Comment by jacquesm | Hacker News Reader

Comment by jacquesm | Hacker News Reader

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This has been exactly my strategy. My first setup had two leafs of 8 panels each, tracking both azimuth and elevation. It was fragile, finicky, required a lot of active components and ultimately cost more per Watt that it put out than if I had simply laid the panels flat. Which is exactly what I did with my current installation (16x265 and 26x365). Another advantage of panels that are flat is that they are much less prone to being lifted up by the wind, you can mount them flush and the wind barely has any grip on them. They also do not shade each other at all, no matter what the angle of the sun.

Double axis tracking systems when they work are very pretty and technically satisfying, but ultimately those are not the right criteria by which to evaluate a system that has to be reliable, storm proof and that has to last a decade or more after installation, preferably without any service.

The weak point in the current installation is the cables and the connectors, that is something you can't really get away from. After dismantling a few older setups and having a good look at what remains there are two things that stand out for me: Make sure all cable joints are made in the shadow of a panel and tie down your cables on the underside of the support structure so they don't flap about in the wind and are not exposed to direct sunlight. Over time they'll get killed and especially with series connected panels (the bulk of them) this can lead to spectacular results (of the wrong kind).

Covered parking and rooftop make so much more sense though. Why do we want to cover more of the natural world, our only world, with more of our silicate-derived trash?

Parking and rooftop ensure the structural protection of your cabling, while at the same time optimizing the positioning of your servicing ports. Slightly elevated rooftop solar can also significantly reduce the a/c bill of a structure (especially smaller houses in sunny environments) and parking helps protect the paint of cars.

Because the usa is huge and full of low value arid desert near areas that need lots of power. In short, economics of the sun God

Can it be delivered from the desert without rising the total cost to high?

High voltage transmission losses can be low, <3%. I have seen previous reports that 5-7% of all electricity is lost to transmission. For a backbone (highly maintained) electrical network, I think that would be fairly marginal cost vs everything else involved in the calculation.

There are plenty of cities near the desert to suck up the power without ultra high power transmission. Like phoenix, Vegas, LA…I’m guessing all those opportunities will be soaked up before they start putting them in them in the middle of nowhere.

There is SO MUCH empty land out in deserts. We aren't going to run out of space.

Deserts ≠ wastelands. They're home to their own ecosystems.

Yes, they are also very fragile and take a long time to recover.

I think solar panels done right could actually help a desert though. Providing shade can allow some plants to thrive but most solar developers aren’t thinking about the ecology of a region.

Large installations usually come with mandatory ecological impact assessment requirements.

How many of these mandatory impact assessments are identifying ways of improving the ecosystem with their installation? Obviously I don’t mean by by displacing carbon.

If you’re providing massive amounts of new shade in an ecosystem that normally doesn’t get it, that is going to change things.

From a purely selfish human point of view, how important are desert ecosystems to the overall health of the planet and the planet's ability to support human life?

I feel like sacrificing the deserts to save the rainforests is a trade worth making - but is such a trade even possible, or is it not that simple?

Deserts are a critical part of our ecosystem just like every other part of the planet.

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/201...

This article actually suggests that desertification is a critical part of the Rainforest ecosystem.

There are important deserts and there are important grasslands and important forests. It seems a valid point that not all ecosystems are of equal importance.

>From a purely selfish human point of view

Well that's a point of view that's never steered us wrong.

Well we've been the dominant species on our planet for tens of thousands of years, so I'd say it's gone pretty well so far.

Pretty well so far for whom? We've initiated a mass global extinction. There wasn't ever a competition to take over the world as a species - no award, no prize - no one and nothing cares.

The only way we've done it is by eliminating everything in our path. We've been excellent at justifying eliminating entire ecosystems - when will we stop?

Probably right before we've justified eliminating entire countries of people with the weapons of death we've developed by extracting every last resource for the ground by digging it up.

As I was told last time I noted there’s lot of arid places you could put panel in, aside from ecological concerns arid places tend to be dusty and abrasive.

Wind kicks up dust, dust clings to panel, no rain for months on end, panels get covered up and scratched. Turns out there’s issues to using these spaces, and you need additional hardware (and thus have additional failure modes) to mitigate them.

It would be interesting paired with some kind of heat sink.

Solar cells need a heat sink to keep them cool or else the efficiency sucks.

Deserts tend to be cold at night.

Capture heat during the day as a byproduct of using the solar panels, and use it at night for heating homes? Maybe I'm being too optimistic, usually things that improve efficiency don't actually work for some reason.

There is SO MUCH empty land on the roof of our buildings - and electricity using devices within said buildings.

