Jump to content

Recommended Posts

Posted

Hi

 

My solar array's design capacity is 2.7kW. This will be the first winter with the panels.

About two weeks ago I noticed the panels generating up to 3kW (peak) but since that day the performance deteriorated (this was about 2 weeks ago). Even on the traditional sunny Jo'burg May days when there isn't a cloud in the sky the system doesn't generate more then 2.2-2.4kW.

I always assumed PV is based on light rather than heat so I would assume it would generate the same peak power in Summer and Winter when the sun is shining or am I wrong? 

Posted
14 minutes ago, MNK1234 said:

I always assumed PV is based on light rather than heat so I would assume it would generate the same peak power in Summer and Winter when the sun is shining or am I wrong? 

You are right, it's based on light, in fact heat makes the output worse as the voltage sags.

The two big differences in winter are the tilt of the sun with respect to the panels (the sun is effectively further north instead of almost overhead at noon), and the days are shorter.

Obviously the shorter days mean less energy is accumulated over the day. But you were concerned about power.

The tilt means that the sunlight has to travel through more atmosphere, which reduces its amplitude at the earth's surface. The other thing is that the panels are usually less square on to the sunlight. But you can compensate for that by increasing the tilt of your panels. I have a set of 6 with a 45° tilt (latitude is only 27.5°), so that those panels are more square to the sunlight in winter. They're then worse in summer, but because of the other effects, this doesn't matter as much. Of course, most people don't want the hassle of frames, so they just use the tilt of their roof, whatever that is.

The average temperature is obviously lower in winter as well, so that helps a little, but it's swamped by the effect of the tilt and shortness of the days.

Posted
48 minutes ago, MNK1234 said:

Hi

 

My solar array's design capacity is 2.7kW. This will be the first winter with the panels.

About two weeks ago I noticed the panels generating up to 3kW (peak) but since that day the performance deteriorated (this was about 2 weeks ago). Even on the traditional sunny Jo'burg May days when there isn't a cloud in the sky the system doesn't generate more then 2.2-2.4kW.

I always assumed PV is based on light rather than heat so I would assume it would generate the same peak power in Summer and Winter when the sun is shining or am I wrong? 

Interestingly, colder panels actually generate more power. 

Has more to do with the inclination of the panels towards the sun.

The highest energy output from the panels is achieved when the panels are directly facing the sun. 

In Winter the sun does not travel as high in the sky as it does in summer, the further South you go the lower it gets so the more angled your panels need to be to get optimum power production.

There is a useful website that gives you the optimum no of degree's of inclination depending on your location. 

http://www.solarelectricityhandbook.com/solar-angle-calculator.html 

 

Posted

Thanks 

my panels are mounted on my pitch roof so the angle is determined but the angle of the roof which I’m assuming is around 45 degrees

Whats strange is that the performance almost deteriorated over night.
 

See attached about 10 days ago when my performance was 110% of design but since then it hasn’t been able to reach much more than 90%. I would assume the deterioration would be more gradual as winter sets in 

 

 

 

1A2FB0FF-A2D5-4E1C-A22D-EEFEAC5F12D2.jpeg

7DE38B8F-A9E7-4B7F-8F5F-04B262B31180.png

Posted
16 hours ago, MNK1234 said:

Hi

 

My solar array's design capacity is 2.7kW. This will be the first winter with the panels.

About two weeks ago I noticed the panels generating up to 3kW (peak) but since that day the performance deteriorated (this was about 2 weeks ago). Even on the traditional sunny Jo'burg May days when there isn't a cloud in the sky the system doesn't generate more then 2.2-2.4kW.

I always assumed PV is based on light rather than heat so I would assume it would generate the same peak power in Summer and Winter when the sun is shining or am I wrong? 

Perhaps one the panels are in shade?.

With the movement of the Sun between the seasons you might now have some shade (from a chimney by example) that you did not have in Summar.

Al it takes is for one cell to have shade

Posted
9 minutes ago, I84RiS said:

Perhaps one the panels are in shade?.

With the movement of the Sun between the seasons you might now have some shade (from a chimney by example) that you did not have in Summar.

Al it takes is for one cell to have shade

Nope all in full sun

 

could the fact that it went over the design max have damaged something?

Posted

I wouldn't be to concerned about it at this stage, my solar production has also gone down significantly over the last few weeks. 

I suspect that it is a combination of the coming of winter and the bad weather that we have had. 

I was getting +-45kw/hr average in Feb, am now getting +-35kw/hr.

Posted
18 hours ago, Coulomb said:

The two big differences in winter are the tilt of the sun with respect to the panels (the sun is effectively further north instead of almost overhead at noon),

This! Ideally in Johannesburg we would have panels that constantly realign themselves, with them being almost flat at mid summer.

So what is the angle from horizontal of your panels? 

Mine are tilted at about 35 degrees, and they perform quite adequately in the winter, are probably falling short of their potential - though still adequate - in summer.

Most summers. As other posters here have noted, this has been a very cloudy summer/early autumn in Johannesburg. I see my monthly figures are down a few % from last year, but on some days I have had close to no useful PV.

