Solar panel on a golf cart

NEWBIEST NEWBIE

I am new to this solar business but very excited about it. I have a shed that i am making into a small cabin that will be solar power only. Bought a couple of the harbor freight kits, cool. But today i am wanting to put a panel on the golf cart to keep the batteries up. Dont know enough to do it. Six 6 cell batts. Can use an 80 watt panel or a 15 watt panel. Is it possible to do?

niel

Re: Solar panel on a golf cart

welcome to the forum.
the harbor freight pvs may be better suited to keep the batteries up on the golf carts.

for the cabin you should start by saying what kind of loads you will have and for how long to come up with a good watt hours figure. once the loads are known we can discuss options further from there.

NorthGuy

Re: Solar panel on a golf cart

Aren't you afraid of golf balls hitting the panel and breaking it?

Cariboocoot

Re: Solar panel on a golf cart

Your golf cart will run a 36 Volt battery bank (the six 6 Volt batteries in series). This is not standard for renewable energy systems. As such you have to either get a rather expensive charge controller and enough panel to provide >54 Volts to charge them as a whole, or divide up the charging into three separate panels with three separate controllers @ 12 Volts (nominal) each.

In practical terms it isn't worth doing. The amount of panel you can fit on a cart will contribute very little to the maintaining of the batteries. And yes, some have done it. I believe Volvo Farmer is one forum member who has such a set-up just for kicks.

NEWBIEST NEWBIE

Re: Solar panel on a golf cart

Thank you for your reply. i havent added up what the demands of the small cabin will be but i know it will be limited to a fan, couple lights and the igniter for a propane water heater. Nothing big. i will come up with specifics on expected draw. i am interested in what you have to say about maintaining the batteries on the golf cart. This cart will drive about 1 1/2 hours a week, total. It will be parked in the sun on my farm and electricity is not easily available. im hoping that a single panel (a 15 and a 85 are available to me) will be enough to keep the batteries maintained with such low usage. i dont know if panels can supply a 36 volt system without special charge controllers.

inetdog

Re: Solar panel on a golf cart

NEWBIEST NEWBIE wrote: »

... to keep the batteries up. ....

As long as all you mean is to keep from having to hook the cart up to a trickle charger when you are not going to use it for a few months and it will be parked outside, then it can be done.

You will have what is known as a battery maintainer rather than a battery charger, and it will not do anything noticeable to extend its range between charges.

You will need three separate "12 volt" low wattage panels, and you can either wire them all in series and connect them across your 36V battery bank, or wire each one separately to one of your three series pairs of batteries (=12V) and insulate them from each other.

bill von novak

Re: Solar panel on a golf cart

NEWBIEST NEWBIE wrote: »

im hoping that a single panel (a 15 and a 85 are available to me) will be enough to keep the batteries maintained with such low usage. i dont know if panels can supply a 36 volt system without special charge controllers.

If they are 12 volt panels you need either:
1) A boost converter/regulator (not an off the shelf item) or
2) A 12V charge controller with a good 3 or 4 cell balancer (not an off the shelf item either)

If you are into electronics you could build either one but they're not going to be something you can just buy off a website.

Might be easier to just get a higher voltage panel (or 3 12 volt panels) and use a 36V controller. They are not common but are available; I believe the Tristar charge controller will do what you want.

NEWBIEST NEWBIE

Re: Solar panel on a golf cart

Wow. I see. More complicated than I thought. I totally get what you mean though. Lots of difference between maintaining and charging. I have an 85 watt panel. Would it be enough instead of three low wattage 12 volt panels? It would have 2 days of no use for every 1/2 hour of use.

NEWBIEST NEWBIE

Re: Solar panel on a golf cart

do you think my 85 watt 12 volt panel with the tristar 36 volt controller could provide charge enough for 1/2 hour use every two days?

inetdog

Re: Solar panel on a golf cart

NEWBIEST NEWBIE wrote: »

do you think my 85 watt 12 volt panel with the tristar 36 volt controller could provide charge enough for 1/2 hour use every two days?

Putting it simply: NO.

NEWBIEST NEWBIE

Re: Solar panel on a golf cart

Bummer. I wish I had your knowledge so that I could come up with another option. Way too new at this.

bill von novak

Re: Solar panel on a golf cart

NEWBIEST NEWBIE wrote: »

do you think my 85 watt 12 volt panel with the tristar 36 volt controller could provide charge enough for 1/2 hour use every two days?

No, your voltage in has to be higher than the voltage you want to charge at. So for a 36V battery, which will charge at about 45 volts, you need a panel that have a Vmp of at least 50 volts or so. (Or several lower voltage panels in series.) Two Trina Solar TSM-240's would do it, for a total of about $512.

NEWBIEST NEWBIE

Re: Solar panel on a golf cart

Ok, let me ask this. What do you think would be the least expensive way to solar recharge a 36 volt golf cart used 1/2 hour every two days?

inetdog

Re: Solar panel on a golf cart

NEWBIEST NEWBIE wrote: »

Bummer. I wish I had your knowledge so that I could come up with another option. Way too new at this.

Applicable rule of thumb, found in several places in the Forum:

The minimum size of solar panel(s) intended to charge a 12V battery bank has the wattage of the panel equal to the AH capacity of the battery bank.

In your case, you probably have 200AH batteries, and at 36V rather than 12V, so the minimum total panel capacity to be able to keep the batteries healthy without also using an AC charger would be 600 watts. That would be at least two fairly expensive panels, which would probably not fit on top of the cart.

