Solar Panels, Reality Check

[rreeves]

Am looking for advice on specific solar panel brand/wattage.

Am rebuilding the charging system on my 30 ft sailboat over this winter.

I mostly singlehand and have limited technology aboard. Am getting ready for Hawaii via Mexico.

Current planned usage is about 64 amps per day at sea and 50 at anchor (and that's fairly generous...don't have much technology...really).

House bank is 315 amp hours.

I would like to rely mostly on Solar. I'm looking at buying two Sharp 80 watt panels, partly because they seem fairly inexpensive (just under $400 each) and partly because the form factor allows for rail mounting without too much difficulty on my small boat.

These two plus the two 18 watt panels I already use for "trickle charge" gives me over 77 amp hours of charge a day (figuring about 4 hours of sun a day, etc.), which seems ample given current needs.

Am I missing a major step in the calculation?

I've not done a ton of shopping. Are there less expensive brands of the same quality?

Thanks in advance,

RR

PS. It seems likely this question has been answered more than once already on this board, but I can't find it. Feel free to just point me to the right post.

[mesquaukee]

A 350 ampHr battery bank cycling 50-64 ampHrs a day will result in good battery life.

77 ampHrs of production compared to 50-64 ampHrs a day of use sounds about right as
charging efficiencies from 50% to 80% state of charge is typically about 80-90% dependant on battery condition. From 80% and up it ranges from 70% down to as low as 10-20% as you reach full charge.

I have found that with my setup I get closer to 5 hours a day at ratted wattage, using 4 hrs a day gives you a good safety margin. We always tend to use more than we had planned on.

[Paul Elliott]

I think you are being a little optimistic about the power you will get from the panels. Unless you use an MPPT controller, you will only get about 80% of the rated panel power, since the battery voltage does not match the optimum panel voltage. I usually assume that I will get a daily Amp-Hours number equal to the panel power in Watts divided by three (this isn't an ohms-law type calculation, it's just how the numbers work out in a 12V system).

So, with your 200W of panels, you should get about 67 Ah per day. This is probably enough to almost keep your batteries charged, at least when there is no cloud cover.

If you use an MPPT controller you will probably increase your charging current by 10 or 15%. If you don't have an LED tricolor (or running lights) do consider it. This is can have a huge impact on your under-sail power budget.

I agree that for your level of power consumption, your battery bank is reasonably sized.

[noelex 77]

3 to 4 times the rated the rated pannel output is a good average rule of thumb, but the actual results can vary dramatically with location and time of year. Here in Greece I have only averaged 18AHrs per day for the last 7 days with 310W of solar, but the weather has been very wet.

[rreeves]

Thanks gents.

Any recommendations on brands? Can I get a much better deal than Sharp 80 watt's at about $400 each w/out sacraficing quality? Are Sharp panels as good a quality as I'm thinking? Is there that much difference between major brands?

RE LED lighting, yes the only way I've been able to get the amp budget so low is by using LED throughout. Have been using LED in the cabin for some time. Am still amazed by the technology. Haven't installed outside yet, but is in the amp hour budget/plan.

RE optimistic. Yes, my output equasion is pretty simple, but I'm hoping the four hour a day expectation captures other innefficiencies too.

Thanks again.

[mesquaukee]

If you want to maximize the use of a minimum of resources and have the time you can minimize all losses during the generation of energy by:

-install a switch bypassing the regulator (an inexpensive one for when you are off the boat or are lazy) eliminates all energy losses due to regulation (10-40%), you need to keep an eye on the voltage which if you are on the boat is no big deal. 200 Watts of solar is 11-12 amps max output, hardly enough to fry a 315 AmpHr battery bank, if you forget to watch it just call it an equalization charge.Spend the cash you saved on all those LEDs.

