Solar -- some real world data

[Cpt Mark]

Originally Posted by SailingYoungs

Looks like there’s a lot of solar experts on here. We don’t live aboard but will be cruising this summer. Our needs are simple and I’ll be running the engine, but don’t want to if I don’t need to get somewhere. I don’t want to go through the effort of mounting and want to use about 2ft x 4ft of deck space. There are so many confusing choices out there. What’s the best, most efficient new panel out there? What technology should I be looking for? OP said bifacial. Is that the ticket?

You're at a high enough latitude that you don't get as much out of a panel as you would on the equator. I'm in PDX. So, this time of year it's about 20% less than rated.

2x4 feet is going to be a small panel. You're going to get what you get with it. If mounting to the deck (you need 3/4" or so airspace for ventilation or it gets hot and doesn't work a well) forget bi facial. You won't have any reflective sunlight.
Are you thinking of walking on them? Permanent install o temp? You have 2 choices. Rigid or flexible. Flex costs more money, not as efficient and a short lifespan compared to rigid. If you have davits in the back. Bifacial would be great.

Theres a lot to this. Not just which one is the best. Mounting. You could have them swing up into position from the lifelines/stanchions. How much power do you need? What battery chemistry are you using? etc.

[mitiempo]

Originally Posted by Mike OReilly

I'm not sure if I'm limiting things. We regularly see upwards of 18-20 amps coming out of the controller. Very occasionally it has exceeded 25 amps. With 400 watts. Voltage outputs at the panels hover in the 21v range -- my panels are rated ~22v. Output voltage varies with stage of charging: 14.4 to 12.8 (I think... I'd have to check. Lead acid batteries).

With 400 watts I have a theoretical max of 33 amps, which of course would exceed the controller capacity. I don't know if the MPPT ever throttles the output, but I really doubt it. I rarely see more than 320 watts coming off the panels.

I am at the max for this controller. I probably should have got the 100/50 version, and if I ever want to add more panels I'd have to go up, but for what I have now, the 100/30 seems fine.


Here's a sample screen shot of some data:

Mike

Victron 100/30 is rated for a max of 440 watts. 440 divided by 30 = 14.66 volts, typically the bulk charge voltage or slightly higher. Your 400 watts should max out at 400 divided by 14.66 = 27.28 amps.

Remember that you cannot charge at 12 volts.

[fxykty]

Originally Posted by Cpt Mark

You're at a high enough latitude that you don't get as much out of a panel as you would on the equator. I'm in PDX. So, this time of year it's about 20% less than rated.

...

While someone at the equator always gets sun within 23* or of vertical, they get many fewer hours relative to boats further away from the equator in the summer. In the winter the panel near the equator will get a few more hours than someone further away. I think the equator panel doesn’t make as much on an annual basis as a panel at least 20* and up to 45* away from the equator.

We spent several years up and down the coasts of Australia (between 20 and 44* S). Most of the time we were producing, on sunny days, 1.5 to 2 times what we have been producing in the last year between 0 and 10* S of the equator. Part of the reduced production could be the increased heat? Our days are always 12 hours, with relatively low sun angles for at least 3 hours. P max 75% of rated right now 30* away from the sun, while at the equinox we were P max 120% for a couple of hours.

BTW, we have 2.65kW of hard panels. They are sufficient when it’s at least 75% sunny for our 24hr usage of about 9kWh. We have a fridge and two freezers working hard 24/7 - those are the biggest constant consumers. The rest is intermittent (electric galley, Starlink (sleeps overnight), device chargers, etc.

[sailingharry]

Originally Posted by Statistical

For anyone else weighing such choices there is no risk. If you exceed the input VOLTAGE limit on a controller that is a problem. If your panels produce more power than the output CURRENT limit it simply caps your output.

Still not sure why you expected >30A. The panels are 400W max under ideal theoretical conditions. If charging at 14V then 30A is 420W which is more than your panel peak output. Maybe something got lost in translation. If you had wired the panels together (series or parallel) and were using only one controller then you would need 50A.

