How accurate are in-game solar panels?

[flightmaster]

I was just wondering how similar to real life the in-game solar panels are in terms of power generation? E.g. the ISS has quite a few solar panels, however, a sngle Gigantic XL Solar Panel in-game provides more than enough power for any reasonable sized ship/station/vehicle. Is it just a question of scale or are the in-game panels very overpowered?

[SalmonellaDingDong]

Nothing in the game really uses power besides probes and drills/kethane scanning. The ISS has lots of systems to power.

[flightmaster]

Ah of course, I think my question still stands though, do they generate similar amounts of power-per-sq. ft?

[M5000]

Ah of course, I think my question still stands though, do they generate similar amounts of power-per-sq. ft?

I'm not 100% sure, but having had my share of education in electronics, I would say that they are not accurate to reality, but are not too far off.

They are slightly overpowered, but not much, I don't think. This is all speculation, however.

[TooManyErrors]

Its less that the solar panels are overpowered and more that KSP doesn't have that many parts that suck power constantly.

[Temstar]

We don't really know what units the energy in KSP are measured in so it's impossible to compare. I've heard of a humorous theory that the "100Z/400Z/500Z" part of the name of the batteries are not commercial part names but actually indicate their capacity in the Kerbal energy unit of "Zap". One zap being equal to the amount of electrical power required to singe an adult Kerbal.

So yes, someone need to work out 1zap = ?kWh

[TwoHedWlf]

Can't really say if they're accurate or not without any real shared units. At the moment the power draw and power generation is pretty much made up. Fudge things around a bit until it works ok and then move on. Yes, I'd say the panels draw significantly more than is plausible, but it's also true there isn't much demand for power right now.

[flightmaster]

We don't really know what units the energy in KSP are measured in so it's impossible to compare. I've heard of a humorous theory that the "100Z/400Z/500Z" part of the name of the batteries are not commercial part names but actually indicate their capacity in the Kerbal energy unit of "Zap". One zap being equal to the amount of electrical power required to singe an adult Kerbal.

So yes, someone need to work out 1zap = ?kWh

Hmm very good point, I didn't realise there wasn't a unit for power. I don't think it'd be too much effort for them to implement, they'd just need to add units to the current rates given for each part. It's not really necessary though.

[Eric S]

Yes, they could. For that matter, we could probably approximate what one unit works out to by examining the work it does, but we'd probably get a lot of contradictory answers that way. Even using the same method, I'm sure that someone would argue over what ion engine we should use as the basis for the comparison, for example.

However, I think the devs want to avoid that, as it would allow them to get cornered by realism-fact-checkers far too easy.

[UmbralRaptor]

I was just wondering how similar to real life the in-game solar panels are in terms of power generation?

Not realistic at all. In particular, KSP solar panels don't follow the inverse square law.

For that matter, we could probably approximate what one unit works out to by examining the work it does, but we'd probably get a lot of contradictory answers that way.

The answers already are. Try an estimate based on how how much the stock ion engine uses. (14.5 units would have to be >20.6 MW) This would imply that the stock lights are pulling at least 28-57 kW o_O

[Temstar]

For that matter, we could probably approximate what one unit works out to by examining the work it does, but we'd probably get a lot of contradictory answers that way. Even using the same method, I'm sure that someone would argue over what ion engine we should use as the basis for the comparison, for example.

In the name of science let's do it!

The KSP's PB-Ion Electric Propulsion System gives 4200s of Isp and consumes (correct me if wrong) 14.442E/s (or Z/s if you like) for 500N of thrust.

NEXT ion thruster has 4190s Isp, drawing 6.9kW for 0.236N of thrust.

In other words, if we tape 2128 NEXT thrusters together we get about the same thrust as one Kerbal B-Ion engine. All that NEXT will draw 14.683 megawatt of power.

Assuming NEXT and PB-Ion are roughly equal in efficiency (clearly a shaky assumption, given the incredible TWR of a Kerbal ion engine) we know 14.442E = 14.683MW, or E = 1.02MW.

What does this mean?

• a Giganator panel generates a maximum of more than 18MW of electricity, that's 64,800MWh per hour! The entire US generates only a bit over 1000GW, so about 60 Giganators at full power can power the entire US.
  
• a Z-500 battery holds about 34.62MWh of energy, or 124,632MJ, or about 30 ton of TNT in a 50kg package - an energy density impossible to achieve without going nuclear
  

Conclusion: KSP ion engine is OP

[ROFLCopter64bit]

• a Giganator panel generates a maximum of more than 18MW of electricity, that's 64,800MWh per hour! The entire US generates only a bit over 1000GW, so about 60 Giganators at full power can power the entire US.
  
