Newbie Project

DMS11X

Working on either trying to find a kit, or piece together a solar system, to provide lighting for a carport. I will be using two 2a 12v LED flood lights, the solar panels will be attached to the flat top carport, the controller and battery will be installed under the carport into a large weatherproof enclosure attached to one of the support posts of the carport. Thus far Im thinking I should use a 200a solar panel, mppt charger and a 100ah 12v agm or sealed lead acid battery. Just not really sure...

I'd like the lights to be able to function for a maximum of 12hrs at night, for 4 nights so thats about 100ah  right? (12ah x 2a floods x 4 nights = 96ah?)

I'd also like the solar panel to recharge the battery in 8 to 12hrs? is that even possible?

100Ah too much or too little?

200 watt panel too much or too little?

mppt or PWM???

So many variables, I'm just not really sure...

BB.

Personally, I would highly suggest a motion detector controlled light... Here is a 10 Watt @ 12 volt LED flood lamp (~$17):

https://www.amazon.com/GLW-Waterproof-Daylight-Security-Equivalent/dp/B00W4ZMIP4

The major issue I have with motion detectors themselves--They seem to only have a 2-4 hour life when out in the sun & weather. Mount them under shade/shielded from rain for a longer life.

Now, instead of 12 hours * 2 amps * 12 volts = 288 Watt*Hour per night... Now you are down to much less than 1 hour of operation per night (point away from trees, don't point at food dishes for pets/racoons). Or 20-30 WH per night (1/10th the amount of energy).

I also suggest motion detector lights for security--They do not "highlight" stuff you don't want stolen, plus a couple bright lights turning on attracts attention.

So, if you want 4 nights on battery power, 50% maximum discharge for longer battery life, 12 volt AGM battery:

• 3 lamps * 10 Watts * 1 hour per night * 1/12 volt battery bank * 4 nights storage * 1/0.50 maximum discharge = 20 AH @ 12 volt AGM battery

Typically, you want a 5% to 10-13% rate of charge to keep the battery "happy":

• 20 AH * 14.4 volts charging * 1/0.77 solar panel derating * 0.05 rate of charge = 19 Watt minimum panel
• 20 AH * 14.4 volts charging * 1/0.77 solar panel derating * 0.10 rate of charge = 37 Watt nominal panel
• 20 AH * 14.4 volts charging * 1/0.77 solar panel derating * 0.13 rate of charge = 63 Watt typical "cost effective" maximum panel

And then there is sizing the system energy used per day and hours of sun per day. Fixed array tilted for maximum winter harvest:
http://www.solarelectricityhandbook.com/solar-irradiance.html

Sacramento California
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 36° angle from vertical:
(Optimal winter settings)

Jan	Feb	Mar	Apr	May	Jun
3.73	4.46	5.61	5.83	5.79	5.84
Jul	Aug	Sep	Oct	Nov	Dec
5.95	6.25	6.39	5.98	4.47	3.66

30 WH per night * 1/0.61 DC off grid power system eff * 1/3.66 hours per day of sun (December) = 13.4 Watt panel minimum

I would suggest that the solar panel be 2x larger than your planned power needs--So that would be a 26 Watt panel.

So, the "optimal" panel for 30 Watt*Hours of light per night, winter, AGM DC battery bank, would be somewhere in the 26 to 63 Watt solar panel range.

I would suggest getting one (or a couple different) lamps and see how they work for you... LED lamps in a dark area throw quite a bit of light for low wattage light.

And our eyes work on a logarithmic scale... More or less we can hardly tell the difference between a 10 Watt and 20 Watt lamp... And a 10x difference is "night vs day" difference (you would hardly notice a 10 Watt lamp next to a 100 Watt lamp).

So, for example, if you only 10 Watts of lights instead of 20 Watts--You will hardly see the difference, but the power system will only need to be 1/2 as large.

Does this help?

-Bill

DMS11X

Bill,

Thank you for taking your time in breaking things down for me with such a wealth of information, I truly appreciate it sir!

