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samkent
2009-Mar-11, 06:03 PM
http://www.space.com/missionlaunches/090311-sts119-solarwings.html



The new solar panels are expected to boost the station's power-generating capability by 25 percent, to a total of about 120 kilowatts of generating capacity, or enough to power about 55 average American houses, Hardison said.


55 American homes?? Where does all this power go?

That's
1800 Laptops or
240 Plasma tvs

It sounds like someone doesnít turn the lights out when they leave the room.

nauthiz
2009-Mar-11, 06:30 PM
According to this DoE FAQ (http://tonto.eia.doe.gov/ask/electricity_faqs.asp), average monthly power consumption in American residences is 936 kilowatt-hours. So 55 sounds about right. It's more like 90 homes if you divide that by the number of hours in a month, but I assume that the ISS is like houses in that the energy consumption varies throughout a day, and presumably they were talking about the production capacity needed to cover peak usage times.

I'm guessing that the real usage of a particular home can vary quite a bit depending on whether they have electric stoves, hot water heaters, air conditioning, etc. I use a lot less electricity, but I'm not really using it for anything but laptops and light bulbs.

Swift
2009-Mar-11, 08:12 PM
55 American homes?? Where does all this power go?
To me, comparing it to an average home is silly (I'm blaming space.com, not you). How about a comparison to the average research laboratory, or the average factory? I know in our labs we have pieces of equipment that use a lot more power than your average dishwasher or toaster.

On top of that, your average home or laboratory on Earth doesn't have to do things like generate breathable air, or deal with the thermal cycling that the ISS does.

Here (http://science.nasa.gov/headlines/y2001/ast13nov_1.htm) is a NASA article about power management, though they don't go into details.

Electrical power is arguably the most critical resource for the International Space Station (ISS). The very air in the ISS is created by splitting water molecules using electricity. Meanwhile, spare oxygen is stored in electrically pressurized tanks. Electric power wins the "most important" debate in a heartbeat.

Electricity keeps the ISS and its crew alive: It powers the air and water systems, keeps the lights on, pumps liquids for recycling, warms meals, runs computers. It even lets crewmembers talk to school children by Ham radio!

Apparently, the visitiing shuttles can also tap into the power supply (reference (http://en.wikipedia.org/wiki/Electrical_system_of_the_International_Space_Stati on#Station_to_shuttle_power_transfer_system))

JustAFriend
2009-Mar-11, 08:36 PM
If you're surrounded by vacuum and temperatures swinging
back-and-forth by 300-400 degrees, are you going to quibble
about how much power it takes to keep you alive???

I don't think your average house has to deal with that.....

slang
2009-Mar-11, 11:56 PM
Apparently, the visiting shuttles can also tap into the power supply (reference (http://en.wikipedia.org/wiki/Electrical_system_of_the_International_Space_Stati on#Station_to_shuttle_power_transfer_system))

That's a very recent feature (http://en.wikipedia.org/wiki/Station-to-Shuttle_Power_Transfer_System), reducing the use of the Shuttle's fuel cells, enabling it to stay up four days longer. I'm not sure if it was planned when designing the ISS solar panels.

Bearded One
2009-Mar-12, 01:40 AM
I used 1,036 last month in a one bedroom apartment. In the summer I'm pushing 3,000.

Ronald Brak
2009-Mar-12, 01:50 AM
The ISS is in sunlight just over half the time so assuming the panels are always angled to receive direct beam sunshine it would generate about 1,050,000 kilowatt-hours or year which is about about as much as 94 US homes if they use an average of 936 kilowatt-hours a month. Of course the cells may not always be at the best angle. It would be simpler and safer just to keep them steady and just have more solar cells than you need.

mto
2009-Mar-12, 03:37 PM
That's a very recent feature (http://en.wikipedia.org/wiki/Station-to-Shuttle_Power_Transfer_System), reducing the use of the Shuttle's fuel cells, enabling it to stay up four days longer. I'm not sure if it was planned when designing the ISS solar panels.

Interestingly there was a mention in a recent launch briefing that have reduced the amount of reactants carried for the fuel cells due to the shuttle being supplied electricity from the the station's solar panels while docked.

NEOWatcher
2009-Mar-12, 04:39 PM
To me, comparing it to an average home is silly (I'm blaming space.com, not you). How about a comparison to the average research laboratory, or the average factory? I know in our labs we have pieces of equipment that use a lot more power than your average dishwasher or toaster.
I'm one that usually get's really irked about apples and oranges comparisons myself (as many can attest to).
But; I don't see this context as one that is comparing to "see how good/bad" or basicall not a comparison on a judgemental basis. I see this as just a comparison for the average Joe to be able to relate. They have no concept what an average lab or factory uses.

samkent
2009-Mar-12, 06:07 PM
Should labs and factories be immune to energy conservation? What makes them so special?

We need those lights on in the back room of the warehouse incase some one has to go in there. Oh that’s alright we’ll just pass the cost onto the consumer or tax payer.

