Given that they generate a whopping 44mj/t for, I think, 1200 silver
What else, praytell, are you doing with your silver? What's important to note is not how it scales out, but how it scales early on. You can very easily get an explosion and maintenance free ~3mj/t early on. Even one mirror will make MJ.
Basically factorization gives you a route to early steam, but lets you replace that mirror array later. And anyone who thinks the steam furnace is great has not put in the minimal investment in a furnace heater and router cluster. It's cheap compared to the furnace and can run much faster. Think about how to lay out the furnaces and heaters to get at least 2 (and in some cases 3) adjacent heaters for overclocking.
Compact Solars were made in response to laggy ic2 solar arrays. I know they generate steam like once a second, probably to mitigate some of the lag, but I'd wager it to be an irresponsible drag on server resources.
The factorization mirrors don't work like this. IC2 solar lag is caused by an inordinate number of energy packets traversing a huge network. Factorization doesn't have this problem as it uses a unified network model. CompactSolars
does reduce the number of ticking blocks in a chunk, but it also compresses all those IC2 energy packets into larger chunks to reduce IC2 energy networks.
IC2 is one of the most expensive energy networks to run. It's not because its coders are bad, but rather because the model involves moving quantized energy units around a physical network rather than treating the network as an energy sink and extracting there. It does this to do things like model power line burn and wire failure.
Note that buildcraft's model has recently improved, and so it's no longer slower than IC2 (if it ever was, reports and my profiling varied wildly on this).
It would be nice if someone with knowledge on servers and tick rates and whatnot could confirm/deny the drag of factorization solar arrays.
Haven't I been doing this? I can both read the code and tell you that after months of running servers with factorization systems, we never see them come up. They are not expensive compared to, say, engines. But Factorization is designed such that you're probably never going to build epically huge solar arrays in conjunction with Railcraft. A small solid-fueled boiler can easily outperform them, so once you can build that your solar network will probably be moved to an outpost.