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The future of solar power

  1. May 17, 2017 #21
    I think Ronald Reagan called that Star Wars...


    Besides, as soon as you have a collection of them, you have... a grid - whether they are connected by wires or not.
  2. May 17, 2017 #22
    i not sure you can create a grid of mirrors. to direct light via mirrors, dont you need a string of 1 or more and only that string can direct the light from source to destination?
  3. May 17, 2017 #23
    I read somewhere, (American Scientific, I believe,) maybe five years ago, about powering communities using electricity transmitted through pipes that were cooled to near absolute zero, which contained liquid hydrogen, which would take the place of propane and natural gas, and gasoline, for heating and transportation. The idea was to bring all required energy sources via one source. (Yeah, your private gas pump in your driveway.) Seems to me that they had a small prototype set up at some University - something like a quarter-mile run. If I recall, they were excited about the minimal loss of power, due to the extreme cold making the pipe function as a super conductor.

    Sadly, I have not heard anything new about this intriguing idea since then.
  4. May 17, 2017 #24
    I would personally consider all of the ones feeding the main mirror to be a "grid"... But that may be more a question of how I use the word, than technical specifications.

    In much the same manner, I consider GPS satellites to be a "grid", even though my device might only connect to several at once. I guess what I mean, is that shown graphically, or geographically, the collector, whatever they are, when represented on a map, would form a grid pattern, when you start connecting them to the consumer. Depending on the deployment, it might look like a fishing net, or it might look like an octopus, but I believe, in the strictest sense, both forms would be considered a grid.

    Unless I'm wrong - and I have an advanced degree in "Wrong"... So this is not unanticipated.
  5. May 17, 2017 #25
    i look at it from a laser perspective. you aim and reflect the laser, so the path is set, to change the path you have to change the direction of the 1st reflected source mirror, but this is not the same as a grid of wires that all transmit the signal at the same time, and if one wire breaks the full signal still flows w/o intervention. if a mirror breaks you lose a part of the signal.

    i could be wrong.
  6. May 17, 2017 #26
    You are looking at it from the micro viewpoint - one mirror/laser can not a grid make. Therefore you are correct.

    I look at it from the macro. Dozens, or perhaps hundreds or more mirrors, stationed all over the planet. No matter where the mirrors point their energy, or even if they are activated at all, when you look at where they are physically located on a map, you have a dispersed pattern. When they are active, it doesn't matter if they are pointing all at the same receiver, or if each points at a unique receiver, you still have a network, or grid. Therefore, I am also correct.

    Don't get hung up on the electrical grid that we have in use to power our homes to formulate a definition. That system is intentionally designed a bit like a fishnet for the sake of redundancy. That is not the only form a grid can take.

    "a framework of spaced bars that are parallel to or cross each other; a grating."

    I would argue that "parallel" is not a requirement either, for our purposes.

    Advanced Degrees in "Wrong". Yes, I have made a study of being wrong.
  7. May 17, 2017 #27
    Was working on a response to nikkom and EnumaElish before the rash of posts.

    I knew that, where did I get the 8-10w/sqft.? Probably just mindlessly copying it off the internet. Panels that I purchased in 2009 where rated 130 watts had an area of about 8sq ft. so that is 15 watt/sq ft..

    Storage will still be needed. Look at replacing all sources with solar. Take the US. The best place for solar farm is the southwest still only getting about 5 full sun hours equivalent per day with about 16 hours of no to near no power output. Considering that they are located in a restricted section of the country a new power grid will be needed
    The power lines will not only have to carry the immediately used energy but also the stored energy which will be 2 to 3 times the energy used during generation. The US has a generating capacity of about 1000G W for a summer day. 8000G Whrs of energy used during the generation period. This will require a storage capacity of from 16000 -24000G w hrs to just carry over to the next day.

