Does this setup look right to you?

jtrevival
jtrevival Registered Users Posts: 3
Hi all,
I have been researching solar power systems for my DIY RV for a few weeks now, and trying to learn as much as I can. This is a ton of information to take in, but I think I'm starting to grasp the general idea, and I want to make sure I am on the right track before I invest the money in to these pieces of the puzzle.

After calculating my usage, my estimate is that I will use a maximum of ~450 amp hours/day. I want the system to be able charge primarily from solar.

I have come across a fantastic deal on some Kyocera 210 panels that were left over from a friends project. I have 4 or 6 panels that I can pick up for a great price, so I would like to utilize this and build this system on Kyocera 210 panels. I understand that these are 24v panels, so I will need and MPPT charge controller to correctly charge a 12 volt battery bank.

The inverter that has been a top contender for me is the Magnum MS10012. 1000 watts of output.

My planned battery bank setup is something like 4 x Trojan T-105's, do give me a total of ~450 usable amp hours/day without going below 50% charge.

My questions are:

-First of all, is this setup realistic (~450 amp hours from solar alone), or am I being a little too optimistic in this goal?

-Am I better off just building a 24v battery bank and system? In other words, am I selling myself short by converting to 12v, or could I make the whole thing more efficient and powerful by must going 24v?

-What kind of input and or wattage rating do I need for the MPPT charge controller, and do you guys have any recommendations there?

Thanks a lot for any help or insight you may have to offer. It will definitely be appreciated! I feel like I'm almost there, I just have a few more questions that are hanging me up. Hoping you guys can give me a little direction.

Best regards,
Jon

Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Does this setup look right to you?

    Welcome to the forum Jon.

    If you need 450 Amp hours @ 12 Volts per day you need at least 900 Amp hours of battery. Four T105's will get you 450 Amp hours @ 12 Volts, but you won't be able to use it all as you cannot discharge a battery below 50% capacity without it suffering damage.

    What you're looking at is (450 * 12) 5.4 kW hours of power. That's rather a lot. You'd need quite a bit of panel to provide that in most daylight conditions. Like about 1400 Watts. Have you got room for six of those 210 Watt panels? Probably not. What's worse is that the actual size battery bank would be double that, and need 90 Amps @ 12 VDC to charge properly. There you're looking at a MidNite Classic controller @ $600.

    And whereas a 24 Volt system is slightly more efficient than 12 Volts the same power problem would be there but without the ability to pull power from the vehicle's system if needed. Usually in RV apps it is best to stick with 12VDC.

    Maybe you should revisit the load calculations.
  • jtrevival
    jtrevival Registered Users Posts: 3
    Re: Does this setup look right to you?

    I truly appreciate the info and the fast response! Here is the spreadsheet for my calculations. Have I made an error here?
    Attachment not found.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Does this setup look right to you?

    Okay, let's start by making a couple of changes to how the calculations are done.

    Best: get a Kill-A-Watt meter and measure everything that plugs in. Why? Because the data given by the manufacturers is wildly inaccurate for estimating use. They inevitably give the operating Voltage and maximum current, which is not always how much is used.

    Second: skip trying to convert into DC Amp hours for each item. Go for Watt hours, because Watts are Watts at any Voltage. So your 200 Watt LCD TV (my 40" uses much less just by changing the video settings) for 4 hours is 800 Watt hours. Not to be sneezed at. Then you have to convert that to DC Watt hours by factoring the inverter efficiency. I can't find numbers for that inverter, but at 1kW it won't be any good trying to run some of your loads anyway. Go for a pure sine 2kW unit like the MS2012. This would be 89% efficient, so that 800 Watt hours becomes 898 Watt hours. You then have to include that the inverter itself draws 25 Watts, so over 4 hours that would be another 100 Watt hours. Bingo: just running the TV you've got 1kW hour DC. On 12 VDC that's 84 Amp hours, or a minimum 168 Amp hours @ 12 Volts just for the TV.

    Air conditioning is probably your worst load. Not only do A/C's have high start demands and running current, but they are unpredictable because they are controlled by a thermostat.

    The more accurate you can get the power consumption figures the better the system will work.
  • jtrevival
    jtrevival Registered Users Posts: 3
    Re: Does this setup look right to you?

