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Old 22-05-2015, 07:15   #1
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Solar Panel efficiency - Should I upgrade

My current solar panel set up is:

2 x 85 watt 12.5% efficient by Solartech (40 inches by 26 inches on the dinghy arch with zero shading)
4 x 55 watts, 13.2% efficient by Solartech (25 by 25 inches each built into hard top)
Total wattage: 390 watts
Solar controller is MPPT by Victron.

I am looking at replacing the panels with 4x 110 watt by Solara to increase wattage by only 50 watts BUT efficiency from 13% to 22%.

Here is my question. The new panels are the same surface area as the old panels and the efficiency is almost double then why are the panels almost the same wattage? Will I just get the same output and have wasted money? My hope is they would produce more during the non peak hours. Two panels with the same wattage and different efficiencies should have different surface areas (just a mathematical fact)?

I placed an amp clamp every hour on the input to my solar controller to give measure the output of the panels. I am in Grenada in May. This was done on a day without clouds.

7am 6 amps
8am 13 amps
9am. 19 amps
10am. 22 amps
11 am. 24 amps
Noon. 24 amps
1pm 22 amps
2pm 18 amps
3pm 15 amps
4pm 9amp
Almost 170amps for the day.

THANK YOU FOR ANY ADVICE!
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Old 22-05-2015, 07:51   #2
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Re: Solar Panel efficiency - Should I upgrade

Something going on there for sure. I am googling trying to discover why with such a high efficiency the wattage isn't higher but haven't found anything. Sounds like marketing hype or something.
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Old 22-05-2015, 08:58   #3
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Re: Solar Panel efficiency - Should I upgrade

Some companies quote the effeciency of the cell, some the effeciency of the whole panel. There is some wasted space around the cells and for the frame etc so cell efficiency is higher than panel efficiency. It is important to compare the same parameters (panel efficiency is what is important).

High efficiency panels allow you to squeeze more watts into the same space. This is important on boats, but 100w at 22% efficiency produces no more power than 100w at 14% efficiency, if all other other things are equal.

Some cells do have slightly better temperature coefficients and low light performance. Some panels are more shade tolerant. This will give a slightly greater output for the same wattage in real world conditions. Efficiency on its own does not give any information about these factors, but generally the new high efficiency panels are better than the older and cheaper panels in this regard. The temp coefficients and performance under lower light levels is often listed in the specifications.

The bottom line is that you are only gaining about 13% (440w verses 330w) in terms of wattage. It is likely the new panels will have better low light performance and temp coefficients (but you need to check the specs to be sure). The panels will also be new and output does drop off slightly with age so the output is likely to be 15-20% more. Only you can decide if this gain is worth the cost and trouble.
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Old 22-05-2015, 09:22   #4
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Re: Solar Panel efficiency - Should I upgrade

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Originally Posted by noelex 77 View Post
but 100w at 22% efficiency produces no more power than 100w at 14% efficiency, if all other other things are equal.
I think that's your answer, but I believe he's asking why with higher efficiency, the energy density isn't higher, and I believe the real truth is there isn't that much actual efficiency difference
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Old 22-05-2015, 12:16   #5
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Re: Solar Panel efficiency - Should I upgrade

The efficiency difference is real, but it only refers to the number of watts you can squeeze into a set area.

You can do the maths yourself. For example, the Kyocera 250W and the Sunpower 337W have almost the same overall area, at 1.65 and 1.63 sq m respectively.

If you do the calculations, the Kyocera produces 152W per sq m (250W with a size of 990x1662mm). The Sunpower produces 207W per sq m (337W with a size of 1046x1559mm). This is in the test conditions with sunlight that contains 1000W per sq m. Thus the panel efficiency of the Koycera is 15.2% and the Sunpower 20.7%.

The efficiency numbers tell us nothing about the low light performance or the output at realistic panel temperatures, just that you can fit more watts in the same total area with the Sunpower panels than the Kyocera panels. For each square metre of space on your arch the Kyocera panels will deliver 152W the Sunpower panels 207w. (Under the test conditions. These STC conditions are bright and very cold. This is also providing the total panel size will fit satisfactorily)

The Sunpower panels do have better low light and temperature coefficients meaning that for the same overall wattage the Sunpower panels will produce (slightly) more AHrs in the real world, but the efficiency rating tells us nothing about this characteristic.

Efficiency is Watts per area, nothing else. A higher efficiency panel will be smaller for the same number of watts.
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Old 22-05-2015, 14:42   #6
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Re: Solar Panel efficiency - Should I upgrade

Isn't a watt and watt no matter what?
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Old 22-05-2015, 18:42   #7
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Re: Solar Panel efficiency - Should I upgrade

A different question you are now getting about 170 ah per day? Is there a reason you want to change panels? If you are swapping panels what do you want for the old ones? Or do you want to add the new panel output to your current scheme?
The other is this an academic question?
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Old 23-05-2015, 07:24   #8
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Re: Solar Panel efficiency - Should I upgrade

I want to increase my amp hours per day. When on passages where the motor is not on I have to run the genset for about 2 hours a day. I burn 20 amps an hour with 2 huge plotters, radar, fridge, freezer and charging iPhones. I will reduce this load on my 3,000 mile leg but was hoping for more from my solar. Looks like I will leave 110 watt panels and ADD some walk on panels. Need to think a bit more.
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Old 23-05-2015, 07:37   #9
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Re: Solar Panel efficiency - Should I upgrade

