Now that the calculator can track electricity usage, a "Power" tab should be added to break down how many of each component would be required to power such a factory, for each of the different sorts of power plants.
It would probably be useful if this tab had a box where an arbitrary amount of additional power could be added to the computed amount. It might also be useful to provide an estimate for the power usage of inserters, etc, but such numbers would necessarily be an educated guess at best. These numbers also tend to be quite trivial compared to the rest of the factory, and could probably be easily ignored.
Power estimates also do not include the power requirements of beacons, which can be quite substantial, but naively multiplying the power needs of a single beacon by the number of beacons implied by the calculator's settings would be the wrong approach: Most factory designs will, as a rule, attempt to spread a single beacon's effect to as many entities as possible, rendering the actual number of beacons in play difficult to estimate from the calculator's settings alone. A dedicated "number of beacons" box might be a useful feature.
The number of entities required is entirely trivial to compute for solar power, though the exact arithmetic is slightly annoying to derive. (12500 ticks full bright, 5000 ticks dusk, 2500 ticks full dark, 5000 ticks dawn. Dawn and dusk are a simple linear rise/drop in light levels. The rest is computing how much excess solar capacity is required during the day, and the quantity of accumulator capacity that is needed to store it for use at night. These numbers are a flat multiple of the required power level, and it may be simplest to hard-code that multiple.)
These numbers are even more trivial for steam power (at least ideally; the actual fluid mechanics of the game might introduce some loss), and it would be useful to provide a number for the rate of fuel consumption, alongside an option for selecting the user's preferred fuel type. (This same option could be used to calculate the fuel needs of stone and steel furnaces.)
Nuclear power is only slightly more difficult, given the need to account for a reactor's neighbor bonus. Mathematically, it seems reasonable to simply provide numbers for a 2xN reactor that satisfies the required power needs. (And even more than steam power, the game's fluid mechanics introduce an incalculable source of loss, which it is easiest to simply ignore.)
Nuclear power could be made more complicated by attempting to provide numbers for a fuel-controlled/steam-buffered nuclear reactor, but this sort of trickery is probably outside the scope of this calculator, and providing the simple numbers needed to satisfy demand is probably adequate.