Off Grid pv system abroad ideas/help/reassurance required!

[unclebob]

Hello!

I’m after some advise/just to bounce ideas off and for someone to pick holes at my plan so I can address any issues at the early stages before I splash the cash and fall on my a$$!.

I’m looking to setup 7 LED lights to come on at dusk and off at dawn (or there about!) in India. Based on what I can find on the web, the shortest day in the year gets approx 10hours 50 min of day light.

The lights:

I have purchased some LED lights, they come with a transformer labelled up as:
12v 175mA output.

However when I measured the voltage using a multi-meter, the transformer was pushing 24v out, with the light connected and lit up. If i connected up 12v the light didnt come on!. The current draw was showing as 0.1A in my meter, but I suspect that this is because the meter can’t measure anything lower! Is there any other way I can confirm the voltage draw?

So calculations for battery requirements are as follows:

1 light:

I= 0.175
V=24
P=VI = 4.2w

7 lights = 4.2w*7 = 29.4w

Assuming I need to run for 14 hours at a max,
29.4w *14 = 411watt Hours required for lighting.
I will also be adding in a circuit to control when the lights come on and off, and also a controller for a fan (PV’s are apparently less efficient above 25 Degrees C so look to see if I can keep them cool using a fan/number of fans).

I am also intending to run a house alarm and CCTV system off this, but as yet I haven’t calculated the requirements for the systems. I’m hoping that I do not need to invert up to 240v AC to then have the alarm/cctv drop it back down to 12v DC (so I’m looking to bypass the transformers built into the devices!)

Add a bit for the controllers, alarms and errors in measurements and estimate 1000w hours

Given that where the property is in India, even a cloudy day is bright sunshine for 99% of the day, I’m not concerned to much about not having enough to go more then 14 hours without light.


Can someone help me with calculating the battery bank sizing and pv array sizing?

Using this calculator:
(Off Grid Calculator)
Given that when its cold at night it gets down to about 5-6 degrees C, the battery bank capacity is:

Battery Bank Capacity: 125 amp hours
3 String Configuration: 42 amp hours per string

• Can someone explain the 3 string config? Is it literally having three sets of batteries connected in parallel? Each providing 42amp hours?

I’ve set average sun-hours as 4 (the property is between 4 and 5 but just to be on the safe side) which then states I need 325w worth of generating solar power, and a charge controller that can handle 17 Amps.

• Does this sound reasonable in terms of requirements?
• Finally, Does anyone have any experiences of using/heard much about PV-T panels? Given that the average daytime temp these panels will be used in will be 35 degrees plus, I'm considering using PV-T to cool the panels for efficient and also to provide hot/warm water as an extra.

 

[moggy1968]

are you sure the lights were DC? if not you were pushing in 12vDC by the sounds of it into an AC light, which is why they didn't work!
As I have suggested elswhere the SOlar Electricity Handbook by Michael Boxwell is specific to this type of setup and well worth a read.

There is an element of experimentation involved in a setup like this. Also don't forget batteries will degrade over time. You may find three strings is better because of the difficulty of stringing enough batteries together to achieve your required amp/hrs.

 

[unclebob]

are you sure the lights were DC? if not you were pushing in 12vDC by the sounds of it into an AC light, which is why they didn't work!

Im 99% sure they are DC - when i connected the multi meter up to measure output from the transformer, it displayed 24vdc, but i will confirm and check it again tonight. I will also check the 2nd 12v source is also 12V DC/AC as the first.

I would take a pic and post it up but cant link pictures yet.

 

[unclebob]

If it makes any difference, I'm looking at the following layout:

Given that i can upload images, ill upload the photo of the transformer and light tonight when i get home too.

 

[unclebob]

So here's the photos for the transformer:


It is DC..

Took a few more measurements today:
if i dont have any load, the voltage on the output is 38V,
When i connect the light, this drops down to 24V...
So is the light actually drawing 14V?

Also here is the other 12V adaptor i tried:


This is 12v with no load, and both have the same polarity.