It's not mysterious, it's that thermal convection is much stronger when the panels are vertical, and production is strongly correlated with lower temperature.
Angled mounts tend to have obnoxious cross-members that block the airflow that should otherwise be sliding up the back of the panel, particularly on roofs where there's basically a bed of hot air trapped underneath with no good way to escape. That boosts the panel temperatures even further than you'd assume given simply lower convection based on their angle alone. Vertical mounts cannot have framing in these places, so they don't.
> It's not mysterious, it's that thermal convection is much stronger when the panels are vertical
I agree that, when you factor in semiconductor physics, it's not a mystery but it isn't necessarily an intuitive result for most. I've been working in aerospace for 5 years and one of the things that has been very clear to me is that peoples' intuition about things breaks down very quickly when there's non-linear factors involved in an analysis. In aero it's primarily square-law/cube-law tradeoffs; in semiconductor physics it'll be more exponential.
For this particular problem you've got an exponential (semiconductor behaviour as a function of temperature) multiplied by a trig function/dot product (cosine of the angle of the sun relative to the normal of the solar panel), with a bit of natural thermal convection thrown in for good measure. Modelling this (digital twin, as they call it) is feasible but it's not something most people are going to have a good intuition on with respect to where the sweet spot is going to be.
The panels themselves are usually made from aluminum U profile and close to the edge there is a substantial amount of trapped air if the panel is at a bad angle. Given that most panels are at a bad angle this will cause the top edge cells to all be over temp and since they're all in series that drops the efficiency of the whole panel. So the cross members certainly don't help but the panel construction itself could do with some more ventilation near the top. I wonder if cutting some slots in the top members would drop the cell temperature in a way that it would show up on a measurement, this is pretty easy to test.
Indeed - I saw the title and thought “because convection” - I actually reinstalled my PV array last year with exactly this in mind, as while it was at an optimal angle for insolation, I was finding that yield was being hampered by them getting devilishly hot - the summer before last, when we hit 47C air, really underlined the issue, as the panels were getting up to over 85C.
The increase in yield from going near vertical (80 degrees was the best I could achieve using existing mounting gear), has been about 20% - I say about as I haven’t done a scientific study of it, just looking at year on year comparisons for cloudless days, and the panels are 60 C cooler, which is far better than I had hoped for.
I'm hoping to get solar on my next house, which we're designing now. Is there a way to install roof panels that improves convection / reduces temperatures, like using a different mounting system, if that's a thing?
Wow, I was just talking to my dad about this. He runs a startup that builds PV-embedded vertical masonry[1], and they have been getting significantly higher-than-expected yield on their installations. Though in their case they were mostly theorizing ground reflections
That's a cool project. One advantage solar masonry might have is the high thermal mass of masonry. The bricks average out day and night temperatures, and probably keep the panels a lot colder than they would be on their own.
I have so many questions! While digging into the Applications section these look like conventionally-sized CMUs, the image on the front page looks like panels/blocks that are large enough to require a crane to lift? If that's the case, how fragile are they?
CMUs and other pre-cast concrete "lego blocks" have intrigued me for a long time. These look like they've got more robust interlocking features than conventional cinderblocks too? The idea of being able to order (even without the solar) say 8'x4' pre-cast "CMU-style" walls, have them show up on a flat deck, stuff rebar and mortar into ready-made holes, and grout between the blocks seems like it could dramatically speed up a lot of exterior construction. Being able to get them ready to wire for solar is delicious icing on the cake!
Please ask your dad or whoever does the work on that website to update the home page so that the content does not do the reverse of its "intro animation" just because you scrolled back in the direction of the top of the page.
I was more distracted by that behavior and totally failed to get any value out of visiting your site.
Interesting, definitely a surprising result. I did wonder when I saw a thumbnail of a video discussing this on YouTube (but I didn’t have time to watch it) - I thought “Surely that only works for bifacial panels” so makes sense that the article confirms that that’s what they were testing.
The other factor is that (compared to where I live in Australia at least, but also all of the US too) the Netherlands is quite far from the equator, so I expect there would be a crossover point a bit closer to the equator where you start to get less efficiency than standard angled horizontal panels?