We have 1150W of solar and on passage average about 20Ah as well. Battery bank is 840Ah
Ok for a week or so but then we have to run the engine for 1hr at night. I don't think more solar is the key for passage making. Next long passage we will reduce power consumption as much as possible. Watt and sea type hydro generators might be a better option. We found the sails shaded the panels a lot heading east to west in the northern hemisphere. We also had 2 fridges and laptop, plotter,radar, etc running full time so there's definitely room to cut back on usage
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Old 23-05-2015, 07:38   #10
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Re: Solar Panel efficiency - Should I upgrade

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Originally Posted by Jaymannyc View Post
I want to increase my amp hours per day. When on passages where the motor is not on I have to run the genset for about 2 hours a day. I burn 20 amps an hour with 2 huge plotters, radar, fridge, freezer and charging iPhones. I will reduce this load on my 3,000 mile leg but was hoping for more from my solar. Looks like I will leave 110 watt panels and ADD some walk on panels. Need to think a bit more.
OK that makes sense now however why do you run two plotters and your radar all the time on a long passage I could see radar at night in low vis but in the middle of the ocean you can see it almost as soon as your radar does. Turn the plotters off most of the time on passage just fire one up every few hours to update position alternate between them to keep both fairly up to date on your position. The radar and your plotters eat quite heavily.
Before adding panels I would look at where all the existing power is going and why it goes there so you have a better idea what you need to add in terms of panels to meet your power needs
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Old 23-05-2015, 08:04   #11
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Re: Solar Panel efficiency - Should I upgrade

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1. The new panels are the same surface area as the old panels and the efficiency is almost double then why are the panels almost the same wattage?

2. I placed an amp clamp every hour on the input to my solar controller to give measure the output of the panels. I am in Grenada in May. This was done on a day without clouds.
1. Because quoting higher efficiencies helps sell more panels at higher prices. Look at Wattage per ft and see what pays and what claims.

2. You can't measure like that. You must make sure there is sufficient and steady load at the other side of the regulator at all times. Switching all equipment on may help create such load. Only then you can measure whatever Amps the panels can deliver at any given moment. Otherwise battery soc will affect the measurement.

BTW We use mono-crystals and the only upgrade I have seen this far is the 'black' (back-linked) panels. However, there are equivalent panels available today that are only a fraction of WEIGHT of what we have here. This may count too, in some installations. These are very expensive though.

Cheers,
b.
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Old 23-05-2015, 08:35   #12
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Re: Solar Panel efficiency - Should I upgrade

If the panels are the same size, and rated for the same wattage, I would ignore the efficiency claims. Maybe they are in metric watts.(G) Doesn't matter, the total wattage of the panel is the only number that counts.


If your panels are mounted "flat" and you can change the mounting style so that you can manually track the sun, you can gain about 15% power over the four or five hours around midday, simply by keeping the panels oriented towards the sun, instead of leaving them flat. That might help somewhat. I don't suggest buying them and having them shipped to Argentina, but take a look at Solarstik.com to get an idea of what one commercial product does to accommodate that. If you could find, or make, similar mounts locally...
Otherwise I think you are going to need to look for other efficiencies or options. The efficiency means nothing, unless it is matched by a higher rated output.
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Old 23-05-2015, 08:51   #13
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Re: Solar Panel efficiency - Should I upgrade

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We have 1150W of solar and on passage average about 20Ah as well. Battery bank is 840Ah
Cats have so much room for solar. Don't for a second think us mono owners are jealous

It is said that the ideal boat length is three foot longer than you own. I suspect there is solar corollary. The idea solar array is 20% more than your current panels.
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Old 23-05-2015, 09:49   #14
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Re: Solar Panel efficiency - Should I upgrade

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Originally Posted by Jaymannyc View Post
I want to increase my amp hours per day. When on passages where the motor is not on I have to run the genset for about 2 hours a day. I burn 20 amps an hour with 2 huge plotters, radar, fridge, freezer and charging iPhones. I will reduce this load on my 3,000 mile leg but was hoping for more from my solar. Looks like I will leave 110 watt panels and ADD some walk on panels. Need to think a bit more.
Why not purchase a smaller, standalone solar charger for the iPhones? I've got one with a USB output that charges my Android phone when I need it, not that I use a lot of battery when out sailing as it's switched off.

I don't get the need for 2 plotters running simultaneously when you are out so you can cut your load by only using 1 at a time and if it's not foggy why use the radar? Also you can cut the load on your instruments by cutting down the backlighting. I generally run my ST70s at 10% backlight or even at 0% and can still see them clearly. My plotter I keep at about 60% but it all helps reduce the load.

How well insulated are the fridge and freezer and are they "over working"? It might be worth checking the internal temperatures to ensure that they are not trying to keep everything too cold. You might find you can save some amps by adjusting the thermostat in one or both which reduces the amount of time the compressors are working.

Presumably you have LED everything for lighting as halogens et al drink amps like a vampire in the blood bank.

Have you considered a towed hydro generator or a wind generator to add the extra amp hours?

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Old 23-05-2015, 10:33   #15
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Re: Solar Panel efficiency - Should I upgrade

On an other forum we discussed solar efficiency, and tested that the efficiency could be improved by as much as 20% by cooling them. The simple test was done by spraing a film of water over the cel. The problem was calcium in the water could reduce efficiency over time (so make an installation to cool from the bottom). This was tested on houses and pumping the water to the roof did negate te increased efficiency.

An other point that could give added efficiency is use a MPPT on each panel. On a ship there is often shadow on one or more panels. If these are all connected to the same MPPT the maximum power point differ per panel. And so you lose efficiency.

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