Looking for input on proposed system...

experimenterexperimenter Registered Users Posts: 20 ✭✭
Hi all. I'm starting to design a solar power off-grid system and am looking for input from people who have done this before. I'm following the overall advice from an Internet RV power write-up (although my system will not be for an RV). The schematic for this system is attached. This is near Seattle.

I have these components already:

1. Morningstar 60amp MPPT controller
2. SunXtender PVX-1040T batteries (3) -- 104 amp hour rating @ 24 hours
3. 3000 watt inverter (some Chinese make -- "AccuratePower" I think)
4. TM2025RV Trimetric 2025RV Battery System Monitor

I am thinking about ordering these panels from NAWS: Kyocera KD315GX-LPB 315 Watt Multicrystalline Solar Module (3).

I hope to power the following:

1. Electric heating panels that currently are wired into 200 amp grid service. They operate via thermostat. I can adjust several variables to alter the power draw of these panels -- I can turn the thermostat down, I can disconnect some of the panels and use fewer, etc. I don't know exactly how much power each panel draws but obviously it is less than 200 amps total (actually the breaker is a 30 amp breaker so it is less than 30 amps total or the breaker would flip).
2. A collection of small battery chargers -- for flashlights, portable power tools like drills, handheld radios, etc.
3. A few 120V lights -- currently all powered together on a 15 amp breaker.

All the above just need to operate 3-5 hours per day.

My questions are:

1. Is the above system "balanced" in terms of components that will work well together without one component "overpowering" another?
2. Given the schematic attached and the collection of components, could any licensed electrician put this safely together, or do I need to try and find a solar power electrician?

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Looking for input on proposed system...

    Welcome to the forum.

    And stop. Before you spend a dime.

    Rule #1 of designing an off-grid system is: Know Your Loads.
    Absolutely everything is dependent on that. Your first problem is those heating panels. Rule #2 is: Don't Use Electricity For Heating Anything.
    Here's why:
    30 Amps @ 240 Volts is 720 Watts. How long does it run for? Half the time? That would be over 8kW hours per day. Even on a 48 Volt system that's 180 Amp hours right there, meaning at least 360 Amp hours of battery to run just that.

    Without knowing how much power you need to supply any design will simply be a guess with a very large chance of being too small or too big.
  • experimenterexperimenter Registered Users Posts: 20 ✭✭
    Re: Looking for input on proposed system...

    What other options for heating are there? I don't have natural gas or propane (and don't want to lug in the tanks every so often). I suppose I can just use firewood, but that is fairly labor intensive also. My thinking was solar means the electricity comes in free (once I have the system paid for and installed) so I'll use what I can get. If that means I use only 1 panel 2 hours a day, so be it.

    Would the Morningstar controller shut off the panel output to the load if the batteries were taken below a set level?
  • offgrid meoffgrid me Solar Expert Posts: 119 ✭✭
    Re: Looking for input on proposed system...

    Actually the heaters alone if run for 3 hrs would draw 21kwh. If on a 48v battery that would be over 450ah and would require a 900ah battery bank just for the heaters. Definately not a good idea. With those 3 panels you could expect to generate about 1.8kwh of ac a day so you would be able to run the heaters for about .25hr. Not quite what you expected.
    Ned
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Looking for input on proposed system...

    Okay the problems with any type of hard-wired electric heater: 1). they are usually 240 VAC (therefore requiring an inverter capable of that Voltage); 2). they tend to be 1000+ Watts (requiring an inverter capable of that Wattage and a battery bank capable of backing it up); 3). they are thermostatically controlled which means you can't accurately predict how much power they will use. That last one is the worst. Who wants to freeze because it got too cold and there wasn't enough battery reserve?

    It is not impossible to heat with electric, but it is impractical. You have to build the system large enough to provide the necessary heat when needed (how cold does it get and for how long?) which usually means you have a large investment in equipment that you don't need/use when it isn't heating season.

    Here's another option: direct solar heat. I don't know your exact install, but if you have the ability to control the design you may be able to use passive solar. Some ideas along those lines can be found at Build It Solar: http://www.builditsolar.com/

    The other question: Some charge controllers have LOAD terminals, some don't. These are NOT for running inverters from! They are strictly for low Voltage, low current loads. Inverters have their own built-in safeguards against low Voltage, with varying degrees of flexibility. Some have a fixed low Voltage disconnect point, others have a programmable one. The latter is better as the fixed points tend to be too low to keep the battery state above 50% DOD.
  • icarusicarus Solar Expert Posts: 5,433 ✭✭✭✭
    Re: Looking for input on proposed system...

    Short on time right now, but if you have enough solar to even think about using PV to heat water, you have plenty to heat water directly. Very much cheaper and way much more efficient on a per BTU basis.

    Tony
  • BB.BB. Super Moderators, Administrators Posts: 31,614 admin
    Re: Looking for input on proposed system...