Lastly how do you have the panels wired in parallel if you have 2 panels and 2 controllers?

1) Agreed, no risk. I initially had them connected to my existing 15A controllers, and they happily limited it to 15A. In the residential world, where space/panels are free, they often "overpanel" the controllers -- install enough controllers to meet the demand, and enough panels to meet the demand in the winter -- and end up with 3X the panels in the summer. The "Risk" was losing a few watts at peak -- and the cost delta was fairly trivial.
2) The potential loss was a bit more than your math. First, my 400W are bifacial, so theoretically maybe as much as 440W (but I have strong doubts about bifacial in my installation, where water is a poor reflector and the stuff under my panels will cut the exposure). But more importantly, with my 800Ah AGM bank, a charge voltage closer to (or under) 13V is quite possible. At 13V, a 440W/13V yields a 34A charge current. At a charge voltage of 12.5 (perhaps unlikely unless well depleted) yields a charge current of 35A. Really, not much left on the table -- but the cost delta was low.
3) You are 100% correct on my mis-statement of the configuration. They are not actually in parallel. They are two panels, each feeding one of two controllers, feeding the battery. So the "systems" are in parallel, not panels.

[sailingharry]

Originally Posted by donradcliffe

Is that 20A per panel/controller, or 20A total?

That 20A output (at 8AM) is total. While I have Victron controllers with slick Bluetooth data, that's not convenient. I have all of my solar going through an ammeter that gives me total output. I use a Hall Effect ammeter, about $15 on Amazon. While I really doubt the ultimate accuracy (and severely doubt the low current accuracy -- I think the zero shifts), I find the situational awareness of glancing at that readout to be really useful.

[sailingharry]

Originally Posted by SailingHarmonie

I am not sure your numbers all add up. 800Wh is only about 66 Amp-hours in a 12 volt system, yet you suggest you actually use about twice this much power. (130 Amp-hrs, I I follow you correctly). Where is the extra coming from? This might not be real, without an integrated consistent measuring system errors do creep in. And the conversion back and forth from Watts to Amps is problematic with changing voltages...

Just to help you calibrate expectations, our 630kW rated system, 6 years after installation, produce 3kWh per day on a normal sunny day. In low latitudes and full sun in June that can get as high as 4kWh/day. That is full output, not throttled by clouds or battery acceptance rate.

You should not be at all surprised by a higher daily kWh output than the panels rating in WATTS. That is expected. The panels are not rated in terms of W-hours/day, but in terms of instantaneous Watts. With 800W worth of panels, you would expect about 3.8kWh per day (plus or minus) if completely unthrottled.

I've had several comments (including yours above) that have made it clear that in my haste of typing, I was less than clear on conveying my thoughts. Oops.


I have been harvesting about 800Wh (or sometimes much more) PER PANEL. Or with two panels, double your math. As you noted, 800Wh is half my daily load -- so double that is, well, my daily load! In addition, we've motored most days, and even on our good days with under an hour (in and out of harbor), our 270A of alternators certainly added significantly to the mix, especially the morning run when they were running in bulk (of course, I am fully aware that 270A of alternators rarely makes more than about 150).


As far as the daily harvest, I had often heard a rule of thumb, where harvest in Wh should be 3X panel rating in W. I've seen a solid 3X, but often well over that, which is why I thought it notable. Perhaps 3X may still be accurate when averaged long term (with rainy/cloudy days).

[sailingharry]

Originally Posted by Cpt Mark

I just completed my solar system and am running off solar only. I have two, 540watt JA panels mounted flat n the bimini and raised 3/4" above the bimini for airflow.

840 AH of Lifepo4 batteries. All electric kitchen. No propane on board. 2 burner induction cooktop, 3 qt instant pot, electric tea kettle, large toaster oven and an electric griddle. Large refer and freezer both on with their own compressor.

