# What legitmate forms of energy do we have to choose from **URL:** \ **Category:** Factual Questions\ **Created:** [August 13, 2004, 6:10pm UTC](https://boards.straightdope.com/t/what-legitmate-forms-of-energy-do-we-have-to-choose-from/259719 "2004-08-13T18:10:28Z")\ **Posts on this page:** 6\ **Page:** 3
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [August 15, 2004, 8:59pm UTC](https://boards.straightdope.com/t/what-legitmate-forms-of-energy-do-we-have-to-choose-from/259719/41 "2004-08-15T20:59:16Z")
waste to energy solar collectors in space or the moon beemed via microwave to earth (ok you said solar) There was a NASA experiment to get power from a long wire set up in orbit (IIRC it went unstable and was abandoned). ---
**Author:** ![InvidiousCourgette](https://avatars.discourse-cdn.com/v4/letter/i/e47c2d/32.png) [@InvidiousCourgette](https://boards.straightdope.com/u/InvidiousCourgette)\ **Post date:** [August 15, 2004, 9:10pm UTC](https://boards.straightdope.com/t/what-legitmate-forms-of-energy-do-we-have-to-choose-from/259719/42 "2004-08-15T21:10:14Z")
> [@Crafter\_Man](#): > > Like I said, I have no cite, and it’s my gut feeling (as an EE) that no PV-based power system has ever produced _one net watt_. It’s also my opinion that if technology progressed to the point where PV-based systems _did_ produce net power, the power companies would be scrambling to build them. I am sorry, but I do not feel that is good enough for GD let alone GQ. Power companies will only be scrambling to build PV arrays if they return a decent ROI, or a 5 year (say) \*financial \* payback. It is now my belief that PV arrays do return an \*energy \* payback in about 10 years, because \*\*Gorsnak \*\* has provided some evidence to suggest that is the case. If you are going to disagree with that evidence you need better justification than > [@](#): > > my gut feeling (as an EE) ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [August 15, 2004, 9:13pm UTC](https://boards.straightdope.com/t/what-legitmate-forms-of-energy-do-we-have-to-choose-from/259719/43 "2004-08-15T21:13:04Z")
> [@kanicbird](#): > > There was a NASA experiment to get power from a long wire set up in orbit (IIRC it went unstable and was abandoned). A [space tether](http://www.tethers.com/TethersGeneral.html) is only good for converting kinetic energy of the spacecraft into electricity, or vice versa. It’s not really an energy source, just a method for converting energy in one form into another. Actually most things mentioned in this thread fall into this category. PV cells are not energy _sources_, but just one method of converting solar radiation into electricity. ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [August 15, 2004, 10:00pm UTC](https://boards.straightdope.com/t/what-legitmate-forms-of-energy-do-we-have-to-choose-from/259719/44 "2004-08-15T22:00:18Z")
First of all I’m talking about _large-scale power distribution systems_, not roof-top units. Such systems require large fields full of mirrors. And you’re correct that cost is not the same as net energy, but the two would be intertwined in any analysis. > [@Gorsnak](#): > > The only reason inversion is necessary is because we happen to use AC for most of our electrical needs - except that half the stuff I’m powering converts it back to DC before it’s finally used. Saying that PV only produces the amount of energy left after converting it to AC and back to DC again is like saying that the US dollar is worth $USD0.95, because that’s what I’d have left after converting it to $CAD and back to $USD. No. For PV systems to be viable (especially large-scale systems) they must convert DC to AC. This is not “because we happen to use AC for most of our electrical needs.” It’s because DC cannot be efficiently transferred over distance. Only AC can be efficiently transferred over distance, regardless of what the load requires. ---
**Author:** ![Gorsnak](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gorsnak/32/7587_2.png) [@Gorsnak](https://boards.straightdope.com/u/Gorsnak)\ **Post date:** [August 15, 2004, 11:46pm UTC](https://boards.straightdope.com/t/what-legitmate-forms-of-energy-do-we-have-to-choose-from/259719/45 "2004-08-15T23:46:38Z")
> [@Crafter\_Man](#): > > First of all I’m talking about _large-scale power distribution systems_, not roof-top units. Such systems require large fields full of mirrors. And you’re correct that cost is not the same as net energy, but the two would be intertwined in any analysis. > > No. For PV systems to be viable (especially large-scale systems) they must convert DC to AC. This is not “because we happen to use AC for most of our electrical needs.” It’s because DC cannot be efficiently transferred over distance. Only AC can be efficiently transferred over distance, regardless of what the load requires. Again, _this has nothing whatsoever to do with whether PV is a net energy source_. The assertion you made was that PV cost more energy than it generated, not that it isn’t a feasible means of large-scale energy production. Secondly, you’re the electrical engineer, do tell us what the efficiency of inverters is. 90%? I’m guessing. You should know quite precisely. The cited study, which I do not fully trust, but which is the only thing resembling evidence before us, states that PV produces about 3x the energy it consumes. A 10% loss doesn’t tip the balance. Third, you’re thinking inside the box. Imagine every house with rooftop PV powering DC appliances in the house, with an inverter plugging excess production into the grid, and drawing off the grid and converting to DC (which half our appliances do anyways) to run things when the panel is insufficient. Distributed power generation. Sure it can’t be the only source, but if every house in North America generated, say, 2 kilowatts per hour of sunshine, tell me what kind of impact that would have on things. ---
**Author:** ![hibernicus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hibernicus/32/2802_2.png) [@hibernicus](https://boards.straightdope.com/u/hibernicus)\ **Post date:** [August 16, 2004, 12:18am UTC](https://boards.straightdope.com/t/what-legitmate-forms-of-energy-do-we-have-to-choose-from/259719/46 "2004-08-16T00:18:30Z")
One more for your list\*: In Ireland we burn peat to make electricity. \*(Unless you want to count peat as a form of ultra-low-grade coal) [Previous page](https://boards.straightdope.com/t/what-legitmate-forms-of-energy-do-we-have-to-choose-from/259719.md?page=2)