It reminds me of the school where my fiancť works. They send out an email instructing the teachers to unplug personal devices as it is costing the system over 20K per year in extra electric charges. It seems that a large percentage of teachers had personal, dorm type, refrigerators, microwaves, and other NON teaching personal devices in their rooms.
Did they listen? Just look at the government and there is your answer.

nauthiz
2009-Mar-12, 06:15 PM
Should labs and factories be immune to energy conservation? What makes them so special?

I don't think anyone's saying they're immune; it's just that autoclaves tend to use a bit more juice than your average residential water heater.

Murphy
2009-Mar-12, 07:06 PM
Are we seriously going to start worrying about the energy usage on the Space Station? :rolleyes:

Come on, what would it save if they reduced their power consumption? A few million dollars on a multi billion dollar program? (not to mention the fact that their using free Solar power). They've got to use as much power as they need, their up there to do a job and should not be distracted from that by having to worry about being power efficient.

I'm all for saving power, but not for big scientific projects. Things like ITER and CERN use plenty of power, but totally justifiably in my opinion.

NEOWatcher
2009-Mar-12, 07:26 PM
Are we seriously going to start worrying about the energy usage on the Space Station? :rolleyes:
I agree, when I first saw the OP, I thought it was general curiosity as to what kinds of equipment and electrical uses were on the station.

Now; the thread's turned into energy conservation. Why? The station is self contained, uses clean energy and no fossil fuels for it's electrical power. Using or saving means nothing up there when the capacity exists.

samkent
2009-Mar-12, 07:31 PM
I’m not concerned about how much they use. I’m just stunned at the amount they can generate. I never conceived that they need anywhere that much power.
Six people and a few rooms need as much power as 50 to 90 average homes? I’m dumbfounded.
I’m in electronics. I know how much a laptop uses. I know how much a desktop, plasma tv, refrigerator, microwave all use. I just wouldn’t expect an order of magnitude difference in requirements.

Are we sure they aren’t doing Death Ray experiments up there? That would explain it.

R.A.F.
2009-Mar-12, 07:41 PM
Iím dumbfounded.

That does not surprise me...

nauthiz
2009-Mar-12, 08:02 PM
Are we seriously going to start worrying about the energy usage on the Space Station? :rolleyes:

I'm guessing that there are already plenty of engineers who are keenly aware of how much money it costs to put anything up in orbit, photovoltaic cells included, and who get paid the big bucks to worry about energy usage on the ISS.

Whatever they're doing with all that juice, it's probably not anything to make the folks at EnergySTAR spend too much time crying in their beer.

Swift
2009-Mar-12, 08:21 PM
I'm one that usually get's really irked about apples and oranges comparisons myself (as many can attest to).
But; I don't see this context as one that is comparing to "see how good/bad" or basicall not a comparison on a judgemental basis. I see this as just a comparison for the average Joe to be able to relate. They have no concept what an average lab or factory uses.
I understand that and thought the same thing. But Samkent seems to think the average laboratory uses the same amount of power as the average home, and in my experience laboratories use A LOT more power, even on Earth.

Swift
2009-Mar-12, 08:39 PM
It doesn't directly answer the question, but I found this article (http://findarticles.com/p/articles/mi_qa3957/is_200602/ai_n16066481) interesting

Station Power and Energy Evaluation Determiner (SPEED) is a Java application program for analyzing the supply and demand aspects of the electrical power system of the International Space Station (ISS). SPEED can be executed on any computer that supports version 1.4 or a subsequent version of the Java Runtime Environment. SPEED includes an analysis module, denoted the Simplified Battery Solar Array Model, which is a simplified engineering model of the ISS primary power system. This simplified model makes it possible to perform analyses quickly. SPEED also includes a user-friendly graphical-interface module, an input file system, a parameter-configuration module, an analysis-configuration-management subsystem, and an output subsystem. SPEED responds to input information on trajectory, shadowing, attitude, and pointing in either a state-of-charge mode or a power-availability mode. In the state-of-charge mode, SPEED calculates battery state-of-charge profiles, given a time-varying power-load profile. In the power-availability mode, SPEED determines the time-varying total available solar array and/or battery power output, given a minimum allowable battery state of charge.


Then there is this site (http://iss.cet.edu/electricity/pages/c11.xml) and the pages within, that seems to be an education site that lets students work through ISS power requirement problems to learn about electrical systems.

Power on the International Space Station (ISS) is needed for the life support of crew and operation of the station. That includes orbital maneuvering, navigation, communication, monitoring and control of all gas exchanges, air temperature, pressure, lighting, cooking, and specialized lab equipment.

Here is some of the lab experiment equipment involved:

Furnaces
Crystal growth chambers
Plant growth chambers
Computers
Centrifuges
Special lighting
Refrigeration systems
Heating systems

samkent
2009-Mar-12, 08:42 PM
That does not surprise me...

Ouch! Anyone have a bandaid?


But Samkent seems to think the average laboratory uses the same amount of power as the average home, and in my experience laboratories use A LOT more power, even on Earth.

I didn’t think they used the same power as the average house. But I didn’t think man for man it would be 10 times as much.

01101001
2009-Mar-12, 09:04 PM
Furnaces
Crystal growth chambers
Plant growth chambers
Computers
Centrifuges
Special lighting
Refrigeration systems
Heating systems

That sounds like my workshop!

