Solar panels

sinnettc · Dec 21, 2010

I mount an older version of the Sensei SE-1500 (http://www.sunsei.com/SE-1500?sc=12&category=62) on our rail. Ours might be an SE-1200. It seems to keep up with our usage quite well. We did a 7 day cruise in the San Juan Islands this summer and I was never concerned about running out of juice. We charged 2 phones, 2 laptops, one marine VHF, ran the LED anchor light, LED interior lights, & GPS/Chartplotter on a single 105 AH group 27.

Here's a picture of it with the homemade pvc & fishing rod holder mount.

I use OpenCPN too, for my route planning. Great program. There was a new release about a week ago. Once I have my routing done and saved I convert the .gpx route/waypoints to Eagle/Lowrance .usr with GPS Babel, save on a sd card, and transfer them to the chartplotter. At the end of the day I reverse the process and copy my actual track back over to the laptop.

walt · Dec 22, 2010

You can find numbers for solar daily output out to three decimal places.. for a an actual output that easily varies by a factor of 2 or 3 per day, varies by the time of year, varies by latitude, etc. The rule of thumb I use (saw it on this forum, don't remember who) is that the solar output in daily amp*hours is in the range of .25 to .5 times the panel watts rating. For example, a 40 watt panel would output about 10 amp*hour to 20 amp*hours per day. Any sort of shading on the solar panels - even the shade of a rope - can easily degrade this by an additional 25%. Lots of good places to mount - up high and to the rear is generally good as even the sail doesn't shade much. On the boat where for example the boom will shade - not so good, might loose more than 50% of output charge.. An MPPT controller gets you an extra 15% as long as the conditions are good (cool, no partial shading) but quickly degrades to only as good as PWM type controllers for not so ideal conditions. I wouldn't bother with MPPT if your panel size is under 80 watts (number pulled from a dark place). Have you considered the square foot of 135 watts solar panel on a 22 foot sailboat - its significant, might be worth looking for lower power on the anchor alarm (like a hand held GPS)

Battery monitor - not a bad idea especially if you are relying on solar since the charge you receive can vary by so much daily. Also consider that a battery monitor to some extent can allow you to have just a single battery that you know in detail what its charge is. This is compared to having two batteries with all the switches, combiners, etc and you only somewhat know about the state of charge of each battery. In a complete battery failure (the main reason to have two separate batteries), you can still generally easily start an under 10 hp outboard manually. I have a battery monitor and a single 200 amp hour battery with no battery switches - never had an issue with this setup. Charge monitor is not necessary but its certainly a fun toy to have on the boat.

FYI, too bad you couldn't use an Ipad for the OpenCPN app. I'm measuring about 1 amp current at 12 volts for the Ipad being charged from an inverter. I don't think you can use the GPS USB accessories with these..

walt · Dec 23, 2010

Maybe Sumner will post here - he put something like 180 watts (??) of solar panel on the back end of Mac 26S, probably can tell you how this worked out in the wind, etc. Who knows, maybe all that panel area back there acts like an anchor sail and actually makes for more stable anchoring???

I think lap tops are typically 3 to 5 amps powered from an inverter.. but didn’t think about the sleep mode. Your number of 1 amp on the radio also sounds about right (based on what my several year old car stereo does). Looked at your pictures, that looks like a cool boat..

Bill Roosa · Dec 23, 2010

Hey c_witch

I think I can make your life easier
Power is measured in watts not watt hours.
You don't multiply volts times amps times hours to get watts.
Volts times amps is watts
So your math is somewhat incorrect.
You are correct that energy is v*a*h= watt hours but nobody uses those units because they are hard to work with when battery storage is concerned. Since everybody has 12 volt systems you can just use amps times hours = Amp Hours