Although perhaps with some reflectors on either side it might still work with a vertical bifacial panel (in areas closer to the equator), maintaining the cooling advantage?
I'm curious about how well this performs in winter when the sun is low in the sky and you have a pretty big deficiency. Usually you use what ever angle the roof is at (typically 30 - 45 degrees) and leave it at that. By adding a vertical component you may be able to substantially offset the summer/winter difference. Vertical panels won't do much in the summer but that's fine, you'll have a surplus anyway. But in winter you need every little bit. But from a ROI point of view those would be pretty expensive KWh, because the total produced versus the capital expense won't be very high. And in plenty of places the local authorities might have something to say about covering the outside of the building with panels. I'm going to play around with this here to see what it does.
Yeah, I'm quite curious about the overall tradeoff here. I'm at about 51 deg N and the solar elevation angle gets very very low during the winter (only 16 degrees elevation at noon) but high in the summer (63 degrees elevation at noon). Because of how low the sun is we end up with very long shadows even mid-day in the winter. Would love to spend the time breaking down:
- land area required for tilted vs. vertical
- net production over the year
- equipment cost for bifacial panels vs single-face panels
Anything that helps solar cost/performance is a huge win around here because we have max energy consumption in the winter when solar doesn't produce a whole lot.
If, like me, you don’t know what PV stands for: A photovoltaic (PV) cell, commonly called a solar cell, is a nonmechanical device that converts sunlight directly into electricity.
Summary (roughly, I skipped some things): while tilted panels produce more voltage, their efficiency drops due to heat absorption. Two sided vertical panels allow for better cooling, and on average produce more power, roughly 2%ish, albeit more expensive to produce.
I imagine installation costs are also substantially lower since the panels rest on a much simpler structure. Cleaning the panels should also be easier in this configuration. I wouldn't be surprised if these findings lead to vertical solar systems becoming a popular option, especially in places as far from the equator as Denmark.
The output can also be timed for better value (for example, increasing production in winter vs. summer, or peaking early and late for N/S aligned modules.)
Combinations of different orientations can smooth output over a day or year, which could reduce the mismatch between module output and inverter capacity.
Here in Australia, News Corp (owned by the same Murdoch family who is also behind Fox News) is currently running a campaign against agricultural solar. A key “argument” being that installing solar panels on fields makes it impossible to grow crops there.
I live in Aus as well, and I don’t expose myself to News Corp at all. Can you explain to me what the heck the issue is? We have so much space and we don’t need that much more solar, how is anyone’s crops at risk? Is this just a complete non issue? Like i agree that solar panels shouldn’t be installed over the top of crops but is that even a thing that is happening? Don’t the farmers have almost complete control of what goes on their property anyway? So confused
This seems like something that should have been verified in lab/field decades ago, before billions in mass solar roll out. I'm assuming it is and large scale solar infra are optimized according to site conditions?
> “For a standard system, we observed that under high irradiance conditions, the increase due to the light is offset by the decrease due to the higher operating temperature,” Van Aken stressed. “However, for the vertical system, we observed that the operating temperature is not increasing so much and the voltage increase and decrease are more or less balancing.”
Facing the bright sun increases temperature enough to offset the gains in voltage (since temperature increases presumably increase resistance if my EE101 classes hold in this era). Not facing the sun? Less heat -> more total power throughput.
Spoiler: vertical panels can rid themselves of excess heat more efficiently, thus operating temperatures are lower and, hence, output better. Vertical panels will also be more susceptible to damage from high winds but less susceptible to precipitation of water and dust, so my guess would be that the fixed slant orientation for PV panels in temperate latitudes will stay with us irrespective. I'm starting to think about having water pipes running along the backsides of the panels to cool them and obtain warm or hot water...
