System to help Cambodia

capitanojuliano

Perhaps you may be able to help me.

I am building a system to provide 12 volt power supply in remote areas of Cambodia, these places are off the grid completely. They use kerosene lamps for lights which is a fire hazard. Also that light is poor for the developing eye sight of children. Anyway enough of explaining my motive.

The question is that I am building my system around the SBC 7120 controller

12 Volts with 20Amp maximum

Question: What is the maximum panel wattage I can run through this controller?

My mounting device will support the weight of 3 X 200 watt panel’s maximum; so nothing bigger than that. However will the controller manage that much panel output? 

BB.

OK, if this is the correct manual:

https://www.powerstream.com/z/7112Manu.pdf

It looks like 20 amps maximum continuous. The largest typical array would be:

• 20 amps * 17.5 volts Vmp (voltage maximum power) = 350 Watt array

If you wanted to be conservative, sometimes solar panels produce more power ("edge of clouds events"). Reduce array size by:

• 350 Watts * 0.85 derating = 298 Watt array (derated)
  

PWM type charge controllers are typically used for smaller systems. If you are going to build a larger system (600 Watts in your case?), you will probably want to look at a MPPT type charge controller (much more expensive) and larger format panels (typically >>140 watts) that are not Vmp~17.5 volts but Vmp~30 volts or more) as these panels are typically cheaper than the "12 volt/17.5Vmp" panels.

And do not forget the battery bank--We recommend a 5% to 13% rate of charge typically for solar systems with lead acid battery banks. For full time off grid, you should really design for 10% to 13% or so rate of charge. For a 20 amp array:

• 20 amps * 1/0.10 rate of charge = 200 AH @ 12 volt battery bank maximum recommended AH capacity

In general, the system will be much more reliable and your battery bank should last much longer.

Also pay attention to what type of batteries you will be using... In north America, a pair of 6 volt @ 200 AH "golf cart" style batteries are a good fit. Rugged and cheap. In other parts of the world, you may be left with car or truck batteries, which really do not like deep cycling (to 50% or less state of charge). "Marine" Batteries are not that much better than starting batteries (as deep cycle).

http://www.windsun.com/Batteries/Battery_FAQ.htm
http://www.batteryfaq.org/
http://batteryuniversity.com/

In many places, people do not pay much attention to the state of charge of the battery bank--They need power and will simply run the batteries until dead and you may get less (sometimes much less) than 1 year of life from the bank--So do not spend to much money on the first 1 to 2 battery banks until everything is working well and the people are trained.

Bringing  a few tools can help. A good hydrometer and DC current clamp/DMM will be handy:

http://www.solar-electric.com/midnite-solar-battery-hydrometer.html (will not break like glass hydrometer--rise after use)
http://www.sears.com/craftsman-digital-clamp-on-ammeter/p-03482369000P (cheap at ~60, good enough for our use)

-Bill

capitanojuliano

Those of you who have commented have been most useful, thank you.

capitanojuliano

Join me at entry level for an exciting and profitable project. Humanitarian and commercial offering of Solar Power in CAMBODIA.

Message me for discussion and to schedule a meeting if you are in Siem Reap

OR if you are still interested you may work from your home, even if it is outside of Cambodia.

capitanojuliano

I shall install 2 x 150 watt panels feeding through my controller to 1 x 100 AH Narada deep cycle 12 volt battery.
This is my demonstration model so I have only 20 x 3 Watt, light bulbs load, and plenty of SUN!
This way I can monitor the performance and build it up to maximum performance, adding more load and more battery storage whilst monitoring supply, load and cycling.

capitanojuliano

Join me at entry level for an exciting and profitable project. Humanitarian and commercial offering of Solar Power. Message me if you are in Siem Reap Cambodia for discussion and to schedule a meeting. Or if outside Cambodia help me from your home.

capitanojuliano

I shall install 2 x 150 watt panels feeding through my controller to 1 x 100 AH Narada deep cycle 12 volt batteries.
Question:
1) How many batteries of this type can I charge at one time (presuming a good supply of sunlight) over a period of 8 hours?
2) How many 3 watt LED lights can I run from each battery over a period of 12 hours to a 60% discharge from a 100%?
3) Given that a 3 watt LED light consumes X amount of energy, what amount of energy does a 12 volt MOBILE PHONE CHARGER need to charge a phone-battery from full discharge to fully charged, please quote in the equivalent of 3 watt LED light bulb hours usage.
Thank you for your help, it is much appreciated and will lead to completion of my project to provide of light and power to rural communities in Cambodia.