Let me supply some data I have from my boat:
Computer with 19" monitor and 14" display running --- 3-5 amps
Computer with just the 14" display running -- 2-4 amps
Computer on but screen blanked -- 1-2 amps
Anchor light (incandescent) --1 amp
Cabin lights (incandescent) -- 1 amp each
Radio --0.5 amp listening, 5 amp transmitting
GPS+wind+knot meter+depth -- 0.5 amps

So for your set up you have:

Radio .5a x 16h =8 amp*hours (AH)
Laptop 5a x 8h =40 AH screen on
Laptop 2.5 x 8h =20 AH screen off
Depth .1a x 16h = 1.6 AH
Anchor light 0.15a x 8h = 1.2 AH
Cabin lights (x2) 2a x 8h = 16 AH
Night energy usage 86.8 AH
-------------------------------------------
A 130 watt panel operating at 12 volts will give you 130/12=10.83 amps max. Given that your panel is not angled toward the sun and it is just horizontal and factoring in summer time and your latitude you can really only expect about 75% of that or 8.12 amps max. Then you factor in the panel not tracking the sun and you get about 0 output till 0900 in the morning and 0 output again after 1500 in the afternoon with the output maximum at local noon (1200). That is a cosine function and that means 0.7 times the max or 5.68 averaged effective amps from 0900-1500 or 6 hours. Grand total for a day is 5.68*6=34.1 amp hours.
Pretty discouraging ain't it
Using the same math but for a 180 watt panel you get 47.25 AH
Only slightly less discouraging
Calculating backward you will need at least (yes there is more bad news) a 265 watt panel. This does not factor in the charging efficiency of the batteries (95%) or the parasitic of the charge regulator which can be pretty high if you buy the wrong one.

Your solution is pretty simple, turn off the laptop, radio and depth meter and use a more traditional form of anchor watch. I have used a weight, some rope and a frying pan with great success. Anchoring in secure little coves helps stop the dragging also. Using a "manual" anchor watch system your energy draw drops dramatically to 17.2 AH which is well within the 130 watt panel’s capability.

When doing this type of work it is important that you consider the charge-storage-loads as a system. You can make some problems go away simply by doing the task at a different time for example. I have a excel spread sheet that calculates all this stuff. If you want a copy email me. Its free.

Sumner · Dec 23, 2010

walt said:
Maybe Sumner will post here - he put something like 180 watts (??) of solar panel on the back end of Mac 26S, probably can tell you how this worked out in the wind, etc. Who knows, maybe all that panel area back there acts like an anchor sail and actually makes for more stable anchoring??? ..........

Like Walt said we added 180 watts (3 panels) where the arrow is in the picture above. It worked well for us on a month trip to Florida that just ended, but didn't supply all of the power.

One important thing is how new/good are your batteries and how long will you be out and where are you sailing. Pulling the batteries down to 50% is not going to be good on them and I think ours (one was new and the other had been used for an 18 day trip--both are the same) are not as good now as at the beginning of the trip.

We were powering a 63 quart EdgeStar frig (real compressor frig) 3.5 amps when running, a CPAP machine at night at 1 amp with out the humidifier running. A dedicated 12 volt computer running SeaClear that uses 1.8 amps normally and 2.3 when the hard disc is accessed and 2.8 when using the WiFi with the router and Bullet 2 HP radio. It ran also all the time underway and a lot every evening when we had WiFi coverage or I was writing. A handheld Garmin Map 76 running 24 hours a day with the anchor set at night and hooked to the computer/seaclear with waypoint from it. A Cuda 350 GPS depth finder when under way. A 2 watt anchor light and a few other items like a cell phone charger.

Driving down, 2200 miles - 4 days the panels supplied power for the frig. We were down there about 4 days and then I finally had to run the 60 amp gen-set for about 1/2 hour. Then over the next 3 1/2 weeks I probably had to run the gen-set an additional 1 1/2 hours total and we also got some charging from the outboard running with it for about 10 hours total in that time. Some of that time though the batteries were topped off and we didn't need the outboard output. If you go out for a week or less chances are the panels might slow down and extend the point where the batteries finally get to low and have to be charged somehow.