I’ve seen people cooling solar panels by using coreflute/Fluteboard at the back of a panel and circulating pool water through the channels. I think I saw this on Linus Tech Tips weirdly enough, not sure though
This was exactly my question, have people looked at the various thermal management techniques used in computing? Heat pipes on the backplane and fan cooled heat sink blocks could go a long way.
myself248|2 years ago
Angled mounts tend to have obnoxious cross-members that block the airflow that should otherwise be sliding up the back of the panel, particularly on roofs where there's basically a bed of hot air trapped underneath with no good way to escape. That boosts the panel temperatures even further than you'd assume given simply lower convection based on their angle alone. Vertical mounts cannot have framing in these places, so they don't.
tonyarkles|2 years ago
I agree that, when you factor in semiconductor physics, it's not a mystery but it isn't necessarily an intuitive result for most. I've been working in aerospace for 5 years and one of the things that has been very clear to me is that peoples' intuition about things breaks down very quickly when there's non-linear factors involved in an analysis. In aero it's primarily square-law/cube-law tradeoffs; in semiconductor physics it'll be more exponential.
For this particular problem you've got an exponential (semiconductor behaviour as a function of temperature) multiplied by a trig function/dot product (cosine of the angle of the sun relative to the normal of the solar panel), with a bit of natural thermal convection thrown in for good measure. Modelling this (digital twin, as they call it) is feasible but it's not something most people are going to have a good intuition on with respect to where the sweet spot is going to be.
jacquesm|2 years ago
madaxe_again|2 years ago
The increase in yield from going near vertical (80 degrees was the best I could achieve using existing mounting gear), has been about 20% - I say about as I haven’t done a scientific study of it, just looking at year on year comparisons for cloudless days, and the panels are 60 C cooler, which is far better than I had hoped for.
vosper|2 years ago
aqme28|2 years ago
[1]: (https://www.solablock.com/, looking for investors!)
wongarsu|2 years ago
tonyarkles|2 years ago
CMUs and other pre-cast concrete "lego blocks" have intrigued me for a long time. These look like they've got more robust interlocking features than conventional cinderblocks too? The idea of being able to order (even without the solar) say 8'x4' pre-cast "CMU-style" walls, have them show up on a flat deck, stuff rebar and mortar into ready-made holes, and grout between the blocks seems like it could dramatically speed up a lot of exterior construction. Being able to get them ready to wire for solar is delicious icing on the cake!
neon_electro|2 years ago
I was more distracted by that behavior and totally failed to get any value out of visiting your site.
taneq|2 years ago
stephen_g|2 years ago
The other factor is that (compared to where I live in Australia at least, but also all of the US too) the Netherlands is quite far from the equator, so I expect there would be a crossover point a bit closer to the equator where you start to get less efficiency than standard angled horizontal panels?
Although perhaps with some reflectors on either side it might still work with a vertical bifacial panel (in areas closer to the equator), maintaining the cooling advantage?
jacquesm|2 years ago
tonyarkles|2 years ago
- land area required for tilted vs. vertical
- net production over the year
- equipment cost for bifacial panels vs single-face panels
Anything that helps solar cost/performance is a huge win around here because we have max energy consumption in the winter when solar doesn't produce a whole lot.
munchler|2 years ago
whycome|2 years ago
jvanderbot|2 years ago
exabrial|2 years ago
1970-01-01|2 years ago
https://www.zdnet.com/article/why-13-year-olds-solar-power-b...
https://web.archive.org/web/20160308193750/http://www.wsj.co...
wongarsu|2 years ago
pfdietz|2 years ago
Combinations of different orientations can smooth output over a day or year, which could reduce the mismatch between module output and inverter capacity.
hankman86|2 years ago
estiaan|2 years ago
maxglute|2 years ago
heavenlyblue|2 years ago
jvanderbot|2 years ago
> “For a standard system, we observed that under high irradiance conditions, the increase due to the light is offset by the decrease due to the higher operating temperature,” Van Aken stressed. “However, for the vertical system, we observed that the operating temperature is not increasing so much and the voltage increase and decrease are more or less balancing.”
Facing the bright sun increases temperature enough to offset the gains in voltage (since temperature increases presumably increase resistance if my EE101 classes hold in this era). Not facing the sun? Less heat -> more total power throughput.
woleium|2 years ago
DemocracyFTW2|2 years ago
estiaan|2 years ago
lostmsu|2 years ago
fnordpiglet|2 years ago
Aspos|2 years ago
mrbgty|2 years ago
If they were on a pole allowing the wind to turn them, could you get both wind and solar power at the same time?