# How Lighthouses Work 2, Exercise 1: fuel for a coal beacon
# A beacon burns 250 kg of coal an hour. Winters have 180 nights of 14 hours lit,
# summers 185 nights of 8 hours. Find the tonnes burned per year, compare with the
# 400 tons a year of the Isle of May beacon, find the burn rate that 400 tons over
# 365 nights of 12 hours implies, and the heat power and yearly heat energy.
# Assumptions (illustrative): burn rate, night lengths, heat content of coal
KG_PER_HOUR = 250            # burn rate while lit
WINTER_H, SUMMER_H = 14, 8   # hours lit per night
WINTER_N, SUMMER_N = 180, 185
MJ_PER_KG = 24               # assumed heat content of coal

winter_t = KG_PER_HOUR * WINTER_H * WINTER_N / 1000
summer_t = KG_PER_HOUR * SUMMER_H * SUMMER_N / 1000
total = winter_t + summer_t
print(winter_t, summer_t, total)
print(round(total / 400, 2))                       # against the 400 t a year figure
print(round(400 * 1000 / (365 * 12), 1))           # kg/h implied by 400 t over 365 nights of 12 h
print(round(KG_PER_HOUR * MJ_PER_KG / 3600, 2), "MW")
print(round(total * 1000 * MJ_PER_KG / 1000), "GJ per year")

# Output when run:
# 630.0 370.0 1000.0
# 2.5
# 91.3
# 1.67 MW
# 24000 GJ per year
#
# Line 1: 630 t from the winter nights, 370 t from the summer nights, 1000 t a year
# in total. Line 2: that is 2.5 times the 400 tons a year quoted for the Isle of May
# beacon, so 250 kg/h for these night lengths is far too high a rate for it. Line 3:
# 400 tons over 365 nights of 12 hours implies about 91 kg/h on average, although the
# sources also say up to 3 tons could go in a single night, so the burn rate swung
# widely with the weather. Line 4: 250 kg/h of coal at 24 MJ/kg (assumed) is 1.67 MW
# of heat. Line 5: 24000 GJ of heat a year. Nearly all of it warmed the sky; only a
# tiny part left as light, which is why later chapters on lamps and lenses matter.