Graph of the Day: Myth of solar PV energy payback time

graph of the day

Today’s Graph of the Day is a simple one, and is designed to dispel the myth about energy pay-back times, at least for solar PV. Some anti-renewable commentators and myth-makers would have us believe that solar PV modules do not pay back the energy used to create it. It’s not true.

This graph of the day was presented by Muriel Watt, the chair of the APVA, at a seminar on Community Power in Sydney that I chaired on Wednesday. It’s not a new graph, but demonstrates that the payback is actually very quick.

The energy payback time in which the energy input during the module life‐cycle is compensated by electricity generated by the PV module depends on several factors, including cell technology, PV system application, irradiation, the sources of energy used in its manufacturing processes and the energy the PV will displace.

For a typical 2 kWp rooftop system, the energy payback time is 2 to 3 years using multi‐crystalline modules and more than 7.5 times the energy used in its manufacture is generated over a 20 year life. For thin film modules, the payback time is half that of crystalline modules, but the lifetime may be shorter.

graph of the day



8 responses to “Graph of the Day: Myth of solar PV energy payback time”

  1. Ron Barnes Avatar

    Theory is not what the results which show, As time goes on the units become less efficent .
    When mine started it is a 5.5 kw fonius IG 40 with 30 pannels , its maximun average power out put was 3.50 kw per hr for peak times.
    It was installed on the 19/9/2008 still not old the expected life was 10 years on unit and 25 years with a drop down of output from the pannels over time this can be offset by adding more pannels at the time of less output another cost.
    I have had this up on only once to 4.5 kwts peak in 4.5 yrs of opperation for 2 hrs approximately on an overcast glary day, my neighbours small unit on the same day regestered its full capicty admitdly his is less than 6mths old..
    The cost of my instulation was $50,600 so I will never recover the initional outlay.
    I installed it to do my bit towards cleaning up the atmosphere as my give back for the years I have lived for the future generations.
    We use very little energy as every item in this has the best star rateing.
    My main computer, and all house Led lightening is all 12 volt ran off an auxliery unit I built my self to battery for stand-by reasons when I had a lot of fish.
    Admitely on my neighbours result his will pay for its self in a relitive short time compaired with mine.
    So not all PVA,s are equal in output ,Mine is a Multicrystaline unit.
    I have built a 2 killawat Solar tracker from scratch running of high efficent 250 watt 24 volt pannels and have started building a 10 kwt unit also as a Solar Tracker but it is costing a lot because of its size and amount of concrete it will require to support it in high wind.
    It is hoped this one will be more efficent but I doubt it will never make 100% as heat losses in conversion are lost power generated in all inverters.
    My unit has failed 5 times over 4.5 years and again is out of service waiting replacement they the repairer stated it is beyond rebuild my supplier of this unit has offered a new replacement of a different brand gratis because of all the trouble it has caused as a good will offer.They are Solar Newcastle. my instalation was the 75 one installed.
    There are many others out there with this problem in Australia .
    They are not covered under the normal house policy it costs more .more cash outlay each year.
    Not taken into account on any therotical graph.
    Neigher is on going maintenance and replacement of failed inverters another cost.
    I also added to my enclosure a thermaticly opperated cooling system which runs of my auxilery system.
    When their batteries fail it will be also another cost Therefor it will never in total will be able to pay for its self in my lifetime which im now almost 65 .

    1. hackle Avatar

      Hi Ron, the graph talks about ENERGY payback, not FINANCIAL payback.
      In regards to your first argument, good quality solar panels have a very low degradation rate of around %0.3 per year. Most warranties nowadays guarantee a maximum degradation of 0.7% per year. So the efficiency loss is minimal compared to any other appliance or a combustion engine.
      Sorry to hear you have so much trouble with your installation. This is certainly not the norm.

  2. hackle Avatar

    does that calculation include the inverter, mounting, cables, etc. ?

  3. Ray Wills Avatar

    A presumably newer source of data on energy payback of PV – presented February 2012 by Wacker Chemie AG – shows a far better performance than the graph presented here

    See slide 12 – suggest an energy payback of less than one year was achieved in about 2010.

  4. Miles Harding Avatar
    Miles Harding

    I would think that the energy payback depends on which components of the system are being considered. One year is believable for the panels themselves, as is two years when the aluminium supports, wiring and inverter are also considered.

    The joys of being an early adopter. I bought 2Kw in 2008, before the recent big price reductions. I seem to have been more fortunate with the battery charger (Xantrex) and the inverter (Latronics 48volt) and used batteries from a big data centre UPS.

    The 2008 panels are performing well, but I have a different story for a 2010 grid feeding system installed at the end of the WA generous feed-in tariff. In the case of this set, they were made with substandard silicone filling compound, which is degrading (turning brown) in the sun. so far it has resulted in approximately a 10-15% reduction of output so far. This is a trend that I expect will continue with these panels.

    The positive side is that new panels are now only slightly more than $1.00 per watt, so are are not prohibitively expensive to replace.

    A big issue in in China is substandard materials substitution, which is so rampant that there are no guarantees that even premier brands are immune its effects. (my substandard panels are a supposedly reputable Chinese brand)
    I expect that this will become less of an issue as the industry consolidates and the disreputable makers are eliminated.

    From a consumer’s point of view, A $1.00 per watt panel that lasts 10 years makes more sense than a $4.00 per watt panel that lasts 25 years. Particularly true if hailstorms are going to destroy panels occasionally.

    Something I find much more disturbing than occasional dodgy materials is a move by the solar industry to prevent parallel imports, which was discussed in another story. This sounds like the music and video industry (region coding of DVDs) that does this to allow price fixing on the local market. If this is allowed to gain traction it will have the sole effect of increasing the importers profits at the expense of all of us, the mug consumers.

  5. melbcity Avatar

    This graph is misleading in that it only compares the cost of production to input, what about teh cost of mark-up installation and structural modifications. By the time we add up all the costs we are looking at a 5-10 year payback period depending on your location and the amount of sun.

    Smart zonal lighting in apartment buildings where light bulbs can talk to neighbouring light bulbs on the building grid to dim down, shut down when there is no activity or brighten up on movement can save much more energy consumption .

    How many apartment have the lights in the hallway or common areas left on 24 x7. Much more can and should be done to retrofit old apartment and office blocks with simple smart techology

    1. darkflame Avatar

      “misleading in that it only compares the cost of production to input, what about teh cost of mark-up installation and structural modifications.”

      umm..a guy with a ladder and a days work for most home installs.
      Not really “structure modifications”
      You could take into account the guys lunch too, but even then not going to be adding much % wise. Certainly not double.

      As for smarter lighting, absolutely….but have you factored in the installation costs for those smart bulbs 😉

      1. melbcity Avatar

        I know of situtations where over $100,000 was spent on structural modifications to support the solar panels.

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