    Elon Musk of Tesla is selling Li-ion storage cells he call the "POWEWALL" which can store 14K Whrs. He currently sell them form $6200 apiece with installation costing $800 to $2000. An average home would need about four to five of these batteries just to meet the maximum energy requirements. The daily average US energy usage is about 11B kWhrs. which means that the country would need 786 M POWERWALL batteries at a current cost of $4.9T. These batteries cost about $400 per stored kWhr but it is believed that new technology will bring this cost down to $100 per kWhr stored which is the same as the current lead-acid batteries. Actually the usable energy stored in a Lead acid battery is only 1/2 of the maximum since taking more out significantly reduces the life of the battery. So the new technology may be a significant improvement.

    As for other storage methods I looked at elevating water and have it drive a turbine since it is technologically straightforward. If you assume that the average home can have a maximum demand of 60 kWhrs (216Mj) per day and are able to elevate the water to a height of 100 m above the generator one would need to pump about 220,000 L which is a sphere about 7.5 m in diameter equivalent to 7.5 4ft x 18ft circular pools. That is for one full day of power, you would need about 1/2 -3/4 of that for the non generating periods There are about 125M households in the US.

    If you want to go off the grid you definitely need batteries or other storage device so for a 60 kwhr max daily energy need and maybe a 12Kw instantaneous power requirement requirement would require about 800 sq ft of solar panels for which most houses do not have adequate roof exposure/area so se aside some of your back yard.

    One nice think about solar panels if you do not need the power you just don't turn anything on. With a generator running with no draw you still use energy . You must turn it off. when not using electricity.

    For the more eastern part of the country where clouds are prevalent you might want 3 days of backup power or about 12 POWEWALL batteries or 150 deep cycle lead acid batteries.

    Rambled a bit but all said and done I think solar will be just one of many power sources we will be using into the foreseeable future. Some countries will use more and some less.
  8. May 17, 2017 #28
    So, if I am using solar, and I don't use the full amount of power generated, is there any negative affect on my system? Can something overheat?, or maybe the Cells degrade?... In other words, if I only need power during generating hours, and I produce more than I need, should I be concerned?.... or can I simply use it "on demand", with no consequences?

    If that were the case, and PV farms providing power "in excess of demand" could be set up around the world in strategic locations, it just might be, that we could do without batteries. I'm not saying that it's very practical, but is it possible?
  9. May 17, 2017 #29
    For large storage projects, Tesla sells Powerpack, a fridge-sized outdoor cabinet with batteries capable of storing 210 kWh (same as 14 Powerwalls). Price for large installations appears to be ~$47k per one Powerpack.


    Last edited: May 17, 2017
  10. May 17, 2017 #30
    yup and using a wrench to hammer a nail doesn't work too well either.

    Perhaps the availability of electricity makes allot of appliances rather impractical for solar cell / battery cell power sources, not to mention the habits associated with a constant supply of electricity.....the losses going from solar cell, to charger, to battery, to power inverter to some device that may in turn convert the electricity again to some other value must be a material amount.

    Not sure that pb batts are practical for electricity storage either, besides the issue you mention they self discharge a material amount. I'd argue that a portable 6v pb is probably the worst available battery for such a use. "Cost effective" for energy storage should be a measure of more than the selling price, AND costed against alternatives.

    imo nothing wrong with the efficiency of panels, nor the power / sq foot in ideal conditions. I find it remarkable such a thing is possible; It's funny you mention maintenance on the panel such as ensuring they're clean. I find them to be the most maintenance free way to generate electricity....we're talking photons doing the "work" here..the panel sits there. No-one will

    Useful life of a panel would be interesting to know.
  11. May 17, 2017 #31
    No negative effects and degradation as far as I know is just what would occur if that sat in the sun unused, No overheating. no moving parts. Use it on demand, nothing to attend to. Just like any power source excess capacity can be transferred to any place on the grid.
  12. May 17, 2017 #32
    The 210kw POWERPACK cost about 1/2 of that of the POWERWALL of equivalent storage capacity and would be perfect for a three day backup supply.

