Solar lights a challenge

[Argyll]

SE & KE I'll upload a YouTube video next time I'm out on site to give you an idea of what I need. Just to make sure it's what I need.

[Someone-Else]

Argyll, you could always describe what you want to do. One thing is for sure though, without sunshine nothing much is going to happen.

[OchAye]

This is interesting.

Could this set up be used to trickle charge a 12v battery?

There are or there have been chargers for car batteries, unless I am missing something.

[Argyll]

I run traffic counters installed in a roadside cabinet. These are powered by 12v 22ah batteries. The batteries normally last about 30 days depending on the temperature. When the voltage on the battery drops to under 6v the traffic counter cuts out. Most of the time I can get out on site before the voltage drops but not always. Sometimes when the voltage drops below 6v I can't recharge the battery so it's kaput.

I want to install a solar panel on top of the roadside cabinet to trickle charge the battery so in case I can't get to the site in time the battery still has enough voltage in it.

[Someone-Else]

Anything to do with Traffic Master?

In your case I would say a solar panel and regulator would be of use, BUT the question is would it be worth it?

You say you would have to mount the panel to the cabinet. We would need to know the dimensions of said cabinets "top" to see which size (capacity) of solar panel would physically fit (Assuming you are fixing it directly to the top and flat) Also we would need to know the current draw of your counter.

The obvious thing to consider is the amount, or lack of sunshine each panel will get.

[kellys_eye]

Self adhesive solar panels are available - generally used on roof tops of boats - which will deliver enough current to keep a battery charged quite easily.

Usual problems would be vandalism and getting the cables routed in.

The chances of going 30 days with zero sunshine is pretty low (even over cast skies can deliver 'some' charge) and with the existing circuitry drawing 22/(30 x 24) only 50mA (or thereabouts) a solar panel delivering only 1 watt could not only power the unit but charge a battery whilst it's at it.

A perfectly feasible solution IF you get the right panel.

[Argyll]

So when you say "the right panel" do you mean in terms of size? Presumably the bigger the panel the higher the outage?

[kellys_eye]

Panel output is stated in wattage - they can vary in voltage so you have to pick'n'chose. Additionally their output isn't stable - it varies depending on the level of light hitting it and the stated voltage is usually the maximum available when the sun is perpendicular to it.

Solar panels, to be properly useful, require what are called Maximum Power Point Transfer (MPPT) controllers to be attached. These deliver a stable output voltage regardless of the input from the solar panel so a device would provide (say) 12V output even if the sun was dimmed by cloud. The total POWER they deliver will vary but the voltage will be constant i.e. they will provide 12V constantly but the maximum current you could draw would vary depending on the light level.

Solar panels used to 'simply' recharge batteries will have an output that exceeds the required battery charging VOLTAGE i.e. to charge a 12V battery you need to apply 14-ish volts minimum, and the current is usually limited by the inclusion of a series resistor. In this scenario the solar panel 'trickle charges' the battery but only when the sunlight is sufficient to deliver the 14V minimum output so it can be a hit and miss solution especially in Scotland!

The end result is, as always, a financial compromise. Stick on a simple solar panel/resistor and hope for the best or spend more money and 'guarantee' the result. Whether either method is more cost effective than replacing the battery (or going out to change/recharge it) is for the user to decide. On a labour-only basis the inclusion of solar trickle charging simply must prove cost-effective and pretty darned quickly too.

It may even be so good that the employers don't need the services of an engineer to attend to the batteries any more......................................

[Someone-Else]

Ok, so it has been around 2 weeks since this project started working. I am going to conclude it now as summer is too far away.

The object of the exercise
To see how well a solar panel, a rechargeable battery, and some solar lights will work.

It went something like this.
The parts

20 watt solar panel to charge a battery to run 2 x 10watt LED lights for 4 hours / day (No specific reason for the time or the lights, it was an easy to choose option)
It should be noted the charge controller I chose to use has an inbuilt timer function that will start when the solar panel stops charging (In other words when its dusk)

What happened
Day 1. Worked as expected. (Lights on for 4 hours)
Day 2. Nothing, no light no charge.
Day 3. Removed battery and charged it elsewhere.
Day 4. Put now charged battery back, reduced "on time" from 4 hours to 2 hours, disconnected 1 of the LED lights.
Ignored it for a few days, but did note (If home early enough) the light was on for some time.
Last day. (Of documentation) see picture below

s12.jpg (245.9 KiB) Viewed 3508 times

You can see the battery is "flat" BUT the solar panel is charging the battery at 11.8v The problem is, the battery is NOT being charged as it will not charge until the voltage is around 13.6 But to be fair it was early in the morning when I took the picture, and from my observations the battery will get more charge as the day progresses.

I can not truthfully say how long the light does come on for as I am not going to sit and watch it all the time and I don't have a timer connected to tell me the exact times the light comes on for. (Not to mention the latter is more money)

For your consideration
If you need to have a solar powered light for your shed / workshop and 2 hours is not enough the obvious answer is to have a bigger capacity battery (so it will last longer) but that then means you will need either one bigger solar panel or several bigger solar panels (You can use the same solar charge controller as that claims to be able to work with upto 20A no problem) I am not going to go into specific costs for a bigger "system" as it depends on what you need, but rest assured it is not cheap. Also, bear in mind my project used odds and ends I had sitting around to mount things on, you will have to buy decent parts if you want it to last.
Not to mention this project was only meant for "remote lighting" if you want to run any type of power tools you are going to need an inverter, bigger / more solar panels, bigger / more batteries all adding to the end cost.

One thing is for sure, no matter how many solar panels you have, they will not work unless there is enough sunshine beaming down on them.

If you have a question regarding any of the above, please ask, I will do my best to answer it.


SMALL PRINT:
I never checked charging current, as this will depend on the condition of the battery and the amount of current available at the time from the panel. It was done purely as a "What happens / is it feasable" project. The answer to that is it depends on if you think its is worth while or not.

[kellys_eye]

You've already informed us of the LED wattage (real world as opposed to claimed) but now we need to know the real world solar panel output. Using an ammeter, use it to SHORT the output of the panel and it will read the shorting current - this is what the panel is delivering 'right now' and will, obviously, be different for overcast versus sunlit skies.

Either way, without knowing the solar panel efficiency you can never really figure out if the system will work as you intend it to.

PS - shorting the panel output is perfectly safe (to the panel).

[Someone-Else]

I chose not to do that when you consider the fact the panels true maximum output will only be known on a bright and sunny day.
If for example, I were to do it now the answer would be 0mA because although it is still not dusk, the flood light has come on which means the panel has switched off. If I were to do it at 09.00 it would be less output than 12.00 The solar panel output will always vary according to the amount of sunshine falling on it, so can not be relied upon unless the amount of sunshine here is known at the time of testing.

This was always intended to be a feasibility project, never a detailed scientific project.

If you really want me to check it, I will, but it will have to wait till next weekend.

[kellys_eye]

Checking solar panel efficiency in full sunlight only gives you the 'best case' answer - you need to know the 'worst case' (which in theory is zero but which, in overcast skies of a typical day may be..... who knows?) to get an overall picture.

Either way, numbers are good!

[Argyll]

[big-all]

that makes it perhaps 0.7 0r 0.8ah or 8-9w per day

[Argyll]

that makes it perhaps 0.7 0r 0.8ah or 8-9w per day

I was told I could get 56 days but I suppose this would be during the summer months and I don't want to leave it that long and ruin the battery.