Yes, as a matter of fact, my waste heat does heat homes for 3 blocks around.

Swift
2009-Mar-12, 09:32 PM
But I didnít think man for man it would be 10 times as much.
And I don't think you have any data to support that notion.

Here (http://www.lentonfurnaces.com/content.asp?id=3&doc=55) for example, is a small (lab scale) commercial crystal growth furnace (I don't know if this is exactly like one of the ones the ISS uses). By itself it uses 13 kW, which is about 1/10 of the number you quoted.

Here (http://www.cyberstar.fr/telecharge/high_pressure_furnace.pdf) is another small crystal growth furnace that uses 5 kW just for the heater.

NEOWatcher
2009-Mar-13, 11:48 AM
I understand that and thought the same thing...
Yep; since I said that, I see where the OP is coming from.
It sounds like a comparison to a well equipped dorm room.
Even without the experiments, I think of things like the waste recycling system and heating and cooling.
I know my house doesn't have to heat and cool in relation to a 500 degree temperature swing. Besides, most are gas and not electric. I once had a home with an electric furnace. I might as well have been smelting ore.

samkent
2009-Mar-13, 11:58 AM
I once had a home with an electric furnace. I might as well have been smelting ore.


My home is all electric and my highest bill ever was $175 (midwest), so it’s not that bad.

Correct me if I’m wrong, but doesn’t waste heat from the equipment provide the atmospheric heat for the crew?

NEOWatcher
2009-Mar-13, 01:34 PM
My home is all electric and my highest bill ever was $175 (midwest), so itís not that bad.
It was forced air which might have something to do with it. Well insulated, but a large open floor plan. I started to conserve much more heavily after the first January with a $400 bill.


Correct me if Iím wrong, but doesnít waste heat from the equipment provide the atmospheric heat for the crew?
That would be my guess, but you do need to distribute that correctly, and that could get complicated.
Besides, whether its waste heat or purposely generated, it's still energy needed for heating.

nauthiz
2009-Mar-13, 03:18 PM
I had electric baseboard heating in one apartment I lived in, and my winter electric bills ranged between $300 and $400. I kept the thermostat between 55F and 60F.

Granted, it wasn't a terribly well-insulated building.

samkent
2009-Mar-13, 05:12 PM
$400 per month??

That's not far from burning the furniture as a cheaper option.

joema
2009-Mar-13, 08:43 PM
Iím not concerned about how much they use. Iím just stunned at the amount they can generate. I never conceived that they need anywhere that much power....I know how much a laptop uses. I know how much a desktop, plasma tv, refrigerator, microwave all use. I just wouldnít expect an order of magnitude difference in requirements....
120 KW is likely the nominal capacity of the solar cells under optimal conditions. IOW if they were perpendicular to the sun, that would be the output at the DC bus bars of the wings themselves.

However ISS is in darkness at least 1/2 the time, so cut that by 50% (or more). The wings likely aren't perfectly perpendicular all the time, also the structure itself may unavoidably shade the arrays a bit. Collectively these factors could reduce the capacity to about 40% of 120 KW, or 48 KW average output.

The power must be conditioned, buffered in batteries, then inverted to AC for internal use. Battery efficiency might be 90%, and inverter efficiency maybe 90%. That's .9 *.9 * 48 KW or 38.9 KW. There are probably additional distribution losses beyond this.

Solar cells degrade with age, typically several % per year. Most of the arrays have been up there several years. It's plausible 50% of them are only producing about 90% of their original capacity. That would cut total average output to roughly 37 KW, or 26,640 KW-hr per month.

That's more power than an average residential home uses, but an average residential home isn't running power consuming lab equipment, nor an HVAC system to deal with +/- 300F temp swings.

publiusr
2009-Mar-13, 09:32 PM
With Ares V, you could orbit very large SPSS demonstrator panels to ISS. Very high power experiments can be had--like smelting of metals in zero g--space manufacture, etc.

Things to really give ISS a purpose. More than just flags on the moon. With Ares V awesome throw-weight, the higher inclination of ISS becomes not such a big deal at all. It can still be used as a way station to interplanetary missions.

Like a beamed propulsion platform? If not ISS itself--then to beam power to other areas. To help SPSS, laser lightcraft, etc.

Ronald Brak
2009-Mar-14, 12:51 AM
I used 1,036 last month in a one bedroom apartment. In the summer I'm pushing 3,000.

I use less than 300 kilowatt-hours a month, in summer, in a bigger home and temperatures up to 45 degrees celcius. Maybe you need to replace your air conditioner? (We do have low humidity here which helps a lot with the heat.)

Jens
2009-Mar-14, 09:30 AM
I didnít think they used the same power as the average house. But I didnít think man for man it would be 10 times as much.

I wouldn't have thought so either. But I think there are at least 2 reasons to think that this must be the minimum necessary. One is that there are some very smart engineers working on the ISS who understand how much it costs to launch solar panels into space. So we can assume that whatever the power consumption is, it's not being wasted. And two, they need more solar panels to be able to support more astronauts, so clearly there is little surplus that can be conserved.