> A balcony solar panel will yield even less than that because it's not positioned optimally.
Non-optimal positioning is already included in your "Measured (not projected) yield in Germany". Because that is the difference between a projected yield (under optimal conditions) and actual measurements of actual panels, which are practically never optimally placed.
> Then you won't consume all that it produces because you're at work during the day and there are no appliances running except the fridge maybe.
That is relevant for an economic calculation, but it is entirely irrelevant if you want to determine the point after which the panel breaks even regarding the energy used for its production vs. the energy produced by it. In that case, every single kWh counts, whether the owner of the panel economically profits from it or whether he or she just donates it to the grid without compensation.
And clearly, we are discussing the energy break-even here, as indicated by "The usual estimate to produce a PV panel is 600-1000 kWh per 1sqm."
> However from the physics/ecology perspective they make no sense at all and many of the panels installed today will never recoup the electricity used to produce them, making them a net-negative impact for the environment.
As I've demonstrated with concrete calculations, that you seemingly accept as valid as you perform the same calculations with roughly the same numbers, the EROI of solar panels even in Germany over their lifespan is clearly in the positive range. Maybe they "only" recoup 3x or 5x their investment, and not 20x, but they are a net positive regardless. Any number above 1x is.
In addition to this, as I've described in another posting here (https://news.ycombinator.com/context?id=45490555) there's the psychological side of things, where cheap and easily profitable balcony panels for everyone are a gateway drug for "normal people" to get actively involved in the field of renewable energy and must not be underestimated in their ability to open the minds of people for other, more efficient actions to get closer to a carbon-neutral energy economy. Since those activities tend to be heavily inhibited by broad refusal that's often not based on factual arguments, but simply on inertia in people's minds ("we've always done it the other way") and a certain lazyness to actively grapple with new technologies and developments, this effect is at least as important as the actual impact on the energy grid. Just like on the stock market, the raw numbers are only half of the story. Psychology is the other half.
> Non-optimal positioning is already included in your "Measured (not projected) yield in Germany". Because that is the difference between a projected yield (under optimal conditions) and actual measurements of actual panels, which are practically never optimally placed.
No, because the figure I have was for normal solar panels, not the balcony ones which are even worse. I haven't seen anyone reporting real yield for balcony panels yet, would be interested to see the numbers.
> That is relevant for an economic calculation, but it is entirely irrelevant if you want to determine the point after which the panel breaks even regarding the energy used for its production vs. the energy produced by it. In that case, every single kWh counts, whether the owner of the panel economically profits from it or whether he or she just donates it to the grid without compensation.
No, because when you get any significant amount of solar installed you start to get negative prices on sunny hours and need to shut them down. If home solar setups won't shutdown then some other panels in the grid would. This is a fundamental tradeoff with solar: it's either too small to make any difference or you never get your projected EROI because you have to shut them down during the very time they produce maximum energy.
> I've demonstrated with concrete calculations, that you seemingly accept as valid as you perform the same calculations with roughly the same numbers, the EROI of solar panels even in Germany over their lifespan is clearly in the positive range. Maybe they "only" recoup 3x or 5x their investment, and not 20x, but they are a net positive regardless. Any number above 1x is
You confuse the "maximum possible outcome" with real life. No one knows if these $300 setups will last 30 years, that was never tested because that requires well 30 years. My estimate is they won't because electronics from the lowest price range very rarely do. Then even if they could last that long, half of them will end up in a dumpster after a few years because people move and can't always take their panels along.
I'm extremely sceptical of all these "concrete calculations", not because they're mathematically incorrect but because they are detached from real life. It's like when they sell you a timeshare cottage on a ski resort and mathematically it's profitable, but in reality it's a huge liability.
> No, because the figure I have was for normal solar panels, not the balcony ones which are even worse. I haven't seen anyone reporting real yield for balcony panels yet, would be interested to see the numbers.
„which are even worse“ is an assumption you make, you do not have any data to back that up. From what I regularly see, they are not worse at all. People without sun on their balconies do not buy balcony solar kits in the first place. Also there’s the fact that people can spend time to meticulously optimize every single panels’ location (which they usually don’t when someone places 30 panels on a roof in a single day, it’s just about getting them up there quickly). If you are interested in numbers, browse https://www.reddit.com/r/Balkonkraftwerk/ - it’s German language but Reddit does quite well with auto-translation as far as I know. Every month, people post their yield numbers for comparison there.
