Nuclear Power Plant

The Nuclear Power Plant is the second source of energy on a planet, after the Solar Array. It produces far more power per field than solar does, and it pays for that by burning hydrogen every hour for as long as it stands.

It is the only structure in SFC2 whose output moves with a research level. Energy Tech raises the energy it makes and does nothing at all to the hydrogen it burns, so the same plant quietly gets better every time you finish another level of that tech.

You will find it on the Buildings page, below the mines and the Solar Array.

Requirements

Hydrogen Synthesizer level 5 on the same planet
Energy Tech level 3

Every player starts with Energy Tech 3, so the synthesizer is the only thing that actually gates it. The game knows this and only lists the synthesizer in the unlock requirements.

Planets only. Moons have no mines and no power plants, and neither does a deployed Hephaestus platform. Every level uses one field, the same as any other structure.

Energy produced

Energy per hour = 30 × Level × (1.05 + 0.01 × Energy Tech level)^Level, rounded up.

The bracket is a growth base: 1.05 at Energy Tech 0, 1.08 at Energy Tech 3, 1.15 at Energy Tech 10. It is raised to the power of the plant level, so a level of Energy Tech is worth more the taller your plant is.

Hydrogen burned

Hydrogen per hour = 10 × Level × 1.1^Level, rounded up, then doubled.

Energy Tech does not appear in that formula. The burn depends on the plant level and nothing else. Things worth knowing about it:

It comes off the planet every hour whether you need the energy or not. A plant producing more power than the mines can use still charges full price.
The plant never shuts itself off. If the burn is larger than the Hydrogen Synthesizer makes, the planet drains to zero hydrogen and sits there, and the plant carries on producing full energy. Nothing warns you. The tell is the Hydrogen line in the Production panel turning red.
If your hydrogen store is already full, the overflow was being thrown away anyway, so a plant on a capped planet costs you close to nothing.
Vacation Mode halts all production on the planet, and that includes the burn.

Energy and hydrogen by level

Energy at a few Energy Tech levels, and the hydrogen it costs to run, both per hour at 100% capacity. The Tech columns are Energy Tech levels.

Level	Tech 3	Tech 5	Tech 8	Tech 10	Tech 12	Tech 15	Hydrogen/hr
1	33	33	34	35	36	36	22
2	70	73	77	80	83	87	50
3	114	120	130	137	145	156	80
4	164	176	196	210	225	249	118
5	221	242	277	302	329	374	162
6	286	319	375	417	462	538	214
7	360	410	495	559	631	753	274
8	445	515	639	735	843	1,032	344
9	540	637	812	950	1,110	1,394	426
10	648	779	1,019	1,214	1,443	1,858	520
11	770	942	1,266	1,536	1,856	2,452	628
12	907	1,130	1,561	1,927	2,369	3,210	754
13	1,061	1,347	1,911	2,400	3,003	4,173	898
14	1,234	1,595	2,325	2,972	3,784	5,393	1,064
15	1,428	1,880	2,815	3,662	4,743	6,934	1,254
16	1,645	2,206	3,393	4,492	5,919	8,875	1,472
17	1,888	2,578	4,073	5,489	7,358	11,315	1,720
18	2,158	3,003	4,874	6,683	9,115	14,377	2,002
19	2,460	3,487	5,813	8,113	11,257	18,211	2,326
20	2,797	4,037	6,914	9,820	13,864	23,003	2,692

Energy Tech 5 is the turning point

The energy side grows at (1.05 + 0.01 × Energy Tech) per level. The hydrogen side grows at a flat 1.1 per level. At Energy Tech 5 those two numbers are the same, they cancel out, and everything about the plant changes shape.

Below Energy Tech 5 the hydrogen curve is the steeper one, so every level you add makes the plant worse value. At Energy Tech 5 the two curves match and the plant returns a flat 1.50 energy per hydrogen at every level. Above Energy Tech 5 the energy curve wins and bigger is better.

Energy returned per unit of hydrogen burned:

Level	Tech 3	Tech 5	Tech 8	Tech 10	Tech 12	Tech 15
1	1.50	1.50	1.55	1.59	1.64	1.64
5	1.36	1.49	1.71	1.86	2.03	2.31
10	1.25	1.50	1.96	2.33	2.78	3.57
15	1.14	1.50	2.24	2.92	3.78	5.53
20	1.04	1.50	2.57	3.65	5.15	8.54

The same thing shows up against the Solar Array, level for level and field for field:

At Energy Tech 3, the level you start with, a Solar Array of the same level passes the plant at level 23.
At Energy Tech 4 it takes until level 45.
At Energy Tech 5 solar never catches it again. The plant is exactly 1.5 times a same level Solar Array, forever.
At Energy Tech 10 it is 2.3 times at level 10 and 3.7 times at level 20.
At Energy Tech 14 it is 3.3 times at level 10 and 7.2 times at level 20.