Rooftops are not that much land area. A few percent of a city landscape?

Further it's dangerous. Installation, maintenance become a headache and a risk.

Then, so many rooftops are not in optimal 'viewing locations'. Shaded by trees; shaded by neighboring buildings especially in a city.

It seems natural to a non-engineer to 'make electricity where you need it'. But rooftops don't scale with need, not at all. An apartment building on a lot with 3 stories or 30, same rooftop area. Terrible economics.

And electricity is fungible! Make it over there; use it over here. Almost free. Certainly cheaper than struggling to mount something delicate in the hardest place you can find.

That might be true in some places, but in Europe for example there really isn't that much room left. And moving large quantities of electricity from a desert to a place where people actually use it is also a challenge

Because on the ground you have have 5 hecrates of solar panels accessible by any joe for repairs and inspection, the same panels on the roof require specialists to climb and inspect, and they are now spread across roofs of 10 different buildings, making maintenance a nightmare

The typical Home Depot store is 105,000 sq feet, which is about 1 hectare. These tend to exist in the same general area as other big box stores and similar huge flat roofed buildings. Those are much closer to where a bunch of electricity is used than the undeveloped or farm land just outside of the burbs.

Add in covered parking lots and distributed batteries (dedicated batteries, cars, etc.) and I bet that we would reduce the need for building even more high voltage lines across the countryside.

We should be looking for ways to generate and store electricity close to where it is needed where we have already destroyed nature.

My company has a warehouse in west london, we looked at putting solar on the roof, but it’s not strong enough.

You can’t simply put solar on a roof

Why? What actually killed it?

Do you mean that you can't meet 100% of your demands, or it can't be done for some other reason?

You could reduce, but not eliminate, the demand for purchased energy. Would that be unacceptable? Is there not a net metering programme there?

For me the big deal is usually demonstrating payback. I'm in British Columbia and my solar experience is only with single family homes; on and off grid.

There was no big cost analysis with off grid homes. You need power, or you don't. It's just another category in the budget and the cost decisions are about balancing desires and cost.

With grid-connected homes, we don't even try to sell it now. Nearly all our customers have mortgages to pay for their new house and factoring in the interest paid makes it much less attractive.

A few years ago, low interest rates and high energy costs made it an easier sale. If you were in the position of having money in the bank, you could get a better return on that money by upgrading your home to save energy. Of course it could only scale as large as the cost of improvements.

Even then, a lot of homeowners didn't intend to own the home long enough to realize the returns, and I don't think small solar systems improve resale value. The feeling in the office is that if you're planning to resell, the money is better spent on the kitchen.

> Why? What actually killed it?

I think the parent was saying the solar was too heavy for the roof to support. The physical structure of the building was not strong enough.

Thanks! If the guy with pinkie ring won't stamp the plans, it's not going anywhere.

> Even then, a lot of homeowners didn't intend to own the home long enough to realize the returns, and I don't think small solar systems improve resale value. The feeling in the office is that if you're planning to resell, the money is better spent on the kitchen.

Not at today's power prices. A typical kitchen will easily cost as much or more than solar and solar ROI is about 20 to 25% right now, no kitchen will come even close to adding that kind of value to a house. If you can afford to do both, do both, but if you have to choose solar is #1 from an investment perspective (assuming you already have a kitchen...).

That's a nice return. Where I am (BC) we can do net metering but no longer get paid the surplus and I think our power costs are at the lower end of things.

Being in a rain forest doesn't help. Don't get me wrong, the summers are as bright as anywhere else, but the cloudy winters are brutal if you want sunshine.

If it's financed with a mortgage that's another thing to consider.

I just don't ever hear solar come up in conversations about resale. I've heard a couple Realtors mention that energy efficient design is something coming up most often. The big questions are still about the area and how many bed/bath rooms there are.

>(assuming you already have a kitchen...).

You can always get a second kitchen....a summer kitchen.

Yes the first step should be to cover every rooftop and parking. I think a law exist in some states that new construction has to have solar panels on. The law should be passed everywhere.

And it's just the first step.

government is like XML, if it doesn't work just use more.

Okay but what if we cover all the roofs with rooftop gardens and cover all of the ground with solar?

Rooftop gardens are not nature, so it’s the same thing

It was meant to be a silly comment, though normally I’d have added some emoji to make that clearer.

This can make sense to do, but it ends up being a lot less cost effective than utility scale solar.

A friend of mine lives off grid in Mexico, and he got double duty out of his solar array by making it a big carport and workshop area. So yeah that totally works.

