Why do we favor photovoltaic over stirling engines for converting solar power into usable energy?

dacracot · 2012-05-23T11:32:17.585789-07:00

On a large scale, you're right. There are a few companies that make stirling engine collectors (google "Stirling Energy Systems"). However, when you get down to the size of a residential setup, you're unable to produce a high enough temperature differential for a stirling engine to perform better than a photovoltaic panel. Utility scale photovoltaics exist mostly because of artifically low prices for panels, which is going to change very soon (in the US anyway). Once that happens I think we'll see mostly power tower setups for utilities (edit: and a few utility-size stirlings) and only panels for residences and businesses.

Kiyokami · 1 day

In the case that all of the backup mechanisms failed (astronomically unlikely) your best chance of survival would be to land on your feet with your legs rigid. This will most likely break both your legs and maybe your back too, but your brain's velocity would come to a stop having experienced the smallest possible acceleraton.

It would be very difficult to jump in a falling elevator because you would be in freefall and not standing firmly on the elevator's floor. Whatever you do, DO NOT lie flat. That deceleration will destroy your brain.

reddit4 · 1 day

None taken.

I'm not going to dispute anything you've said. However, simply because one major does considerably more work than another does not mean that the harder major is actually hard.

It makes sense that there is a higher dropout rate for more difficult majors because they're more difficult, but I think that generally one would find that students majoring in something today have a considerably easier time than if they were majoring in the same thing 50 years ago when going to college was a great privilege requiring intense dedication.

The availability of information and the use of computers to perfom calculations comes into play here, obviously, but I think that higher education should have adapted to cover more information while maintaining difficulty rather than covering the same amount and decreasing the difficulty.

reddit4 · 1 day

I feel that this only serves to prove my point. You're double majoring in two ostensibly difficult scientific fields and you haven't failed out yet. Having two majors used to mean you had gone to college twice. I think the level of difficulty you're seeing with two majors is what I expected to see with one.

reddit4 · 1 day

Fairly recent mechanical engineering grad here. Honestly, while my major may have been more rigorous than some of the non-scientific ones, I still found that I wasn't ever truly consumed by my studies. A lot of this article rang true for me. It didn't feel as hard as I thought it should have while I was there. I feel that there should have been more demanded of me. Of course, the more an educational system demands, the higher the incidence of dropouts, so I understand the race to the bottom.

EDIT: I went to UW-Madison. I imagine my experience would have been different had I gone somewhere like MIT, but if this is going on at the level of a flagship state school, I can only imagine how light the load must be at a for-profit institution.

Baracka_Obama · 2 days

I find it unfortunate that this sub is slowly turning from a forum for people who do not want kids into one for people who just hate kids. That's not what I came here for, despite the fact that I actually do hate kids. I'm here for the support and logical/financial reasoning behind the decisions people have made.

york100 · 3 days

I agree. A college degree signifies that you're willing/able to put up with something unpleasant and tedious for a long time. It does not, unfortunately, signify that you learned anything worthwhile. However, a lot of companies are looking for just that: patient people who will simply put up with conditions so that they can earn a paycheck. Having a degree says to employers, "Sit in a cubicle 8 hours a day? No problem!"

aschapm · 13 days

I noticed a few days ago that Digg right now is very similar to what Reddit was like 5 years ago. Someone named Eliwood explained:

It's because fewer people use it.

What does a group of 20 people have in common? Maybe they're your classmates. Maybe they share a specific intellectual interest. Maybe they come together because of a common culture or purpose.

What does a group of 100,000 people from all across the world have in common? Culture? No. Intellectualism? No. These people come to Reddit because they heard it was "good" and "funny". The only thing they have in common are the most basest human instincts; sex, gross AskReddit questions, and funny cat videos. Intellectual articles will NEVER cater to such a large and diverse majority.

So yes, it's a combination of all three of those things you mentioned.

Frontrunner453 · 17 days

I was in your boat. Try r/AdvancedRunning and you'll never see a "You guys I just ran a 30 minute 5k!!!" post ever again. r/Running is for people just getting started. r/AdvancedRunning is for people who will never stop. It really heats up during cross country season. Summer training is good too.

AlwaysKindaLost · 17 days

Powerpoint didn't ruin anything. People who don't understand how to keep an audience engaged is what ruins things. Keep the number of words on each slide below 5 (yes, only 5 words!), don't use distracting templates, and only include relevant pictures. This forces the presenter to move quickly from one slide to the next, keeping the audience awake. Most of the information should come from the presenter, not the slides. A 5-minute presentation should have about 60 slides, or one for every 5 seconds, each with very little on it. I've seen too many hour-long college lectures that had a total of 10 slides. They're using Powerpoint as a list of notes, not as a presentation tool. The presenter should be clicking through them like it's going out of style while walking around the room and talking.

EDIT: And screw those people who print off the lecture slides so they don't have to pay attention!

big_fear · 18 days

Upvoted for #4. To me, death is preferable to a life of disability.

carpadium · 18 days

I just popped over to Digg for the first time since 2008 after reading what I assume you meant as a joke. The entire front page is intellectual articles and hard news. This is how Reddit was when I got started all those years ago. I...what is this feeling? Am I going back to Digg?

titaniumtom · 1 month

I'm not a doctor. Based on my own experience with Patellofemoral pain syndrome, I'd guess that's what it is. Admittedly, it tends to strike less-experienced runners when they hit the 40-mile-per-week mark, but the change in shoes at high volume might have done it for you. I found that doing leg lifts one leg at a time strengthens the muscles in your thighs and can reverse this condition in a matter of weeks.