Also, are your panels clean? OK... recent rains will have helped, but if you get a build up of grime on the panels, that reduces their efficiency.

Posted (edited)
20 hours ago, Coulomb said:

You are right, it's based on light, in fact heat makes the output worse as the voltage sags.

The two big differences in winter are the tilt of the sun with respect to the panels (the sun is effectively further north instead of almost overhead at noon), and the days are shorter.

Obviously the shorter days mean less energy is accumulated over the day. But you were concerned about power.

 

Temp is always an interesting topic. Why? My stats from the APP shows the highest power happens to be the time that we have the highest irradiation and also the time when the panels are at their highest temp as per the graph.

I belief the cells generate their own heat under high power. Thus the high output is at midday and at a temp over 50 deg when the ambient temp is 25-28 deg.

Power graph 07h to 17h and temp graph 06h to 17h.

peak-power.jpg.f46e9bbf7a5f18d917a8abb5a94923d4.jpg

 

Temp graph:

peak-temp.jpg.53a35bbe759fbbd5b56dc5e67dd9b28f.jpg

 

My winter production is not as low as most calculators would calculate. Winter days are shorter but with no cloud it get close to summer days with lots of cloud. Jan '21 to Aug '21.

summer-winter.jpg.fe464fc068fa7a7eaf3463f222babfc6.jpg

 

My power peaks are still as high as during summer but only for the brief period of cloud edge. In full sunshine it is also down about 10%.

Edited by Scorp007
Posted (edited)
On 2022/04/23 at 8:40 PM, Scorp007 said:

Temp is always an interesting topic. Why? My stats from the APP shows the highest power happens to be the time that we have the highest irradiation and also the time when the panels are at their highest temp as per the graph.

Yes. But the value would be even higher if the panels were cooler. Try hosing your panels some time. While hosing, the output will go down as the water blocks some of the light, but you will get a boost for a few minutes thereafter as the cooler panels have higher voltage (and less current, but that's a lesser effect).

I don't have a sample handy (and it's 1am here), but I notice when a cloud passes, my output briefly goes over where a smooth sine wave would have been. That's because the cloud allows the panels to cool, when the sun comes back out, for a few tens of seconds you have a cooler panel than usual, so you do better than the sine wave. Then the panel heats up again, and you go back to the sine wave.

If you don't see this boost after a cloud reappears, perhaps your MPPT isn't performing as well as it could. You also have to have pretty high resolution graphing; I have updates every 10 seconds (for 5 minutes total) on one of my graphs. I can't keep that going for the whole day, as it would overwhelm Node Red. But I have all the data there on an SD card. I'd drag it out, but 1am and sleep beckons.

Edited by Coulomb
Posted (edited)
40 minutes ago, Coulomb said:

 

If you don't see this boost after a cloud reappears, perhaps your MPPT isn't performing as well as it could. You also have to have pretty high resolution graphing; I have updates every 10 seconds (for 5 minutes total) on one of my graphs. I can't keep that going for the whole day, as it would overwhelm Node Red. But I have all the data there on an SD card. I'd drag it out, but 1am and sleep beckons.

Thanks. Sweet dreams.

Yes I do see those peaks during each cloud edge but I always thought it is due to the reflection from the cloud producing a short term higher irradiation rather than the slight cooling affect.

I have cooled the panels down by washing but the difference was very small. With tick marks 5 min apart the sampling is very slow but the MPPT is reacting quite fast. This I can see on the inverter instantaneous display.

Clear to see with lots of cloud how cloud edge higher outside the sinus wave. The sinus wave would be about 250W below the peaks.

cloud-edge.jpg.2eae3ed02e5c6a57b83faacbed16cb78.jpg

Edited by Scorp007
Posted

The driver of PV production is solar radiation, below are the figures for Pmb extracted from what I assume is EU modeled information for my location.  You can see how variable it is from one year to another and month to month.  April to August is poor in general. I also show data from Mt Home for 2020 and 2021 a new weather station 5 km from my house, 2020 was an excelent year for power generation.

I think these figures probably reflect the general pattern of solar radiation in South Africa. Solar radiation in Jhb will be higher.  On a monthly basis solar radiation vs kWh generated accounts for 90% of the variation in PV production.  If you can access weather data it would explain if the drop was caused by weather.

kWh/m2/month   Solar radiation for location from European Union      
Sum of H(i)_m Column Labels                    
Row Labels Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Grand Total
2005 145 142 146 119 120 101 115 122 136 145 144 155 1589
2006 150 113 138 120 113 107 117 119 137 142 145 155 1554
2007 189 169 157 122 132 99 121 129 131 120 138 174 1682
2008 154 151 148 122 114 93 114 127 138 135 129 150 1576
2009 134 126 156 128 117 90 114 125 129 127 123 130 1498
2010 146 163 151 125 123 98 111 138 150 148 142 140 1635
2011 159 173 161 115 106 99 101 129 141 156 149 158 1648
2012 179 148 148 138 110 100 116 118 125 118 122 169 1590
2013 147 150 134 131 112 101 111 136 143 146 156 137 1605
2014 187 160 150 136 117 101 114 127 160 132 117 152 1653
2015 170 142 143 116 118 102 98 133 125 165 154 177 1644
2016 220 183 175 135 118 104 112 151 145 178 159 201 1882
average 165 152 151 126 117 100 112 129 138 143 140 158 1630
Mt Home 2020 178 159 176 121 125 110 121 136 143 148 153 164 1736
Mt Home 2021 157 144 165 138 119 99 115 119 132 141 147 143 1619

 

  • 2 years later...
Posted
On 2022/04/22 at 3:36 PM, MNK1234 said:

Hi

 

My solar array's design capacity is 2.7kW. This will be the first winter with the panels.