I'm at 45.30 N in Portland Oregon. I'm getting just over 6.1 kwh per day now. I'd get more but in the later afternoon around 3, I get shading from the spreader on 1 panel

Actually, as great as that is, I suspect you would NOT get more. Unless you are plugged in or running a generator (or slowly depleting your bank), your daily harvest is going to be exactly equal to your daily demand. If you are using 6.1kWh per day, you can only harvest 6.1kWh per day. My panels are typically limited in that fashion as well -- looking at the Victron reports, large perecentages of the output occur at float, where they are only making up for demand.


Actually, on AGM that I have, that isn't completely true. The solar chargers have no idea what my battery SOC is, and often go to float before the battery is fully charged. That's far less of an issue with LFP. MaineSail has often grumbled about what he calls "Premature Floatulation" where alternator regulators go to float long before the bank is full -- and this applies equally to solar controllers.

[sailingharry]

Originally Posted by SailingYoungs

Looks like there’s a lot of solar experts on here. We don’t live aboard but will be cruising this summer. Our needs are simple and I’ll be running the engine, but don’t want to if I don’t need to get somewhere. I don’t want to go through the effort of mounting and want to use about 2ft x 4ft of deck space. There are so many confusing choices out there. What’s the best, most efficient new panel out there? What technology should I be looking for? OP said bifacial. Is that the ticket?

A few comments.
1) efficiency is a marketing thing. The difference between 20% and 22% is only 10% in output. Meaningful, but not really. And the difference between a 100W panel operating at 20% and a 100W panel operating at 22% is ZERO (100W is equal to 100W).
2) As a very rough rule of thumb, solar output is 200W per square meter (or 10W per square foot). You have 8 square feet, or 80W.
3) Bifacial REQUIRES the panel backside to be exposed. It takes the minor, but still significant, reflected light that illuminates the backside of the panel to make a few more watts. If you are mounting them (or laying them) on the deck, bifacial doesn't work.
4) I struggled mightily with dimensions. In the residential world, you buy "X" amount of solar, and bolt it to appropriate framing. In the boat world, you have "X" dimensions (in your case, 2x4). A 2.5x5 panel won't work for you at all. And a 2.5 x 3 would waste a foot in one direction and still not fit. And a 20" by 40" would be 40% less output than your theoretical 2x4. And the vendors emphasize things like efficiency over dimensions --it is HARD to find one that maximizes your available (and limited) footprint.

[noelex 77]

Originally Posted by sailingharry

Actually, on AGM that I have, that isn't completely true. The solar chargers have no idea what my battery SOC is, and often go to float before the battery is fully charged.

If this is the case, adjust the absorption time.

However, an absorption time that is too long is more common than one that is too short on most cruising boats.

[noelex 77]

Originally Posted by sailingharry

I've seen a solid 3X, but often well over that, which is why I thought it notable. Perhaps 3X may still be accurate when averaged long term (with rainy/cloudy days).

These rules of thumb are rather silly in my opinion. Average solar output can be significantly greater or much less than this formula predicts.

Consider the solar insolation in the area and season where you are sailing.

[noelex 77]

Originally Posted by sailingharry

A few comments.
1) efficiency is a marketing thing. The difference between 20% and 22% is only 10% in output. Meaningful, but not really. And the difference between a 100W panel operating at 20% and a 100W panel operating at 22% is ZERO (.

Higher efficiency panels have a smaller area for the same wattage. This is useful for sailboats where the area (especially the shade free area) available for installing solar panels is limited.

It is not just a marketing thing. It has real world implications.

[Statistical]

Originally Posted by noelex 77

Higher efficiency panels have a smaller area for the same wattage. This is useful for sailboats where the area (especially the shade free area) available for installing solar panels is limited.

It is not just a marketing thing. It has real world implications.

Yeah sailboats are probably one of the few area outside of satellites where efficiency matters. For a given amount of usable space (say over dinghy davits) using 22% panels vs 19% panels means ~16% higher daily output.

