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Non-rectangular PV Panels: do they exist?

  1. Jul 25, 2017 #1

    sophiecentaur

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    If anyone wants to maximise panel area on a non-rectangular roof (a pretty common domestic situation), where can they go to find panels to fill in the wasted areas?
    I have searched with all combinations of terms I can think of and (with the exception of over optimistic hits from Alibaba - and they claim to have absolutely anything available) I can't find anything. I can't think there can be much of a problem in laying out a triangular array of cells to produce 12V.
    What's the problem? Is it just not worth while making them? Or does a PF member know of a source?
     
  2. jcsd
  3. Jul 25, 2017 #2
    I think with the cells being square - any triangular shape module (panel) does not have a good fill ratio, so ether blank space in the module, or blank space on the roof. So much price pressure making anything in lower volume is not worth it.
     
  4. Jul 25, 2017 #3

    sophiecentaur

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    Yep. I rather thought it would be like that.
    It's the low volume and - hell - they don't actually have to try very hard, do they?
     
  5. Jul 25, 2017 #4

    dlgoff

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    Maybe you should take advantage of this niche market and start a Custom PV Panel manufacturing company.
     
  6. Jul 26, 2017 #5

    sophiecentaur

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    I didn't make myself too clear there. I meant that the manufacturers don't have to try very hard to sell what they make already. They can probably sell as many rectangular ones as they can make. Perhaps what would be easier to use would be smaller, 'fill in' rectangular units. It would represent an efficiency increase, which people would understand.
     
  7. Jul 26, 2017 #6

    Baluncore

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    What angles would you select for standard triangular panels?

    It might be easier to modify the roof. You could do it so as to increase the area that faces the available sun. The sooner you change the roof, the sooner you will start to acumulate the energy advantage.

    Convert the pyramidal shape of a hip roof into a gable roof by extending the PV panel mountings. Avoid cross-gables on the sunny side.
    Consider a latitude sloped shed roof, optimised to face the sun.
    A sawtooth roof with north-lights allows diffuse light to enter while providing an area for PV that faces the sun.

    To go off grid it is usually best to design a roof that maximises energy during winter when times are hard.
     
  8. Jul 26, 2017 #7

    sophiecentaur

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    I did wonder about a suitable set of possible angles. Sounds expensive to have more than a 45 degree option but, even with just 45 degrees, the utilisation of an odd shaped area would be much better.
    In the UK, at least, the cost of PV installation gives a payback time in the region of 20 years. Changing the roof shape would make it 40 or 50 years so it's not an attractive solution.
    I look upwards everywhere I go but I have not seen installations where there has been much attempt to maximise use of roof area. You just get a 2X4, 2X5, 2X6 type panel layouts. The public is naive about the market and they are not in a position to have opinions about the economics of PV installations, except to make a go-no-go decision on money up front and pay back time. I guess I will just have to accept this as you can only get a grid connection in UK, using one of the certified companies and there is no scope for doing my own design.
    An old neighbour of mine recently built an eco house in which the roof size and slope and the way the house faces were chosen to be optimum before anything else was planned. The only think he missed out on was the fact that the Feed In Tariff has gone down drastically over the years. Our house was built about 110 years ago so the parameters are more or less given.
    Off grid would have appeal but I think the market price of a house near London wouldn't be as good as it would be with On-grid. It's all down to money.
     
  9. Jul 26, 2017 #8

    Baluncore

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    If all panels were triangular the game could be different. Equilateral triangular panels could make only hexagons and equilateral triangles with 60° boundaries. 45° right triangles would also be restricted in choice.

    But if the panels were 3,4,5 right triangles with 37°, 53° and 90°, it would give you something to play with. Two 3,4,5 triangles will make a 3 x 4 ratio rectangle.
    A ratio of 1.732 gives angles of 30° and 60°.
    If the golden ratio = 1.61803 was used, the angles would be 31.7° and 58.3°.
    If a √2 = 1.4142 ratio was used, (like A4 paper), the angles would be 35.3° and 54.7°.
     
  10. Jul 26, 2017 #9
    Also - the market (buyers) are sensitive to how these look on their houses. Trying to match roof geometry it opening a can of (satisfaction) worms.
     
  11. Jul 27, 2017 #10

    sophiecentaur

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    I'm not so sure about that. The buyers of the systems that I see around here have accepted that the array will just be rectangular and that it won't fit in with the original aesthetics of their (sometimes originally interesting) roof shape / design. I am sure that, if they had been given the choice of having their trapezoidal roof area filled neatly to the edges, they would have preferred it to an ugly rectangle of PV panels and two odd triangles of slate. But it was, of course, never suggested to them. They went for the Function over Form argument (=£££).
    I have seen some high end installations, advertised with wavy PV panels that match the size and shapes of the slates over the rest of the house. But they are seriously high end and out of my reach.
    I do like the @Baluncore suggestion for 3:4:5 triangles. I can just see him sitting at the desk, sketching the idea on the proverbial fag packet and muttering "I'll show 'em". Good thinking there!
     
  12. Jul 27, 2017 #11

    Baluncore

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    I prefer the back of an envelope. I have spent quite some time turning over ideas for modified roofs that facilitate PV. No envelopes were harmed in the geometric excursion. Those triangles have always annoyed me, not because of the aesthetics but because of the blatant imperfection of wasted energy.

