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What's wrong with tracking on large solar arrays?

  • 1.  What's wrong with tracking on large solar arrays?

    Posted 03-16-2022 08:58 AM
    I am no expert, just trying to understand.  When I see pictures of large solar arrays, the panels are stacked together in a way that would make efficient solar tracking impossible.  Tracking should allow efficient collection over a wider period of the day, thereby reducing the need for expensive storage.  Are power companies stupid?  What am I missing?

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    Ernie Rogers
    Partner
    ernie.e.rogers@gmail.com
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  • 2.  RE: What's wrong with tracking on large solar arrays?

    ASES Life Member
    Posted 03-17-2022 09:19 AM
    GCR -  ground cover ratio - can be deceptive when a photographer is trying to show off the panels at an angle that hides the space between.

    Next time you play with https://pvwatts.nrel.gov, on "System Info" page, "Advanced Parameters", "Ground Cover Ratio:", you'll see a current default of ".4" - 40% of the ground is covered with panels. In utility scale solar, single-axis backtracking arrays are very common, and in Albuquerque, utility scale fields have used 33% coverage to maximize early morning and late afternoon energy production to better match the two daily peaks.  Land cost might push for more coverage at the expense of maximal energy production.

    PVWatts includes handy "i" information buttons as a built in tutorial, thank you NREL!


    Andrew Stone
    Commercial Solar Lending











  • 3.  RE: What's wrong with tracking on large solar arrays?

    Chapter Leader
    Posted 03-17-2022 09:20 AM
    Ernie - As you know the 'tracking' mechanism is 'mechanical' and will tend to break down regularly ! If you have a tracking PV array, on a small scale the problem may be accessible for repairs ! On a large scale the mechanical apparatus involved may not break down, but when it does, it's beyond the scale that would make it easy to repair ! Therefore, the size of many community solar projects allow for the advantage of simple south facing PV array, in addition to the slant angle of 'latitude (+/-) 15 degrees' will be optimum for these PV projects ! I work with small scale, 'off-grid' solar and do appreciate your question !

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    John Burke
    Director, MESEA, Maine
    Maine Solar Energy Association; Downeast Alternative Design Solar, Inc
    Jonesport ME
    dadsolar@yahoo.com
    ------------------------------



  • 4.  RE: What's wrong with tracking on large solar arrays?

    Posted 03-17-2022 09:49 AM
    Hey, John, thanks for the reply.
          If you are right on the reason, that just means to me that this is a problem that needs attention--to develop a reliable, low-cost tracking system.  Only one-axis tracking is enough to gain 90% of the benefit.  But, I would imagine that someone has already published a paper digging into this question.
          Hey, you live way up north.  Long summer days should be very good for tracking.

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    Ernie Rogers
    Partner
    ernie.e.rogers@gmail.com
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  • 5.  RE: What's wrong with tracking on large solar arrays?

    Chapter Leader
    Posted 03-21-2022 10:54 AM
    Ernie - We do live 'up north' in the most northern state in the US, (other that Alaska !) ... although we're in the 'furthest East', and 'Downeast' as they say ! (We're as far south as you can go, when you're at the 'far eastern' ... Washington County, Maine) ... "The Sunrise County, USA" ! Of course we do get the earliest 'sunset' as well ! We have a small, 'off-grid' PV array on the passive solar 'owner built' home ... here on the coast of Maine, Jonesport. The four 240W PV modules give the 'required' electric power we desire here ! Tracking has it's advantage in some circumstances, but I stand by the 'old adage' ... You are better off with additional PV modules, (as others have agreed with me here), than the possible 'headache' of a tracking system ('mechanical breakdown'), ... and if you happen to be 'away' ... then you may almost cut you PV power completely 'OFF' ! ... since how often would a tracker 'quit' when the modules are facing directly South' ??? Keep up the effort for an 'inexpensive, fool-proof' tracking system ! Thank you

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    John Burke
    Director, MESEA, Maine
    Maine Solar Energy Association; Downeast Alternative Design Solar, Inc
    Jonesport ME
    dadsolar@yahoo.com
    ------------------------------



  • 6.  RE: What's wrong with tracking on large solar arrays?