But, if you're going to invest $X in solar, it's better to spend it on utility scale stuff than even commercial versions of covering parking lots. This is because the utility scale operation better amortizes the equipment needed to tie into the grid, as well as operationally will keep the panels clean and working at peak efficiency.

If land cover is the issue, isn't this a great use case for the airship tech that refuses to die? No land issues, no roof issues, relatively clean area, movable according to weather.. It would be crazy expensive, but airships are keep getting invested in anyway, so why not try adding solar?

Could you post a couple pics of your setup? Did you just use an off-the-shelf support structure?

Yes I can, I am planning a write up on the current installation.

As for the support structure: the ones on the flat roofs are part homebrew and part standard components, the ones on the slanted roof are on a standard off-the-shelf support.

I'm not agile enough any more to work on a roof so I had the slanted roof done, the other part I did myself.

Another advantage of flat: when angled panels are placed wide enough to not shade each other at noon they will at all other times of the day allow light to hit the ground (and it gets worse with seasons, far worse with 2d tracking). That's good when you want some agrovoltaic dual use, but not good when you want to maximise electricity from a given acreage. Only a flat layout will at any time of day and season collect 100% of the light that would hit a given ground area.

But tilted panels will collect from a larger area than the ground area they occupy (collecting from the area of the shadow they cast)

A larger area per panel, sure. But not a larger area per ground area, if you look at a larger installation than a single module (or a single row of modules)

Yes and no, yes, all the light will initially be captured but if the angle is off then a part will be reflected and if the angle is off > 45 degrees then most of it will be reflected.

Surface reflectivity can be an issue, that's true. And the numbers aren't as easily compared as the simple geometry of casting shadows. And I assume that there must be large differences between different module types?

The big difference is the kind of glass and coatings used, this can make a few % difference at the same angle of incidence. Typically the yield below a 45 degree mismatch is the maximum panel yield x cosine(angle of incidence) x transmissions (anywhere from 90 to 95% depending on coating and base material). Beyond 45 degree mismatch there is a sharp drop off.

Certainly a topic where it's impossible to judge without knowing actual curves. Even looking at actual panels (without measuring output) you'd be prone to misjudge because some that look promisingly low in terms of specular reflection might pay for it with higher diffuse which won't notice as long as it's not particularly bright.

That leaves armchair-level pondering to theoreticals: is the perfect "any angle" surface even physically possible or are there physical limits that only leave tradeoffs?

And another aspect I don't know: do the cells mind? Does that "punch an electron" principle still work out when photons come in almost parallel to the electrodes? (in practical terms: if we compensated the lower effective cross section and reflectivity with higher light intensity, would we still get the same voltage?) When I was a kid I had a miniature cell in an experiment kit that had a deep plastic top layer with angled prism structures under the surface almost like those of a retro-reflector and I always wondered why it would have that. Was it because the cell could only collect from photons coming in almost perpendicular, and the job of the plastic structure was to make sure that there would always be some photons making the angle threshold (certainly by sacrificing a huge amount of power in the well-aimed case)

This all almost sounds like an argument for heliostats (which get the best yield per module surface, but the worst yield per acre), and which would be a perfect match for agrivoltaics. But that's an approach that hinges entirely on the cost and (far more importantly, at scale) resource use of the mechanical structures required. Which is a mechanical engineering problem that you'd have no problem explaining to a victorian era engineer. Genius "inventors" to the rescue?

I have 26 panels set up like that of two different types and the figures pretty much match that formula.

I've used two heliostats in the past (see other comment in this thread) and on a $/Watt basis you're better off putting them flat, regardless of the perceived advantages, after all is said and done you will have more power, be out less money and have a more reliable system.

Now if only the sun would shine...

That possible heliostat future I keep bringing up wouldn't be about $/Watt (that was an argument for helostat back when modules were much more expensive, but certainly isn't the case anyone), but about finding a sweet spot in agrivoltaics between energy and nutrient harvest: Watts per impact on farming. Or more specifically, electricity dollars per impact on farming. Because when there is a large installed base of photovoltaics, watts at noon won't be worth much compared to watts at deeper sun hours. And for the same amount of off-noon watts, a heliostat setup would cause less shading to the plants below than any other setup. And as a bonus benefit, the east/west spacing inherent to heliostat installations would give a nice distribution of shading, at least nicer than with fixed east/west lines. I believe that the advantages are quite clear, but of course only if the mechanical parts can be cheap enough (in terms of resource use). Flat north/south lines that only pivot east/west would surely be a sweet spot, up to a certain latitude.

The amount of land required to supply ample energy to some random region (bar Switzerland) is usually a small fraction of what is dedicated to agriculture / barren land.

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