Electric charge, also called electricity or energy, is a resource that is needed to operate various parts in the game. It is critical for unmanned spacecraft, which are generally uncontrollable without any electric charge. However, manned spacecraft usually also need some electricity, mainly for reaction wheels.
|Rocket engines||LV-T30 Liquid Fuel Engine||7.0 ⚡/s||1.691 /⚡|
|LV-T45 Liquid Fuel Engine||6.0 ⚡/s||1.835 /⚡|
|Toroidal Aerospike Rocket||5.0 ⚡/s||1.828 /⚡|
|LV-N Atomic Rocket Motor||5.0 ⚡/s||0.3055 /⚡|
|Rockomax "Poodle" Liquid Engine||8.0 ⚡/s||1.436 /⚡|
|Rockomax "Skipper" Liquid Engine||10.0 ⚡/s||3.782 /⚡|
|Rockomax "Mainsail" Liquid Engine||12.0 ⚡/s||7.715 /⚡|
|Kerbodyne KR-2L Advanced Engine||12.0 ⚡/s||11.176 /⚡|
|S3 KS-25x4 Engine Cluster||12.0 ⚡/s||15.102 /⚡|
|Jet engines||Basic Jet Engine||4.0 ⚡/s||0.0239 /⚡|
|TurboJet Engine||5.0 ⚡/s||0.0716 /⚡|
Many rocket and jet engines have alternators installed which produce electricity. The exact output varies based on throttle level, and engines not running will not produce any electricity. The adjacent table shows the engines which provide electricity, their production at full throttle and fuel usage in vacuum. Jet engines only generate electricity when supplied with intake air.
Solar panels are a lightweight source of electrical energy. However, they need direct sunlight to work, so they won't produce electricity on the night side of a planet, in the shadow of a spacecraft or during eclipses of the sun, although the craft is illuminated while in an eclipse. Due to this unreliability, it is recommended to have some energy storage as a buffer when supplying a craft solely with solar panels.
All panels except for the OX-STAT Photovoltaic Panels and the OX-STAT-XL Photovoltaic Panels need to be extended using the right-click menu (Extend Panels option, and for the retraction choose the Retract Panels) or action groups (using the Toggle Panels command, the player can extend and retract several solar panels with a single keystroke) before they will generate energy. Unpacked solar panels are very fragile and will easily break off when colliding or experiencing atmospheric drag, so they must be retracted during liftoff, aerobraking, or atmospheric re-entry. Note that, as of version 1.0, the unshielded OX-4 series solar panels cannot be retracted once deployed, so they are not suited for aerobraking missions.
The energy output of solar panels depends on their orientation to Kerbol. Except for the surface-mounted OX-STAT Photovoltaic Panels, all panels will automatically pivot around one axis to face the sun as much as possible. Reorienting a vessel to manually aim the panels at the sun and eliminate shadows cast on them will also improve power generation.
Generated power will also decrease with increasing distance from Kerbol, following the real-life inverse-square law:
|5,263,138,304||6.68x||Moho's semi-major axis|
|9,832,684,544||1.91x||Eve's semi-major axis|
|20,726,155,264||0.431x||Duna's semi-major axis|
|40,839,348,203||0.111x||Dres's semi-major axis|
|68,773,560,320||0.0391x||Jool's semi-major axis|
|90,118,820,000||0.0228x||Eeloo's semi-major axis|
|135,998,402,560||0.01x||Over 20 Gm beyond Eeloo's apoapsis.|
|430,064,710,234||0.001x||Very very far away.|
Radioisotope thermoelectric generator
The PB-NUK Radioisotope Thermoelectric Generator is a constant and reliable source of energy which doesn't require any sunlight and is much more resistant to atmospheric drag than solar arrays. Unfortunately it has a very impractical shape and is significantly heavier than solar panels with a comparable output of electricity.
The fuel cell, like the Fuel Cell and Fuel Cell Array, converts liquid fuel and oxidizer directly into electric charge, similarly to generators. As now the electricity production is the only purpose: they consume 0.0025 units of fuel for each electric charge unit (0,0025 /⚡), means they produce 400 units of electricity from a single unit of fuel.
TT18-A Launch Stability Enhancers provide attached craft with 1.0 charge units per second per clamp and thus prevent running out of energy on the launch pad.
Storing electric charge helps a craft survive longer without energy supply, deal with peak loads (like transmitting science results) or bridge time gaps when solar panels aren't usable. The following parts store energy:
- Unmanned command modules such as the Stayputnik Mk. 1 and Probodobodyne RoveMate offer very low capacities and constantly consume energy.
- Manned command modules offer significant storage capacities and do not consume energy (unless when reaction wheels or SAS are used) but are relatively large and heavy and put Kerbals at risk.
- Batteries are small and offer high storage capacities at the same time. All have the same capacity/mass ratio of 50 g/⚡ or 20 ⚡/kg.
- Fuel Cells also store a modest amount of electric charge in addition to their fuel to electricity conversion function.
All energy storage modules on a craft are fully loaded at launch by default.
Consumption and requisition
- Unmanned command modules constantly use 1.7 or 3.0 units of electric charge per minute and can only store enough internally for a few minutes of operation.
- Reaction wheels, both the stand-alone parts and as part of command capsules, consume energy while operating.
- In science and career modes, antennae require large amounts of energy for a short time when they transmit science to the space center.
- Electric lights and environmental sensors use small quantities of electricity when switched on.
- Ion engines and rover wheels require particularly large amounts of electricity to operate.
If an unmanned craft has no electric charge available, it becomes entirely nonfunctional and no parts may be operated (notably, this includes motorized solar panels which might have allowed it to recover). However, it can still be saved if another craft docks to it and supplies it with electricity (using either a docking port or an Advanced Grabbing Unit) or if a kerbonaut on EVA manually extends the solar panels. This is why it is good design practice to always include at least one surface mount solar panel or an RTG.