I have a volt meter and amp meter running all of the time that both read to .1 of a volt or amp. I usually decide when to run the gen-set by monitoring the voltage with no real load on. I determine when to stop charging by watching the amp meter and usually stop when it gets under 10 amps as I'm down to diminishing returns by then. The gen-set will put out 60 amps, but the most I ever saw was about 28 and usually about 22-24 when I would start charging.

In the winter the sun angles are very low, even in Florida and the days very short. When we go back down after the first of April I'll bet we probably won't have to run the gen-set at all. We had clouds, but not near as many as someone would have further north in the eastern part of the U.S. or maybe Canada, so take that into account. I think the figures the others have posted are pretty realistic.

Since we don't have any more real room for panels I went with the more expensive MPPT controller to try and maximize the efficiency of the ones we do have.

I didn't notice any difference in sailing characteristics on the water, but we are beginner sailors and really just care about moving from point A to B. Someone else might notice some difference.

Good luck and put as much wattage as you can up there if you are a cruiser and want to stay out for long periods.

On our site (link below) I have the panel installation pictures,

Sum

Our Trips to Lake Powell, UT - Kootenay Lake, Canada - Priest Lake, ID

Our Mac Pages

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walt · Dec 23, 2010

Sumner, how were you using your two batteries? Always in parallel?

If you used them this way, did you happen to check the water level at the end of the trip? Just curious if you had one battery use a lot more water than the other? Sounds like you were working the batteries pretty hard.

C_witch, one note on the radio.. If the radio you mention is a VHF running off the 12 volt, mine uses more like .27 amps when its just listening and no one is talking. When someone is talking, it uses about .8 amps. If I’m talking, 5 amps.

My experience is more like Sinnetics. I have a 40 watt solar panel and along with the occasional use of the outboard, it provides all the power I need. This is for a family of four on the boat. No fridge... hand held GPS, LED lights, depth gauge, DVD player (kids would watch several movies per day), use the Ipod/car stereo. We typically would use about 25 amp hours per day when we are trying hard to use as much as possible. I think it would have been easy to get by with just 15 amp hours daily. C_witch originally asked about a battery monitor, knowing things like this is possible with the battery monitor. If you had a cloudy day and didnt get much solar, you would know the net sum for the day and could be frugal with the power use.

I also made use of fishing rod holder like Sinnetics for the solar panel.

Sumner · Dec 23, 2010

walt said:
Sumner, how were you using your two batteries? Always in parallel?.......

Yes they have always been in parallel both in use and charging. One is hooked to the outboard no matter what, but I can separate them with 2 separate switches if needed from the load, but don't after your post a year or so ago.

I did fill the water in both before the trip. Neither was down much. I didn't get a chance to check them after. We took out in the rain and just got out of the storage area 17 minutes before it locked down for the night. I'll check them when I go back, but they are hooked to the panels and charge controller while we are gone. The frig is off and there is no load on them.

I think when these batteries are shot I'll try switching to 2 6 volt golf cart batteries like you did.

I had the zen-pole electrodes in the water all the time and they look pretty much like the day we started. I'll try and take some pictures and send them. I took them off and have them here in PA and I'm debating on mailing them home and sharpening them or just leaving them as is? Any thoughts?

c ya,

Sum

Our Trips to Lake Powell, UT - Kootenay Lake, Canada - Priest Lake, ID

Our Mac Pages

Mac Links

John Nantz · Dec 23, 2010

Solar panel controller = Blue Sky 2000E

This is somewhat of a piecemeal post, but to answer just your one question about a controller for the solar panel, like Sumner said, a MPPT is a good way to go. I don't know which one Sumner has but I'd sure recommend the Blue Sky 2000E model.

http://www.blueskyenergyinc.com/products/details/solar_boost_2000e/

My reason being is that it has what they call a "solar boost". Why is this important?

