Solar anyone?

thetoddjohnson

This isn’t exactly an “Extreme DC” question, but I figured this would be the most appropriate forum.

It has been a while since solar charging has been discussed on BGW. Does anyone have any experience (good or bad) with any particular solar chargers? I’m contemplating getting the 100W Universal Kit made by SolarEvSystems to put on a Yamaha G29. My use case is somewhat unique and I figure 100W is enough juice, I’m more interested in the quality of the kits that are available.

My use case is that the cart gets parked for long periods of time without access to electricity. I always leave the cart fully charged but times are changing and I’m no longer able to make sure the cart gets a proper charge every few weeks. I anticipate that the new norm is going to be 3 to 4 months between charges. I figure since the cart will be sitting in the sun I’d like to have mother nature keep the batteries fully charged rather than letting them deteriorate.

Any thoughts?

TJ

BGW

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rottie

well....
Solar will help a little, but don't expect getting a full charge. That would take a couple of weeks.
assume you have a 36V system.
100watts/36V= 2.7 amps at full sun. Not a real lot of amps.
Your 120V charger is ~15 amps and it take how many hours to charge your battery?
Just set you expectations realistically. Get the maximum power solar panel that will fit on you cart.
Yes, I am going to add solar to my cart, to give me a longer run.

If you add a solar cell(s), get the voltage at MPP the same as your battery system at full voltage.
Make sure you use a solar controller or at least a series diode in series solar panel so it does not back feed to panel at night and drain your batteries.
Good luck

thetoddjohnson

All I'm trying to do is keep a dormant set of batteries fully charged. Is it unrealistic to think that 100 watts can do that?

TJ

rottie

If cart sets inside a garage or shed, then no use a battery tender.
If cart sits outside, then definitely, but use a solar controller.

What battery voltage/type is your cart? ie. 36V/lead acid or 48V/lithium or???

thetoddjohnson

The pack is 48V wet cells. The cart sits out in the sun all day.

TJ

rottie

Do you have a solar panel in mind?
I would look at a panel where the Voc (voltage open circuit) is 60-70V range and MPP is ~56V in a single panel.
Look into thin film as they are higher voltage 70-90V for a single panel.

Crystalline at generally in to 30-40Voc range, it would require two panels in series.

Sergio

Some quick ballpark calculations (using conservative safety error margins):

Flooded lead acid batteries self-discharge at about 1% capacity per day.

A 200AmpHours battery bank has a discharge capacity of 10amps (200AH/20H).

That equates to a self-discharge rate of 1% = 0.1amps, let's double that for a worst case scenario during the hot summer = 0.2 amps discharge.

If is only sunny every other day, 0.2amps x 2 = 0.4 amps needed.

If You only get 8 hours of sun on those days, 0.4 x 3 = 1.2amps needed.

So You would need a charge rate of about 1.2amps during those sunny hours to fully counter balance the self-discharge rate.

The panel You posted is able to provide 2 amps, so it is more than enough.

I would be more concerned with the cart left outside, the hot sun while good for the solar panel, it is not so good on the rubber tires, vinyl seats, etc....

Depending on the area you leave the cart, You may want to consider keeping the cart under cover/roof and place only the solar panel where it gets the most sun.

You can always run a cable from the solar panel to the cart.

thetoddjohnson

Sergio

Thanks for those rough calculations. It was very informative. Is the self-discharge non-linear? i.e. Is the loss proportional to the SoC? What I’m driving at is this: Is it twice as bad to leave a cart unattended for 8 weeks as opposed to just leaving it unattended for 4 weeks? Or after 4 weeks have the batteries been depleted so much that at that point it isn’t much more harmful to leave them for an additional month?

You are correct that the hot sun isn’t great for the cart. The vinyl seats are all cracked, the body is really faded, and the tires do wear out much faster than the carts that are kept indoors. Unfortunately for this cart sun isn’t the worst of it. The salt air is far more problematic. The cart is on an island that is only accessible by boat. The cart lives right next to the bulkhead in the harbor. When we arrive on the island by boat the cart is what we use to get to the house. (That is unless it has been more than a month or 2 in which case the cart is too dead to make the journey, hence my desire to put on a solar panel.) Unfortunately there is just no way to keep this cart out of the elements. I just slather POR on the frame, a-arms, etc. on a fairly regular basis.

Now, what happens with the output of the solar charger once the pack is at 100% SoC? Presumably the controller that comes with the panel would be programmed to deal with that, right? Am I naive to think that all I’ve got to do is install the solar kit and my cart will always be charged no matter how long I let it rot away in the sun?

TJ

Sergio

The kit you posted from solarevsystems has a charging regulator so it will keep the batteries from overcharging.

While the self-discharge rate is non-linear, meaning it is a lot higher when the battery is fully charged, the harmful effects of the battery sitting on a partially discharged state is far more critical than the additional SOC reduction after the first 4 weeks.

SC Carts

We have been using our solar charging systems on many of our customers carts for over the past 5 years with great results. Our customers do exactly what you are saying in that they charge their cart fully before they leave it, and when they come back to use it, it has stayed fully charged.

Now with that being said there is no solar charging system that will fit on the top of a golf cart roof that would deep cycle charge your carts batteries. However so long as you can give the cart a full charge before you park it, and it is sitting in the sun you will most certainly keep the cart charged and your batteries happy, happy, happy!