    Lead acid batteries are what is commonly used by those who live on boats. Right now a 6V AGM Pb-acid battery bank is the best for storing charge and a properly maintained 6V regular vented Pb-acid wet cell (golf cart) is the best value.

    Solar cells are often warranted for 20Yrs although the output does drop with age.

    Yes they are maintenance free as such but where they will be most likely use in dry desert areas dust will be a problem. in addition dust storms may pit the glass and reducing the transmission of the solar energy

    Every conversion and transfer results in a loss of power. Batteries typically loss 10% in the charge/discharge cycle, I think inverter are only 90% efficient in the transfer. Transmission line losses are kept low about 1.5%.
  13. May 17, 2017 #33
    I completely disagree, and what's more peeps on boats, RV ect are tending towards LI based batts, as is the entire industry because it's better. Good value? Do you mean most popular?

    I don't know what to say regarding the issue with dust in a desert, or pitting of glass? What's the alternative you are considering? I think a solar panel has the lowest maintenance for most work...

    Where are you hearing that AGM pb is best for storage? everything I read says Li is best. From my experience it is and make pb seem archaic, particularly when weight is considered. And I think on all but one or two points Li is superior to pb for batts.

    My point was to do with "compatibility" of appliances and solar and using "current US household energy usage" as the target generation and storage values.

    I imagine those who are completely reliant on solar power would laugh at the idea of generating heat using electricity, what if we take that out of the "average daily usage".

    Is thousand of miles of cabling and unusable land an efficient way to deliver power? right, 1.5% loss and pb is best value, and agm pb is best for storage.
    Last edited: May 17, 2017
  14. May 17, 2017 #34
    Li is best when weight is a consideration; also, most advances happen in Li because of laptops/phones and electric cars.

    Utility-scale storage has different requirements: not sensitive to weight, but sensitive to cost per stored Joule and to longevity. I think when batteries will be optimized to _those_ parameters, they may end up being not Lithium batteries, but something else. As an example, iron-nickel batteries have _extremely_ long service lives (~50 years).
  15. May 17, 2017 #35
    I think solar will continue to improve and grow rapidly. Which technology will come to dominate is still unknown; new methods and materials keep being discovered and developed. Because solar pv can be achieved with thin films the potential for mass production at low cost is enormous. Whether it's solar paints or printed film like this example - http://www.newcastle.edu.au/newsroo...r-electronic-inks-rewriting-our-energy-future - it's going to become ubiquitous and low cost. Ultimately it will become incorporated into roofing and cladding and installed at little extra cost. There is good reason to think the advances will continue.

    Intermittency is a real issue, but not insurmountable. Solar won't exist in isolation, but as a major part of a broad mix of technologies and be deployed in conjunction with ongoing improvements in energy efficiency, time shifting of loads, geographically widened networks and storage.

    Intermittency is an issue yet it can become an important and positive driver of change, potentially providing a de-facto carbon price that will encourage investment in solutions -
    Rooftop solar for example, has already shaved the highs off wholesale power pricing during the daytime demand peak here in Australia and that, like it or not, is forcing fixed fossil fuel plant into periods of slowdown and intermittency. ie the right direction. Storage under such conditions does not have to do more than carry PV owning users through one afternoon and evening following each sunny day to have profound impacts on the economics of fossil fuel plant. Without foresight and planning - and with denial of climate consequences - that will be seen as disruptive, yet with it, the economic incentive to invest in low emissions solutions can be strengthened.The true value of storage is much greater than any average daily electricity costs can properly reflect, even a small amount going a long way. Wherever there is hydro it will have opportunities - it doesn't need to be pumped hydro, as just seeking to preferentially service the periods when the sun isn't shining and wind isn't blowing will be economically attractive in an intermittent renewables rich network.

