its a modifier against the total of all base production

Total MP= {Initial + N Factores (where N=number of factories)} x P where P = total modifier (1.2, 1.5, etc etc)

Remember not to multiply by 0.10, but by 1.10 (10% increase); power plants are still best used on heavy production worlds.  Planets with onyl 1-2 factories dont really get the cost/benefit to justify them.  But since the percent modifier grows as the tech grows (fusion is 10%, antimatter and quantum plants are even higher) coupled with passive bonuses from techs and anomalies, it can get pretty strong,.

each power plant modifies all production produced on that planet that it is placed.

There are TWO kinds of bonuses, Civilization Wide, and Planetary Only.  However, in the Details Screen they get added together (so you can't tell what is from where)

You can see your PASSIVE bonuses by going to the Stats screen.

For example, my custom race with its starting techs started with a 10% passive social production bonus that will be applied to ALL worlds.  My HW, since it has a Moon, gains another 10% PLANETATY only bonus, giving it a starting 20% bonus.  However, Planet II does not have a Moon so it only has a 10% bonus.

Some improvements give a Civ Wide, but most a Planet Only bonus.  Power Plants are a Per Planet bonus.

You replied while I was typing my clarification...

But yeah, I think I'm getting it.

So if I have a choice between a power plant at "10%" of planetary production, or just adding another factory, I'm "probably" better off just building another factory.  Until I reach 10 factories or have some other equivalent bonus (bonus manufacturing tiles, race bonus, etc).

In other words, for the power plant to become beneficial and surpass the "break even point," (the MP value of a factory), I have to be sure that the power plant will add more than 6 MPs (given this discussion, "regular" factories).

I will check the stats screen and see if my hunch is correct.

Which is a whopping 1 more than adding another factory.

And face it, going from 81 to 82 is really no big deal. Less than 1% in the overall scheme of things.

So how does that make it worth it to any extent, unless the Power Plant is the same or cheaper to build than a single factory?

Slightly OT here, but the Korath and to a lesser extent, the Dregin have tons of these % manufacturing buildings which aren't upgrades on each other so can be placed individually.  It gets to the point that I'd place about 4 or 5 Slave Canyons on a planet and then the 6 or so % buildings the Korath get.  Maintenance is lower on almost all fronts too.

Okay, couple things.

Silver, manufacturing capital/power plants do not apply to mining.  However, moons do-except when the aforementioned structures are present.  Additionally, economic starbases apply, as well as (obviously enough) racial passives.  I've tested this quite thoroughly and it's the same in DA and TA.  Unless my version is bugado, anyway.

Also, Loupdinour makes an extremely valid point regarding TA-the Drengin and Korath are production monsters.

More ontopic:

First level power plants aren't worthwhile.  From a build cost and research cost standpoint, second level power plants might be-250 industry to produce versus 400 for third level (quantum), and 20% as compared to 30% increase in production.  The kicker here is the fact that quantum is 5000 RP/TP by itself, whereas the first two levels of power plants total 2000.

For a quantum with normal factories, you gain a benefit by using a power plant when you have one or more factories (16+6=22, 22>20).  For a quantum with industrial sectors, you gain a benefit by using a power plant when you have three or more industrial sectors (16+48=64, 64>54).  For an antimatter (second level) with normal factories, you gain a benefit when you have three or more factories (two doesn't quite cut it-16+12=28, 28<30, but 16+18=34, 34>30).  For an antimatter with industrial sectors, you gain a benefit when you have four industrial sectors or more (16+64=80, 80=80).

As pointed out by CaptainYar (and potentially others), there is also the issue of maintenance.  Additionally, by the time you reach industrial sectors, which cost 400 industry a piece to produce, 450 for a quantum power plant is quite valuable.

With all of this said.  While it is not advisable to build the first level power plant, and circumstances can decide the usage of the second and third levels for you, it is worth noting that the manufacturing capital, even though it has been reduced to 33% from its former 100% (now 50% in DL, but I remember those days...), it is still useful, both late game to turn an otherwise borderline world into a reliable source of ships, and early game for either the homeworld or something large nearby to increase colony ship build quality or capacity.

As an addendum, a long long time ago in a galaxy far far away, if you guys can remember back that far, power plants gave 25%, 50%, and 100% with the varying levels.  At that point in time, they were most definitely useful, but also most definitely overpowered as well.

Wow, it seems I opened a can of fireworks here!  This is wonderful; having an active discussion on this matter is a great thing.

I need to do some more playtesting, but even so, having an "actual number" on the colony "Summary  Screen" would help, EVEN IF that number is partially or wholly a product of various ability levels, race benefits, government style, good vs. evil, etc.

Just seeing "+10%" doesn't help me much.  Unless, that is, I take the time to go find the number in another status/report screen (which I haven't yet done, but I will do later this week; just didn't have time yesterday after my playtime was up).

I'm not contesting the notion that power plants might not be beneficial early on.  In fact, that might make sense on a deep-space colony.  Nor am I opposed to the idea that a power plant (or any other improvement tile or asset) might have unequal values from colony-to-colony or from one race to another.

I just want it easy to see the actual, discrete number for my race's colonies in the game that I am currently playing.  Sure, put up the percentage; that helps in a macro-economic way.  But by also easily seeing that discrete number, it eases the burden on me, the game-player, better empowering me to make better decisions for that specific game.

Thanks again, everybody.  Additional observations in this area would be very much welcome.

And also the running costs of said buildings.  While the Drath do have a 12 base factory it's maintenance is considerably higher than the slave canyon.  This is offset though by the drath having access to the stock market, while the dregin/korath are playing in the mud still in comparison.

BTW whispermill, you may want to edit your post, the background around the text is white.

yup I hate that forum HTML editing instead of other forums "simple tags" which are easier to read and edit

fortunately I managed to "purify" the look of it by cut/paste to a standard notepad (or else there was like 30 background tags to delete manually )

Anyway back on subject, the upkeep is a minor thing as far as I'm concerned, it's an advantage early on only...

Though the realy winning point for drengin/korath factories is their really low production cost ... 120 for a slave canyon Vs 400 for an industrial sector

that means a slave canyon is faster and cheaper to build than having the super hive ability with regular industrial sectors...

Must not forget the influence malus though -3% multiplied by the number of factories becomes quite big for production worlds

(one may want to offset this by building embassies for drengin or the totally overkill "Dark Influence" as the korath)