Cheap storage is a vastly easier problem than cheap/sustainable fusion, though.
I actually agree that space based solar power may make more sense than fusion, though. The path for space based solar power is through well-understood engineering. The path for fusion (while I'm certain it's possible) lies through less-well-understood plasma physics.
Cheap storage is much easier than either problem, IMHO. We've already pretty much solved it to the extent needed for civilization, it's just not as cheap as our existing sources of industrial energy. But we're very close.
If you actually spent significant time looking at what fusion and space based solar power require, then cheap storage looks much easier.
Cheap storage doesn't look all that easy. None of our current technologies can pull it off; we simply run out of raw materials for existing battery technologies, and we're close to geographic limits for hydropower storage. There's research on new batteries using more abundant materials like sodium, but like many things, battery breakthroughs have a history of taking a long time to pan out.
I read the above book cover to cover so you could say I've spent a decent amount of time looking into space solar. It's well worth a read. The early designs from the 1970s would have been hugely expensive even if launch were free, but new work since the late 90s has changed matters enormously. One key innovation is a change from a monolithic design to a self-assembling modular design, with a limited number of component types that are churned out in factories in large quantities. Another is retrodirective arrays, which use a ground signal to allow an array of small microwave transmitters to return a coherent focused beam to the signal source. The book estimates a retail cost of 15 cents/kWh; substituting the estimated BFR launch cost takes that down to 4.5 cents.
Tokamak scaling laws are very well established at this point, and MIT's ARC design actually looks quite practical. The construction is modular, the inner wall is 3D printed and replaced annually, the coolant/blanket is FLiBe molten salt, and the whole thing is about ten times smaller than ITER with similar power output. The JET reactor is about the same size and was built in four years.
It really, really does if you look at the challenges of making either fusion or space based solar power cheap enough in real life. In fact, it's so easy we're already doing it in places. For the other two, we're decades away from useful commercial output.
I've also done considerable calculations about space-based solar power. It's obvious why Elon Musk doesn't consider it a good idea. Even if your launch is free. (I still hope people try to make it work, though...)
Doing it in places is not at all the same as doing it at the scale where you run out of the resources you were using.
Since you're interested enough to have done those calculations on SPS, I really think you'd like that book, which works out the cost and efficiency numbers in great detail.
The only comment I've seen from Musk was "You'd have to convert photon to electron to photon back to electron. What's the conversion rate? Stab that bloody thing in the heart!"
Meanwhile he wants to convert photon to electron to chemistry to electron.
To answer his question, the overall conversion rate is 40% with today's tech, and probably 60% with some more R&D. That's not bad given that you don't need storage at all, and at all times you have 30% more energy hitting your solar panels than if they were on Earth at noon on a sunny day. You're in sun 99.5% of the time.
The system works especially well with other renewables, because the ground stations are a small portion of the total cost; you can build extras, and point the power to the places you need it most.
Photon to electron to chemistry to electron definitely has a huge efficiency advantage over photon to electron to photon to electron. The battery has about >90% round-trip efficiency while the wireless power transmission over thousands of miles has on the order of 33% round-trip efficiency once you add everything up. That means that in order to get the same energy, you need almost as big of a solar array as you would in a good desert location even though you get 24/7 sunlight!
And it's not even the conversion efficiency that's the problem. It's the cost of the conversion equipment. The power electronics, the microwave amplifier, the array, the receiver array, rectifiers, and power electronics as well as transmission all has a MUCH higher cost than the actual solar cells. Additionally, the minimum size space based solar power satellite and receiver station is super expensive, and the situation only starts looking like it might be worth it when you approach multiple Gigawatts per installation.
In some ways, space based solar power is based on the idea that solar cells are expensive and scarce and their output should be maximized. Nowadays, that's a strange thing to believe because solar cells go for 16 cents per Watt on the spot market, so we tend to emphasize the constancy. But really, even that is falling prey to technological advances in battery technology.
As far as "ground stations are a small portion of the total cost" and "point power to the places you need it most," that's simply not true. The ground stations would rival an equivalent solar array in cost, not even counting the space-based portion at all! But I suppose the in-space portion WILL be crazily expensive, so you might still have the ground-stations a "small portion of the total cost" while still being crazy expensive.
And due to the diffraction limit and required safety margins, your ground stations will have to be huge. You're not just going to beam power into the middle of cities with high aircraft traffic and safety concerns. The exception to this would be if you used much shorter wavelengths, such as mm waves or lasers, but there the cost of everything (amplifiers, optics, etc) is much greater, the realistic round-trip efficiency drops to like 10-20%, and you become much more susceptible to weather. Oh, and what you're building now looks a HECK of a lot like a weapon.
Well all I can say is check my source, which covers all of this, with extensive references on efficiency, cost, and lots of other practical concerns. Some of the key research was done by NASA in the past decade.
The cost of a 2GW ground station is $700M, which is pretty decent for a peaking plant that doesn't require fuel.
The idea isn't so much that you have to minimize solar panel size, as that you can entirely eliminate the need for storage, which is a big deal once we try to get past fossil backup. To see the scale of that problem, read A Nation-Sized Battery, by Berkeley physics prof Tom Murphy. Even if he's too pessimistic by a factor of ten, storage looks like a daunting problem.
Yeah, I've read that blog many times. The author wastes his intelligence by refusing to pursue creative solutions to problems vs just trying to find ways to make the problem unsolvable.
The answer to season storage for solar, for instance, is to make the solar array larger, not to have a nation-sized battery. That means you only need a day or so of battery, not a week or months.
Also, why would you want to eliminate storage? Just like nuclear power, you'd want to use storage at very least to help convert a constant baseload power source into one that can follow day vs night demand. That is ultimately cheaper. And his complaint that batteries might require service? Well first of all he's off by at least an order of magnitude in cycle life, and second of all, yeah, why wouldn't we do a lot of service on batteries like we do on the rest of our energy infrastructure? That's a weird thing to focus on.
As far as material shortages: I find this highly doubtful. Lithium is not fundamentally rare. "Proven reserves" might be, but that is almost entirely a function of demand (provided your mineral isn't fundamentally rare, which lithium isn't). Other metals used in batteries, like cobalt, can be substituted by other more abundant minerals if desired, especially in grid storage. (LiFePO4 is one such chemistry.) That the author of that blog seems to not realize this pretty obvious fact strikes me as naivete dressed as "skepticism."
I actually agree that space based solar power may make more sense than fusion, though. The path for space based solar power is through well-understood engineering. The path for fusion (while I'm certain it's possible) lies through less-well-understood plasma physics.
Cheap storage is much easier than either problem, IMHO. We've already pretty much solved it to the extent needed for civilization, it's just not as cheap as our existing sources of industrial energy. But we're very close.
If you actually spent significant time looking at what fusion and space based solar power require, then cheap storage looks much easier.