    Ok. I feel like Im almost more confused now. Doesn't the 200 watt rating of the tv mean it would just use 20% of a 1000 watt inverter? What difference does it make how long you use it? Isn't that just dependent on the size of your battery bank?

    Also, after seeing my general ballpark usage requirements, what do you think would be the best thing I could do with 4 (I just measured and that's the max I can fit) Kyocera 210 panels? What kind of setup would you do? Is the bottom line that I am just going to have to supplement them with some other kind of power to charge my bank? I really wanted to avoid having to use a generator if possible. The chassis is a dual alternator Ford E450 7.3 with dual batteries. Knowing that, would you take this in any kind of different direction? Would it be smart to supplement my system with something like this?: http://www.bluesea.com/products/7622/ML-ACR_Automatic_Charging_Relay_with_Manual_Control_-_12V_DC_500A

    Sorry for all the questions, Im just feeling a little overwhelmed, and like I just circled back around to square one. Better I learn the error of my ways now than later though! Thanks so much for the help.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Does this setup look right to you?

    You always plan an off-grid system around the battery bank. So the primary consideration for that is the number of Watt hours you expect to use in a day. What you do not want to come up against is the power going out because the batteries are low and it's 9:00 PM. Nor do you want to drag the batteries down low repeatedly, if you can at all avoid it; that will shorten their lifespan.

    The inverter is sized to meet the total Watt demand at any given time. If you have a 1kW inverter and try to run a 1kW microwave from it, for example, you'd better not expect to run anything else at the same time. So if you add up all the running Watts of what you expect to be on at the same time you can 'run out of inverter' if it's only capable of 1000 Watts.

    Your coffee maker is 1kW (look into alternatives for that), your microwave is 1kW (do not rely on 'cooking power' as they draw more than that), and your A/C is 1kW (probably less as most 'window rattlers' run around 500 Watts). Have one of those on and turn on the light switch ... will the inverter handle it? Remember that some items (like the 'frige) will have a start surge that can be many times the running Wattage, and the inverter has to supply that too.

    Lastly, no one wants their inverter running at 100% capacity for long stretches. They produce more heat at full power and no electrical component likes heat.

    What can you manage with four 210 Watt panels? Quite a lot. That's 840 Watts; more than I run the whole cabin on. As such you could probably rely on it for 2 to 3 kW hours per day, with good sun and careful management. One of the problems with off-grid systems is that the more power that has to be stored in and taken from the batteries the less efficient they are. If you can make use of the power the panels are capable of during daylight after charging the batteries the efficiency improves. Otherwise that is power potential wasted. This is known as using opportunity loads.

    That same size array can charge 500 to 600 Amp hours of 12 Volt battery fairly well. If you were to go with your four T105's (450 Amp hours) it would work and possibly have a bit of extra capacity for less-than-sunny days (you'd be amazed how panel power drops off with clouds). That much battery, if limited to 25% DOD, would yield 1.35 kW hours. You could take the DOD up if needed and/or utilize some opportunity loads you could have that 2kW hours per day. You could use larger capacity batteries, but they may not fit in the available space and they will cost more per Watt hour.

    Dual battery/charging systems in RV's are quite common. I have heard people complain a lot about them, though, as they aren't all the same. A manual switch is often preferred to an automatic one. But the charging profile of an alternator isn't the same as what deep cycle batteries require. As such it can be a help for Bulk charging but don't expect it to do the Absorb stage.

    We're here to answer questions, so ask away. I know several of the forum members have RV applications and they can give you further insight from their experiences good and bad.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Does this setup look right to you?

    Also look at your devices and make sure you are using the most efficient possible for the job...

    200 watts for an LCD TV is a lot these days... You should be able to find a TV that uses a fraction of that amount (assuming you are not looking for a 60+ inch TV).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Does this setup look right to you?
    jtrevival wrote: »
    Here is the spreadsheet for my calculations. Have I made an error here?

    Your refrigerator is a problem. Your minifridge uses much more power than most full sized home refrigerators. This is either because your mini fridge is a huge energy hog, or because you calculated it wrong. Tell us more about your minifridge... Does it have a compressor? If so, it probably doesn't run 24 hrs/day. Is it a peltier device, or a dual fuel (propane/electric) running on electric?

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i