New to Solar need help with setup

1 Posts

Sep 16, 2004 01:52 am

I have a freind who's dad works for a company that uses Solar Panels...for running radios at night....gas wells i think....anyway

He gave me a 20watt Solarex Panel...i was told it was 20Watt...i can read Solarex off the back..its multi-colored blue if that helps..
He also gave me a UB12180 battery (18AH 5.4Amps Max out)

I am good with wiring since I work on cars...and just need alittle help with this..

Have a freind that is a trucker, he runs nation wide. We want to setup this Solar Panel on his truck, thats the easy part..
We want to do this to run a 400Watt inverter of which we "should" be only pulling 79watts...for a Playstation 2...he has a "12v AC/DC TV" so we don't need to worry about that...
we only need to run the PS2 for max of 3 hours..so i figure i need 6-10 of runtime off battery
a Summary:
PS2    79 watts 79/120
   .658 amps 120volt
rough    158AH to run PS2 for ?20hrs?
Panel   20watts 12volts puts out 18volts Max?
   20/12=1.6amp (trickle charge)

What am I missing.....do i need a blocking diode or charge controler? Huh

Thanks for all your help in advance
James

Thomas Allen Schmidt

679 Posts

Sep 18, 2004 10:37 am

Re: New to Solar need help with setup

If I were to do this for myself.
More than likely, I would wire the inverter and the PV module to the trucks accessory batteries (assuming it has them.) I would use a charge controller (cc) mainly because of the chance that there would be times when the batteries would be fully charge but not being used and of course the sun was shining. The cc should disconect the PV module when there is no voltage coming off of the module and/or when the battery voltage is high enough.
Even though I might plan on using only one device of a given wattage on the inverter, I would still size the vdc wires for the inverters continuous rated output in watts at the inverters automatic low battery voltage disconnect set point. In this case at least a pair of #8 awg copper wires with at least a 30 amp fuse, #6 if its a long wire run.
A set up like this sould keep the batteries charged via an isolator and the 20 watt panel would provide a trickle charge that would keep the batteries more or less "topped off" when the trucks not running.
Idealy, although not nessessary, the trucks accessory batteries would be true deep cycle and would be used only in an emergency for cranking and the inverter could not pull from the main cranking batteries when the trucks not running but should get a charge from the trucks altenator when the truck is running. A good quality isolator would do all of this. Or if I wanted to challenge my electrical skills I might try to design a system with a dc contactor(s) to do all of this instead.
Putting a fuse between the module and the cc and the cc and the battery is not a bad idea. Allthough some PV modules can have an open circuit voltage higher than what most automotive fues are rated for.

Or I might just mount the module, a fuse, a small cc, another fuse, wire it all into what ever batteries are there, then plug the inverter into a cigarette lighter (if made that way) and go with it.
Its hard for me to say. I would have to actually see what I had to work with to know for sure. Even then I might just have to experiment.
I hope something in this helps. Most of it you probably allready know.
Post back when you've finished. Let us know how you chose to installed it and how it preforms.

Ken Hall

351 Posts

Sep 18, 2004 02:30 pm

Re: New to Solar need help with setup

Sunour has a workable alternative suggestion.

But, back to the solar question.

You did your calculations for 120 volts when you needed to be on the 12V side.
To produce 79 watts on the 120V side, you are going to be pulling about 90 watts on the 12V side, depending on the specs for your inverter. 90watts/12v=7.5 amps.
So, your 18AH battery will last about 2 hours. You would also be exceeding the 5.4 amp current. (Are you sure that is a discharge current and not a charging current limit ?) If you really need the three hours (and to help prolong the battery life), I would either go with a larger battery or wire two of the UB12180�s in parallel.

Your solar panel is way to small to support your intended usage. The 20 watt rating is a full sun rating, which is for a stationary mounted panel that is pointing south and aligned for the sun angle. In that situation, it would take about 4.5 hours to produce the 90 watts required for one hour of playstation time. Many US locations do not get 4.5 hours of full sun, for parts of the year.

In a flat mount (and mobile) situation, your panel will produce significantly less than the 20 watt rating. My guess is that you have about 1/10th of the PV power that you would need to make the system reliable.

If you already have the inverter, you could do an experiment. With the battery fully charged, hook up the inverter and play station and see how long you can run it. Next day, wire the PV panel directly to the battery and lay the panel flat in the yard. At the end of the day, hook up the inverter and play station, and see how long you can run it.

Inverters that are designed for solar applications generally have a blocking diode or equivalent circuitry in them. If you are using an automotive type inverter, you will definitely need a blocking diode to prevent discharge during non-sun hours.

If you end up linking multiple smaller panels, you should also have by-pass diodes on each panel to prevent them from affecting the systems output as individual panels are shaded or otherwise limited in output.

Thomas Allen Schmidt

679 Posts

Sep 18, 2004 05:55 pm

Re: New to Solar need help with setup

>Inverters that are designed for solar applications
>generally have a blocking diode or
>equivalent circuitry in them. If you
>are using an automotive type inverter,
>you will definitely need a blocking
>diode to prevent discharge during non-sun
>hours.
I am curious about this.
An inverter that requires a blocking diode to prevent discharge during non-sun ours?
Why?
I understand that the 20 watt PV module may not produce a high enough voltage to cause the battery voltage to exceed a safe limit at any time. This would of course depend on the size and type of battery and its use. So depending on the battery, there may not be a need for a charge controller but there may be a need for a blocking diode in the PV source circuit instead. Remember a diode consumes power as well, quite possibly as much as the 20 watt module would without it.
I personally have had an array of 6- 77 watt PV modules temporarily bypassing the cc at night without any diodes and the battery monitor reported a draw of only 0.03 amps @ 12 vdc nominal and 0.01 of them is the monitor.

If you would explain the diode for the inverter.

Ken Hall

351 Posts

Sep 19, 2004 12:49 am

Re: New to Solar need help with setup

In his "automotive" set up the wiring is pv panel to battery to inverter, so you need the blocking diode between the PV panel and battery to prevent the panel from siphoning power off of the battery. In solar setups where the wiring is panel to inverter/charger to battery, the inverter often performs this function and the blocking diodes may not be necessay.

Sorry if my verbal shorthand was misleading.

Thomas Allen Schmidt

679 Posts

Sep 22, 2004 03:20 am

Re: New to Solar need help with setup

Wow, I knew that some inverters have charge controll for there own built in transformer/rectifier charging system from an outside source (typically 120 vac), but I did not know there is an inverter on the market that has a built in PV source charge controller. Would you tell me the brand name? I'd like to learn more about them. Thanks.

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