[felgueres]

The reason they are tilted is to maximize irradiance hitting the panel. At a 0 degree angle (flat on the ground) you get a a lot around noon and then very little.

This approach surely reduces land usage but what is the output per acre?

I’d be really surprised if it’s higher than with tilted modules.

[whatshisface]

The amount of power landing on an acre is fixed, what you can achieve by tilting is having less solar panel surface area per ground cover area. If solar panels are cheaper than the mounting hardware (wow) then there is no reason not to let them lie flat on the ground (it's not as if the racks were holding them above tree shadows, or anything).

[nkurz]

This is a great way of thinking about it, but don't you lose a bit more due to increased reflection from the glass surface at low incident angles? Probably not enough to make a difference a low latitudes in the summer, but at high latitudes in the winter I think it might be a significant difference: https://en.wikipedia.org/wiki/Fresnel_equations#/media/File:...

[nkurz]

Partially answering myself, 'sacred_numbers' posted a link elsewhere in this thread that suggests this effect might be quite small: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6611928/. The paper concludes that for a cell with a good Anti-Reflective Coating (ARC), the reduction in efficiency due to reflection at a 60 deg incidence is only 2%.

On the other hand, the incidence for a flat mounted panel beyond 37 degrees of latitude on the winter solstice is greater than 60 degrees, and it's not clear (to me at least) how well the ARC on an average panel will continue working after years of outdoor usage. My guess is reflection is probably a real issue, but not a stopper unless one is already in a marginal situation.

[fy20]

The biggest issue going north is probably snow.

I'm at 54N and my output has been 0 for the past month as we've had a lot of snowfall. My panels are at 20 degrees, so even in the few sunny days we've had it's not been enough to melt the snow. A steeper angle probably would have cleared it a few times.

Usually the beginning of the year has more sun but it's colder, so I'll see what happens then.

[michae4]

The solar radiation wattage per unit of surface area is dependent on the angle that surface is to the sun. The angle is dependent on the season and time of day, so the amount of power is not fixed.

[danbruc]

What the comment wanted to say is that the power per unit of ground surface area is fixed for a given location and time, i.e. it does not matter [1] whether you cover a given area with panels angled towards the sun or lying flat on the ground, at least if one only looks at the available power. There is of course a difference in the solar panel area required to cover a given area of ground surface - solar panels lying flat on the ground will obviously have to have the same area as the ground surface area while panels angled towards the sun will only require a fraction of the ground surface area equal to the sine of the angle of the sun above the horizon.

[1] For a sufficiently large area so that effects on the edge are negligible.

[whatshisface]

You could write a few pages of all the things that the power available depends on, but you don't need to because it's fixed relative to the variables under consideration.

[apendleton]

Per unit of panel surface area, not per unit of land area. If the sun is coming in at an angle, you'd be able to collect all that's available with less panel area than total land area by angling them (or equivalently, in this new configuration you need more panel area than you otherwise would), but in their estimation, it's cheaper to just get more panels than it is to buy and install racks.

[imtringued]

>The solar radiation wattage per unit of surface area is dependent on the angle that surface is to the sun.

A tilted solar panel casts a shadow that is bigger than its actual area. Mounting the panel flush to the ground means it casts a shadow exactly equal to its area.

The shadow represents the captured sunlight so the first panel covers more surface area than the second panel, which allows you to reduce the number of panels to cover the same amount of surface area. The entire point of this article is that you can just put the saved costs into buying more solar panels.

Used solar panels are very cheap but usually only the solar panels are replaced and the mounts are kept and fitted with new panels. So for companies that want to use used panels their primary cost is actually in the mounting hardware and not the panels.

[davelondon]

It's amazing how so few people understand this.

[whatshisface]

I think people are imagining that solar panels have directionality like most photodetectors do.

[guerrilla]

> If solar panels are cheaper than the mounting hardware (wow)

I'm surprised this surprises people... Every electronics hobbyist knows that electronics are cheap as dirt while any kind of box, mount, rail or whatever is BY REALLY FAR the most expensive part of a project, even when buying massivly mass produced cheap Chinese junk.

[whatshisface]

The electronics you're talking about are rice grain sized little things, while the solar panels are big sheets of silicon inside of glass, etc.

[imtringued]

Those grain sized things have pretty high packaging costs in relation to what you are actually buying.

[guerrilla]

Economies of scale make that irrelevant.

[DoesntMatter22]

You are surprised that this surprised people because electronic hobbyists know this? Most people are not electronic hobbyists so this should probably not surprise you

[guerrilla]

I just find it interesting, the difference different perspectives can make, especially on a website where people are often bikeshedding things they have no experience with.

[kragen]

the article claims 15¢ per watt of mounting hardware; last i checked solarserver says pv modules are about 20¢ per peak watt

presumably that was 15¢ per peak watt but the article doesn't actually say

[nimos]

Texas is pretty far south. If you use https://pvwatts.nrel.gov/pvwatts.php there is about a 9% increase in total output over the year for optimal tilt(27 vs 0) but then you also need to space modules.

There is hourly data if you are interested but even Jan 1 the panels produce for ~7-8 hours. The 3 hour around noon it's about 1/2 the output for the day (for Jan 1).

[rootusrootus]

> you get a a lot around noon and then very little.

That's a little harsher than reality. You get a very pretty bell curve. I have a flat panel on the roof of my RV and I track the output over time. I'm not 100% how much of the loss in output is because the incidence to the panel is changing, or because the light from the sun is going through more atmosphere. Probably a little of both, but in any case the panel is still plenty useful even when not pointed directly at the sun.

[elihu]

With tilted modules, you'd normally space them out quite a bit so the shadows of one aren't falling on the module next to it. If they're all flat, that's not a problem so you can space them closer. So, it makes sense that they'd get more power per acre than the conventional approach -- the panels are individually less efficient, but there's a lot more total solar panel area per acre.

That might not always be a good tradeoff, but maybe at least some of the time it is.

[celtain]

I expect that they are getting lower output per acre, but in places where land is cheap and as solar panels continue to get cheaper, the money saved on building the support structures could be worth those losses.

[rootusrootus]

They're getting quite a lot more output per acre, by being able to use more panels.

[avip]

They don't claim to outperform fixed-tile or SAT on that KPI. They claim to reduce upfront cost of installation, construction time, and general project risk.

[HellsMaddy]

Seems lying them flat also makes their cleaning robot able to easily maneuver, meaning they don't need to leave any space in between panels for humans to perform maintenance. Pros: reduces land usage as you mention, but also less humans needed for maintenance.

[mkl]

The article claims it's much higher output per acre:

> conventional solar technologies, which typically require five to 10 acres of land per megawatt of capacity. Erthos claims that its mounting scheme requires less than 2.5 acres per megawatt.

[JoeAltmaier]

Per day? Per acre? Per dollar?

It's all about the metric you choose. That's the true issue.

[fulafel]

Going to the other direction, I wonder what would be the maximum archieveable output per acre without height limitations.

Would you have a forest of tall towers, or one really tall panel covered building, or something in between?

[s1artibartfast]

They claim the power per acre is 4x higher than tilted panels. Seems like a stretch, but I don't know how bad the density is in tilted installations. I guess I have seen some where you can drive between rows

[sacred_numbers]

Density in tilted installations is quite bad. If you want to capture morning and evening sun at an optimal angle you have to space the panels out a lot, like 5-10 panel heights. You can have them closer, but then you get shading, which defeats the purpose of tilting the panels.

[hindsightbias]

Seems like they would have to do some grading to clear anyway, why not grade with some tilt.