Help me choose the best solar panel for the low light conditions.

[robby]

Hey. Thanks for your suggestions! I had just got on the roof and measured the angle that my solar panel is laid currently, it is at literally 77.7 degrees. Could that be the issue during my winter season? I want to explore every bit of option to not go with the more expensive solar panels. I would really like to stay with my Jinkos, they perform much better than my Canadian ones, and the cost isn't space reaching. Awaiting reply, Vermont citizen!

David sorry to take so long to get back to you.
I am just going to give it to you straight.
You are not going to get any significant gains in power unless you have a Ton of money and a lot of property space to throw at this problem.
At your location in the Winter months you just don't have enough Light energy hitting each square Meter of Area to generate sufficient power and at best even if you bought the most expensive Panels on the planet you may go from 20W to 30W per panel.

The approach you would need is strings of panels eg 8 Panels in series and then parallel them with three more strings of 8 to create just one normal string and even then we are talking about maybe 650W per string of 32 x 485W panels. I am not 100% sure that is even a safe approach but I just wanted to at least present one possible solution. Now that is just one string and you would at least need one more to get up to 1300W or about 6Kwh of production per day in the Winter.
As you can see it's not very practical and in the Summer months you will literally be producing so much PV power that the MPPT will be current limited and cannot even use a quarter of what it could produce.
There are no simple answers, because you are literally trying to get water to Shower out of damp sand.

 

[12VoltInstalls]

Summer months you will literally be producing so much PV power that the MPPT will be current limited and cannot even use a quarter of what it could produce.

That is my scenario at N 44*+ here in Vermont. His location is N 55* so guestulating that nearly vertical (80* from horizontal) is what he needs and ‘may’ already have that?

 

[12VoltInstalls]

.dupe

 

[PVGeezer]

Summer or winter, you get most of your production when it's sunny. You can prove this to yourself for your location by running a good hourly PV performance model like PVWatts, downloading the output, and then sorting the hourly data by solar irradiance level.

What you'll find is that it doesnt matter that much how well the modules do under very low light conditions because there's very little energy to be collected then anyway. Kinda obvious when you think about it.

So what you want if youre off grid is a system that's ready to collect and store energy on those sunny winter days when they do occur. That means a steep tiit angle so the snow is off as quickly as possible, a good MPPT, and a big battery to carry you through the very cloudy periods.

 

[JustHank]

From vertical or horizontal?

If he did it using an iPhone, it looks like nearly vertical. But my phone (iOS 18.2.1) won’t give 77 degrees in the Measure/Level app - only minus 13 - so maybe a Samsung owner can chime in.

 

[KingDavid]

If he did it using an iPhone, it looks like nearly vertical. But my phone (iOS 18.2.1) won’t give 77 degrees in the Measure/Level app - only minus 13 - so maybe a Samsung owner can chime in.

Hi. Want to say thank you all for your suggestions. I used an app on my Samsung phone, I got 77 degrees. I will send a picture tomorrow, Lord willing. I wouldn't call the solar panel vertical by any means. Changing the tilt of solar panels didn't dawn on me before, to be honest. Will experiment tomorrow, and will attach a picture as well.

 

[KingDavid]

I thought it might be a good idea to also attach the solar panel manufacturer's PDF file:

https://www.v-tac.eu/images/certificates/Technical-Specs/12262-EU-JKM475-500N-60HL4-V-F8-EN-Technical-Specs.pdf

 

[Warpspeed]

In my testing, the poly did perform slightly better than the mono under difficult lighting conditions, but also had a somewhat wider acceptance angle, which helped with sun angle.

What I found is that I got the most benefit from aiming them toward as late in the day as possible, as that is when the sky was the most clear ( here) in the winter.

Also used a solar controller that turns on at a very low voltage.

Nonetheless, there just is not much sunlight sometimes, and 300 watts of solar might still only produce 20 - 30 watts, so not zero, but also not much.

I have both mono and poly panels, and can confirm, the poly panels are slightly better in low light, the mono better in a clear blue sky.

