Lightning rod

Lightning rod

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Recipe
5 + 12 + 8 + 4 → 1
Total raw
8 + 6 + 8 + 4
Map color
Health	100 130 160 190 250
Resistances	Electric: 0/100% Fire: 0/90%
Stack size	50
Rocket capacity	50
Range	15 19.5 24 28.5 37.5 + Lightning reach
Efficiency	20% 26% 32% 38% 50%
Dimensions	1×1
Drain	150 MW (electric)
Energy capacity	500.0 MJ (electric)
Mining time	0.1
Buildable only on
Crafted only on
Prototype type	lightning-attractor
Internal name	lightning-rod
Required technologies
Produced by
Consumed by

Object description

Space Age expansion exclusive feature.

The lightning rod is a building from Fulgora that protects an area from getting struck by lightning from the nightly storms. When struck, they generate power for a limited time. The peak power production is limited only by the demands of the connected electric system, but the internal storage is subject to a 150 MW drain in addition to the load from the electric system. It is unlocked by researching the Planet discovery Fulgora technology.

The lightning rod cannot be crafted on any planet other than Fulgora, as other planets lack the same strong magnetic field.

Lightning and Coverage

Each lightning strike is 1 GJ and, when averaged over the night, strike approximately once every 10 seconds per chunk. This means the power-density of lightning is ~100 MW per chunk at night when averaged over the night but this can only be used to recharge lightning rods. The net efficiency of the lightning rods will significantly lower the amount that can be converted to usable energy (see net efficiency below).

A large island on Fulgora can be ~25 chunks and even with only 10% net efficiency the lightning rods can provide 250 MW averaged over the night. This is plenty for early-Fulgora but modules and beacons can quickly exceed this amount requiring higher quality lightning rods or lightning collectors.

Coverage and Tiling

Lightning rods can protect further than their listed radius due to their ability to bridge small gaps between the default coverage areas. As quality increases this becomes less important but for normal and uncommon quality this can result in a substantial boost to coverage per lightning rod.

An equilateral triangular tiling is most efficient as this can be placed in a hexagonal pattern that maximizes sphere packing and leverages the gap-bridging mechanism. For all lightning rods a triangle of base: 2 x Range and height: 0.87 x Range will work and provide plenty of flexibility to move the vertices to accommodate interference from buildings. If flexibility is not needed, one can stretch out tiling up to the maximums described below.

Quality	Triangle	Square
Normal	Base: 41 Height: 34	Side: 34
Uncommon	Base: 51 Height: 43	Side: 40
Rare	Base: 59 Height: 50	Side: 47
Epic	Base: 65 Height: 56	Side: 54
Legendary	Base: 81 Height: 70	Side: 66

However islands on Fulgora are relatively small so one will still be required to fill in gaps on the edges in an ad-hoc manner. Effective tiling means that lightning rods will, on average, cover at least the circular coverage implied by their range (3.14 x Range²) even accounting for the edges of islands. This makes circular coverage a useful estimator for max power.

To align with a 50x50 grid of roboports one can tile rare lightning rods in an isosceles triangle pattern or epic lightning rods in a square pattern.

Building Protection

The center of a building must be within the blue highlighted area to guarantee protection. Hovering over any lightning rod will cause unprotected buildings to display a red border around them. This can be useful when buildings lack power as the plug warning icon will override the thundercloud warning icon.

Net Efficiency

Lightning rods are ultimately energy storage devices which are recharged with lightning strikes and have unlimited power output potential. However the 150MW drain-to-ground means that they are very lossy storage devices which will rapidly dissipate their stored energy even if unconnected. The actual usable energy we get out of a lightning rod per lightning strike is thus less than strike energy times efficiency. This section provides an overview of this relationship.

Definition of Net Efficiency

Energy stored in a lightning rod will inevitably go to one of two sources: base power or drain. With P representing power and d representing the drain-to-ground, it can be readily seen that the fraction of total energy that goes to each is simply P/(P+d) or d/(P+d) respectively. To see this note that energy-to-source = power-to-source x time and taking the ratio of energy-to-source over total energy will lead to cancelation leaving one with the desired result.

This means we can define a "net efficiency" (which depends on power) of the lightning rod that takes into account the drain by simply multiplying efficiency by the fraction of power we can actually use:

Net Efficiency(power) = Efficiency x power/(drain + power)

If we have N active lightning rods on average then for the purposes of net efficiency analysis, this is effectively 1 big lightning rod with 10 drain sources. Thus for N lightning rods we have a net efficiency of:

Net Efficiency(power, N) = Efficiency x power / (drain x N + power)

Implications

Adding coverage area increases the maximum sustainable net efficiency achievable by increasing the highest sustainable base demand that can be met. For an isolated large island of ~25 chunks, this implies the following table. The table below assumes 25 chunks must be covered and coverage per rod equivalent to 3.14 x Range². Also even at very high power consumption the stochastic nature of lightning strikes and large area means that multiple lightning rods will be powered simultaneously. The number of powered rods expected at any one time is shown in the table.

Quality	Coverage (Chunks)	Rods per Large Island	Simultaneous Powered Rods	Night-time Power (MW)	Net Efficiency Achieved
Normal	0.7	44	2	300	10%
Uncommon	1.2	26	2	490	16%
Rare	1.8	17	2.5	580	19%
Epic	2.5	13	3	770	24%
Legendary	4.3	8	4	1100	32%

Total continuous power achievable over the entire day requires halving the above. In general, larger tilings of connected lightning rods will be able to achieve higher net efficiencies. However, even arrays ten times larger than the table above will have net efficiencies which are still 90%-95% of listed efficiency.

In practice, net efficiency will be significantly lower than listed efficiency due to the drain wasting large amounts of energy. One should note that increased quality leads to rods staying powered longer due to higher efficiency and coverage area. This usually leads to more rods being powered simultaneously even at high power demand levels. This ironically reduces the benefit of upgrading quality somewhat, though rarely enough to fully negate the benefit. One should also note that the variance for number of powered rods is quite high for low quality rods due to the chance of lightning strikes being clustered in time but not in area. Higher quality rods reduce this variance by making larger areas only power single rods.

History

• 2.0.7:
  • Introduced in Space Age expansion.

See also

• Fulgora
• Lightning collector
• Electric system