    Posted 03-17-2022 10:35 AM
    solar tracking, if used in a LARGE, array, is generally setup as E/W tracking only. By using only a single axis, more panels can be moved, with less energy, less cost, and better wind resistance.  2 axis tracking is a VERY expensive installation cost, and on a UTILITY SCALE would be cost prohibitive. With the significant reduction in cost of panels, simply installing an extra 15% of panels on a fixed array gathers the equivalent of a much smaller array that is tracking. The MONEY NUMBERS just don't work out in favor of any tracking other than single axis - and even with single axis tracking, the MAINTENANCE COST is a very significant part of the lifetime operation expense. it all boils down to math, money, profit and payback time.

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    Joe Utasi
    PV Solar Consultant
    Cinci Home Solar, Keowee Home Solar, DIY Solar Helper
    joe@cincihomesolar.com
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  • 7.  RE: What's wrong with tracking on large solar arrays?

    ASES Life Member
    Posted 03-17-2022 11:18 AM
    Dual axis tracking is possible.  Due to the additional installation and maintenance cost, it is usually more cost effective to use a fixed ground mount to obtain the same amount of electrical energy.

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    Stu Besnoff
    owner
    Alpine Solar Heat and Hot Water, LLC
    stu@AlpineSolarHeat.com
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  • 8.  RE: What's wrong with tracking on large solar arrays?

    Posted 03-17-2022 05:12 PM
    There is nothing wrong with tracking per-say.  It is just that extra movmement adds GREATLY to the cost of a system and then adds maintenance to what is normally maintenance free.  It is just much more cost effective to add a few more panels to a fixed array.

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    David Hrivnak
    Sales/Engineering
    EcoLogical (part time)
    dhrivnak@chartertn.net
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  • 9.  RE: What's wrong with tracking on large solar arrays?

    Posted 03-18-2022 03:55 PM
    In a nutshell,...
    Bankability and LCOE are gods in utility scale solar.

    Complexity robs profits if not cost justified. It is cheaper to simply orient more fixed panels toward the most profitable azimuth. For us in the western US,..that means WEST.

    Tracking typically only makes sense when you are space constrained.

    Vic Aguilar
    Sustainable Energy Consultant
    NABCEP COK#081309
    (626)633-6682
    Please consider your environmental responsibility. Before printing this e-mail message, ask yourself whether you really need a hard copy.






  • 10.  RE: What's wrong with tracking on large solar arrays?

    Posted 03-21-2022 09:44 AM
    Mar 18, 2022 3:55 PM
    https://community.ases.org/network/members/profile?UserKey=d77f39fd-47d3-4768-9490-7761bdeece0e. Click or tap to follow the link." data-linkindex="30" style="margin: 0; color: #57B1B5; text-decoration: underline">Victor Aguilar
    Question - How is WEST the most profitable? >  Would not 50% of each day and a large amount of gain in the winter months be lost? 


    Mar 18, 2022 3:55 PM
    https://community.ases.org/network/members/profile?UserKey=d77f39fd-47d3-4768-9490-7761bdeece0e. Click or tap to follow the link." data-linkindex="30" style="margin: 0; color: #57B1B5; text-decoration: underline">Victor Aguilar
    In a nutshell,...
    Bankability and LCOE are gods in utility scale solar.

    Complexity robs profits if not cost justified. It is cheaper to simply orient more fixed panels toward the most profitable azimuth. For us in the western US,..that means WEST.

    Tracking typically only makes sense when you are space constrained.

    Vic Aguilar
    Sustainable Energy Consultant






  • 11.  RE: What's wrong with tracking on large solar arrays?

    Posted 03-22-2022 06:18 PM
    South orientation will produce the most energy but West can be more profitable depending on the Time-of-Day rates of the utility. A West orientation delays the peak production time by several hours compared to a South orientation. If the electric usage is higher in the late afternoon/early evening when it is hotter and more air conditioners are on, and the utility rates are higher to compensate for this, then it could make economic sense to orient your panels to the West.