Also I agree, panels in series give the solar controller a decent voltage above the battery voltage to work with, and will be more efficient.
The exception to that is if partial shading is your problem, where parallel wins.
But in low light and no shading problems, series connection wins.

Third observation. When you have total cloud cover all day, and only weak diffused grey light, best panel orientation is pointing straight up.
But as Harry says, your local weather conditions early morning versus late afternoon, a bit of extra sun might be worth chasing.

Doing all of the above, solar recovery will still be pretty pitiful, but its the best you can possibly do in truly awful conditions.

 

[quantum`]

Alot of wisdom here.

I would only add to never exceed any MPPT's max voltage, even on the coldest days (when in bright Sun the panels are performing their best).

 

[KingDavid]

Hello everyone. As promised I got on the roof, and took a few pictures. Note: I experimented with tilting the panel to a vertical positions, and the result was positive. This was done 9am in the morning, where the sun wasn't at its peak. As a result, without changing the tilt I was getting maximum of 28watts, changed the tilt by 30-40degrees (nearly vertical position) and started receiving 34 watts of input max. The test was positive. I believe this might be useful for other individuals as well, this can act as a proof.

First, here's the picture of my solar panel (77.7 degrees), again, I can't verify if this angle is correct, used my samsung phone's app to measure it. Does it look like it is at 77.7 degrees?

Second picture shows my electricity production. Got 34watts max when turning it to a much more vertical position.

 

[CaliSunHarvester]

you are literally trying to get water to Shower out of damp sand.

That line is noted, will come in handy

 

[PVGeezer]

Tilt angle is measured as flat = 0, vertical = 90. It looks like your device is measuring the other way around, with vertical = 0 and flat = 90. In which case you're at 90-78 = 12 degrees there.

It's actually pretty rare to see an asphalt shingle roof below a 3 in 12 pitch (because that type of roof is prone to leaks if at a lower slope than that). 3:12 pitch is 14 degrees.

Anyhow regardless of whether it's 12 or 14 degrees, you're at a low tilt angle, which is perfectly fine if youre trying to optimize annual production (my solar array is at 13 degrees for that reason). But if youre trying to maximize winter production you want to be at a much higher tilt.

One thing you should consider before you reorient your present solar array is the aforementioned roof leaks. Be very careful to seal all your attachments carefully.

There are specialty roof attachments you can buy for solar arrays that make that easier, but no matter how you do it you run a pretty high risk of getting leaks when you make holes in low slope roofs like that. Id remove the solar array from the roof and mount it on the ground. But that's me.

 

[KingDavid]

Tilt angle is measured as flat = 0, vertical = 90. It looks like your device is measuring the other way around, with vertical = 0 and flat = 90. In which case you're at 90-78 = 12 degrees there.

It's actually pretty rare to see an asphalt shingle roof below a 3 in 12 pitch (because that type of roof is prone to leaks if at a lower slope than that). 3:12 pitch is 14 degrees.

Anyhow regardless of whether it's 12 or 14 degrees, you're at a low tilt angle, which is perfectly fine if youre trying to optimize annual production (my solar array is at 13 degrees for that reason). But if youre trying to maximize winter production you want to be at a much higher tilt.

One thing you should consider before you reorient your present solar array is the aforementioned roof leaks. Be very careful to seal all your attachments carefully.

There are specialty roof attachments you can buy for solar arrays that make that easier, but no matter how you do it you run a pretty high risk of getting leaks when you make holes in low slope roofs like that. Id remove the solar array from the roof and mount it on the ground. But that's me.

Thank you, I will definitely look into it. I knew there was a problem with the way the app was measuring the angle, based on what people said here. Will try to figure out a way to change the settings, and will give an update. So far, I hadn't had any visible leaks, I used weathermaster silicone around the screws, that should have left a positive effect. It is a shame that I no longer have the cloudy days as I did a month ago, so I can't replicate the low light conditions in order to test my solar panels. I will definitely implement a more vertical solar panel angle, and will pay attention to the cabling more. I am quite confused really whether it is even worth investing in the top-notch solar panels, there's a mixed opinion about it here. I still suspect my Canadian solar panels were the problem, but that's just speculation. Appreciate the feedback, Geezer.

