Some orders of magnitudes to check engine internals and try to display realistic units.

POWER
=====
Power unit is 1kW
=> Coal unit = 100 kg   (coal power plant and coal_make_power)

Discussion power:
_________________

some RL indicators picked in wikipedia and other sites in 2007:
 1 ton equivalent oil
    = 40 GJ
    = 1.5 tons of coal
    = gives 11 MW.h of thermic power
    = gives less than 5 MW.h of electic power in thermic power plant
    = production of 1 ton biofuel by 1 hectare (4t of biomass)
        sometimes 2 crops/year.
         (variable by a factor 0.5 to 2) 
         (need to add work and water and fertilizer ...)
    = sun at midday on 1 hectare during one hour 
         (1000 W/m2, average on earth= 350 W/m2)
    = power produced by a 10 ha solarplant.(10% efficiency)

Big offshore windmill = 5 MW
Big solar plant = 350 MW
Big coal powerplant = 700 MW

100 MW = 50 000 citizens

build cost:
-----------
 clean coal power station:  1 MW = 1 M€  +need to be fed by tons of coal/day
 solar plant / bio / wind:  1 MW = 2 M€

prices:
-------
 oil 350€/ton equivalent oil
 coal 50~100€/ton equivalent oil
 bio  50~500€/ton equivalent oil
 sun/wind/river  0€

=> in NG
--------
 Windmill and solar power prices are rather realistic
 but coal_power plants are far too much cheap 
 even if we consider 10% efficiency for windmill and sunplant, there is still
 a factor 3 in favor of coal plants. (moreover they don't pay the coal in NG
 except when it is imported.
 The only counter-part is the coal reserve are finite, even if sometimes they
 are huge.

=> idea:
--------
Like windmill add high tech thermic power plant and change as little as possible:
 - price *=  1 + 2 * (tech - coalpower_tech)   (doesn't break too much)
 - pollution -= some % tech
 - check box to use food or coal

Production of one farm of tech T gives enough biomass to produce the same amount
of power as a solar plant of the same tech.


ORE/STEEL
=========
RL:
---
average earth crust is 4% iron
rich iron ore = 50% iron

NG:
--
heavy industry : 16 ore -> 1 steel
this is ok considering that ore is average earth crust (we can dig everywhere)

need to find energy needed for producing steel to have steel weight unit in NG,
then ore weight unit :)

MAX_COAL_ON_TRACK 64    unit = 100 kg
MAX_ORE_ON_TRACK 4096
MAX_STEEL_ON_TRACK 128

MAX_COAL_ON_ROAD (MAX_COAL_ON_TRACK * 8) = 512*100 = 51.2 tons
MAX_ORE_ON_ROAD (MAX_ORE_ON_TRACK * 4) = 16384 ore_unit
MAX_STEEL_ON_ROAD (MAX_STEEL_ON_TRACK * 4) = 512 steel_unit

MAX_XXX_ON_RAIL (MAX_XXXX_ON_ROAD * same_coeff_as_road_vs_track)
