Although I’ve referred to there being approximately 1 OOM more capital invested than granted in any one year, there’s some nuance – of the granted funds, all of them are in fact being allocated in that year (by definition); whereas of the invested funds, some of the assets may well have allocated to impact funds some years ago.

This could be 1 OOM effect, if you invest for 10 years, so that's pretty important.

Although 90% (or whatever) of your assets could be invested in impact investing funds, you probably won’t allocate all of your assets to impact investments. For example, you will probably want to hold some of your capital in listed equities, and you might consider it too hard to find effective impact investments in that asset class.

If you do a significant fraction, it's pretty easy to reduce your overall return significantly (if you are trying to maximize returns), which really cuts into your charitable impact. So overall, it doesn't look very promising to me.

Hey David, thanks for this excellent comment.

I'm glad it was helpful!

If we correct the absorptivity for Earth IR and take the low end view factor,  I get your 522 W/m². That looks like a ~1% increase in total cost for ODCs if you’re right. 

I was using 550 km, so I agree that higher up, you would have more net radiation leaving the radiator. 

As for your bent configuration, that is creative to avoid the sun incidence. However, then you would have radiation from the solar panels to the radiator, and since the solar panels will be warmer than the Earth, I think it will work out worse overall. 

Agree loss from averaging over radiator temp looks. 

Incomplete?

Your other points make sense.

I'm glad to see this rigorous analysis!

I was skeptical of the cooling being cheaper in space. It is true that you can radiate to a much colder temperature in space, about -60°C equivalent. It does look like space cooling would be cheaper with your future launch costs for your constellation model. However, for your modular station model, you would need around 1 m diameter pipes to start, which would weigh a lot and pose a large single source of failure. Also, you would have to pump long distances, increasing the pump mass and energy use.

I think inference would be challenging because the satellite is in view for only a few minutes. I guess most queries take less time than this, but would you keep handing off the session memory?

Baseline A (100% renewable off-grid, $20,307/kW-continuous): Solar at 28% CF, $1.10/W installed, 4,643 W nameplate per kW-continuous ($5,107). Battery storage 80 kWh at $175/kWh ($14,000 or 69% of total). Other $1,200. 5-year LCOE: $463/MWh. Battery storage dominates because 99.9%+ uptime without fossil backup requires multi-day autonomy.

This is much more reasonable than people claiming that going off grid is cheaper than grid electricity with the same reliability. Still, you note that this capacity factor is reasonable for the desert, but typically there is around a two times seasonal variation. Since 80 hours of storage can't handle that, you would need to oversize your PV more. But it wouldn't change the results that much (~10%). And the gas turbine in your Baseline B solves this seasonal problem.

We include Baseline A however, since backlogs for turbines versus the abundance of solar and battery available suggest that it may be the fastest way to quickly scale energy production on Earth.

If you want 80 hours of storage for 100 GW, that is 8 TWh, which is years worth of current production, so I think you'd have to pay a premium.

P_net = 2εσT⁴ − αS − αF(Al × S + σT_earth⁴)
where ε = 0.92 (AZ-93 selective white paint emissivity), α = 0.09 (solar absorptivity), S = 1,366 W/m², F ≈ 0.25 (Earth view factor), Al = 0.3 (albedo), T_earth ≈ 253 K.

For the longwave radiation coming from the earth, you would get ε absorption, not α absorption. So the equation should be:
P_net = 2εσT⁴ − αS − αF(Al × S) − εF(σT_earth⁴)

Also, the view factor to the Earth is 0.25 for one side of the radiator, but you are counting both sides for the emission, so I think the view factor should be 0.5.

So then at 20°C: emitted 770 W/m², absorbed 248 W/m², net rejected 522 W/m² (not 633 W/m²).

Also note that if your fluid temp is 20°C, the radiator will be lower average temp because of conductive thermal gradient. But with 1 mm of high-modulus pitch-based carbon fibre reinforced polymer, it doesn't look like too much of a loss.

Footnote 17 seems to end abruptly: "The scenarios in a bit more detail are as follows:"

Ok - so if one believes that wild invertebrate lives are net positive, then offsetting with animal welfare interventions means more feed is required, resulting in fewer wild invertebrates (and more deaths from pesticides, but I think this is small compared to the impact on the population of soil invertebrates of farming more land), meaning less utility overall. So this person would prefer an offset that is a scalable way of convincing people to go vegan. Though this may seem contradictory, I think there is a large variation in difficulty of going vegan (taste preferences, opportunity cost of time, impact on health, etc), so it is most effective if the people for whom it is easier to go vegan are exposed to the arguments.
However, if the person thinks that wild invertebrates lives are net negative, they would prefer the animal welfare interventions offset, because not only would that help the farmed animals, but it would also reduce the bad utilities of wild invertebrates lives.

Are you suggesting that all non-vegans offset the impact on wild animals? How does one do that, even if it were agreed that wild animals had net positive lives?

There is huge uncertainty once you consider wild animals - more feed could increase wild animal welfare.

Seaweed is also an important resilient food for global catastrophes - it can be scaled up quickly as it grows even faster if the sun is partially blocked, and it is cost effective.

I've mainly worked at the cause area level, where I think these considerations are less relevant. But I have observed that if people are so enthusiastic about an area that many will volunteer (or take lower salaries), that does make progress in an area easier.

Maybe if the offsetting is convincing people to go vegan. But I think a lot of the offsetting is corporate campaigns to get higher welfare standards. That has much higher leverage than individual actions to eat higher welfare meat. Maybe once all the corporations have reformed, individual actions could start being competitive, but we can re-evaluate then.

About that example: I think you meant to write "at charity B" instead of "at charity A"?

Yes - thank you - fixed!

* Charity C: 1 employee and 10000 volunteers, 10001 impact total. Should the donor really get 10001 impact? To me that feels really off

Very unlikely to be the case in the real world, but if the donor makes the whole chain of events happen, then I think that is the counterfactual impact.

* Charity D: The employee also becomes a volunteer but does the same job. In a way the employee is "donating" their salary and becomes the donor. Should the employee now get "2 impacts"? That again feels off? Are they somehow better than the other volunteer?

Again, if without that person, there would be no impact, I think that's the counterfactual. In general, a volunteer who could manage other volunteers I think would be more valuable.

* Charity E: 100 donors, all donating $1. It's a blind kickstarter campaign and the charity can only do the intervention if they raise 100, otherwise money back, but the donors don't know how many others already donated, so order doesn't matter. In a way each donor should get the full "counterfactual" impact because without each individual donor the fundraise would've failed. But again attributing the same full impact 100 times feels wrong.

Yeah - an even more extreme case would be an election with 100,000,001 votes versus 100,000,000 votes - would all 100,000,001 people get to claim they cast the deciding vote for the election? Perhaps someone who has thought more about this wants to weigh in? @aaronhamlin ?