NEWBIEST NEWBIE

Re: Solar panel on a golf cart

okay. I see. I really appreciate your input. I think my wife may not see the 'necessity' of such an expense right now. Thank you very much.

niel

Re: Solar panel on a golf cart

what about your cabin as that is an expense? does she see a necessity there? if so then tell us the approximate watt hours you will typically need in a day as you may still be able to use the 85w pv. batteries and controller will also be needed, but will depend somewhat on the needs presented in watt hours (wh)

Volvo Farmer

Re: Solar panel on a golf cart

Mine is hooked up with no charge controller. Sometimes it goes a week or two charging and then gets used for an hour or so. The batteries are a little mis-matched and a couple of them died from old age recently, so I don't know exactly how much we could use it without plugging it in. The panels charge at about 3.5A and last time I checked SG, my batteries were all up over 90%. Everyone says batteries need a 5% minimum charge rate and I'm at something under 2% with the three panels on the roof. I'm just letting kids drive it around a bit and checking SG after a few days of recharging and it seems to be mostly working that way. A long deep discharge might be a whole 'nother story though.

NEWBIEST NEWBIE

Re: Solar panel on a golf cart

Volvo Farmer wrote: »

Mine is hooked up with no charge controller. Sometimes it goes a week or two charging and then gets used for an hour or so. The batteries are a little mis-matched and a couple of them died from old age recently, so I don't know exactly how much we could use it without plugging it in. The panels charge at about 3.5A and last time I checked SG, my batteries were all up over 90%. Everyone says batteries need a 5% minimum charge rate and I'm at something under 2% with the three panels on the roof. I'm just letting kids drive it around a bit and checking SG after a few days of recharging and it seems to be mostly working that way. A long deep discharge might be a whole 'nother story though.

Wow. Okay. Thats what I was hoping for. Im willing to give it a try. Last night after getting lots of good advice on this forum I looked at the golf cart again. What I thought was six 6 cell batteries is actually six 8 cell batteries. So not 36 volts, but 48 volts. I was hoping that the 85 watt 12 volt panel would provide at least something to those batteries but didnt know.

NEWBIEST NEWBIE

Re: Solar panel on a golf cart

niel wrote: »

what about your cabin as that is an expense? does she see a necessity there? if so then tell us the approximate watt hours you will typically need in a day as you may still be able to use the 85w pv. batteries and controller will also be needed, but will depend somewhat on the needs presented in watt hours (wh)

Okay, this cabin is 8x12 feet. Will have two 12 volt lamps and a rv water pump. There will be a small fan used occasionally and an rv propane water heater that uses 12 volt for thermostat and ignition only. We visit there one weekend a month. I have one 12 volt big agricultural battery. I dont remember what you call that size but its about two to three times the size of the regular car battery. I have the harbor freight three 15 watt panel kit with a charge controller.

Cariboocoot

Re: Solar panel on a golf cart

NEWBIEST NEWBIE wrote: »

Wow. Okay. Thats what I was hoping for. Im willing to give it a try. Last night after getting lots of good advice on this forum I looked at the golf cart again. What I thought was six 6 cell batteries is actually six 8 cell batteries. So not 36 volts, but 48 volts. I was hoping that the 85 watt 12 volt panel would provide at least something to those batteries but didnt know.

You're in a bit better position, but still have the problem that the panel is "12 Volt" and won't provide any charging to a 48 Volt battery bank. You'll need four "12 Volt" panels in series to get there, and either a single charge controller that can handle 48 Volts (not common is the less expensive stuff) or four separate ones as I suggested before or do like Volvo Farmer and take your chances with straight current.

If you choose the latter option notice that he has a charge rate <2% - which is fine for maintenance purposes (keeping a battery up rather than recharging it fully from a discharged state. The 5% rate he mentions is for recharging.) So from that POV you can size the panels based on 2% of the battery capacity times Vmp for a 12 Volt panel or about 4 Amps * 17.5 Volts = four 70 Watt panels. Less than that will add a bit of power, but won't accomplish very much. Remember that a panel's output is highly dependent on how much direct sun it gets, so they are likely to be less efficient flat on the roof and moving around rather than pointed directly at solar South in a fixed location.

As for the cabin use, you need some fixed numbers. 12 Volt lights and other loads may be any amount of Watts and could be on for variable times. The battery may be a 8D truck battery, but that would be guessing.

You will find the HF panels don't manage their rated output even at the best of times. You have maybe 40 Watts worth there, and that won't supply much power: about 2 Amps and perhaps 100 Watt hours per day depending on insolation.

The 85 watt panel would be better for the cabin and the HF panels (with one added) for the golf cart.

NEWBIEST NEWBIE

Re: Solar panel on a golf cart

Thank you Moderator. I printed your reply for future reference of the equations. Can you help me with the abbreviations. POV? Vmp?

Cariboocoot

Re: Solar panel on a golf cart

Well "POV" is just "point of view" - not a solar-specific acronym.

Vmp is Voltage at maximum power - a standard specification on solar panels.

We have a whole glossary of terms used around here: http://forum.solar-electric.com/showthread.php?6136-Glossary

It may help your understanding the banter.

NEWBIEST NEWBIE

Re: Solar panel on a golf cart

thank you for your assistance

niel

Re: Solar panel on a golf cart

you still need to determine the loads and the amount of time for them in watt hours. this means you are far from done in the preliminary figuring as you are just getting started. you state you already have a battery and you need to know what the capacity of it is in amp hours (ah) as the charge to that battery needs to be at least 5% and maybe more depending on the loads. that battery could be losing its capacity due to inadequate charging right now.