An idiotic idea which will go nowhere just the one about putting PV modules on road surfaces was.
this post was submitted on 19 Oct 2024
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have we run out of convenient places to put panels? that's news to me, last i checked we still had a hilarious amount of free roof space and stuff like parking lots where we can just slap up the panels.
Putting a solar roofs over any open-air carpark you happen to own is just a hilariously easier option. Hell, you could erect these OVER the train tracks.
https://greenox-group.de/photovoltaik-carport/ (Article is in German, but it's really more around the picture)
According to a completely un-sourced picture I found online, one carpark (in the USA) is typically around 5.5 x 2.6m, so if you had even 50 carparks on your site you could have ~715 square metres of panels. More, if you figure a way to cover the aisles between the rows of carparks too.
At the top end of all applicable figures (panel efficiency, solar irradiance, inverter efficiency), that could net you ~160kW at solar midday.
Now on the other side, standard-gauge railway is around 1.4m wide, and maybe you could cram a 1m width of panels between the rails.
That sounds like a lot - 1000 square metres per kilometre, and there are thousands of kilometres of railway lines out there - but it's harder to install, harder to service, gets dirty faster, is liable to get damaged, and now you have to figure out how to extract power from somehing a kilometre long, instead of an area that could be a square only around 35m (~115') on a side (for the above 50 carparks).
I know which one of those I'd want to run the cables for.
As has been pointed out many times when this dumb-ass idea comes up, only once you've exhausted every other possibility (carparks, rooftops, putting panels ABOVE roads/rivers/canals/cycleways/railways) and have literally no other viable installation locations, then we can talk.
solar canopys are actually quite expensive. Needs a very sturdy structure to hold panels high up and deal with wind loads. Solar panels are getting so cheap, that it becomes very reasonable to lay them on the ground instead of optimal angles, higher up.
My dad worked with a guy who is designing a system like this and it makes all the sense.
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you shade the parking spaces
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you absorb less heat into the ground than tarmac
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free energy
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direct panel-to-car charging for EVs
i think they'll crack from the vibrations, or to avoid that they'll need to be built a lot sturdier than normal.
In which case just make the cheap version put them on top of buildings, in cities, near to demand; like everyone with a quarter of a brain has known since their invention.
Don't install sensitive/ fragile equiipment in dangerous places near massive energetic machines uness it's neccesay for those machines or there is really no where else to put it.
Can I get 60 grand to shove a solar panel up my arse as an "experiment"? Maybe some of these dumb experiments will help figure out a way to manage all the challenges of idiots who have more money than sense - that might be worth it.
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Even if not between the tracks, aside the tracks there is quite a bit of empty space. That space gets a lot less of a hard time from the trains rolling by
Also, costing €623,000 over three years sounds rather expensive for just 100m
It's hugely expensive, but I expect most of the cost to be in the wagon that lays panels down and picks them up - and could hopefully service a big stretch of railway (if it works). That kind of systems will cost a pretty big penny.
I doubt if this project will "fly", however. A totally horizontal solar panel at ground level is a far cry from producing energy efficiently.
What’s the plan for when people start stealing the solar panels? Good luck trying to stop people
A lot of the comments here are, pretty fairly, sceptical of whether this is a viable idea.
My question is, what's the advantage meant to be over just having an electrical railway and seperately some solar panels plugged into the grid? Especially since the article mentions the solar railway would be grid connected?
Wouldn't it be better to place panels on the train roofs?
Or, hear me out: on the roof of the train stations
Panels on the roof of everything, the roof of cars, the roof of buildings, the roof of your mouth...
Doesn't see the light often in there
Take a Siesta outdoors at noon with your mouth open
Sorry boss, can't come to work I'm generating energy
As always with these fancy ideas it is a solution for something that is not a problem: We aren't even close to running out of suitable space to put solar panels. The problems for solar are usually just willingness, bureaucracy, or the electrical grid not being able to handle the additional load.
