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Comment by devonkim | Hacker News Reader

The estimate for cats is widely disputed and was a complete WAG with little empirical backing and more like extrapolation from a non-representative sample. There are studies currently in progress to more accurately measure the impact of cats upon bird populations and last I saw the results were showing the prior estimates were grossly overestimated because cats kill many more kinds of animals than just birds like squirrels, lizards, and rodents.

Also, I have a 9kw solar setup and simply can’t add more without sacrificing land or basically tearing my house down to make a new, more optimal roof, at which point all the environmental pros of using solar are more than wiped out by the construction carbon footprint. Old homes really are terrible oftentimes for solar installations, sadly.

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Domestic cats should be illegal anywhere outside of a major city. It’s such low hanging fruit in reducing loss of small native animals, with virtually no downside.

If you care about the planet pets should be illegal.

Look at CO2 footprint of pets and your toenails will curl.

E.g. https://newsroom.ucla.edu/releases/the-truth-about-cats-and-...

What about people?

Don’t give them ideas

2% that of humans? Doesn't seem like that much.

That also means if more then 1 in 50 people decide to have a pet instead of another child it's a good trade.

[1] https://klima.com/blog/how-to-cut-your-pet-carbon-footprint-...

[2] https://www.nature.org/en-us/get-involved/how-to-help/carbon....

Or at least 'illegal, outside'.

In my experience, it very much depends on the individual cat. Besides general levels of hunting competence overall, cats seem to have a good bit of variety in their preferred prey types. Some catch everything, but some specialize in small rodents (never catching birds) and others I have know did catch primarily birds. I had one who loved young rabbits above all else, and I've even known some for whom a nice fat moth was the gourmet treat above any.

The exact numbers re: what kills birds here aren't really what matters. What matters is the relative orders of magnitude. Even if the number for cats is a WAG and wildly off by a factor of 2 in either direction, we can safely say that buildings and windows are far more dangerous to birds than Felis catus.

If cats are in fact half as dangerous to birds as estimated, then the danger is still of the same order of magnitude as that from power lines, vehicles, and pesticides. If they are twice as dangerous as estimated, then the danger is still not far off from those other things in terms of order of magnitude.

Ultimately, these things are all factors to keep in mind in terms of how we can prioritize actions that benefit the bird population.

TL;DR: focus on orders of magnitude here, don't get fixated on exact numbers.

I think part of my point should be taken further that we don’t even have the correct order of magnitude for cats and the numbers for windmills are so small it’s probably negligible although care should be taken to see if there is some disproportionate externalities observable now such as when Australia changed its own ecosystems with changes to farming practices. What isn’t under so much debate though that does unequivocally matter is the amount of land necessary to convert to renewables which is a function of energy density in urban areas where land use is much more expensive and total energy used per area is quite high. While systems do get more efficient over time the efficiency isn’t exponential and portable energy is a big issue that is mostly orthogonal to renewable sources in funding mechanisms yet also part of the incredibly complex energy supply chain of the world economy.

Presumably that’s a 9kWp system, with peak potential on a good day to generate 9kW at the optimal time of the day

Is there any way to work out how many kWh such a system would tend to generate for a given latitude throughout the year? If I wanted to charge a 10kWh battery once a day for 12 months what kWp system would I need. What would it produce in June vs December etc.

There’s websites to calculate it based upon satellite photos of your roof alone (what the installer and system designers did for me along with permitting that would have taken me far too much time / effort). Your panel type, inverter, etc. all matter as well. A meter to determine your electricity usage throughout the year is good to have as well although I didn’t do that before I installed my system and expected to try to size a battery backup system only once I had sufficient data. But basically so far my house is pretty much a dud in terms of ROI for any more modernization efforts without tearing it down basically and this is what I’ve been thinking about a lot more than the usual trend of renewables and such. Old homes in the US are really, really, really hard to retrofit remotely economically and are burdens upon the energy grid and infrastructure throughout the lifetime of the structures. The costs fall disproportionately upon our population that can least afford it as well and subsidies are laughably minuscule and mostly taken by more affluent homeowners in practice.

https://pvwatts.nrel.gov/

The main issues are cloudy days, and angle of the sun. Do you still want to fully charge that battery on cloudy days? If not, then you need to size the battery based on how many cloudy days in a row you can tolerate before needing to cut back on energy use.

The angle of the sun affects the number of hours of sunlight in the day, as well as the angle of incidence to the panel (and you can adjust the panel angle). The default is to angle your panels equal to your latitude. If you angle them more horizontal, you will have more summer generation. If you angle them more vertical, you will have more winter generation. Which is your design constraint - heating or air conditioning loads? You can also use adjustable mounts that can be changed over the year. When I ran this for myself, adjusting the panels a few times a year would only net me a negligible amount of additional generation.

There's so much we take for granted with the grid abstraction. Net metering was a huge subsidy to drive adoption of solar, but ultimately if you want a truly independent setup you need to think like an off gridder. The hard truth is that you're probably better off designing for the 95% or whatever common case, and falling back to a gas generator for the few times conditions are worse.

PVGis does that:

https://joint-research-centre.ec.europa.eu/pvgis-photovoltai...

https://re.jrc.ec.europa.eu/pvg_tools/en/

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