- insure that the panels are not shaded in any way, even the shadow of a rigging line has a large effect (adaptable, easily moveable mounting system)

-pay attention to how they are inclined or angled to the sun(30 deg result in more than a 30% drop in output, 45 deg is over 40% less output)(think about a simple adjustable mounting system)

-keep them clean, dirt limits the amount of light transmitted reducing output.

-keep them cool, hot panels produce less power (allow air to blow both over and under them, don't mount them tight to cabin roofs etc.)

-use one gauge or more larger wire than required, a 5% voltage drop result in a 10% loss in charging capacity
Energy = time x (100-5%) x(100-5%)
= time x .95 x .95
=time x 0.9025
> only 90% of power produced ends up in the batteries
- a 10% voltage drop>>>19% energy loss.

A few % here and there adds up quickly to more than 50% reduction in potential charging capacity.
A little bit of thought, a flexable mounting system, diligence, effort and time (what else do you have at sea) will produce a lot more power.

With 320 watts of panels doing (most of) the above in the tropics (little if any cloud cover) gives me 110-140 amphrs a day of energy as measured by a dedicated E-meter.

[noelex 77]

Originally Posted by mesquaukee

-install a switch bypassing the regulator (an inexpensive one for when you are off the boat or are lazy) eliminates all energy losses due to regulation (10-40%), you need to keep an eye on the voltage which if you are on the boat is no big deal. 200 Watts of solar is 11-12 amps max output, hardly enough to fry a 315 AmpHr battery bank, if you forget to watch it just call it an equalization charge.Spend the cash you saved on all those LEDs.

The MPPT regulators are more efficent than no regulator at all.

[Charlesc]

I can only speak from experience on what i have so hear goes.
1 KYOCERA 130 watt panel.
1 Morning star controller " A MUST HAVE "
3 each grp 27 batteries total 190 AHS house bank 90 AH start.

With this sset up I get 7.3 AMPS current going to charging batteries for abt 4 - 5 hrs a day.
Of cousre another panel would be 14.0 AMPS charging rate for 4-5 hrs a day.

I can usually stay on the hook without running engine 2 or 3 days then run engine 1 hr a day for longer times on the hook.

This is where i bought my sytem. Great customer service before aand after the sale.

www.wholesalesolar.com

[Gnitfar]

What works and doesn't work. There are so many many variables here to measure, I'm still working on it all. I lived aboard my sailboat on anchor last summer up here in the north east. Here is what I found...I employ two 135w Kyocera panels, a single Blue Sky 3024i MPPT charge controller, and three 185 amp hour Rolls batteries.

I have a ketch rig, my panels are mounted on my cabin top, forward from the main mast (best practical location for my boat) although I think the panels might be best located on a metal bracket off the stern (another future project) Finding an ideal place to mount panels on a sailboat may not exist. Shadows across the panels caused by masts and rigging are inevitable. In my case, it's either the main mast, or furled head sail, that cast a shadow which diminished my panel output drastically. It was rare that my panels put out their full potential, even on a bright sunny day. On average, my battery banks only filled about 75%

Usage...I quickly learned that my Adler Barbour top load fridge used too many amps to run more than three days and so I shut it off, and began using ice in a cooler to keep perishables instead. Conservative daily usage included three 12-v 5 watt energy saving cabin lights, LED anchor light, domestic 12-v water pump usage for daily dish washing, 5 min daily shower, and the biggest drain, a 26" lcd tv, a desk top pc, both run 1 hr. each daily, and a small a/c coffee maker in the morning, all run off the inverter. In the morning, my batteries registered on average around 12.3 volts and on a sunny day, and after the sun set, the batteries topped out at around 12.9 I only noticed the batteries achieved full charge, or finding their way to float, on a few occasions, mostly during the months of June and July.

I did needed to run my engine about 30 min. everyday to heat water and the additional benefit allowed the alternator to partially charge the batteries. All in all, the system worked well for my needs, as I was never without enough juice. Adding up amp hour output and amp hour input, is only a close estimation to measure with for ones needs with many other factors coming into play, IMO.