We've also had proposals for solar bricks for paving roads/parking lots, putting the panels as dividers between highway roads. It just doesn't make sense to overcomplicate things.
Come back once every single parking lot, large roof, unused radom patch of land, or even agricultural land (there are some interesting setups where the shade provided by solar panels is actually beneficial for the plants) is fully utilized. But chances are that at that point we already have more than enough capacity.
On the contrary, I'm afraid. Land is in very short supply. The issue is that even if the land is not currently developed it is doing vital stuff already. If it's used for food production, if it's a bit of forest storing massive amounts of CO2, if it's home the insects pollinating our food supply, if it's....
Finding scrap pieces of land, like roof tops/already developed land for solar will be crucial going forward.
On the contrary, I’m afraid. Land is in very short supply. The issue is that even if the land is not currently developed it is doing vital stuff already. If it’s used for food production, if it’s a bit of forest storing massive amounts of CO2, if it’s home the insects pollinating our food supply, if it’s…
I won't claim to be an expert, but I'm gonna push back on this point. Local conditions will ofc always vary, but take Germany for example, which is probably one of the more densely populated countries.
Based on the numbers i can find anywhere from 14%-16% of our agriculturally used land is used to produce biomass. This is significantly less efficient than if even a fraction of this area were used for photvoltaics. And those rapeseed or corn monocultures probably have close to zero value for biodiversity, on the contrary i'd imagine that pesticide use will negatively impact nature overall. With solar panels on the other hand you can still use the underlying land to plant stuff like wild flowers and so on, if you wanted. There are also the already mentioned hybrid uses in agriculture where you plant crops below the panels or just use the land for grazing.
On a side note since you mention forests. Just recently there was a number of articles on how due to their poor condition german forests have actually gone from being carbon sinks to carbon sources, releasing more CO2 than they bind.
One more limiting factor that i forgot to mention above is lack of qualified contractors to actually build solar farms or put panels on roofs. Particularly with residential homes that seems to be another common complaint.
Could be a difference in availability of land, but in Sweden you'd not be granted permission for something as mundane as a solar farm if it meant taking farmland out of production.
As for the forests... That's my greatest fear, that climate change will kill off large swathes of Oxygen producers by increasing ocean temperatures or making trees unable to thrive!
How is agricultural land defined if it isn't used to grow biomass?
How is agricultural land defined if it isn’t used to grow biomass?
I can see how i wasn't specific enough with my wording. This is what i am talking about. Basically growing plants for the purpose of energy production, rather than e.g. food or material useage.
Oh, i see😊 When the EED takes effect in 2025/2026 id wager the return will be better for that use than solar panels, as all public buildings will be fitted with some sort of solar capture. Wood is a great energy store, as well, which we need more of.
Oh, and in roughly the same time frame the steps of mandatory mixing of renewable sources in central heating will start, so such agricultural land will be economically more important.
You could be right that that this may lead to more biomass demand due to regulations, but honestly i hope it doesn't. It's great when done with actual waste, but when done purposely it just seems much less efficient than the solar/wind alternative.
"Growing plants -> carrying them to a biomass facility -> converting it to gas/biofuels -> using those in cars, for heating with gas or conversion to electricity in gas power plants" seems so much less efficient than just "put solar panels/wind turbine on a field -> use the electricity for EVs or heat pumps". The former has just so many extra conversion steps where energy is lost.
Wood is a great energy store, as well, which we need more of.
Another point that i have somewhat mixed feelings about, but it probably depends on the context.
If we are talking use for energy production e.g. heating with wood chips/biomass, then as mentioned above it is imo only useful when done with waste (the production of which you'd ideally reduce in search for efficiency). If done by purposely growing trees to cut down and completly burn for their stored energy then logically you are at best carbon neutral (you release the CO2 that was stored), but realistically slightly worse because of transport costs and so on. Plus depending on your setup it may lead to air polution, particularly an issue if done in urban settings.
It is however great as carbon storage and to reduce emissions when used as building material to replace something like concrete.
