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How rooftop solar is causing big falls in peak demand

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The big push by utilities across Australia to hit solar households with higher network charges is underpinned by the claim that rooftop solar does little to reduce peak demand.

There is increasing evidence that that is not the case. Peak demand has been pushed in some states to the evening, after the sun comes down, but what is often not displayed is what the peak would have looked like without rooftop solar.

In short, it would have occurred earlier in the day, and at a much higher peak. This is critical, because networks super-sized their grid in anticipation of big rises in peak demand. The combination of energy efficiency and rooftop solar and declining industrial demand has junked those forecasts. But we’re still paying for the investment.


This graph released last week by the Australian Energy Market Operator, in a presentation on the WA market that it now manages, illustrates the point in Western Australia.

The peak – without solar PV – would have appeared at 3pm in Perth, and be considerably higher than the peak level with solar PV, which now occurs at 4.30p. Yet still, the network wants solar households to be hit with higher network fees, another example of where the benefits of rooftop solar are not factored in.

aemo WA pv  

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  • trackdaze

    So if there was an incentive for western facing panels and storage we could reduce the 4.30 peak?

    The trouble is the network is psuedo government. They find it very hard to manage their labor resources and other asset when there is a reduction in utilisation.

    • Calamity_Jean

      “So if there was an incentive for western facing panels and storage we could reduce the 4.30 peak?”

      Very probably. Western facing panels would lower the peak and shift it to still later in the day. Storage would lower the peak or help to meet it, depending on which side of the meter the battery was on. .

      • trackdaze

        Im thinking it wouldn’t matter the side of the battery for affecting the peak. even if its invisible to the network as long as its being drawn upon its displacing (peak) demand?

        The trouble for the network and retailers is a behind the meter scenario withdraws what they see as a contributor.

        • Calamity_Jean

          Well, if the battery is on the customer side of the customer’s meter, using power from the battery just looks to the utility like a reduction in demand.

  • Jonathan Prendergast

    I have never like those duck curves, that show a big hollowing out of day time demand. They seem to cherry pick data to show a particular point.

    The actual effect of solar on peak demand (or required network capacity) really depends on whether peak is seen in summer (AC) or winter (heating), and whether load in an area is more residential or commercial.

    As I casually watch the wholesale market, in NSW it seems that higher demands are in summer with predominently commercial/industrial load, seeing peak demand at around 2-3pm where more solar would certainly help.

    It would be good to know more about the context of the AEMO study that the graph is from.

    • Jacob

      Nope.

      The peak demand is in summer. (due to air con use).

      Heating is provided by more often by LNG rather than by electricity.

      Some houses still burn firewood.

      Electric heaters tend to be used after schools, shopping malls, and offices shut for the day.

      • Jonathan Prendergast

        I think you are actually agreeing with me.

        But I would not agree with your generalisation in towns in southern states without town gas. Even in Taree in northern NSW the peak demand is the same in summer and winter.

        Nonetheless I think the duck curve graphs have been created to make a particular (anti-solar) point

  • Aerial Fencer

    When you say “Networks” are you refering to transmission or distribtution? Total area usage and wholesale prices are only really relevant in a discussion about the transmission networks.

  • JohnRD

    The networks are in trouble because they made bad business calls and may have deliberaterly over invested to game the system. Needs a royal comission.

  • Beat Odermatt

    When I was working for an electricity company in the late 90th, hot weather meant a massive peak demand and an excellent bonus. It also meant many blackouts and a number of elderly people died. Rooftop solar has reduced large bonuses for electricity workers but also we have now fewer blackouts and death. How can any decent human being be so miserable to punish good environmental action and increased safety for all?
    We must also remember for every watt generated by the sun some fossil fuel stays in the ground to provide essential resources for future generations. Are we the generation of future burners?

    • Jacob

      What did they die from?

      • Beat Odermatt

        Blackouts caused heat exhaustion and death. People also dies because traffic lights did not work. People with life support systems had to be rushed to hospitals because equipment stopped. You must be very young not too know why these people died.

        • Jacob

          My point is, did they die due to a lack of air con or did they die because medical equipment stopped working due to a lack of electrons.

          • Beat Odermatt

            I am sure you know that elderly people did die because of heat exhaustion, medical equipment not working and traffic accidents. We got good bonuses but people died.