I should be a bit more specific in the scope of this project:

I am a licensed electrical contractor in Sacramento California and have very little experience in solar so please forgive me if I am incorrect in any of the following.

My client has decided to use two specific 10 Watt 12vdc led flood lights to mount under the carport, he wants them on at night via photocell (no motion activation). I have run the load calcs to be about  936Wh or 78Ah of maximum use for 3 days (no sun) at 12hrs "on-time" at night via photocell controlled at a 30% over estimation. 

So Im assuming I will need a 200ah battery to stay above the 50% discharge of the 200Ah battery?

I would like to use just one panel about 350-400 watts (faster charging?) I calculated it to be about 5hrs to recharge from half discharge of a 200ah battery.

I also want to use an MPPT controller - Will I benifit from a 24v panel instead of a 12v panel using an MPPT controller?
The battery and controlled will be mounted inside a steel locking electrical enclosure to one of the support legs of the carport. 

What are your thoughts?

Please if I am incorrect in any of my calculations or assumptions feel free to advise me as I have very little experience in solar.

Thank you sooooo much for your time!

NANOcontrol

If you are going to use a MPPT controller, I would use grid tie panels which are much cheaper. Over 500W of panels would be less than $250 total. Many installers have loosies left over from a pallet they sell cheap. Instead of more battery, use an additional solar panel which will enable some charging even in poor lighting.  I do this at my camp with a small battery and it charges enough even in the rain to run my fridge without draining the battery.

BB.

DMS,

Yes you are correct... Ideally, 1x 6 volt @ ~200 AH Golf Cart batteries in series would be a good match.

Golf Cart Batteries are cheap, rugged, and forgiving... Plus, you can use a hydrometer to measure the state of charge (and rinse the hydrometer with a couple of draws of distilled water to keep it from sticking).

HOWEVER, they do need to have their electrolyte level checked every month (all six cells) and have distilled water added when needed (keep a 1 gallon jug handy).

If your customer is not one to check the water levels--Then perhaps an AGM would be a better choice:

https://www.solar-electric.com/fullriver-dc224-6-agm-sealed-battery-6v-224ah.html

But they are, roughly, 2-3x the cost of a "cheap" golf cart battery (~$300 vs ~$100 per battery).

The other issue is that Lead Acid batteries do not like to be taken "dead"... You really want something that shuts off the lights if the battery drops to ~12.0 to ~11.5 volts.

To estimate the sizing of the charge controller and solar panels... Say 330 WH per day and 3.6 hours of "average December sun":

• 330 WH per day * 1/0.61 end to end DC System eff * 1/3.6 hours of sun per day = 150 Watt solar panel
• 150 Watt solar panel / 18 volts Vmp = ~8.3 amps

Now... That is assuming everything is "nominal"... I would humbly suggest ~2x larger solar array minimum (allow for some dark winter days)...

That would be a ~300 Watt array and a minimum of ~20 Watt charge controller. If you use 2x ~140 Watt panels with Vmp~18 volts, this lighting controller would be nice:

https://www.solar-electric.com/sunsolligcon1.html

For a 140-160 Watt "12 volt" solar panel, you will have to call NAWS when they are back from holiday... They are out of stock (it appears) for the ~140 Watt Vmp~18 volt panels.

Or you can use an MPPT controller with a (for example) ~300 watt solar panel (charge controller costs more, large format panels cost less).

But finding a MPPT controller with LVD (low voltage disconnect for loads) may be a bit more difficult.

-Bill

BB.

There is also one other solar calculation... Generally 5% to 13% rate of charge for the battery bank.

• 200 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 188 Watt array minimum rate of charge
• 200 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 377 Watt array nominal
• 200 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 470 Watt array "cost effective" maximum
  

Generally, a 10% minimum rate of charge is recommended for full time off grid charging of Lead Acid batteries... So, ~300 to 377 Watt array would be a good size.

-Bill

stmoloud

On the load side you might want one of these or similar LVD's
https://www.kemo-electronic.de/en/Car/Modules/M148A-Battery-guard-12-V-DC.php

Mine is set at 12.2 volts and works good
You can then use a cheap PWM controller