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    Thomas Grant
    Director
    XanaduEnergy
    Fairway KS
    tjg4@aol.com
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  • 12.  RE: What's wrong with tracking on large solar arrays?

    Silver
    Contributor
    Posted 03-22-2022 10:39 AM
    Edited by william fitch 03-22-2022 07:35 PM
    A quick note. Be careful when having all these "what's the best" conversations. What is most profitable may not mean maximum production, especially in commercial arrays. I would stay away from all financial aspects, especially for res and focus on site maximum production (Engineering). Other wise things like 'West is best' can seem off the rails... The RE goal is to produce as much energy as possible which will yield the maximum displacement of FF. Focusing on the money is the wrong primary reason. Design for max efficiency and max power but meeting the engineering requirements for the particular system design and function. A justifiable reason for choosing a flatter production profile might be when an array is being designed to charge batteries. A longer flat curve might be better than a peak'ie curve despite yielding more energy. There are other engineering situations which also could arise, etc.. Tracking over the course of a day yields a much flatter profile and yields the most energy per KW installed. The challenge with tracking is wind loadings. Over design for that along with the movement engineering and maint. will be minimized. 

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    william fitch
    Owner
    www.WeAreSolar.com
    fcfcfc@ptd.net
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  • 13.  RE: What's wrong with tracking on large solar arrays?

    ASES Life Member
    Posted 03-23-2022 12:20 PM
      |   view attached
    Bill Fitch makes a good point. There is no single metric of 'best'. A paper from the now defunct Solar Pro magazine (issue 11.1 2018) authored by Paul Grana called 'Design Optimization in Constrained Applications' makes the case that the same commercial rooftop could have three different installations depending on the goal. I attached it here. See table below. You can optimized for different constraints:  by area, budget, or power injections.  Can result in different tilt, kW installed, energy produced. And in net revenue or NPV. Similar with tracking.

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    Steven Hegedus
    Professor and Senior Scientist
    University of Delaware
    Newark Delaware
    ssh@udel.edu
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  • 14.  RE: What's wrong with tracking on large solar arrays?

    Chapter Leader
    Posted 03-23-2022 12:41 PM
    William Fitch - Than k you, I agree with your comments ... "I would stay away from all financial aspects, especially for res, and focus on site maximum production (Engineering). Other wise things like 'West is best' can seem off the rails... The RE goal is to produce as much energy as possible which will yield the maximum displacement of FF." ...
         I work with small 'off-grid' res PV systems and help folks with a 'D-I-Y' ambition ! Of course we do want maximum output, to keep the 'storage' up, and ready for the times we need to use the system ! A motivating factor for all 'clean renewable energy' projects should be to 'accelerate the move away from FF' ... and we all know that the FF industry and Wall Street are fighting this, from 'ground zero' !
         I also agree with your sentiment that we should be "designing for max efficiency and max power but meeting the engineering requirements for the particular system design and function" ! Please keep up this focus ... and the effort to 'End the Fossil Fuel Addiction' that we all suffer from ... thanks again !

    ------------------------------
    John Burke
    Director, MESEA, Maine
    Maine Solar Energy Association; Downeast Alternative Design Solar, Inc
    Jonesport ME
    dadsolar@yahoo.com
    ------------------------------



  • 15.  RE: What's wrong with tracking on large solar arrays?

    Posted 03-24-2022 07:22 AM
    Wrong, Wrong, Wrong,..
    To reparaphrase the question, 'why not track on large (utility scale) ground mount arrays?'
    The answer..
    As I stayed originally, is that LCOE, ROI, MTBF, etc. are the KPI's for utility scale solar, which is facilitated by it's economics.
    But this also affects it's power to offset FF.
    California is a macrocosom of what happens when you build out massive amounts of PV without grid scale storage (search: 'CAISO duck'). People are watching California around the world to see how we manage the challenge of assimilating all this renewable and maintaining a reliable grid at the same time.
    The reason that West is so important and is becoming more important in any grid system facing the same challenges relates to the fact that there is a massive ramp in demand in the afternoon just when solar starts to wane(CAISO duck quacking). In what's known as a 'North/South' grid like California, this demand is currently met by some of the least efficient most expensive and dirty sources of power called peaker plants. This is why economically, societally, and environmentally, we need systems that are designed to meet all three of these objectives and not ones that are blindly designed for maximum output that would flood the grid with power at a time when it's worth less than zero. Not helpful not economically optimal. Also bad for the success of our energy transition.