BB.

I shall install 2 x 150 watt panels feeding through my controller to 1 x 100 AH Narada deep cycle 12 volt batteries.
Question:

OK, the typical current would be:

• 300 Watts * 0.77 panel+controller derating * 1/14.5 volts charging = 15.9 Amps
• 15.9 amps / 100 AH battery = 0.159 = 15.9% rate of charge

Certainly a good start.... I would prefer to see you with a larger array vs a smaller array (we usually recommend around 5% to 13% rate of charge with solar array). Just watch the battery temperature (possible to over heat battery if you charge it "very hard" (high voltage) with a larger array.

1) How many batteries of this type can I charge at one time (presuming a good supply of sunlight) over a period of 8 hours?

Ideally for a deep cycle battery--10% rate of charge is recommended minimum by many battery manufacturers. The minimum rate of charge (again what we recommend) is 5%. So, you could (in theory) charge 3x 100 AH batteries for ~5% rate of charge (one battery is ~16% rate of charge, 3 of them in parallel would be ~5%).

Note--With lead acid batteries... You do need to recharge them between uses... Say you want 50% to 90% cycling. With 10% rate of charge, that would take ~4 hours minimum of sun (most places get ~4-6 hours per day of "noon time sun" energy over the entire day. And remember that Lead Acid batteries take ~2-4+ hours of "absorb" (or constant voltage charging) to fully recharge.

With 10% rate of charge on one battery (50-90%+ state of charge cycling)--You can recharge ~1 1/2x 100 AH batteries per day.

If you have 5% rate of charge and discharge to 50%, and you want to recharge 3x 100 AH batteries, your system would take ~2-3 days to fully recharge a set of batteries.

2) How many 3 watt LED lights can I run from each battery over a period of 12 hours to a 60% discharge from a 100%?

Assuming 100 AH battery cycling 90% to 60% state of charge (40% or 0.40 cycling of capacity):

• 0.40 cycling * 100 AH battery bank * 12 volt battery voltage = 480 Watt*Hours
• 480 Watt*Hours / 12 hours = 40 Watt average load
  
• 40 Watt total load / 3 Watt lights = 13.3 loads ~ 13x (3 watt) Lights (for 12 hours a night)
  

3) Given that a 3 watt LED light consumes X amount of energy, what amount of energy does a 12 volt MOBILE PHONE CHARGER need to charge a phone-battery from full discharge to fully charged, please quote in the equivalent of 3 watt LED light bulb hours usage.

Mobile phone usage is a bit more difficult to estimate... A "dumb" phone may draw 0.5 amps @ 5 volts for 1 hour... A "smart phone" may draw 1.5 amps @ 5 volts for 2-3 hours...

• 0.5 amps * 5 volts * 1 hours = 2.5 Watt*hours (i.e., about 1x 3 watt light for 1 hour)
• 1.5 amps * 5 volts * 3 hours = 22.5 Watt*hours (about 1x 3 watt light for ~8 hours)

You can measure smaller DC loads with a DC AH/WH meter like this one (there are a dozen knock offs from China that are almost identical--if not sometimes better):

http://www.rc-electronics-usa.com/electrical-test-equipment.html (Watts Up or Doc Wattson or similar)

Just connect your (small--~15 amp maximum) DC loads through the meter and it will tell you pretty much all you need to know about your loads/energy usage. Note: These are not "Battery Monitors" like we use the term (keep track of battery state of charge). Typically, battery monitors cost 3x or more the price of a Doc Wattson.

http://www.solar-electric.com/batteries-meters-accessories/metersmonitors.html

-Bill