          • Jacob

            Road accidents are a minor part.

            So I guess the biggest killer is a lack of cooling or air cons.

          • patb2009

            Why do you care so much… Suffice that people died, each time the power failed.

          • Jacob

            Hey yeah, stem cells injections to repair joints.

            Why do they work in some patients and not others?

            “Why do you care so much…do not try to improve stem cell technology…continue the scattergun approach”

          • Elisabeth Meehan

            Not every old person has air conditioning.
            Old people are often afraid to open their windows at night because of security concerns.
            Even fans won’t work without electricity.
            Ever heat wave causes deaths.

          • Elisabeth Meehan

            Lack of electricity. How difficult is that to understand?

          • Jacob

            Lots of old people in villages still do not have electricity.

            How hard is that to comprehend?

            “Car crashes kill”

            How exactly?

            “Occupants hits dash/windscreen”

            Ok, we need to invent seat belts.

          • Greg

            Gee Jacob what 3rd world nation or backwater town do you live in to not know COMMON SENSE answers …. sheeeeeeeesh

          • patb2009

            Yes… Sometimes people died because they tripped in dark basements or bathrooms, sometimes they were killed working on an electrical system they thought was dead when power was restored, sometimes they died from heat stroke, sometimes they died from food poisoning from spoilt food. As a critical component of modern life, the loss of electricity leads to fatalities.

  • Chris Fraser

    Notes on the tenuous and weak argument that solar doesn’t reduce the evening peak (and shirley are they serious ?)Sister site ‘One Step’ shows that about half of the smart meters being fed by the solar are the Gross type with generous FiTs. Such is the case the solar Owners are not necessarily incentivised to consume solar for household loads during the day. Of course, the situation changes in NSW at end of 2016, when potentially Gross meters there get replaced by Net. Solar then gets used during the day. There would be many daily household tasks even if the owner is not home – battery charging, pools, hot water, washing, air con.It is not hard to imagine why Owners would shift this load, and that is they know they have a much higher tariff waiting for them in the evening. A perfect incentive to limit evening consumption.After a few months, watch that ‘Demand minus Solar’ curve drop substantially. There, that small thing just killed the argument of the empire builders. By definition, every task that becomes powered by home solar, regardless of the time the task is completed, reduces the peak demand.

    • Mathew

      I agree well said 🙂
      I live in the Latrobe Valley Victoria, and there are some very large gas peaker power plants here that are barely used. We could have many times more solar in Victoria without running into afternoon peak issues.
      Also fast response gas turbines (aircraft engines basically) hate the heat and are de-rated big time at the hottest times making solar even more important.
      From Wikipedia:
      In summary, the performance of a gas turbine, its efficiency (heat rate) and the generated power output strongly depend on the climate conditions, decreasing the output power ratings by around 20 to 40%

      • Jason

        True enough about gas turbines hating hot weather [1]. But commercial plants in Australia know that there two weeks in February where spot prices of electricity skyrocket, and those weeks pay for a big chunk of the rest of the year.
        Accordingly, many commercial gas turbines have inlet air coolers; either chillers (very big air conditioners) or evaporative coolers. So the summer / winter difference doesn’t result in a 20% de-rating for chiller-equipped turbines. If there’s enough water around that evaporative cooling can be used, the de-rating is under 2% (from memory – feel free to correct). Chillers pull more like 5% to 10% power, but you can use them where there’s no spare water.
        Whether the inlet cooling pays for itself depends on how often you plan to run the turbine in summer. If it’ll only start up during summer peak periods, it might not be worth it, as it’ll be printing money just by turning it on.
        [1] Their intake is a fixed size, and hotter weather means they can fit fewer oxygen molecules into the intake, which means less combustion.

        • Mathew

          I’ll trust you on your efficiency percentages though they seem cutting edge and I highly doubt that any of the old gas turbines in Victoria would be getting figures anywhere near as good.
          In the hot north of Australia intake cooling would be mandatory with current gas prices.
          As you said the summer heat wave spot price goes very high when intermittent use turbines are needed so efficiency would not have been of great importance at anyrate. Also to be clear I’m not referring to combined cycle gas power stations which are more for base load and are far more efficient.
          My overall point was that in cooler Vic we could use the peaker turbines to boost low power outputs in winter or cloudy days and transition away from the 24/7 high output polluting brown coal power more quickly if we installed around 5 times more solar than we have now with without the grid collapsing.

