Newbie need to build a system

eriepiper
eriepiper Registered Users Posts: 3
Hello,

I am working with a group of high school students to re-purpose a shipping container as a medical/dental clinic. It will be shipped to the slums of Mexico City in September. We have received a donation of 4 solar panels. I've done the math, calculated loads and have put together some off grid system components. I have had a couple local people offer to help spec this out and both flaked out on me so I've put together something I think should get them started. I would appreciate any comments or thoughts.

These are the specs on the components I've selected:

• 4 Panels @ 250 watts each, output voltage is 30v. Wired in parallel for total of 1kw (we have these)

Yet to purchase:

• 60 amp PWM Morningstar charge controller
• 2-12v 105ah deep cycle batteries wired in series
• 2400 watt 24v modified sine wave inverter/charger

These are the major components. We are running some led lights on the DC side. On the AC side will be small medical tools, dental drill, small pump. Cost and expandability are important. What jumps out at me is battery storage looks low, but we can add more later and I am up against my budget with just those two. Considering this is going into an area where there is no available power at all my hope is this will get them something to work with.

We're shipping the clinic to Mexico City in about a month and want to ship the system with the clinic, so I want to order this week.

Thank you in advance!

David Clark

Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Newbie need to build a system

    Welcome to the forum David.

    You can not use those panels in parallel on a 24 Volt system. The Vmp is too low to properly charge it, especially in Mexico's heat. The V-drop will bring the Voltage down below the Absorb charge level.

    You need to use an MPPT type controller and wire the panels as two parallel strings of two in series. That should get you around 32 Amps peak output. You could do his on a MidNite Kid and sacrifice two Amps.

    The good news is that it will handle more than 105 Amp hours @ 24 Volts. You have enough charge power there for at least a string of GC2's (220 Amp hour 6 Volts) and up to 300 Amp hours. You may think this is unnecessary but having the extra stored capacity will be a big improvement. As it is with 105 Amp hours you have about 1kW hour available at 50% DOD. If you could go up to Crown 305 Amp hour units you'd have 3kW hours available. Even the GC2's @ 220 would be an improvement. Otherwise you are limiting your "non sun hour" capacity. Adding more later is not as easy as it sounds: old batteries rob power from new batteries. The older and more used, the worse the problem.

    Skip the MSW inverter. I'm not sure the power specs on dental equipment but it isn't worth the risk. Motors and such do not like MSW waveform and will draw more power and run hotter. Samlex/Cotek makes some decent lower-cost sine wave inverters. I doubt you will need 2400 Watts. A 2kW Samlex unit is <$650 and you probably could get by with 1500 Watts for <$500.
  • eriepiper
    eriepiper Registered Users Posts: 3
    Re: Newbie need to build a system

    Thank you so much. Based on your reply it now looks like this:

    Four panels @250 watts each, two parallel strings of two in series
    MNKid MPPT Controller
    4-6v GC2 Batteries in series
    Samlex SA-1500-124 1500-watt 24V Pure Sine Wave converter

    This all comes in right around the price point I was looking at for my first pass, glad I asked!
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Newbie need to build a system
    eriepiper wrote: »
    Thank you so much. Based on your reply it now looks like this:

    Four panels @250 watts each, two parallel strings of two in series
    MNKid MPPT Controller
    4-6v GC2 Batteries in series
    Samlex SA-1500-124 1500-watt 24V Pure Sine Wave converter

    This all comes in right around the price point I was looking at for my first pass, glad I asked!

    It will work better too. :D
  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    Re: Newbie need to build a system

    Believe that dental drills still use compressed air. You should determine the requirements needed to run the drills. Dental lighting can be expensive, and the older low-tech Halogen lights may burn a bit of power, too.

    AND, perhaps one of the largest issues could be cooling/ventilation for the interior space.

    You MIGHT also need a bit of refrigeration, as well, for some of the supplies. Many of these items may need quite a bit of power to run, and some could have high start-up surges. Not to precip on the parade.

    Sounds like a very worthy project, especially for the students. FWIW, Good Luck, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Newbie need to build a system

    A big question would be: is a generator available? Back-up power, both for running things and charging batteries, is a good thing.

    If motors are an issue you may want to switch up to the Samlex SA series inverter: http://www.solar-electric.com/inverters-controllers-accessories/inverters/sasiwain1/samlex-sa-series-pure-sine-wave-inverters/samlex-sa-1500-124-sine-wave-inverter.html Not much difference in price but better at handling motor loads.
  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Newbie need to build a system

    Do you anticipate the use to be during the day or at night? If during the day you will need the batteries for handling the surge of the electric motor(s) startup but lights etc can be run , essentially , right from the panels. Caveat, you have to make sure the batteries get charged up as well is you are going to use what we call 'Opportunity loads' that is, using the power available after the batteries reach Float stage of charge. The power a PV panel makes is lost if not used...

    If you are going to have a generator there are other strategies available. It doesn't necessarily have to be a big one either...

    hth
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • eriepiper
    eriepiper Registered Users Posts: 3
    Re: Newbie need to build a system

    Thank you all for your wonderful help, I feel much more confident that we can actually pull this off. We'll be cutting five windows in the container, so we hope that will create enough ambient light and ventilation. The clinic is nearly done and you can see pics of it at http://davincilab.org/container if interested. I'll be going down with a few students end of October to set it up, I'm sure I'll have questions then and know a friendly group where I can get answers. :D