• a Z-500 battery holds about 34.62MWh of energy, or 124,632MJ, or about 30 ton of TNT in a 50kg package - an energy density impossible to achieve without going nuclear
  

Conclusion: KSP ion engine is OP

Actual Conclusion: Pretty much everything in KSP is OP

[NannerManCan]

How big are the Giganator solar panels if they were in real life?

[rkman]

Not realistic at all. In particular, KSP solar panels don't follow the inverse square law.

The answers already are. Try an estimate based on how how much the stock ion engine uses. (14.5 units would have to be >20.6 MW) This would imply that the stock lights are pulling at least 28-57 kW o_O

Real world ion engines draw power in the order of kilo Watts (http://en.wikipedia.org/wiki/Ion_thruster), not Mega Watts. In comparison the lights would draw 100's of Watts to maybe a few kW.

18MW of electricity, that's 64,800MWh per hour!

It doesn't work like that. 18MW is not 18MW per second, it's just 18MW. 18MW for an hour is 18MWh.

[Flowz0r]

You can put a single tiny solar panel on a ship with 4 lights on it, and power them indefinitely while they light up the area around the ship brighter than the sun does.

Make of that what you will.

[UmbralRaptor]

Actual Conclusion: Pretty much everything in KSP is OP

Chemical engines and tankage are not. Quite the opposite, really.

[The Space]

I don't think any of the solar panels are "overpowered" because once we get parts like resource processing units and such we might actually need all the power solar panels can generate.

[azazel1024]

Yes/No.

In part Yes, because hey, why not.

In part no, because at least storage energy density to energy generation for the RTG, solar panels and batteries is not remotely realistic.

If you assume a .05mt battery, like one of the small guys, that works out to 50kg. If we assume 50% of that is casing, circuitry, etc and the other 50% is actual battery, you come out to around 7kw/hr of energy storage. Based on a 4x1m solar panel, roughly the size of one of the small jobs, running at 35% efficiency (roughly what you'll find in a crystaline silicone solar cell) in orbit around Earth, you'd get roughly 1.2kw of generating power. That would take roughly 5hrs or so to charge the battery.

In game time it takes, what, about 60 seconds to recharge the small size battery with the small size deployable solar cell?

Two things I'd like to see occur in the game is both the inverse square law being applied to solar power generation at some point, so the further you were from the star, the lower the power generation. The next is, I'd like to see battery energy storage jump dramatically. At least 10x higher than what it is now. Otherwise batteries are ridiculously under rated.

The solar panels themselves, just looking at how much power a light uses, actually don't appear terribly far off from what they should be. Same with rover wheels. Ion engine...okay, that is badly off.

Batteries, way under rated. If you figure even a halogen light for the lights in the game, one of those big floods is probably roughly a 200-300w flood light (the brighter, more concentrated floods are probably more like 500-1000w floods). Supposing those batteries were anything like real world batteries, that should take around 20-30hrs for a single flood light to burn through the entire charge of one of the smallest batteries. Right now it takes, what? About an hour or two to do that?

Edited April 23, 2013 by azazel1024

[stibbons]

[*]a Z-500 battery holds about 34.62MWh of energy, or 124,632MJ, or about 30 ton of TNT in a 50kg package - an energy density impossible to achieve without going nuclear

I went the other way, looking at the power to weight ratio of the Z-100 and Z-400 batteries and comparing that to the nickel-hydrogen batteries on the ISS. That comes out to 1E = 11W. Then I got lost trying to convert the E/s rating of KSP's solar panels to a wattage. But they still seem overpowered - a single OX-STAT panel can recharge a Z-100 in just over two minutes.

[WhiteWeasel]

Get MatthewPatrick13!

Edited April 24, 2013 by WhiteWeasel

[rkman]

I did a conversion from KSP units to Watts and Watt-hours when i proposed that KSP should adopt real-world units for electricity just as it uses real world units for distance, time, mass etc.

- KSP units

OX4 solar panel (production) ElectricCharge 2/sec

RTG (production) ElectricCharge 60/min

ion engine (consumption) ElectricCharge 12/sec

illuminator MK1 spotlight (consumption) ElectricCharge 2.4/min

Z500 battery (storage) ElectricCharge 500

Normalize all time units to hours: if VAB info shows per-second multiply by 3600, if info shows per-minute multiply by 60.