 

[kommando]

I am quite confused really whether it is even worth investing in the top-notch solar panels

Based on the likely small gains then no its not worth it, instead optimise what you have by having a winter and summer angle you change between twice a year.

 

[PVGeezer]

I don't think your solar modules are the problem. Small differences in low light performance are really not that significant overall because the energy produced is so low to start with on dark cloudy winter days. It's a difference of at most a few percent of a small number. Some solar module manufacturers like to claim "better low light performance" but it's really mostly marketing nonsense.

If you want better winter output you'll need more solar at a steeper angle. It looks like you have space to put a larger array on the ground where it can get good reflection from the snow. Also consider bifacial modules because at a steep tiit they can get good light collection on the back side.

Overall though most off grid folks in high lattitude places with dark winters find it difficult and costly to supply all their electricity with solar. It is usually more cost effective to run a fossil fuel generator part of the time in December, January, and February. The better hybrid inverters will automatically start and stop the generator as needed to keep your batteries charged.

 

[Brucey]

I am quite confused really whether it is even worth investing in the top-notch solar panels, there's a mixed opinion about it here.

Its usually more effective to just buy panels based on cents per watt (i.e. more of them) versus spending more per watt for a little higher density or less sq footage.

 

[PVGeezer]

Regarding roof sealants I don't personally like silicone. It doesn't have great adhesive properties so won't stick well to the gritty surface of asphalt shingle type roofing. So it can peel off and water can get under it eventually.

Id recommend a butyl sealant because it's very sticky and stays that way. Apply it when it's warm with a lot of compressive force and it will conform and adhere well to the shingle surface. Other people like polyurethane sealants.

Everyone has different opinions on how to seal roof mounts. Or go with a ground mount so you don't need to worry about leaks and your solar array is accessible for clearing snow or adjusting tilt angle.

 

[quantum`]

WRT sealant I recommend Lexel, if you have it there. It's a co-polymer rubber sealer (blend of Polyurethane, Silicone, and Polyester), it may be painted, is 19 times more flexible than silicone, and can seal gaps up to 2" wide. (Ask me how I know) So sticky if you use your hand to smooth it you'll have hell getting it off. (Ask me how I know)

I would add more high-efficiency panels, as their cost is comparable to average panels. Not particularly impressed with the AIKO 600WP 144.

 

[KingDavid]

WRT sealant I recommend Lexel, if you have it there. It's a co-polymer rubber sealer (blend of Polyurethane, Silicone, and Polyester), it may be painted, is 19 times more flexible than silicone, and can seal gaps up to 2" wide. (Ask me how I know) So sticky if you use your hand to smooth it you'll have hell getting it off. (Ask me how I know)

I would add more high-efficiency panels, as their cost is comparable to average panels. Not particularly impressed with the AIKO 600WP 144.

I will explore all my options. By the way, was curious, do you think the overall surface area of the panel aid in capturing light? My Jinko is 1903x1134x30mm, maybe it would be worth going for something over 2000mm in length? Thanks, Quantum.

 

[CaliSunHarvester]

it would be worth going for something over 2000mm in length?

I would just buy the cheapest used panel per Watt, and if they don't make enough power, double the number of panels. That works for me.

Here in USA, I see 25 cents per Watt for used panels with free shipping.

I have an old installation from 2004 and it still produces. Nominally 5kW, it hits 3.8kW daily (in January!) I tried washing them a few years ago, not worth it.

 

[quantum`]

I will explore all my options. By the way, was curious, do you think the overall surface area of the panel aid in capturing light? My Jinko is 1903x1134x30mm, maybe it would be worth going for something over 2000mm in length? Thanks, Quantum.

Panels are usually stated in the number of 'cells' they have. Obviously more cells (up to 144) gather more light and the panel is larger, but it's also important to consider efficiency of those cells, especially if you are space-constrained. Higher efficiency means more advanced technology and less physical space required for a given wattage.