That's a whole lot of extra steps you added there. Why not simply go harvest -> burn for heat. It's not complicated and it's been done for the last 10000 years or so😊
As for energy storage: Electricity can not practically be stored between seasons. Wood can. So sunlight from summer will not be able to power a EV in winter, but it will heat your home. And it is a way better solution than trying to produce electricity to heat your home, even if it's just recycling CO2. At least it will not add CO2, unlike the coal that would have been used instead.
68 million Europeans heat their home with some kind of central heating system. It not common in west, or central Europe, but it is in the Nordics and in the eastern part. Energy forests will be important going forward.
That’s a whole lot of extra steps you added there
I added those steps, because it is exactly what is currently done at least here in Germany and at scale. Although we might need to clarify here if we want to limit the discussion to just wood and heating specifically, or also other plants such as corn/rapeseed that are grown for biomass often converted into gas/biofuels (like with E10 petrol) to make existing technologies use less fossil fuels without need to immediately replace them.
And it is a way better solution than trying to produce electricity to heat your home,
Yes, directly heating with electricity e.g. with infrared heating panels is not the way to go and uses a ton of energy.
But heat pumps are a great piece of technology and pretty popular in nordic countires aswell, aren't they? With well designed ones having a COP (coefficient of performance) of 3-5. Technically they aren't creating heat, but moving it, however i think we can ignore this distinction, since both leads to the desired effect of a warm house. Added bonus that depending on the device they might also work for cooling, which will sadly become more relevant.
As for energy storage: Electricity can not practically be stored between seasons
There definitely are ways to store energy, although of course this comes at a price and the conversion steps are associated with energy losses. Besides the obvious batteries (which are improving, but admittedly probably not at a point sufficient enough to fully scale as needed), there are other options. Pumped-storage hydroelectricity is a in my opinion cool solution. You can also convert excess to hydrogen gas and store that.
Obviously a tree standing in the forest is stored great, but between the time to grow and sufficient supply for each season, how much space would we actually need for this solution if it were actually adpoted at scale (enough to replace existing fossile solutions)? Probably hard to estimate, but i'd imagine it would be a lot. And comercial forests like that probably aren't great for bio diversity either, and not risk free looking at the current health of existing ones and the increase in wildfires.
At least it will not add CO2, unlike the coal that would have been used instead.
That is true for sure. Although being better than coal in regard to climate impact is a low bar.
68 million Europeans heat their home with some kind of central heating system. It not common in west, or central Europe, but it is in the Nordics and in the eastern part.
I'm not certain if i understand what exactly you mean with "central heating system". Do you just mean having something like a boiler that uses e.g. gas or wood pellets in the basement? If so those are common in Germany aswell. Particularly the gas boilers are something we want to move away from (there was huge outcry when the green party of our government moved to ban new installation of those).
So i guess in the context of our discussion the question would be if the better replacement for those would be a wood pellet burner or something like a heat pump. And at scale my opinion is that the later is the way to go. As stated both because i doubt that wood production could scale that large and air quality is also a factor; see e.g. here. If too many people in dense residential areas would start to use them it could have health impacts. Not that we don't have those already from ICE cars, but no need to replace those as a source with something else, now that we are finally starting to get rid of them.
I'm learning a lot about energy in Germany this way. Thanks! So basically farmers in Germany grow food to make fuel for cars? Like ethanol? Thats an abundance of agricultural lands!
Pumped hydro is great, but will only cover that much energy. Of course, there are no alps in the Nordics, but even so.
The batteries available today cover the need for an hour of the city they are situated in. That's not enough. So for seasonal storage you'd need to store energy as heat, as chemical energy (wood/methanol) or as H2/bio, which I think is what you describe. H2 has much of the problems of batteries in terms of storage space and the risk of fires/explosions, which limits the possibilities somewhat. But if I've understood correctly from the TEN-T directive, Germany and Switzerland has invested pretty much in H2?