  • 16.  RE: What's wrong with tracking on large solar arrays?

    Silver
    Contributor
    Posted 03-24-2022 08:02 AM
    Edited by william fitch 03-24-2022 02:14 PM
    If you have people dying of thirst and you find a water source that can give you the volume but it comes out faster than they can drink it, the answer is not to slow it down and loose the output, but to find buckets to store the water until they can drink it. You pretty much said so when you used the phrase, "....without grid scale storage...." So the answer is not to curtail the production but to increase storage. FF's are self contained energy and storage where direct energy sources like Wind and Sun be it Thermal or Electric are not. This has always been known BUT often ignored. So the answer is to push harder for storage and not treat it as a separate issue. Rise to the occasion not stifle the opportunity.
    Edit: For those readers who may not know all the above acronyms"
    LCOE- Levelized Cost Of Energy (Total cost over entire time)
    ROI- Return On Investment
    MTBF- Mean Time Between Failures (Proportional to Complexity usually)
    KPI's- Key Performance Indicators

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    william fitch
    Owner
    www.WeAreSolar.com
    fcfcfc@ptd.net
    ------------------------------



  • 17.  RE: What's wrong with tracking on large solar arrays?

    Posted 03-25-2022 04:33 PM
    Why concurrent production is important.
    Batteries are not free.
    Neither to install, nor to charge.
    RTE, or round trip efficiency tops out typically at around 85-90%, which means you lose 10-15% of your energy in the process of (AC coupled example)rectifying AC, charging stack, then inverting DC after discharge, or (DC coupled example) charging, then inverting to AC on discharge.
    Virtually everything we have installed for the last 5 or more years have had storage(specifically BESS) involved. Hundred and hundreds of Kwh of behind the meter resi batteries!
    Nonetheless, real time consumption at the times of production always delivers a better LCOE. On the large scale (Ie.utilty scale) the questioner mentioned, this can be sink or swim.
    Finally, a huge eye roll to those expounding in their answer that 'we need more batteries'.
    When I was younger I would have quipped, No S*** Sherlock! 
    'Solar Vic Aguilar
    NABCEP since 2008 (someone had the temerity to ask)






  • 18.  RE: What's wrong with tracking on large solar arrays?

    Silver
    Contributor
    Posted 03-25-2022 11:16 PM
    Edited by william fitch 03-25-2022 11:20 PM
    "When I was younger I would have quipped, No S*** Sherlock! "
    Wow...OK.. now its a party!
    Well than pick a side. Don't sit there with I wish you could see my eye roll while expounding the inefficiencies of coupled storage. Everything in the universe uses storage, including human cells. Planets store heat in there mass. Wow! How inefficient. Oh my batteries cause us to use production energy to transform back and forth from AC to DC and back. Oh the agony of it. Help me, help me, fix my broken wing. Oh I know, lets force the world to match their loads to our maximum production capabilities so we can maximize that wonderful human construct called currency and profit. Lets choose the non-real over the real because that has brought us to our current best place in history. We currently choose RE because it just todays whim. No real need in REALITY to stop the planet from cooking us. Its just fun. I mean its not like the seeking of profit over what's really right for us, brought us to this point in time. I mean its just
    coincidence if it looks that way. People are always quick to say, "well then what's your solution that's better than what we have?" The solution is to get EVERYONE to actually realize what the problem is!! Then, and only then will functional solutions present themselves.
    So yes cheaper storage. I wonder if economies to scale has anything to do with this....maybe....
    It didn't seem to stop the introduction and the explosion of the ICE that 80% of the production energy goes straight to heat bypassing kinetic energy. OMG!! How could this be.... Super-duper inefficiency being chosen by the market place!! Oh my... Engineering rules...!!
    And now for what I really think...

