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The future of solar power

  1. 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.
  2. 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.
  3. 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?
  4. 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
  5. 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.
  6. 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.
  7. 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%.
  8. 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
  9. 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).
  10. 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.
  11. 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.
  12. 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
  13. 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
  14. 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.
  15. 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.
  16. May 18, 2017 #41
    Im hoping this is a fairly significant year for batt storage with the Tesla batt factory nearing completion, Daimler getting into the market, Panasonic getting new competition on their heels.

    Reading about energy storage and ignoring portability it seems to me that electrochemical may not be the best solution. The mechanical simplicity of gravitational potential energy and solar power makes me drool. lol

    Apparently even flywheels are used to "store" energy. kept in vacuums supported with magnetic bearings, made of carbon fiber and rotating at up 60k rpm! Oh that's a cool one too! So cool when star trek complexity and flinstone simplicity converge.
  17. May 18, 2017 #42
    So, using these numbers, I would spend $23,000 on these batteries; they would last 10 years; and in those 10 years I'd use 10 * 365 * 30 = 109,500 kw-hr.

    Then the battery cost is $23000/109500 = $0.21 per kwhr. That's more than I pay for my grid power (even where I live, and the power cost is high here).

    Or, say you took a loan for the battery; 10 years at 4%, the monthly payment is ~$235, and that's just for the battery. That's more than my monthly power bill.

    So, there's plenty of room for improvement in the numbers before I can see widespread adoption of solar.
  18. May 18, 2017 #43
    Yeah, exactly why I don't have a system set up for back-up power at my house.
    That, and lead batteries take up a lot of space, take a lot of babysitting, and put off deadly gas...
  19. May 18, 2017 #44
    I lived in south Florida for awhile. The house I rented in had solar hot water heater on the roof. Now that made sense! On a sunny afternoon the relief valve lifted to vent steam from the storage tank. No electric conversion, just sunshine to hot water. Takes the load off the electric or gas hot water heater. Storage takes care of itself as the tank stays hot overnite.
  20. May 18, 2017 #45
    Re: storing electrical energy, it seems about ten years ago everyone was talking about supercapacitors. I haven't heard anything about them in a long time.
  21. May 18, 2017 #46
    I would not worry. Market forces would "magically" do their thing. Whatever kind of cell would be optimal wrt cost/efficiency, market will eventually mass-produce exactly that one :D

    Well, in fact all other kinds of plants, except maybe wind, have WAY MORE other equipment. Maze of piping for water, air, oil (usually more than one kind: say, "instrument air" and "pneumatic air" are two different systems). Valves everywhere. Gaskets. Pumps, pumps. I remember when I was reading about a 6 MW pump in a nuclear plant and was amused to discover that its sealing system required high-pressure air which... required another small pump just for that purpose! :)

    Solar is winning hands down here. It needs only a handful of kinds of equipment, and it is all electric. No oils, water, gases, high pressures...

    Yes, solar needs transformers. This is not at all different form any other plant.
  22. May 18, 2017 #47
    Tesla's Powerwall is not optimal economically (it's too costly, and I have doubts about longevity). Tesla is just repackaging and selling excess production originally designed for cars. They are, as a business, certainly justified in doing so, but we as consumers need storage tailored for non-mobile, large scale storage.
  23. May 18, 2017 #48
    Aside from cost, or scalability, what disadvantages would a battery designed for mobile use present in a non-mobile application?
  24. May 18, 2017 #49
    Cost is the key factor. A cell which is 4 times heavier, but twice as cheap as car battery, (and all other parameters are same), would win hands down for utility storage.

    Car battery which needs replacement in 5-10 years is okayish for cars. Utilities would want to install them once and run them for as long as possible.

    Car battery needs to be able to provide spiky output. Utility storage does not need that. This means that batteries which have many good params, but require only slow discharge can be suitable for utility but useless for cars.
  25. May 18, 2017 #50


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    ... a gas or coal or nuclear or hydro plant. Intermittent power may throttle these back a bit, but does not replace any of them, and thus only adds to the total equipment installed.
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