What is the intended way to deal with the steam output? You can't vent it, despite that being the most reasonable and realistic solution.

Am I supposed to hook up some accumulators and a power switch to attach a pile of beacons doing nothing to waste all that energy when the accumulators are near capacity?

Well, I tried the power switch beacon thing and it doesn't work with a basic circuit setup and the number of turbines you'd expect, because the beacons constantly drain themselves and whenever I need to waste steam they suddenly want to fill up their empty battery and that drains the system for more than 12MW each. This results in absolutely blasting the power grid with a kind of stuttering brownout. Reducing the number of beacons until the brownout stutter no longer happens results in not enough power draw and steam fills up.
So, I see two ways of dealing with this. Either gradually open up more beacons as the steam tanks fill, or send steam to steam engines instead which will produce less energy from the high temperature steam than the turbines do. A mixture of both could work I guess.
Oh, a third method would be to set up a more complicated circuit, like an SR-Latch or something, so that the circuit doesn't stutter and instead keeps going for a while to allow the beacons to fill up (but then you need a bunch of accumulators too)

It's far from elegant however and I really AM curious as to what the intended way is to deal with this.

Sorry for not responding earlier!
The idea is just "yay, free power", so you don't have to build power generation on that island, or transport batteries in. Presumably the problem is that unless you build lots else on that island, it will produce far more power than you need. So yes the main solution is place lots of radars or beacons to waste the power, or charge lots of batteries and transport them to other islands to power those. I don't love the idea of requiring radars/beacons to waste electricity, so perhaps I should just add a chemical plant recipe for converting steam back to water? If you are trying to get power out of the steam, then you'll still need to circuit-control the inputs to the steam condensing, but that is probably a more 'expected' thing to be trying to solve anyway. You'll also have to manage the recirculation of the output water, so overall sounds like a fun thing to add.

Looks like the steam to water recipe went in. I approve, it's a nice little side problem that has a relatively straightforward circuit-based solution.

I went with the steam engine solution in my save(I sent steam to the engines when the tanks got near full capacity), and it worked fine with a couple of beacons to up the power requirement alongside that. The beacons never ran out of power this way so I didn't get spikes in consumption. In hindsight my original circuit system might have worked if I used a circuit to check accumulators as well and had enough accumulators to handle the spikes.