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Solar panels between railway tracks? (www.euronews.com)

submitted 1 week ago by [email protected] to c/[email protected]

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I'm all for putting solar panels all over the place, but won't these get dusty and oily and need loads of cleaning after trains pass over?

Also, costing €623,000 over three years sounds rather expensive for just 100m (although that roughly equates to 11KW).

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[–] [email protected] 1 points 5 days ago (2 children)

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.

[–] [email protected] 2 points 5 days ago

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.

[–] [email protected] 1 points 5 days ago (1 children)

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?

[–] [email protected] 1 points 4 days ago* (last edited 4 days ago) (1 children)

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.

[–] [email protected] 1 points 4 days ago* (last edited 4 days ago) (1 children)

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.

[–] [email protected] 1 points 4 days ago

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.