    Right now, solar PV with batteries is edging towards being lower cost than grid power for households around here; some further cost reductions and that choice begins looking very attractive purely on grounds of costs. Whatever the market for PV with batteries may have been prior to crossing that price threshold, it will balloon once it has. And I think it is safe to assume that larger scale grid scale storage will ultimately have cost advantages even if that kind of investment will not occur until it has proven itself at smaller scales - but likely only where a mature electricity network already exists; all those poles and wires will increasingly look like a poor investment for much of the developing world.
  16. May 17, 2017 #36
    Low cost of PV cells is a yesterdays' problem. Now, cost of the cell per se is only about half of the module cost. Therefore, now the focus is not on the lowest cost of cell, but on reasonable cost of cell combined with reasonable efficiency.

    At the moment, 20% efficiency is considered sweet spot, slowly creeping to 23%.
    Theoretical maximum for single-junction Si is 29%, for single-junction of any semiconductor is 33%.
    People are trying to make double-junction cells of 30% efficiency practical for cheap mass-production.
  17. May 18, 2017 #37
    I do not disagree about the desirability of a Li-ion battery with regard to maintenance, discharge characteristics and weight but currently prices are much too high. A check of cost of replacing a 600 Ahr Pb acid 12 volt house battery system with Li-ion show a factor of 7 difference in price. When the price difference comes down to about a factor of two then I would consider them a good value. Once there is a good demand I expect the price to come down. And scaling batteries to higher capacities at least for residential/commercial purposes is doing just that the smaller Tesla POWERWALL at 14kwhrs is twice as expensive per kwhrs compared to their POWERPACK at 210kwhrs.

    Certainly not direct conversion to heat but driving a heat pump/air conditioner should be fine where applicable otherwise fossil fuel, super insulation, or dress warmly where it is cold and run fans where it is warm.

    Solar cell costs are about $0.70 per cell and may come down more for current cell design but who knows about the more efficient cells. there are other costs to consider for solar generating plants which fossil fuel plants do not have as inverters, and storage devices and the need to house and cool these devices. Solar power systems still need transformers and power lines etc., Fossil fuel generators like a GE 2000KVA model produces an AC terminal voltage of 26kV which is stepped up to 67kV to 765kV for transmission. The max voltage I've found for a panel is 48 VDC. How do you produce 1Gw at 26kV AC.

    It is beginning to seem to me the current idea of using residential and commercial installations and tying into the grid locally to augment the power grid may be the more efficient way to incorporate this energy source (thoughts?). No additional transmission lines, no storage facilities, power disruption is minimized.

    There are 125M houses in the US installing just 4kw systems would increase the US max capacity by 50%.. require less than 275 sq ft of roof space that should work for 99% of houses. Need emergency power? 5kw generator would probably work for most people.

    A model Ohio installation 5.1kw cost $19,000, produces 540kWhrs per month average which translates into about $1000 saving in electricity per year. http://dovetailsolar.com/Solar-Electric/Pricing-for-Solar-Electric-Systems.aspx
  18. May 18, 2017 #38
    I generally agree with what you have to say.

    Also, I am not disputing the validity of your numbers on this factoid, but I do wonder what percentage of households are in extremely dense residential zones, like, say, downtown New York, where the ratio of roof area to households is arguably small, not to mention building that get no significant length of time in full sun, because taller buildings shade them out? It probably doesn't significantly skew your numbers, but I do wonder
  19. May 18, 2017 #39
    Good point. I checked again from what I could glean it seems you can count on at least 90M single family house with another 16M being occupied only part of the year (second homes?) 18M households are apartments. and may include multi family dwelling.

    And yes some may not be suitable for solar or minimally. Example. A neighbor of mine had Solar City install panels. I believe these are leased not purchased. The array was installed on an east facing roof among significant shade from nearby trees a real stupid installation. He is lucky to get two hours of sun each day.
    So houses with north south orientations a roof installation is not very good.
  20. May 18, 2017 #40
    So I was right, it doesn't skew the numbers too badly, just ups the required square footage on the year-round single family homes by what?...15% or so? That's 320 square foot per residence?...let me tell you, that's a tiny roof - that's like the size of the concrete slab of a 1-1/2 car garage - definitely do-able.
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