Remove the time unit from parts that consume or produce electric power, apply time unit (hours) to batteries (storage).

Use "kilo" where applicable:

OX4 solar panel (production) 7.2 kiloWatt

RTG (production) 3.6 kiloWatt

ion engine (consumption) 43.2 kiloWatt (*

Illuminator MK1 spotlight (consumption) 144 Watt

Z500 battery (storage) 500Watt-hour (0.5 kiloWatt-hour)

On the face of it these numbers are fairly realistic, until we look at how solar panel energy production compares to panel size.

7 kiloWatt is rather a lot for a panel measuring ~2m by ~0.4m (less than 1 meter square), even for 'NASA quality' panels. The sun delivers only a little over 1kW per square meter on Earth. http://earthobservatory.nasa.gov/Features/SORCE/

*) The numbers for the ion engine are a bit off. The consumption number shown in the VAB is not units/second. Calculating the actual electric charge consumption of the ion engine is rather complicated but the result is close to the numbers i ended up with here.

[azazel1024]

And look at the battery.

Z-500 is .05. I assume that is .05 metric tons, or 50kg. If you assume half is casing, support and circuitry (charge regulation), and that is excessive, realistic is maybe 30% casing and other at most...you get 25kg of battery. That is 25wh per kg.

Energy density of lead acid batteries are 30-40wh/kg, so even assume these are lead acid batteries, which would be stupid to use these days, you come in at around 60-80% of the real world energy density for KSP batteries.

Now look at ni-cad batteries. Probably the "lowest tech" rechargable batteries you'd ever consider for space flight. You have 40-60wh/kg. Now the KSP batteries have between 40-60% of real world energy density.

Now lets look at NiMh batteries, 60-120wh/kg. Now we are at 20-40% of real world energy density (NiMh would not be an ideal type to use unless there is an over abundance of generating capacity, but excessive periods of no generating capacity inbetween as NiMh have a charge/discharge efficiency of 66%, which means 33% of the energy put in to the batteries will be wasted as heat instead of extractable as electricity. NiMh have a lower efficiency than most "main stream" rechargable batteries. NiCad run 70-90% charge/discharge efficiency, lead acid are 50-92% and LiIon are 80-90%).

Lithium Ion batteries run 100-265wh/kg. KSP batteries by comparison run 9-25% as efficient.

So...please, please, please, please, at the very least increase the battery storage density by double. Preferably 3-4x higher. Or maybe in the future with career mode, offer different "technologies" of batteries, with higher storage density ones costing more and/or unlockable later down the tech tree or something. However, please make higher storage density batteries a possibility. I'd start at at least 50% higher and then offer at least one set of batteries with double the storage density of the base batteries.

That would at least get batteries in to bunting range of real world battery storage densities.

PS as a comparison my car battery weighs about 30lbs total, or a bit over 13kg and has a 90 minute reserve capacity. That is 20 amps for 90 minutes from 13.2v down to 11.5v. Roughly 380wh of capacity at a high discharge rate. At something lower, like maybe 2amps, the overall capacity is probably closer to 500wh. Even using the 380wh, that is 29wh/kg including casing, terminals, etc. KSP batteries, 10wh/kg including casing.

Edited April 24, 2013 by azazel1024

[rkman]

And look at the battery.

Z-500 is .05. I assume that is .05 metric tons, or 50kg. If you assume half is casing, support and circuitry (charge regulation), and that is excessive, realistic is maybe 30% casing and other at most...you get 25kg of battery. That is 25wh per kg.

True, but that's off by only a factor 2, arguably well within the KSP fudge factor.

Solar panel electricity production otoh is off by more than a factor 10.

[azazel1024]

Well, it depends on how you are looking at it, on the low end it is around a factor of two. On the high end it is off by a factor of about 10 (for lithium Ion batteries).

I guess my biggest complaint with the batteries is that has a large negative impact a lot of times either with probes running out of juice, rovers not having enough power driving in shadow or bases running dry through a long night.

I certainly wouldn't mind seeing solar panels get scaled back by a factor of 2 or 3, but I'd like to see batteries at least double or better yet quadruple in storage density.

I'd also love to see rovers be able to be throttleable as well, but that is sort of a different story.

[That guy who builds stuff]

Try an estimate based on how how much the stock ion engine uses.

Wouldn't work. We have no way of knowing how much power in the ion engine comes from burning the fuel.