    Also, what is your weather at your location... If you are near Seattle Washington, would not you have a lot of marine layer issues (poor sun)? Using PV Watts for Seattle, fixed array tilted to latitude:
    Month    Solar Radiation (kWh/m 2/day)
    1      1.54     
    2      2.50     
    3      3.71     
    4      4.37     
    5      5.31     
    6      5.52     
    7      5.88     
    8      5.17     
    9      4.98     
    10      3.00     
    11      1.76     
    12      1.26     
    Year      3.76
    

    The winter sun is really poor... And with a fixed array, the summers are not great either.

    If you go with two axis tracking solar arrays (not cheap in itself), you can get some very nice summer power collection, but winter is still poor.
    Month    Solar Radiation (kWh/m 2/day)
    1      1.74     
    2      2.85     
    3      4.50     
    4      5.57     
    5      7.15     
    6      8.03     
    7      8.65     
    8      6.85     
    9      6.57     
    10      3.57     
    11      1.96     
    12      1.38     
    Year      4.91
    

    Nominally, I would suggest conservation: lots of insulation, double pane windows, construction with windows to collect winter sun, etc... And perhaps even a mini-split heat pump (can be 2+ times more efficient than a standard resistance heater--this thread is about the Sanyo product--which is no longer available--but still has a lot of information).

    Anything can be done, but it requires a lot of thought and planning to do it in a cost effective manner.

    Just to give you an idea--Say you had a fixed array, picked February as your "break even" month, and wanted 3.3 kWH per day (100 kWH per month)--That is enough to power an average small, every efficient/conservative power usage, off grid home/cabin in a mostly "modern" electrical world (excluding heat and air conditioning):
    • 3,300 WH per day * 1/0.52 off grid system efficiency * 1/2.50 hours of sun Feb fixed array = 2,538 Watt solar array minimum

    Assuming a 2 day battery backup (1-3 days recommended) and 50% maximum discharge (for longer battery life) with a 24 volt battery bank (larger battery banks usually need higher battery bank voltage), you would need around:
    • 3,300 WH * 1/0.85 inverter eff * 1/24 volt battery bank * 2 days no sun * 1/0.50 max discharge = 647 AH @ 24 volt battery bank (very near needing a 48 volt battery bank to reduce current/wire sizes)

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • experimenterexperimenter Registered Users Posts: 20 ✭✭
    Re: Looking for input on proposed system...

    OK, I can see the heating panels are out. I will check into the solar heating options.

    Will the system with components I laid out originally work well together to power the lights and battery chargers? And my other question -- do I need a specialized type of electrician to hook it all up?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Looking for input on proposed system...

    To tell the truth, the original diagram is a bit convoluted because it is for an RV not a fixed location off-grid system.

    For instance if you buy an inverter-charger you do not need an AC transfer switch (because it's built in) or a power converter (because the charger is built in). In fact you'll find the wiring is simpler.

    AC IN can be from a gen set or utility grid (although usually you don't go off grid if grid is available). When AC IN is energized it feeds all the loads on the inverter's output and causes the inverter to go into charge mode. When there is no power on the input the inverter draw from the batteries to supply the loads. The second (usually main) source of battery charging is from the panels via the charge controller.

    There are basically five separate but inter-acting circuits involved: Three DC and two AC. The DC circuits are between the panels and the charge controller, the charge controller to the batteries, and the batteries to the inverter (and any other DC loads). The AC circuits are the AC IN and AC OUT. The size of wiring and circuit protection used will depend on the final design, as Voltage, current, and wire length all have to be figured in.

    As for hiring an electrician, you would need one with experience in solar installs. For real, not just someone who thinks they can do it. Most electricians do not have DC experience and probably are not up on the NEC regulations regarding them.
  • experimenterexperimenter Registered Users Posts: 20 ✭✭
    Re: Looking for input on proposed system...

    So the Morningstar 60 amp controller has a transfer switch built in?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Looking for input on proposed system...
    So the Morningstar 60 amp controller has a transfer switch built in?

    No. An inverter-charger has a transfer switch built in. This is not the same thing as a charge controller.
  • BB.BB. Super Moderators, Administrators Posts: 31,614 admin
    Re: Looking for input on proposed system...

    An "inverter/charger" being an AC Inverter that usually has a AC power input (typically mains, sometimes an AC1 and AC2 for Mains and Backup Generator) where the Inverter will have three modes (sometimes more):
    1. Pass thru--AC power from Main (or generator) to AC Loads
    2. Pass thru+Charging--Same as #1, but also uses AC power to recharge battery bank
    3. Inverter--AC inverter supplying "protected" loads with AC power derived from DC Battery Bank (which may have its own solar panels+charge controller or even a DC genset or ACtoDC battery charger suppling power to the battery bank).

    The newer Inverter/Chargers have become quite complex... Some including Grid Tie operation (XW family), or ability to support AC loads with smaller AC backup genset (generator support mode), or ability to cut back on DC Charging current if the AC loads approach Generator/Main fuse capacity.

    Best way to start--define what you need (GT, Off Grid, Hybrid) and the basic operations (AC Genset, solar array, etc.)... Then we can help suggest a couple of products that may meet your needs--Then read the manuals.

    Starting a complex design with a complete blank slate (i.e, not knowing loads, on grid/off grid, etc.) conditions makes choosing an acceptable Inverter/Charge Controller/Battery bank a roll of the dice.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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