Efficiency Modules vs More Solar

[MadZuri]

A question was posed to me recently. Is is cheaper to use efficiency modules or just build more solar panels? Well, I aim to find out.
I'll start out with just an electric furnace. I'm doing the math as I go, didn't prepare anything so let's see how this goes.
An electric furnace uses 180kW, and we'll assume it is running full blast. We aren't interested in the initial 20% of the power it will use, there is no escaping that. It is the remaining 80% power that would either be reduced by the modules or supplied by solar that interests us.

180kW * 0.8 = 144kW
since solar produces an average 42kW that is 3.43 solar panels, and 2.88 accumulators.
For solar it is 137.2 iron and 94.3 copper
For accumulators it is 49 iron, 14.4 copper, and 432 petroleum gas.
Total cost: 181.6 iron, 108.7 copper, 432 gas.

Now for the 2 level 2 modules:
Total cost: 385 Iron, 710 copper, 495 petroleum gas, 140 coal.

So, you can save a lot of copper and half the iron by just building more solar panels. However, that brings up another cost that is hard to compare to material costs: pollution. That coal, iron, and tons of copper will permanently reduce pollution production.

For mining drills, since the power usage is exactly half, the solar costs will also be halved, so:
90.8 iron, 54.4 copper, 216 gas.
the 3 level 1 modules would need:
45 iron, 97.5 copper, 90 gas, 30 coal.

So for mining drills, efficiency wins out over solar. That was fun, I like math.

[DaveMcW]

It seems to me that you proved module 1's win, and module 2's lose.

[sillyfly]

One more point to consider, which is also hard to quantify, is space - with modules you don't need any more space than the machines already take. For more solar panels you need more space, which may be problematic or a non-issue, depending on your map.

[Xuhybrid]

I wouldn't bother with Efficiency 2, most machinery ends up having 3 slots and 60% is still pretty good. Perhaps rerun this with 2 x Efficiency 1
You could get really deep and compare Assembling machine 1, 2 and 3 as well as Pumpjacks/Refineries