[sailingharry]

Originally Posted by noelex 77

Higher efficiency panels have a smaller area for the same wattage. This is useful for sailboats where the area (especially the shade free area) available for installing solar panels is limited.

It is not just a marketing thing. It has real world implications.

I don't agree. I think sailboats focus on maximum output for a given footprint limitation. Let's assume you have my array. Lets assume I found 3 panels that fit my length and width constraints. Lets assume they are:
1) A 20% efficient panel, that is almost a perfect fit, and makes 400W.
2) A slightly smaller, 21% efficient panel, that makes 380W.
3) An even smaller 22% efficient panel, that makes 360W.
And lets assume I also find
4) A 23% efficient panel, making 450W, that is 2 inches wider than my maximum fit.
Which should I buy?
Obviously, 1, even though it is the worst efficiency it is the most power that will fit in my footprint.


Seriously, as I searched, I looked at only 2 criteria -- dimensions and power. I searched for the maximum power that would fit my dimension constraint. I never even looked at efficiency, as it was irrelevant. And as a sailboat, where cost is fairly trivial, I didn't even look at cost as a first criteria (when I found nice panels that fit, but came in pallet minimum orders with huge S&H, it did come into play). I searched on Watts as a general criteria (I probably bracketed 300-500), and then dug into the specs for LxW, but I never even glanced at efficiency. Perhaps irrationally, I did heavily favor bifacial. But after that, my sole criteria was "how many Watts that fit my footprint."


It is true that as efficiency goes up, size per watt goes down, so high efficiency panels are favored in the search, but dimensional criteria was so constraining that panel dimensions completely overrode efficiency.


In residential, I suspect that cost per watt overrides efficiency. Say I'm building a backyard panel array, and want say 10kW. Say I can get 23% panels to get that power for $15K. But perhaps I can get 20% panels for $10K, but I have to make my array 2 panels longer. If I have the room, I'd get the lower % panels and save $5K.


I just can't see an arrangement where efficiency trumps other criteria -- cost, dimensions, output. It drives those factors, of course, but I can't imagine sorting a spreadsheet of panels by efficiency, with the idea that the highest efficiency is my goal.

[Statistical]

Originally Posted by more

year 2012-2022 i have germany made 2x 100w solar panel and victron 70/15 mppt not smart my winston cell 400ah 12v be full charged around 12-14.00 depend .by victron average day harvest 1000-1250 wh lot time i see 15a charging ussualy sun and wind condition
but last year buy some brand but made in china 2 x150 w 21v soc series and change to 30a mppt i never see 12A charging yesterday first time i see 15A(i put in conector eletrical greas in conector) charging. first in real world mistake i change mppt from 15A to 30A second evry day i need engine +- 1 hour to work. my frige is end of life becouse now working without stop and cooling is week. i try everthing charging gas,changing gas.
but i must change solar panel for premium 445W but dimension 170x 110 cm and must be high voltage more volt beter over 100 v be perfect.

soon new hanse 505 must have 3 or 4 445-450W maybe Trina Solar Vertex S+ i must order 10 pices for 74-78 € pices rest go to reserve.

amazing how old 200W solar panel harvest more energy from fake biger also in size 150W solar panel.

Your example is pretty contrived. Higher efficiency panels are rarely smaller they are usually the same size with higher output. So a more realistic example if there is a 360W, 380W, and 400W panel all roughly the same size which fit. If you care about max output the 400W panel is the highest efficiency.

You effectively said that just in reverse. You said what matters the most to you is getting the highest output in a given space and that is going to be the very rare exceptions aside the highest efficiency panels.

Yes in residential applications people usually have so much space relative to energy demands that efficiency is not a major factor.

[JeffAtomms]

That is the same system we have (we have the 150/70 victron and two LG 390 watt panels). We are thinking of doing a Cerbo GX so that we can dump load 24 VDC to our water heaters 24VDC x 600W element. I'm confused how to set it up.