[witzgall]

Rreeves;

Your system sounds ok, but I don't follow your math. If you use 12v nominal, I come up with 65AH a day figuring on 4 hours.

If you can figure out a way to mount them off of the stern, you will get more juice because you will mostly eliminate shading. Make the mount adjustable, and you will do even better. Check out the Atom Voyages website to see what I mean.

Chris



An MPPT controller is highly recommended.

[mesquaukee]

Originally Posted by witzgall

Your system sounds ok, but I don't follow your math. If you use 12v nominal, I come up with 65AH a day figuring on 4 hours.

One needs to use 17.4 Volts not 12 volts to calculate the amperage, 200 Watts is roughly 10.4 amps of current. You need that extra voltage to "shove" the energy into the batteries.

Kyocera Solar KC85TS Solar Panel
Rated Power 87.3 Watts Peak Power
Voltage (Vmpp) 17.4 Volts
Peak Power Amps (Impp) 5.02 Amps
Open Circuit Voltage (Voc) 21.7 Volts
Short Circuit Amps (Isc) 5.34 Amps

[witzgall]

Yeah, I know that 12v is low. I don't think you need to go as high as 17, more like 14ish. This means that the AH put into the batteries is even lower than the 65AH I mentioned. It would be in the 40-50 range.

Chris

Originally Posted by mesquaukee

One needs to use 17.4 Volts not 12 volts to calculate the amperage, 200 Watts is roughly 10.4 amps of current. You need that extra voltage to "shove" the energy into the batteries.

Kyocera Solar KC85TS Solar Panel
Rated Power 87.3 Watts Peak Power
Voltage (Vmpp) 17.4 Volts
Peak Power Amps (Impp) 5.02 Amps
Open Circuit Voltage (Voc) 21.7 Volts
Short Circuit Amps (Isc) 5.34 Amps

[Gnitfar]

[QUOTE=witzgall;395611]Reeves;

Your system sounds ok, but I don't follow your math. If you use 12v nominal, I come up with 65AH a day figuring on 4 hours.

If you can figure out a way to mount them off of the stern, you will get more juice because you will mostly eliminate shading. Make the mount adjustable, and you will do even better. Check out the Atom Voyages website to see what I mean.

Chris



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On paper, your math may be right on, but my point was that I couldn't rely on the math, too many other factors. For example, my four year old Rolls batteries are now beginning to show age, due likely to sulfation, (never equalized) and many many cycles, and as a result their capacity is diminished, probably was last summer, but I didn't notice then. Input and output varies, I had only an estimate of daily amp usage and based my system on that, but in the real world, I found things to be different and that was the ultimate test. In hind sight, I might have added two more panels and another 185 ah battery, but I can live with what I have. As mentioned, I will at some point construct a stern bracket for the panels, also I have seen where some people hang them from life lines, so they can be raised when in use, or lowered out of the way when not.

[mesquaukee]

If you look at the data sheet/specifications of a panel such as the Kyocera KC85TS solar panel you will notice that that there is a rated wattage at a voltage
87.3 watts peak output at 17.4 volt. giving a Peak Power Amps of 5.02 amps

The last figure of 5.34 Amps is if there output wires were shorted or essentially 0 volts.

A panel rated at 85 watts actually produces at most 62.5 watts of usable power since 5.02 amps at 12.5 volts is 62.5 watts.

[Windsun]

Originally Posted by mesquaukee

If you want to maximize the use of a minimum of resources and have the time you can minimize all losses during the generation of energy by:

-install a switch bypassing the regulator (an inexpensive one for when you are off the boat or are lazy) eliminates all energy losses due to regulation (10-40%),

Not quite true. Solar panels are "constant current" devices - which means that the amperage will stay just about the same even if shorted out.

If you take the regulator out, you get more voltage, but only about 2% more amps, plus you run the danger of overcharging.