When it is overcast or foggy and the voltage output of the panel drops down to, say, 8 volts, it won't charge anything. What their solar boost does then, is take the little bit of power the panel can put out and up the voltage to something useable, but this is done as the expense of some amps. Never mind though, a little amperage is better than nothing.

We've got two 130 Watt panels on board, one on each side of the pushpit, and I can angle them to a large degree. There is almost always one that I can angle to optimize output. Even on a dark overcast day with rain or drizzle, which we get a lot of, I've seen output in the range of around 3 to 5 amps with this setup which is enough to keep up with, or even get ahead of, the refrigeration.

Along with the controller, go with large conductors to minimize loss and try to keep the wire runs short. Remember, it's the round trip that counts, too.

I've used this controller for several years now and, if you can't tell, I really like it.

See picture of our cheap-and-dirty "temporary" panel setup. They are manually adjustable from full down to up at about, say 130 degrees. They pivot on a 1/2-inch plastic pipe and are adjustable with a few lengths of plastic pipe in various lengths, tethered off, of course. Panels have to be tied down - use shock cord - to keep the wind from catching them and flipping them up. I've used these under sail in winds up to 40 knots. The temporary setup is going on it's 5th year.

Well, so much for that idea (uploading photo). Guess I don't have my cookies enabled.

sinnettc · Dec 23, 2010

Walt, I like your mount better than mine. Might have to think about redesigning mine to a pole in the spring.

walt · Dec 24, 2010

Sumner, thanks for doing that testing!

John, don’t have any numbers but I’ve always questioned whether or not a MPPT controller can do much when the panel voltage drops much below the normal operating voltage. When the panel voltage drops, usually the current has also dropped way off also and there just isn’t much power available. The MPPT idea is still valid except that now the current just to run the MPPT controller might actually be higher than what you are extracting from the panel. The MPPT controller I bought about five years ago uses about .1 amp when running (about 10X of a PWM controller), wouldn’t surprise me that what gets "extracted" from the solar panel when the voltage is that low is less than .1 amp. I think you could easily end up with a net loss.

If you do go with MPPT, you are correct about the loss in wires being important. Interesting that with the PWM controller, the wire loss becomes a lot less important as the controller is not taking advantage of all the voltage available anyhow. The temperature issue with solar panels is also mostly an MPPT issue - reason is that panel voltage is much more sensitive to temperature than panel current is.

Sumner · Dec 24, 2010

John Nantz said:
........ I don't know which one Sumner has but I'd sure recommend the Blue Sky 2000E model.

http://www.blueskyenergyinc.com/products/details/solar_boost_2000e/

My reason being is that it has what they call a "solar boost". Why is this important?

When it is overcast or foggy and the voltage output of the panel drops down to, say, 8 volts, it won't charge anything. What their solar boost does then, is take the little bit of power the panel can put out and up the voltage to something useable, but this is done as the expense of some amps. Never mind though, a little amperage is better than nothing....

We also got a Blue Sky....

http://www.solarblvd.com/Charge-Con...V-3-Stage-Charge-Controller/product_info.html

....but it doesn't have quite all the bells and whistles that the one John has, but we have been very happy with it and would buy it again. It does have equalization and will charge a separate battery other than the main bank or control a load such as a light and turn it on or off and you can hook up a temp sensor to make it even more efficient. We aren't using any of those at this time.

................I was also surprised to see some small but decent charge rates with full cloud coverage and even rain. All of it helps. It would also get up to 3 amps or so very early with very low sun angles. Walt I don't know if it makes a difference or not but there is a LED on the front of ours and once the unit isn't seeing any light, night, it goes off and and I don't think the controller is using any electricity. If I turn the amp meter and volt meter on and nothing else, I can switch the panels and controller out of the circuit, I see negative .1 amp and feel that is what the amp and volt meter or taking. With the controller in the circuit and its light off I still see negative .1 amp. Any time the light is on I'm seeing positive amps.

http://purplesagetradingpost.com/sumner/macgregor2/inside-25.html

I moved the meters overhead and watch.....