  • Phil

    Just go 100% off grid. Quite do-able , and affordable for an average detached home of the average 2 people north of Sydney Australia.

  • Ian

    Looking at the graph, on the face of it, solar takes a big chunk out of the day time peak, but actually solar contributes very little to total energy output. The y axis starts at 700MWH and Solar’s best contribution is 200MWH. Installed capacity and capacity factor is measured in MW usually ( look at the units of the live generation chart on this website). But for the sake of analysis MWH will do. Quite clearly this graph is not designed to inform but to persuade! Maybe some reinterpretation is needed. Coal is best suited to continuous generation. That is 800MWH of demand does not vary. In a scenario where generation is coal , gas and solar, coal would be useful only up to 800MWH. The difference between peak and trough is 700MWH. This peak happily occurs at 2pm. An installed capacity of 700MWH solar could quite easily compliment the base generation of coal. The remaining peaks at sun rise and sunset could be covered by gas peaker plants. So, using the AEMO’s own graph it can be seen that there is a deficit of solar rooftop installations of 300MWH. For grid reliability more rooftop solar is needed not less.

    • Ian

      Another thing, for coal to be economical, it needs to run 24/7. The trough level of consumption represents cheap electricity. The variable part represents either coal plants ramping up or reducing production which is more expensive or previously, gas peaker plants turning on – again more expensive. Previously, meeting the variable part of the demand curve was where money could be made. Rooftop solar reduces the peak demand right at the time when electricity production used to be most lucrative. Even though rooftop solar penetrance of the total electricity supply can be a lot higher without causing grid instability or causing any disruption to the continuous operation of coal plants, the utilities don’t like behind the meter solar because of its disproportionate effect on their revenue stream. Domestic solar is cherry picking their profits and they feel like sitting ducks! ( Duck curve they call it) .

      Here’s a further thing: the AEMO’s graph suggests that current variable capacity has got to be about 700MWH or roughly half the total demand. That means solar can completely supply the daytime demand with variable generation taking up the deficit. That is without resorting to storage . Wind is complimentary to solar, so with existing variable generation technology, wind and solar can cover most of WA’s power requirements. Old style coal can be completely phased out. South Australia demonstrates this quite nicely. As said , the existing gas peaker plants in WA can take up the slack, obviating the need for an interconnector.

      • patb2009

        you nailed it, the merit order effect is that every watt of solar destroys one watt of the most expensive electricity, and destroys the marginal rate that each producer earns… The most expensive marginal producer sets revenue for the other producers… When cheap solar comes in, it just ruins the party.

      • Miles Harding

        The coal generators have been dependent on these merit order peaks for years. They make as much or more profit from the short peak events as they do the remainder of the time.

        Where the merit order argument falls down is when it’s translated to consumer revenue:
        The end consumer is shielded from merit order costs by their retail tariffs, making the complaints by the generators largely about profit shifting away form them towards the retailer who now buy fewer units of expensive electricity, a problem sure to be exacerbated by batteries.

        An additional insult for the generators would have to be the large export to import discrepancy seen by solar consumers, with the retailer effectively pocketing the difference here as well.

        This sort of issue sounds like an application for blood letting between the generators, network and retailers before the consumer is blamed.

    • John Herbst

      Your point about the y-axis not starting at zero is valid criticism. Why use misleading graphics when the author has a strong case without it? Displaying MWH vs MW is not as big a deal to me, since it doesn’t change the interpretation that solar has reduced peak demand by roughly 10% in WA.
      Peak demand is the largest cost-driver for networks, thus Solar has truly helped reduce network costs by around 5%. Unfortunately, 5% less costs means 5% less allowed revenue, which means 5% less profit to the distributor. Herein lies the problem.

  • Math Geurts
  • Miles Harding

    If the generators think it’s bad now, just wait…

    The WA we a state treasurer that openly says the future is solar and battery. Apart from new wind, domestic and industrial solar projects, the advent of cost effective batteries will allow existing solar customers to be revisited with a new offering: more panels and battery. All this new capacity could easly drive overall demand well below 2008 levels and potentially eliminate the daily peak.

    The incumbents have a choice to either embrace this future or be ruined by it.

  • Jason

    So utilities aren’t in the Resource Conservation business? This changes everything!
    😉