Goatpam: Golf Cart charging system in Tampa, FL

System

This discussion was created from comments split from: 36v Golf Cart Solar Panels.

Goatpam

I am also in Tampa, FL and use my 36v EZ Go golf cart about 6-10 hours a week around the farm.  I park it under a  6 x 10 "cart-port" beside an open porch.  I would like to put solar panels on the cart port roof (and it gets sun at least 8 hours a day) facing west.   The solar panels would need to be removable in the event of hurricane (roof is just tall enough to drive the golf cart under so access is good).  Beyond that, I am not sure how to match up all we need.  We also use a station under the "cart-port" roof to charge all our batteries for weed trimmers, drills, and a couple car batteries that I use with an inverter for weekend markets where I am a vendor.  I would like to be able to use the solar to charge all the items (obviously not all at the same time) as well as the batteries of the golf cart.  What should I look at in panels - 100, 2 x 100 or 3 x 100?? I know I will need a controller, an inverter and a power strip.  Opinions on what size panels to use are solicited! 

mike95490

Thinking correction.
 You need to charge a 12V (or 24 or 48V )  battery to run the inverter.  I don't know of any inverters that take
PV input, and simply produce 120VAC remotely.  GT inverters do, but only if there is Grid Power


The most watt/bucks panels are the 300w ballpark panels, made by the zillions for GT use, but you need a MPPT controller to match it to your battery voltage.  300w @ 12V is 25A, so a couple of those and you are forced into 24V battery system. Over 30A, and wires get real thick and heavy - a PITA !
 

BB.

There are some 36 VDC inverters out there... In the "olden days", marine installations had a far amount of 36 VDC usage... Today, for off grid power, 36 VDC has generally been skipped in favor of the 12/24/48 VDC options.

Generally, we like to design a solar power system based on the energy needs of the owner. A good place to start is to monitor the charging needed for you golf cart. Using a Kill-a-Watt or similar meter, you can estimate your daily power needs and go from there:

https://www.amazon.com/s?k=kill-a-watt+electricity+monitor

I don't know the power requirements of your present golf cart charger--120 or 240 VAC--If 240 VAC, you need to look for the 240 VAC version of a power/energy meter.

Just to give you an idea... And guessing about your cart. Nominally, suggest 5% to 13%+ rate of charge from solar for Flooded Cell Lead Acid batteries. 5% can be OK for systems that mostly float, with weekend or a couple months a year (summer) usage. For full time off grid power systems, suggest 10%-13%+ rate of charge. If your cart has 6x 6 volt @ 200 AH batteries in series for a 36 volt @ 200 AH battery bank--An array size would be:

• 200 AH * 43.5 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 565 Watt array minimum
• 200 AH * 43.5 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 1,130 Watt array nominal
• 200 AH * 43.5 volts charging * 1/0.77 panel+controller deratings * 0.03 rate of charge = 1,469 Watt array "typical" cost effective maximum

Picking the array operating voltage Vmp-array (voltage maximum power, standard conditions)... For various reasons, use 1.3x the battery charging voltage for an MPPT type charge controller (more expensive than PWM, but more flexible for installation/system requirements). Not all MPPT/PWM controllers support 36 VDC, but the major brands of MPPT controllers generally can be programmed to operate a 36 volt bank. Assuming that you will need a minimum of 45 volts to charge/EQ an FLA battery bank:

• 45 volts charging * 1.3 MPPT fudge factor =58.5 volts Vmp-array
• 58.5 volts Vmp-array / 30 volts (a typical Vmp for many panels) = 1.95 panels in series (a bit less than 2x, but close enough to work--3x panels in series would be better)
• 58.5 volts Vmp-array / 36 volts (another typical Vmp for many panels) = 1.625 panels ~ 2 panels minimum in series (to a maximum of 3 panels in series for "typical" MPPT higher end charge controller)

So, your array should be somewhere in the 564 to 1,469 Watt array... And you have to pick the series/parallel array configuration to match the needs of the charge controller (around 58.5 volts minimum to around ~110 volts maximum--Details matter here--Just very rough numbers to understand how this all fits together).

For example, one option would be 3x 250 Watt panels in series (Vmp~30 volts). Another would be 2x 300 Watt (Vmp~36 volt panels)... One is a 750 Watt array, and other is a 600 Watt array, Both >5% rate of charge.

You could also take the above strings and make 2x parallel connections... 1,500 Watt (6x 250 watt panels) or 1,200 Watt (4x 300 Watt panels) for a larger array (over 10% rate of charge).

And to estimate how much power per day you can harvest... Assuming a fixed 1,200 Watt array facing south for Tampa Florida, the numbers would look like:
http://www.solarelectricityhandbook.com/solar-irradiance.html

Tampa
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 62° angle from Vertical:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
4.60	5.30	5.99	6.40	6.63	5.99
Jul	Aug	Sep	Oct	Nov	Dec
5.58	5.54	5.41	5.66	5.08	4.47

Pick February at 5.30 Hours of sun per average day (assume you use less energy in winter, or use backup charging from Mains/Genset when needed):

• 1,200 Watt array * 0.52 end to end AC solar system eff * 5.30 hours of sun per day (Feb Average) = 3,307 WH per average Feb day (some more, some less)

A 3.3 kWH per day off grid solar power system is pretty good size--Enough to run a home's Fridge, LED Lighting, Washing Machine, possibly a small well pump, LED TV, Laptop Computer, Cell Phone charging pretty nicely.

Or for charging your golf cart:

• 1,200 Watts * 0.61 DC solar system eff * 5.30 Feb average sun day * 1/43.5 volts charging = 89 AH per day DC loads from GC battery bank
• 89 AH per day / 200 AH battery bank = 0.445 ~ 45% of your GC bank capacity (per February average day harvest)

So--If you use 45% of your GC battery bank on a February day--Your system will recharge the bank in one day (roughly--some days more sun, some days less, etc.).

Hope this helps. Please feel free to ask more questions. Lots of guesses at this point on our part.

And Goatpam, I have moved your question to another thread (discussion) for your system. It makes it easier to follow your Q&A and not get confused with the original posters questions.

-Bill