So the short version is: do not build a tall plant on low Energy Tech. Below 5 you are paying more hydrogen per point of energy with every level you add.

Build cost

Ore = 900 × 1.8^{Level - 1}, crystal = 360 × 1.8^{Level - 1}, hydrogen = 180 × 1.8^{Level - 1}.

Level	Ore	Crystal	Hydrogen
1	900	360	180
2	1,620	648	324
3	2,916	1,167	584
4	5,249	2,100	1,050
5	9,448	3,780	1,890
6	17,007	6,803	3,402
7	30,612	12,245	6,123
8	55,100	22,040	11,020
9	99,180	39,672	19,836
10	178,524	71,410	35,705
11	321,343	128,537	64,269
12	578,416	231,367	115,684
13	1,041,149	416,460	208,230
14	1,874,067	749,627	374,814
15	3,373,321	1,349,329	674,665
16	6,071,977	2,428,791	1,214,396
17	10,929,558	4,371,824	2,185,912
18	19,673,205	7,869,282	3,934,641
19	35,411,768	14,164,707	7,082,354
20	63,741,182	25,496,473	12,748,237

That 1.8 multiplier is steeper than the Solar Array's 1.5, and it is the plant's real weakness. Getting a Solar Array to level 20 costs about 499,000 ore and 199,000 crystal all in. Getting a Nuclear Power Plant to level 20 costs about 143 million ore, 57 million crystal and 29 million hydrogen.

Build time is worked out from the ore and crystal cost like every other structure, so the Capitol and the Foundry cut it in the usual way.

What it is actually for

It is not cheap energy. At the Energy Tech levels most players sit at, the Solar Array is far better value in resources for the same amount of power. A level 12 plant at Energy Tech 10 makes 1,927 energy an hour and costs roughly 2.7 million ore-equivalent to get there, counting crystal at 1.5 ore and hydrogen at 2.5 the way the Trade Merchant does. A Solar Array at level 18 makes the same 1,927 and costs about 354,000.

What you are buying is fields. That level 12 plant does the job of a Solar Array 18, so it does it on 12 fields instead of 18. On a planet that has run out of room and is still short on power, that is the only trade available. The higher your Energy Tech, the better the trade gets: at Energy Tech 15 a level 12 plant is worth a Solar Array 22, which is ten fields saved.

Push Energy Tech high enough and it stops being just a field trade. Around Energy Tech 14 to 15 the plant becomes cheaper in raw resources than the equivalent solar at the top end, and by Energy Tech 20 it is cheaper from level 9 up.

Two more things that point the same way:

Cold planets suit it. Hydrogen output rises the further out the slot sits, and satellites pay almost nothing out there, so an outer colony has the hydrogen to feed a plant and no better use for its fields.
Power plant levels cannot be raided off you. Satellites are ships parked on the planet and one attack wipes them out. Anything you have in plant levels survives.

The Capacity setting

Every power plant row has a Capacity dropdown running from 0% to 100% in steps of 5. On the Nuclear Power Plant it scales the energy and the hydrogen burn together: a level 8 plant at 50% makes 483 energy for 172 hydrogen instead of 966 for 344. Changing it is free and takes effect straight away.

Two reasons to use it:

You are producing more energy than the mines can use. Surplus energy does absolutely nothing, so any of it coming out of the plant is hydrogen burned for no reason. Wind the plant back until the Energy panel reads roughly the same on both sides.
You built the plant bigger than the planet can feed. Rather than tear a level off, run it at partial capacity until the synthesizer catches up.

Watching the numbers

The Production panel in the Buildings sidebar splits the hydrogen line into what the synthesizer makes and what the plant takes, and turns the total red if the plant is winning. The Energy panel below it shows what the mines want against what you produce.

The Mines & Production panel on Overview, All Planets has a Nuclear column, and the hydrogen figure in that table is already net of the burn on every planet.

The More Info button on the plant's row lists the next few levels with the energy and the hydrogen side by side, worked out at your current Energy Tech, plus a teardown row for the level below.

Tearing it down

Tearing down a level costs a third of what that level cost to build, gives the field back and removes both the energy and the hydrogen burn. There is no refund. If the only problem is that the plant is drinking too much, the Capacity dropdown does the same job for free.