my occasional loads, a circular saw, a hair dryer, a vacuum cleaner or a waffle iron should run without an issue there. The inverter eats up about 50 watts of power just being on and maybe a smaller one would consume less. I'm not all that familiar with inverters. Maybe that's a big energy debt to pay for the small amount of power I actually need?
    Using a modified wave inverter is way more efficient on standby power usage. It's what I use in my RV right now, since I don't have any AC motors that need to be driven. (the only real need for pure sine wave) You may want to consider getting a second inverter to run the lighting and resistive loads, and save the pure sine for your AC motor needs.

    My charge controller can handle another 500 watts of PV if I want to add them later. But I'm just going to see how well this works first before I start to tinker.
    Usually charge controllers are rated in amps. What do you got? I STRONGLY recommend MPPT charge controllers. (that's a type, not a brand)

    Anyway, anybody want to critique my design, feel free.

    Paul
    All my bad forum habits I learned from LHN

    Rod Reidnauer
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  3. #3
    LHBA Member rreidnauer's Avatar
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    Oh, and is that AC switch being used on DC?
    All my bad forum habits I learned from LHN

    Rod Reidnauer
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    Thinking outside the vinyl sided box

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    LHBA Member loghousenut's Avatar
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    Quote Originally Posted by rreidnauer View Post
    Oh, and is that AC switch being used on DC?
    I think that switch is on the AC side. I'm wondering if you couldn't bump up the wire size from battery to inverter. Not a long run but that is the side where less resistance really matters.

    I can't chime in on the sine wave inverter thing. When we bought our inverter, we thought we were getting a bargain at $1 per watt for our 2,000 watt Trace square wave. I guess it has been a few years. By the way, that inverter and the expensive solar panels are still going strong in the bus after all those years.
    Every time I have strayed from the teachings of Skip Ellsworth it has cost me money.

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    LHBA Member kahle's Avatar
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    Quote Originally Posted by rreidnauer View Post
    Oh, and is that AC switch being used on DC?
    I must confess that that standard light switch is the one I use to isolate the PV array from the rest. I figured it wouldn't matter much since it's only a 10 amp load. Did I figure wrong?

  6. #6
    LHBA Member rreidnauer's Avatar
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    I thought so. Yes, it could come back to haunt you. DC can carry an arc quite easily when opening contacts. And in an AC only rated switch, the open contact gap is small, and opens relatively slow, which allows a DC arc to burn the contacts. The main time you'd do damage, is turning the switch off when the panels are in full sunlight. Eventually, the switch won't turn back on, or worse, could catch on fire with a sustained arc. (you'll hear the hiss of an arc in the switch)
    All my bad forum habits I learned from LHN

    Rod Reidnauer
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    Thinking outside the vinyl sided box

  7. #7
    LHBA Member kahle's Avatar
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    The charge controller I got is http://www.theinverterstore.com/30-a...-24-volt.html# this one which does not specifically say it is MPPT but from the description, I figured that it was the same thing. This is rated at 30 amps.

    The reason I used the AC switch is that I didn't see any DC switches listed anywhere. Can you point me to a supplier? Or better yet, an actual switch?
    I'm not sure it makes much difference, I only use the switch when I'm working on the control panel and I'm hoping that part is done with for now.

    Ron mentioned the size of the wires I have used between the battery and the inverter. I thought they looked small too. But those are the wires that came with the inverter so I figured they had to be sized correctly. No? Should I upgrade?

  8. #8
    LHBA Member loghousenut's Avatar
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    They are not the largest battery cables in the world. In the dark ages the folks over at Home Power Magazine always preached upsizing those inverter cables. Said it was cheap efficiency that lasted longer than the installer. We used 0000 size on our 2000w system but twice the length you have.

    As for the AC switch, I thought Rod was talking about the master switch. When I built the 12 system in the bus some 30 years ago I put in mostly used 110v switches and they are still going strong. They don't work anymore but they look good.

    Probably ought to either change it or eliminate it altogether. I'd feel safe with no switch there at all.
    Every time I have strayed from the teachings of Skip Ellsworth it has cost me money.

  9. #9
    LHBA Member rreidnauer's Avatar
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    That charge controller you have is PWM. (pulse width modulation) You won't get all the power available out of your panels, like you would with an MPPT. (maximum power point tracking) It's all in how they function, and I won't go into all that, but PWM will create panel performance losses of around 30%. (you will only get about 70% of the rated power of the panel) MPPT will have practically no losses. (in fact, I've seen slightly over 400 watts being extracted from my 350 watt array at one point!) But the real advantage isn't the performance loss advantage. It's the flexibility the controller provides. I can use the same controller to run a 12, 24, 36, 48, or 60 volt battery bank, and I can send any PV voltage from bank voltage up to 150 volts to the controller. The advantages being, it makes expanding the system easy, and your wire sizes can be much smaller and have lower loses at those high PV voltages. Granted, you will pay for that benefit.

    The switch: I'd trade it out for a DC breaker instead.

    As for wire size to the inverter, like LHN said, bigger is always better. I found the cheapest places to get heavy cables made up are at those battery warehouse store locations. But you don't have to abandon you existing cables either. You can always parallel on another of equal gauge.

    I put in mostly used 110v switches and they are still going strong. They don't work anymore but they look good.
    I'm still trying to figure out what politician LHN is trying to mimic with that line.
    All my bad forum habits I learned from LHN

    Rod Reidnauer
    Class of Apr. 9-10, 2005
    Thinking outside the vinyl sided box

  10. #10
    LHBA Member StressMan79's Avatar
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    Don't remember but I think ac switches are OK up to 50 volts dc.

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