Sure the AIKOs benefit from having back contacts so a bit more silicon can gather light, but their efficiency in converting that light isn't that impressive. And without knowing exactly what techs they're using and who makes their cells, raises for me the suspicion that they may be inflating their figures since they are uncheckable. Also if bifacial, back contacts impair light-gathering on the obverse side.

I did extensive research and broke down the characteristics vs techs vs price and efficiency of various manufacturers in a spreadsheet. Some manufacturers are shy about giving their techs or real expected performance. (NOCT, or as a fallback NMOT) (For cost always use cost per watt - I used NOCT/NMOT, not STD) I've settled on Longi and Risen as the safest and highest quality bets. Given their known techs I have evidence to believe that they will perform better on cloudy days with the resulting incident (scattered) light. But everyone makes their own decisions.

 

[Norwasian]

I would add more high-efficiency panels, as their cost is comparable to average panels.

I bought LONGi HiMo 6 panels and designed the system to have more panels than necessary specifically over the fears I had that during rainy season the clouds would not allow for full recharging of the batteries. Now, I am in Thailand, so ambient light levels must certainly be higher, especially with rainy season being during our "summer" time. But the panels seemed to perform much better in the low-light conditions than I had expected, and even when we had days of clouds, the battery was topped up almost every day--just took a little longer (on a sunny day, two hours was enough, but on a cloudy day, seven hours still did the job).

I believe LONGi is a top-tier panel maker, and does its own research into making efficient panels. They now sell even more efficient panels than the monofacial ones I got. The bifacials can accept light from virtually anywhere, and a little reflection from the roof could give them more efficiency.

We have Trina and Jinko panels available in this market area, but my research led me to the LONGi panels as the superior option.

 

[KingDavid]

Thank you so much for all your help. I have learned so much reading all of your comments. Will put Longi solar panels in my close consideration for sure. Just wanted to say that I am truly grateful and thankful for the people in this forum who don't mind taking their precious time to help someone in need. I would shake all of your hands if I could. You have definitely given me more wisdom and understanding regarding solar production. Thank you, again.

 

[JanisD]

Hi from the neighborhood - Latvia. Having 6 years experience with small autonomous systems, I won't bother so much about brand of panels, but for angle and the way to keep them clean. As well as good MPPT controller is what could bring some extra Watts when the light is limited.
Anyway at our locations You could expect ratio between production during June to be 7-20 times more than during December at conditions close to ideal.

 

[12VoltInstalls]

Got
34watts max when turning it to a much more vertical position.

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So that angle is like ~15* ish
Therefore you are ~30*+ lower than your summer solstice ideal, and 60*+ lower than your winter solstice ideal position.

Id remove the solar array from the roof and mount it on the ground.

If you get snow and ice there just mount them vertically and go with it. The ‘missed’ watts in summer (from too steep of an angle) will not be noticed once you have achieved enough panels to satisfy your winter goals- you will way over produce.

used weathermaster silicone around the screws, that should have left a positive effect

Silicone is mostly a terrible long-term sealer. Use polyurethane caulking, butyl rubber or lexel

confused really whether it is even worth investing in the top-notch solar panels

It’s not worth it. For the small price of a few more panels of what you have already you will spend way more replacing the existing panels for maybe 10 minutes of 24hrs worth of electricity

you want better winter output you'll need more solar at a steeper angle.

Absolutely correct

do you think the overall surface area of the panel aid in capturing light? My Jinko is 1903x1134x30mm, maybe it would be worth going for something over 2000mm in length?

You are way overthinking this.
It is NOT what you are missing but rather what you cannot get.

sealant I recommend Lexel, if you have it there. It's a co-polymer rubber sealer

Yes, barring all else. Polyurethane will perform better under UV than lexel, butyl rubber sealant if not flexed/moved in the cured installation will go 50 years or more at that latitude.

25 cents per Watt for used panels

There are new panels in that range

won't bother so much about brand of panels, but for angle and the way to keep them clean

that IS the answer.