.... them a lot, what else is there to do

.

One thing to consider is where you mount them as far as hitting things. Prior to Florida where we were sailing had docks like in ....

...John's picture (beautiful boat John) and things off the sides of the boat weren't a problem. In Florida the docks we used...

.... all had tall pilings and we about tore the BBQ grill off on one and got the panels hung up on another, but didn't damage them. If I sailed in Florida all of the time I would not have things hanging out on the sides of our boat as far as they do now. Something to consider.

Our panels are all fixed and we could gain by being able to position them, but from past experience with a panel on a camper I decided I was probably going to be too busy or too lazy to do that, so just did what I did.

Put at least 50% more panels up there than you think you will need and you might be happy.

Good luck,

Sum

Our Trips to Lake Powell, UT - Kootenay Lake, Canada - Priest Lake, ID

Our Mac Pages

Mac Links

walt · Dec 24, 2010

I don't know if it makes a difference or not but there is a LED on the front of ours and once the unit isn't seeing any light, night, it goes off and I don't think the controller is using any electricity.

I would think it’s very likely that you are correct, the MPPT controller goes into some sort of "sleep mode" when the solar output gets low and the controller determines that it’s not going to contribute anything. The one I have is older and it displays current coming in from the panel, current out to the battery and also battery voltage. It doesn’t display panel voltage - one reason I’m not really sure what happens when panel voltage gets low.

Another John who posts here (flynfoil) I believe said he had a case where snow covered his panel and the MPPT charge controller discharged the batteries. So maybe there is also something else going on - or maybe the sleep current is much smaller - but somehow still significant. Of course, maybe he would have had the same thing happen with a PPM controller?

I’ve also been surprised by how much current the panel will put out when the angle of incidence to the sun is fairly bad. This is with a PPM controller, I think it has more to do with the panel design than the controller.

Johns picture - that is really a nice picture by the way..

flynfol · Dec 26, 2010

Hi All,

Happy Holidays and all that good stuff. Walt, I had a desulfator(homemade), an inverter(sleep mode), and the charge controller in the circuit and it sat for months like that. The panel angle was not reset for winter(wasn't able to get up there) allowing snow to pile up and stop charging the batts. This power system has been autonomous(except for panel angle and battery water) for almost ten years. But if the voltage drops below a certain level(don't remember what it was....10volts maybe?), the charge controller(RV Products/solar boost2000e) will not let the relay close to charge the batteries. The controller does draw a small amount of current(like you said sleep mode) but I think negligible in short term. Panel angle should be set to make the biggest shadow( or use you ammeter on a sunny day)....or + or - 23 degrees of latitude at the solstices. Example: 69 degrees for winter, 23 degrees for summer for me at 46 degrees latitude. You can see why snow piled up

Open circuit voltage on a 12 volt panel(36 cell) is about 21 VDC.....working voltage is about 17 VDC. Sice panels are more of a constant current device, if you hook them directly to a battery(or using a shunt regulator), they will only charge at battery voltage until the battery voltage increases, thus losing some output wattage. A boost regulator is nothing more than a switching power supply that takes incoming voltage "boosts" it to provide the higher current at the battery......using most of the panel output. When battery voltage is high.....not much boost....when battery voltage low......more boost...particularly when panel temps are cool. Edge of cloud effect in the winter, mine will max out.

Clear as mud?.....

John

LloydB · Jan 2, 2011

still muddy. I thought a solar cell was constant voltage variable current device rather than visa/versa.

walt · Jan 3, 2011

what flynfoil said is correct - solar panels are constant current for some given solar radiation. Even the short circuit current of a panel is usually close to the rated or maximun power current (ie, constant over a very large voltage range). If you hook a solar panel up to a battery without a regulator, it would put out the same current regardless if the battery voltage was 10 volts or 14.5 volts (as long as the open circuit voltage of the panel is significantly above 14.5 volts - usually the case).

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