A design for a 12 volt supply in rural communities of Cambodia.

I am designing a system for rural communities in Cambodia who are totally off-grid and unlikely to be in the near future. (Starting with a singular power-plant, which may well lead toward a ‘Micro-Grid’ by adding and linking other power-plants).

Appliance load would initially be just 12 volt LED lighting at night and 12 volt fans during the day and night. Plus charging of mobile phones. Luxury option would be to run a 12 volt TV. (The option to use inverters and 220 volt appliances would not be offered which simplifies things). This will be distributed to households.

As yet the demand amount is not known but it would be better to back-engineer and restrict the consumption dependent upon the supply.

I have built a swivel and tilt pole which supports the solar panel array. The apparatus restriction would be merely that of weight and windage. So let’s presume 4 panels of about 650 mm x 1200 mm dimensions (and the relevant weight); maximum.

So depending on the output of the panels comes the Amp rating of the Controller and whether to wire as 12 volt or 24 volt.

Question: If the panels and controller are wired at 24 volt, can 12 volt supply be taken from the battery bank? (I may be showing some naivety here, please excuse me).

Having produced X amount of amps from the panels, given that Cambodia has abundant sunshine even during the ‘Rainy’ season (which due to Global Warming isn’t happening dramatically) How many amp- hour/batteries are needed?


The communities chosen will be as dense as possible so that cable runs can be kept to a minimum. However houses could be 500 feet or more away from the batteries, what would a reasonable cable length and size be to carry the load without too much voltage drop?

Question: Can a large cable be connected between batteries and house and then a smaller size cable be used inside the house. (let’s say feeding a load 4 x 3Watt LED lights per household plus occasional phone charging and 12 volt TV use).

The solar controller could be set to deliver power until say 11pm and start up again at first light. That way nobody can leave a power demand on.

Question is there a device which will shut off the supply when the batteries have reached say 60% discharge? (or whatever you recommend).

I understand I am asking many questions and this is a multi-faceted topic, however I have confidence that you can help me build a rugged, perhaps over engineered power supply for rural communities.

Your help is assisting me in my humanitarian efforts to help people who have never experienced good quality lighting, which so often we take for granted. I thank you in advance of your reply.



  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    "houses could be 500 feet or more away from the batteries"

    If you are dealing with this much distance I believe, others may differ, that you will need to consider an inverter to send higher voltage, which will have less loss, to those houses.. you are dealing with "line loss" and you have to consider it in your planning of the system...
    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
  • BB.BB. Super Moderators, Administrators Posts: 30,505 admin
    Find a metric version (if needed) of voltage drop calculator like this:


    To send 1 amp @ 12 volts 500 feet with 0.5 volt maximum drop would take around 6 AWG cable. Almost $370 from our local hardware store (just for copper cable, 2x 500 feet).

    I would suggest, for very small installations, that you have each home setup with its own system. That way, each family is responsible for their equipment/maintenance/security.


    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • capitanojulianocapitanojuliano Registered Users Posts: 20
    Another approach: How about installing an inverter at the 'solar power station' and distributing 220 volts to re-chargeable bulbs at the household. Would the inverter have to be pure-sine-wave? Over what distance could 220 volts achieved to supply charging power for how many low wattage re-chargeable bulbs?
  • JohannJohann Solar Expert Posts: 244 ✭✭✭
    You got to know the power needs.
    If you have 10 families and each family uses one 10 watt led light bulb, that is 100 watt you need to generate per hour without losses, but you need to calculate the losses in.
    What about i-phones that may take 10 -15 watts or more per charge per phone, that would be about 300 watts per day if the phone is charged twice a day for 10 families.
    How much power does a fan take? just add this to your power needs 24 hrs a day. lets say a fan takes 30 watts an hr that is 7200 watts needed per day for 10 families.

    I am afraid,  you will outgrow your 4 panels ( about 120 watts each per dimensions you gave) by the time you hook 1 or 2 families up.
    And the batteries needed would be the financial killer since you would need a whole lot of them for just 10 families without the luxury package.

  • capitanojulianocapitanojuliano Registered Users Posts: 20
    Thank you all for your input. I have decided to go the route of including an inverter so that I can transport the power at 220 volts, lessening the need for particularly large cables.
    I know that my 20 amp unit is grossly under-powered but i have the controller already. I shall definitely build a much larger more powerful unit later.
    I am going to use the 20 amp unit and build to capacity and monitor the results. This will demonstrate feasibility albeit on a small scale.
    I will post the results and perhaps then you can suggest the required up-grade to increase the performance and number of households at a certain radius from the power-plant. Thank you in anticipation of your reply in a couple of weeks time when I get some performance figures.
  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    What brand is that charge controller?
    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
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