> No, because when you get any significant amount of solar installed you start to get negative prices on sunny hours and need to shut them down. If home solar setups won't shutdown then some other panels in the grid would.
You are equating the time during which a home solar owner cannot use his own solar power with the time during which there are negative electricity prices. This is grossly wrong. In 2024, Germany had 457 hours of negative power prices (see https://www.pv-magazine.de/2025/01/03/bundesnetzagentur-457-...). That’s roughly 5% of the year. Typical home solar power usage if no battery at all is installed is about 50%. If we talk about batteries, which are increasingly getting common in balcony solar installations due to significant price drops, it’s more like 80-90% of power that the owner can use directly.
> You confuse the "maximum possible outcome" with real life. No one knows if these $300 setups will last 30 years, that was never tested because that requires well 30 years. My estimate is they won't because electronics from the lowest price range very rarely do.
The panels are the exact same panels used for large-scale solar installations. These are tested and guaranteed by the manufacturer for 30+ years. Nobody doubts that they’ll reach that lifespan in most cases.
The inverters are a negligible amount of kWh invested, as I pointed out in the parallel threads’ posting. So you can easily buy one or two replacements over the 30 year timespan without impacting the EROI of the panel at all. Also, a lifespan of 30 years does not mean that the panel fails after 30 years. It just goes below a defined point of efficiency (80% of original peak power). You can very well use it for another 10 or 20 years, you just have to accept that it produces only 80% of the original output.
> Then even if they could last that long, half of them will end up in a dumpster after a few years because people move and can't always take their panels along.
That’s not what I see, because it is surprisingly hard to dispose of solar panels in practice. They do not fit into the typical „dumpsters“ people use to dispose their regular trash. You would be able to dispose of them for free at the next recycling center in Germany, as they are mandated to take them, but most cars cannot be used to transport solar panels as they are too large, so it’s not trivial to get them there. From what I observe, people therefore simply sell or donate the panels to the next renter/owner when they move, which is obviously a good idea as they are usually installed on a balcony or garden house or whatever and you usually buy the matching installation equipment for a particular situation which you wouldn’t be able to use at your future home anyway.
I find it quite interesting that you did not object to my second argument about the psychological impact/use of this technology.
Non-optimal positioning is already included in your "Measured (not projected) yield in Germany". Because that is the difference between a projected yield (under optimal conditions) and actual measurements of actual panels, which are practically never optimally placed.
> Then you won't consume all that it produces because you're at work during the day and there are no appliances running except the fridge maybe.
That is relevant for an economic calculation, but it is entirely irrelevant if you want to determine the point after which the panel breaks even regarding the energy used for its production vs. the energy produced by it. In that case, every single kWh counts, whether the owner of the panel economically profits from it or whether he or she just donates it to the grid without compensation.
And clearly, we are discussing the energy break-even here, as indicated by "The usual estimate to produce a PV panel is 600-1000 kWh per 1sqm."
> However from the physics/ecology perspective they make no sense at all and many of the panels installed today will never recoup the electricity used to produce them, making them a net-negative impact for the environment.
As I've demonstrated with concrete calculations, that you seemingly accept as valid as you perform the same calculations with roughly the same numbers, the EROI of solar panels even in Germany over their lifespan is clearly in the positive range. Maybe they "only" recoup 3x or 5x their investment, and not 20x, but they are a net positive regardless. Any number above 1x is.
In addition to this, as I've described in another posting here (https://news.ycombinator.com/context?id=45490555) there's the psychological side of things, where cheap and easily profitable balcony panels for everyone are a gateway drug for "normal people" to get actively involved in the field of renewable energy and must not be underestimated in their ability to open the minds of people for other, more efficient actions to get closer to a carbon-neutral energy economy. Since those activities tend to be heavily inhibited by broad refusal that's often not based on factual arguments, but simply on inertia in people's minds ("we've always done it the other way") and a certain lazyness to actively grapple with new technologies and developments, this effect is at least as important as the actual impact on the energy grid. Just like on the stock market, the raw numbers are only half of the story. Psychology is the other half.