You don't know if it's always on. Those details aren't present (that I saw), and it's likely that they would throttle when the grid was under heavy load. A reasonable inference from what the company (who make "smart" electric panels) is saying about power management.
As for cooling, "Span is incorporating technology from Nvidia into its system, including a liquid-cooled, fanless component inside the server. The design helps eliminate the noise typically associated with data centers—a frequent complaint in communities near large facilities."
It's also possible to pair it with a large residential roof solar installation. I installed solar recently (just in time to grab the 30% credit) and my system routinely generates 3X what my home uses in the course of a day (I typically use about 40 kWh per day, and often generate 130+kWh per day). I've been thinking I'd really like to find something to suck up that extra power, because the monthly net billing plan I have means that once I've zeroed out my bill for the month, I get no benefit from additional production.
As deployment of renewables continue, this "problem" of what do do with excess capacity will increase and spread.
However, if power for the mini-datacenter is only intermittently available, the cost of the hardware effectively increases on a per-token (or per FLOP or however you want to measure the system's work) basis... and hardware cost is already going to be a tough problem for this kind of deployment. Even if it could count on 100% utilization, it will struggle to compete with large datacenters for exactly the reason we build large datacenters: Economies of scale. Enclosures (buildings), cooling, maintenance... all of the overheads fall with scale.
Intermittent utilization just makes that problem worse.
On balance, I'm skeptical that this makes sense, unless the cost of the hardware falls significantly. It seems like that's a baseline requirement for a lot of the alternative datacenter ideas, though: orbital datacenters, floating datacenters, etc.