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    william fitch
    Owner
    www.WeAreSolar.com
    fcfcfc@ptd.net
    ------------------------------



  • 19.  RE: What's wrong with tracking on large solar arrays?

    Posted 03-23-2022 09:47 AM
    As others have stated, the basic goal of solar project development in utility and industrial applications is always to maximize economic factors such as  levelized cost of energy (LCOE) or return on investment (ROI). Every project is subject to financial and engineering review. While this is a conservative exercise by nature, there is nothing "stupid" about it or the stakeholders involved in the process.

    In terms of optimizing for LCOE, revenues associated with solar plant energy production are one input to the equation only; the other inputs include up-front capital expenditures (CapEx) and long-term operation expenditures (OpEx). All else being equal, developers are clearly incentivized to generate more energy. But not at any cost. Dual-axis tracking, for example, can increase energy harvest (kWh) and yield (kWh/kW). But it also increases CapEx and OpEx beyond what is beneficial for LCOE. 

    In utility-scale applications, bifacial modules mounted on single-axis trackers are currently the most favorable plant design, on average, based on LCOE. This is in part due to the fact that single-axis tracking is considerably more efficient in terms of land usage as compared to dual-axis trackers. If land cost were zero, then dual-axis trackers might be leading the market. Since land isn't free, developers need to co-optimize for revenue, yield and ground coverage. As a result, tightly packed single-axis trackers almost always win the day based on LCOE.

    In commercial and industrial applications, plant optimization is further complicated by utility rate structures. If a utility is charging a premium rate for energy during the 4pm to 6pm window in summer, for example, then a west-facing solar array may generate considerably more revenue over the course of the year than a south-facing array-even though the south-facing array will generate more energy. 

    In the future, energy storage costs may factor more directly into project development considerations. Today, most solar farms do not include storage. However, more storage will be required to accommodate high levels of solar penetration. Also, co-located storage can turn a "variable" solar power plant into a "dispatchable" solar power plant, which is beneficial for power system balancing. In practice, those higher-level considerations are not part of solar project development or utility planning today, outside of very few niche markets.

    While utilities are often offtakers of solar power plants, they are rarely the project developers or operators. So, there are a lot of competing interests at play. Also, utility regulation lags behind the market and technology. It's complex. But it is all highly studied and scrutinized and driven by dollars and cents.

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    David Brearley
    Board of Directors
    David Brearley
    david.charles.brearley@gmail.com
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  • 20.  RE: What's wrong with tracking on large solar arrays?

    Silver
    Contributor
    Posted 03-23-2022 01:09 PM
    Regarding commercial specifically, single axis wide row spaced tracking running North South, can reclaim some of the reduced energy yield with the tracking from the wide spacing, but allowing low height yield crops in between (Duel land use). Trackers can be "verticalized" during farming equipment use, lowering damage possibility and almost eliminate snow build up where applicable. This has a real benefit from a "total use" perspective for the land, and can quiet NIMBY'ism regarding the loss of our farm lands "thinking".

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    william fitch
    Owner
    www.WeAreSolar.com
    fcfcfc@ptd.net
    ------------------------------



  • 21.  RE: What's wrong with tracking on large solar arrays?

    Posted 03-24-2022 02:23 PM
    I am a little surprised by parts of this thread that want to dismiss cost as a decision factor. Companies, utilities, consumers, and you and I will always weigh costs when making any decision. We dont always take the cheapest alternative, but the added expense has to be outweighed by other benefits to the buyer. Renewable energy is a cost effective alternative to fossil fuels, and that fact has powered the great growth of renewable energy. Look at any solar company's marketing material and it will emphasize the savings to the consumer. So the fact of the matter today is solar panels are cheap; complex tracking systems and storage are not so cheap. So you want to change the equation? Make storage cheaper and the matter will take care of itself.

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    Thomas Grant
    Director
    XanaduEnergy
    Fairway KS
    tjg4@aol.com
    ------------------------------