Is Space Solar worth it?

Last week I posted about Mercury as a potential energy hub in r/energy. The response pushed me to dig deeper — and the deeper I went, the more genuinely uncertain I became.

JAXA has been researching Space-Based Solar Power for 40+ years. ESA launched their SOLARIS program more recently. Institutional patience at that scale deserves attention — but longevity alone doesn't validate an idea. So I ran the numbers myself.

Using the IPCC SRES A1 scenario, global electricity demand in 2100 reaches approximately 898 EJ/year — roughly 250,000 TWh/year, or 28.5 TW of continuous power.

Using De Castro et al. (2013), which measured real-world utility solar at 3.3 W/m², meeting that demand entirely with ground PV would require approximately 8.6 million km² —roughly comparable to the combined area of India, Mexico, Argentina and Egypt.

Then I ran the same calculation using LBNL 2022 data, which shows modern US utility solar achieving 12.6 W/m². The land requirement dropped to approximately 2.3 million km² — roughly two Mexicos. Still enormous by any measure.

But here's what stopped me: that 78% reduction happened in just nine years of technological progress.

We have 74 more years until 2100. If solar density improved fourfold in under a decade, what becomes possible across seven more decades of human ingenuity? Physics has ceilings — but we don't yet know where that ceiling is for solar.

This is genuinely where my thinking broke down. I came in favoring space-based solar. The numbers complicated that.

Is SSPS a rational next layer for a civilization scaling toward unprecedented energy demand — or an expensive solution to a problem Earth will quietly solve on its own?

I'm curious what you think. Not looking for a verdict — just honest perspectives from people who've thought about this longer than I have.