About two weeks ago I noticed the panels generating up to 3kW (peak) but since that day the performance deteriorated (this was about 2 weeks ago). Even on the traditional sunny Jo'burg May days when there isn't a cloud in the sky the system doesn't generate more then 2.2-2.4kW.

I always assumed PV is based on light rather than heat so I would assume it would generate the same peak power in Summer and Winter when the sun is shining or am I wrong? 

Cleaning solar panels sometimes helps to maximize its performance, this might sound a joke but might be the underlying truth

Posted
23 minutes ago, Ma kwavo said:

Cleaning solar panels sometimes helps to maximize its performance, this might sound a joke but might be the underlying truth

That is undeniable the truth. Cleaning panels makes a huge difference in output especially during winter with plenty of dust around and minimal rain. I have brought in 2 containers of Seraphim silver frame 460w panels for various installations planned. My brother in Gauteng is running trials on 1 Seraphim 460w panel on various tilt angles and orientations. Soiled panel is part of the trial and will continue until October 24. The results of the trial will give us exact figures when planning an solar array installation. The data recorded will be shared on the forum after completion. It takes out any and all assumptions regarding output when planning a solar array.

Posted

I have found the website at https://pvwatts.nrel.gov/ to be very useful in the past for getting an indication of monthly solar production from your panels. 

You need to capture your address, inverters max solar array production, solar array size, the heading/direction it is facing in degrees and the angle it is at from horizontal. The site will give you an estimation for the monthly production for your panels.

It is very interesting to see the difference the inclination angle makes to the monthly production numbers. 

5Kw 0° Facing Panels @ 5° inclination

image.png.b9ece2569537daddf37e839edf194510.png 

5Kw 0° Facing Panels @ 30° inclination

image.png.54f3192b9fe839138653b55c4b6c621f.png

 

 

 

Posted
1 hour ago, Sc00bs said:

I have found the website at https://pvwatts.nrel.gov/ to be very useful in the past for getting an indication of monthly solar production from your panels. 

You need to capture your address, inverters max solar array production, solar array size, the heading/direction it is facing in degrees and the angle it is at from horizontal. The site will give you an estimation for the monthly production for your panels.

It is very interesting to see the difference the inclination angle makes to the monthly production numbers. 

5Kw 0° Facing Panels @ 5° inclination

image.png.b9ece2569537daddf37e839edf194510.png 

5Kw 0° Facing Panels @ 30° inclination

image.png.54f3192b9fe839138653b55c4b6c621f.png

 

 

 

This website is extremely accurate in my experience. Sadly in Cape Town the AC Energy out is less than half in winter than in the summer. So to get decent winter performance you have to install double the solar capacity than in Pretoria/Johannesburg.

Posted
2 minutes ago, HendrikBigChief said:

This website is extremely accurate in my experience. Sadly in Cape Town the AC Energy out is less than half in winter than in the summer. So to get decent winter performance you have to install double the solar capacity than in Pretoria/Johannesburg.

Very well said. This being the reason we have to ask for the region when trying to work out production. With this we have to know the angle and direction. 

Some of us can be a pain by asking questions before we give guidance :(

Posted
21 minutes ago, HendrikBigChief said:

This website is extremely accurate in my experience. Sadly in Cape Town the AC Energy out is less than half in winter than in the summer. So to get decent winter performance you have to install double the solar capacity than in Pretoria/Johannesburg.

I agree Cpt is on average lower output during winter months due to rain and overcast conditions. As our trial in Gauteng (Alberton) revealed these figures during July this year and even in Gauteng your output is cut in half.

What is interesting is that the voltage output is above Vmp namplate value and consistently very close to Voc. 

20240708_215028.thumb.jpg.42584356c40a8bb9d328d3434809cd20.jpg

Screenshot_20240826_084653_Chrome.thumb.jpg.89513c0c0be8ba760237634c0d8a0df7.jpg

Screenshot_20240826_084708_Chrome.thumb.jpg.d641bbdcc9342d1af78ee67f32b29c7d.jpg

 

 

  • 2 weeks later...
  • 2 weeks later...
Posted

You're right that solar panels rely on sunlight, not heat, to generate power.

However, cooler temperatures help panels perform more efficiently! The drop in performance you're seeing could be due to some factors—dust buildup, shading, or even a slight alignment shift over time.

Since you're in Jo'burg with lots of sunny days.

 

 

 

 

it might be worth checking for any maintenance issues or monitoring software for insights. Getting those panels cleaned or inspected could make a big difference! ☀️

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...