Heat pumps are great, and are indeed well used, they run out of steam when its below -5C, which isn't rare up here. And it's seldom used in cities. Heat pumps collecting hear from the bedrock (through a drilled 100m hole in the ground) is more common, but most common is district heating. (I got the name wrong in translation earlier)
Instead of one boiler in every house, there is one boiler per 50-100000 inhabitants or so. Efficiency is great and heat is pipes to where it is used. When it's cold (-20 or so) those boilers go through tens of semitrucks of wood every day. And as I said, it's a fairly common set up in parts of Europe, although i understand its not common i Germany.
I’m learning a lot about energy in Germany this way. Thanks!
Glad to hear it, by doing some more digging i am learning new things aswell. I actually came across this site (sadly only available in German) by one of our environmental agencies, which i found quite good and mirrors pretty much my opinion (but maybe that is why).
One particularly interesting piece of information is that they give specific numbers for the energy yield per hectare of biomass vs solar. They estimate using corn as an example crop that for biomass it is on average 20MWh/hectare vs 800MWh/hectare for solar, so a difference by a factor of 40x. Further for load balancing renewables they estimate 10% loss for short term storage through batteries and 40% loss when converted to chemical energy sources (presumably hydrogen).
And while biomass currently plays a substantial role particularly in electricity production, they link to studies that long term (2050 being the target date) energy demands can be met completely without biomass useage.
So basically farmers in Germany grow food to make fuel for cars? Like ethanol? Thats an abundance of agricultural lands!
I mentioned E10 fuel earlier, which mixes 10% bioethanol into petrol. Seems like according to wikipedia it is also a thing in Sweden/Finland/Denmark. So that would be an example where plants ultimately get fed into cars. I think this is also a case where demand is induced by some EU directive that requires reduced emissions in the transport sector, and mixing in biofuels was one of the solutions to achieve this goal.
I am not 100% certain on the specifics and i assume that it isn't a pure play where literally nothing from those plants is used for other purposes. But it's still fair to say that these crops are primarily planted for extracting energy from them, not for feeding livestock or food. So they are directly competing with those and without this demand farmers would plant different things.
But if I’ve understood correctly from the TEN-T directive, Germany and Switzerland has invested pretty much in H2?
Yeah, seems like we are investing a good amount in clean hydrogen. That includes storage and pipelines. I wasn't particularly aware of the ten-t directive, but if i undestand it correctly this is about transportation? I think as far as hydrogen goes here in Germany the main focus for that is on use in industrial settings (particularly stuff like chemical processes and steel production). But ofc it'll also be used in other areas.
but most common is district heating. (I got the name wrong in translation earlier)
Instead of one boiler in every house, there is one boiler per 50-100000 inhabitants or so. Efficiency is great and heat is pipes to where it is used. When it’s cold (-20 or so) those boilers go through tens of semitrucks of wood every day. And as I said, it’s a fairly common set up in parts of Europe, although i understand its not common i Germany.
Not as common, but Munich for example has a large network, which currently is still mostly based around fossil fuels, but they are investing a lot in renewables (particularly geothermal) and plan to get it climate neutral in the longterm while expanding its reach.
Also because of a recent law every municipality has to create a strategy paper for heating (until mid 2026 for larger, 2028 for smaller ones), which includes feasibility studies for district heating. So we might see them become more widespread.
I thought about your numbers again and realised that the difference is bigger than it should be based on efficiency alone (about 3-6x all spectrum), what was their method of assessment?
I'll try to track it down, but am kind of having a hard time finding their methology for those stats. Which ones do you think are unsure about? the 20MWh/year/hectare biomass, 800 MWh/year/hectare solar or the energy loss through stroage with batteries/hydrogen? Or something else?