Xzumo · 1 month

What if she is a potato? Then he'd say "Would you like to go in some time?"

redditnoob_toss · 1 month

It all just came back to me. Someone submitted a picture to reddit. It was a picture of his balls with a small, red, hair-like object sticking out. It seemed rather garish at the time because it wasn't on one of those subreddits where you expect that sort of thing. I wasn't expecting to see a picture of balls that day at all. ~~I didn't upvote it so now I can't find it.~~ See edit. Anyway, he wanted to know what it was so naturally he came to reddit. I looked at the comments because I wanted to at least get some return on my investment of looking at the picture by finding out the answer to his question. Someone linked this.

EDIT: Enkaybee delivers!

redditnoob_toss · 1 month

I remember this. The words I remember were "nerve cluster." Also he found this thing on his balls and didn't pull it out but but rather cut it off with a scissors.

gloves_off · 1 month

I don't know if you meant to say 'excretion' instead of exertion, but I like it and I'm going to use 'excretion of effort' from now on.

soonersfan · 1 month

I've heard people say that simply because the main storyline is weak and the show relies primarily on flashbacks and cop-outs for humor, that it's a bad show. I agree that it's unconventional and that no other show takes it anywhere near as far as Family Guy does, but that doesn't make the show bad. I think of it more as an animated standup comedy routine - a narrative of mostly-unrelated jokes - and in that context I think it does rather well. It's a little heavy on the fart jokes though.

DiegoLego · 1 month

The moment you move into your dorm, start meeting people. If you wait too long it will be much harder to get into the groups that will form. Go out with some people and get hammered on one of the nights before classes start.
Never buy your books at the bookstore. Never buy an optional book. See if the library has the books you need. Go to class for a few days and see if the book is even used - you might not even have to buy them at all.
Don't skip class. Going to class and getting good grades is your only real job.
Avoid the early classes whenever possible. You won't be able to pay attention.
Don't waste your money at Starbucks.
Professors are not paid to be teachers. You're going to have to do a lot of the learning yourself.
If you're doing poorly in a class, drop it and save your GPA. Having a 'drop' on your transcript (which nobody ever even looks at) is much much better than getting an F or even a low grade. I dropped 3 classes through college; nobody has ever asked about them.
Don't bring a computer to class. It's a distraction.

t90ad · 1 month

Can I give you an equation that you can solve for the enthalpy, entropy, etc of water at any temperature and pressure? No I can't. Can I give you one that will get close for a specific range of temperature and pressure? Sure.

Equations of state have been a subject of intense study since the middle ages. The ones used most commonly in industry today are the Peng-Robinson and Soave-Redlich-Kwong equations. Both can be found on the Wikipedia for the subject. As mentioned, there is no equation that works for all temperatures and pressures. It's important to know the limits of the equations by testing their results experimentally.

bryhelix · 1 month

You bring up an interesting question. I wonder if the automatic response to finger injury is learned. Some regions will have a mostly "shake it" response, others will have a mostly "squeeze it" response, etc. All will have been passed on from the previous generation. Someone should do some research and make a map like the one that shows where people say pop/soda/coke.

AvidWikipedian · 1 month

This does not answer the question in any way. It does, however, answer yesterday's question about why rockets are launched starting vertically.

EDIT: he's talking about this quarter turn.

ISS5731 · 1 month

Every single object that is above absolute zero in the entire universe emits radiation at a frequency dependent on its temperature. So yes, there are photons everywhere. Most of them are not visible.

cardboardkills · 1 month

You asked a lot of questions here and you're right about everything, but some clarifications need to be made. It all has to do with the fact that electricity is a "high-quality" form of energy. You can do things with it that will eventually turn it into heat instead of turning it directly into heat.

Running a 500-watt electric heater will produce 500 watts of heat (100% efficient). Running a 500-watt computer will also produce 500 watts of heat, plus you'll get to be on the internet. (100% efficient + internet). So yes, using your appliances as space heaters is just as energy efficient as using real space heaters. As someone mentioned though, it may shorten their lifespan.

HOWEVER, if you're talking about using electricity to run a heat pump, then you're much better off than you would be running appliances/electric heaters. A heat pump can deliver 3 or 4 times the amount of electricity it consumes as heat (300-400% efficient, but that makes no sense. Engineers call if the Coefficient of Performance: 3 to 4). It does this by moving heat from outside to inside. Yes, there is heat outside even though it feels cold. The efficiency of a heat pump decreases as it gets colder outside, but if it's 10-15C you will always be better off running a heat pump than using an electric heater. As a rough estimate, it would have to be well below freezing outside for a heat pump to be less efficient than an electric heater.

EDIT: spelling and grammar.

Obviouslydoesntgetit · 1 month

I've heard this question asked about a falling elevator, and I think it's easier to answer using that situation. Could you survive a falling elevator if you jumped just before it hit the bottom of the shaft?

Maybe.

Here's the problem: if you're in a falling elevator, you're not standing on the floor. You're floating weightless inside of the elevator as it falls. You would need to find a way to hold yourself against the floor in order to jump.

So let's say you manage to do just that. You grab onto the hand rails and hold yourself against the floor until just the right moment and then you jump. Don't ask me how you know when to jump. You just know. Doing this will reduce your downward velocity, but you'll be unlikely to slow it down enough that you won't still get hurt. To answer your question, yes. Jumping just before impact (if you can overcome the weightlessness issue) will improve your odds of survival.

If you're talking about a car, I don't know. the ergonomics and cushiness of the seat might help to absorb the fall whereas jumping might cause you to land on something and snap your neck. Don't try it.

Enkaybee

TROPHY CASE

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