    If it is the visual impact of the partial coverage that is the problem, then maybe consider dummy panels that can be made to fill the triangular gaps. The provision of that low-tech service could be offered to house proud owners with too much cash.

    I expect with time we will see progressively more roofing that integrates the PV panels. Meanwhile my very old wrinkly tin roof is better insulated since I put the panels up there. The house is cooler in summer and warmer in winter. Dummy triangular panels would have a positive effect on the roof insulation here.
     
  13. Jul 27, 2017 #12

    sophiecentaur

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    But the cost of modification is such a factor. Surely making the panels fit the roof should be cheaper, once they are prepared to consider the idea.
    As you have PV, perhaps you could give us an indication of the capacity, area and expected payback time. My roof is a lovely interesting structure (three gables of different sizes) but the house is small and 10m2 is all that's available for PV.
     
  14. Jul 27, 2017 #13

    mfb

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    Do you really think the idea hasn't been considered?

    If solar panels usually don't come in 50 different shapes, then it has an economic reason. The demand per special shape is small, that makes highly streamlined production difficult.

    Non-rectangular shapes are also a nightmare for the design if you want to use them. The panels are made out of smaller elements, multiple elements in a row are connected in series, and these series are connected in parallel. That works great with rectangular shapes where all series connections have the same number of elements of the same size, but with other shapes you have to re-route all the connections to get the same output voltages, and you get some leftover elements that you cannot connect. Possible? Sure. Cheap? No. Dummy modules purely for the optics that don't contribute to electricity production are possible as well, but they are not free either and don't contribute to the point of the installation.
     
  15. Jul 27, 2017 #14

    Baluncore

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    It is not my economy so much as environmental politics that drive my energy decisions. I installed the minimum PV possible, at a time when the Federal Government gave a financial rebate to new renewable energy installations. https://en.wikipedia.org/wiki/Solar_power_in_Australia#Rebates

    I did not care about my cost or payback time so much as the principle of renewable energy, and getting a registered installation before any PV installed capacity restriction. I enjoy spending federal funds to reduce my payments to the state power authority. I am economic even without solar since I have been improving my energy economy here for many years. While my friends were being arrested at the Franklin Blockade, https://en.wikipedia.org/wiki/Franklin_Dam_controversy I was helping improve the efficiency of federal government buildings in the state that purchased energy from the state authority. That saw a net reduction in energy usage in this state over the years of the environmental campaign. It removed the financial justification for economically inefficient and environmentally destructive projects. It is the flow of money, not energy that decides political decisions.

    There is no need to put solar on your house. If you finance solar at a better site you generate more energy per dollar invested. Since the 1:1 feed-in tariff here is set to fall next year it would be silly to install more PV than my daytime baseload. Meanwhile I look for ways to invest excess energy during the day, rather than give it away to a bureaucracy. I have not expanded my installation here, but I have invested in bigger installations at better sites.

    I have a net energy credit for my home, the last three quarters were economically positive, this winter quarter will balance that. But it will change when the tariffs become directionally asymmetric.

    In the past I have stored my excess daytime energy by delaying the fall of water in the state hydroelectric system until later. With the feed-in tariff change next year that goes from 100% to 25% economic efficiency. The grid connection fees here are now greater than the cost of the power, so the incentive is to go off-grid with a battery. That is incompatible with the current state energy marketing strategy. The only negotiation leverage that house-holders have is to withdraw provision of available excess energy to the grid, which necessitates reprogramming grid-tie inverters to one way energy flow. It is bad short term environmental, economic and energy policy, but is a sensible long term strategy for house holders. Why should we buy batteries when cyclic hydroelectric delay already banks our energy ?
     
  16. Jul 28, 2017 #15

    sophiecentaur

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    Yes. That point has been made. But the state of the domestic Solar Electric industry, up till now, is such that the aim is a quick buck for the installers and a quick political fix by politicians to get their names down as green pioneers. If consumers are not aware that their houses could look better and that they could be getting more yield, they won't question the situation.
    The example of my house is typical. I have a trapezoidal roof space and there is room for at least one extra square panel in the lost triangle (=10% extra). A few smaller square panels would yield an extra 5%. Would the installation be that much more expensive to instal?
    I had so-called surveys of a previous house and not one of the visiting surveyors suggested anything other than a (area wasteful) array of identical panels. There can't be many technical arguments against that idea and the difference in cost would hardly be significant. It is sheer laziness and lack of incentive for suppliers to put any more than minimal effort into the One Size Fits All system that's used these days.
    "50 different shapes": Actually, there is a vast range of smaller (rectangular) panels available of low power systems with different aspect ratios. They mostly have 12V outputs. I was spoiled for choice when considering 'PVing' my boat and my shed.
    I appreciate the commercial aspect to this but installations in the future are sure to have more care and ingenuity applied. This will only happen when the public become more savvy. PV should be championing improvements like this, I think.
     
  17. Jul 28, 2017 #16

    russ_watters

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    Why not just use a combination of larger and smaller panels to fill in most of the gaps?
     
  18. Jul 28, 2017 #17

    sophiecentaur

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    I agree that is a good intermediate step. Problem is that I have never seen even that on roofs in my part of the World. They always go for identical panels and I can't think of a good reason except that it's less trouble and the client still pays his money.
     
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