I'll try a bit further to find their specific methology when i find the time. But for the solar part i also did a quick google search and found for example this paper. To quote from their conclusion:
Based on empirical observations drawn from a large, nearly complete sample of utility-scale PV plants built in the United States through 2019, we find that both power and energy density have increased significantly over the past decade. Modelers and analysts, policymakers and regulators, and others who continue to rely on outdated benchmarks from the last comprehensive U.S.-based assessment of power and energy density conducted nearly a decade ago [6] will, therefore, significantly overstate the land requirements, and by extension perhaps also the land-use impacts, of utility-scale PV.
Updated benchmarks as of 2019 established by this study are as follows.
- Power density: 0.35 MWDC/acre (0.87 MWDC/hectare) for fixed-tilt and 0.24 MWDC/acre (0.59 MWDC/hectare) for tracking plants.
- Energy density: 447 MWh/year/acre (1.10 GWh/year/ hectare) for fixed-tilt and 394 MWh/year/acre (0.97 GWh/year/hectare) for tracking plants.
It is about the US and not Germany, but i wouldn't expect there to be massive differences. If we assume that Germany has slightly worse conditions for solar, then 800MWh/year/hectare seem in the right ballpark.
It was more the relation between them (40x) that struck me as bigger than I expected given the relative performance between photovoltaic and photosynthetic efficiency.
If they compare 1-year crops for human consumption, there will be a lot of tilling, sowing etc. but then we compare two different use cases with different purposes.
Wood intended for burning for district heating, where the heat is taken care of with high efficiency, would be an energy usage more akin to electricity. In that case I would expect the harvesting and transportation part to be different.
As a swede, energy usage in the winter is warm at heart which is something that is hard to compare and muddles the numbers. In Dec-Jan energy (kWh) output from solar is at best 9-10% of their peak output during summer at my latitudes, (further north, this goes towards zero as there is no sunlight in winter), so with that in mind, the stored 20MWh/hectare, available round the clock, looks apetizing until we find a better solution to store energy.
It was more the relation between them (40x) that struck me as bigger than I expected given the relative performance between photovoltaic and photosynthetic efficiency.
Honestly i was suprised aswell by the difference. I did some further digging and while i think i found the german source they used, it was a bit harder to comprehend.
But i also looked at this paper which forexample seems to support the rough numbers for energy/hectare biomass (it's also on scihub if you dont have institutional access). It's using fast growing tropical tree varieties as an example, but i imagine that if anything this would influence results favorably for biomass. If you look at figure 5 the yield is between 15-25 MWh/hectare.
As a swede, energy usage in the winter is warm at heart which is something that is hard to compare and muddles the numbers. In Dec-Jan energy (kWh) output from solar is at best 9-10% of their peak output during summer at my latitudes, (further north, this goes towards zero as there is no sunlight in winter), so with that in mind, the stored 20MWh/hectare, available round the clock, looks apetizing until we find a better solution to store energy.
Yeah, in the end there probably isn't one solution. In Sweden for example area efficiency probably doesn't matter as much due to your low population and large areas of woodland (that wouldn't be suitable for much else). And you are right that PV probably wouldn't work, so wind/hydro or maybe even tidal power generation would be the more appropriate competitors to compare biomass to, although those have more specific needs in terms of location.
Aye, it corresponds with the numbers I've seen for photosynthesis efficiency as well. However, and here I believe we return to the root of the discussion, A: vertical solar panels in a field of crops both produce electricity and increase crop output (due to heat shelter and better moisture retention) and B: solar isn't abundant during winter, so we need some sort of energy storage and biomass is pretty good at that.
So, while it is not enough to offset that 40x, it will go a pretty long way of evening things out. Besides, if we produce more electricity than what is needed, the final solution, today, is to lower a heating coil into the ocean to burn off excess electricity. We will need to find energy users at the same pace we install solar, so leaving some ground for crops might not be a bad idea.
As for the energy plan, it's a requirement in the EED, it's the same here.
Covered Highways. The benefits of additional PV and the benefits less rain and less sun glare on drivers. You could also install a tram like wires above in one lane for maintaining the EV charge on trucks and buses.
To clean them, simply attach a big brush to the underside of the trains. 👍
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