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Why networks need a thin pipe to keep solar guerrillas at bay

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About half way through a presentation last week at the All Energy conference in Melbourne, it seemed that the end had come for one of Australia’s biggest network operators.

Barbara Elliston, from the Australian Solar Council, was explaining her concept of “guerrilla solar” and the business model of her company.

Essentially, this is an idea that households would install rooftop solar PV to satisfy the needs of their greatest single energy demand – hot water. The panels, rather than being connected to the grid, would be used to heat the water. Elliston says there was nothing the grid operator could do prevent the installation. Indeed wouldn’t even know, apart from wondering what had caused a sudden reduction in demand.

At around this point, Mike Swanston, the head of customer advocacy at Energex, and one of the country’s most incisive speakers about the challenge of rooftop solar and battery storage, and its impacts on networks, threw himself to the floor. “What are you trying to do to us,” he seemed to be saying. Swanston survived the experience, but there is no telling that networks will.

Concepts such a guerrilla solar exist because there is a mutual suspicion between network operators and the rising prosumer, a natural product of a rivalry that seems to pitch a centralised business model and the arrival of technology that is delivering the so-called “democratisation” of energy.

Solar consumers worry that network operators are going to find some way of loading up costs on consumers to recover their investment in the networks. It’s a suspicion reciprocated by many network operators, who fear that solar exists only to destroy their business.

Australia wide, nearly $50 billion will be spent on network upgrades and extension in the current five year regulatory period, and the networks want their money back. How exactly they do so in a world of reduced demand – thanks to the increased self consumption of solar households and increased energy efficiency – is one of the great debates of the electricity industry, both here and overseas.

In Germany, as we mentioned yesterday, consumers are responding by seeking to buy back the grid. It is happening in thousands of towns and villages, and even in major cities such as Hamburg and Berlin. Similar moves are being made in the US.

In Australia, there is no mechanism for that to happen. Quite how the networks get their money back – and keep their customers and avoid the prospect of stranded assets – is a mystery to all.

As Swanston said in his own presentation in that same session, the arrival of solar, and the imminent arrival of solar storage, is creating a “new normal” for distribution networks. “The paradigms that worked for last few decades are starting to fail us,” he said.

And he mentioned in a previous speech that we reported on, this is less a technical challenge than it is an community and social one – and for the network operators, a business one.

Energex has one of the highest penetrations of rooftop solar in Australia. In its corner of the world, in south-east Queensland, one-quarter of all houses have solar on the roof, or 232,000 homes. Even after the removal of the generous feed-in tariffs, new customers keep coming.

That is having a major impact on how Energex deals with its customers and operates its network. In many feeders, demand is disappearing during the mid-day hours as empty houses export electricity back into the grid. This graph below gives just one example. It shows successive years of demand on one feeder over the past four years, as solar PV has grown. The red line is from just last week.

energex feeder1

The problem with responding to these issues by imposing high fixed charges for all – the favoured means of most network operators to date – is that it penalises those who don’t consumer much, including those where that is caused by energy poverty, and it removes the signal for households to be energy efficient. And it provides an incentive to those who don’t like it will simply leave the grid, leaving the network with the increased danger of stranded assets.

Swanston says one idea might be one that is gaining currency in energy debates around the world – to charge people based on the capacity of the wire that links the grid with their home.

He calls this the “thin pipe” model. It basically puts an upper limit on consumption, and caps the connection charges for the customer. And it allows the network operator to make plans, knowing what the maximum demand can be. Network operators say population and the economy will grow, so aggregate demand will increase.

Screen Shot 2013-10-15 at 8.41.13 PMHaving thin pipes means that new demand can be used to fill in the gaps, rather than having to build new network. Swanston says it is all about optimising the use of the grid.

And the thin pipe models means that those who use the grid less, or consume little energy, are not penalised. Those who want to run six air conditioners and half a dozen plasma TVs can do so, but they get to pay their fair share. He used this image with water to illustrate it. Water is drawn through the day to be stored at time of maximum use.

Swanston admits that the modeling is yet to be done. It could be that the “thin pipe” concept need only apply in certain hours of the day – say between 3pm and 10pm – or it could be 24 hours. Those who wish to export large amounts back to the grid will also have to pay for a larger pipe.

As the illustration suggests, the “thin pipe” model lends itself to exploit storage, but Swanston also wants the storage debate to move beyond batteries.

Swanston notes there is potentially 1,000MW storage in the form of stored thermal energy– where the energy is stored in the hot water tanks or by pre-cooling air-conditioned spaces – that can be exploited if the incentives are right. Ditto for “chemical” storage – timing the chlorination of pools and the use of pumps outside traditional hours.  He says until the market can get the right incentives for customers to continue storing residential hot water, then it will be difficult to get batteries right either.

The big problem for the networks, though, is that much of the costs they have already made, and are committed to, are built into the system. Energex customers could face another 10 per cent rise in distribution costs in the next decade – offsetting any gains delivered if the carbon price is repealed in time.

Ultimately, as RenewEconomy has said previously, the networks will probably have to take a writedown. But as much as many people would like to go off-grid, and self-serve much of their energy needs, the network will have to exist in some form. A thin pipe sounds like the best answer put forward so far. And it already has support from some sectors of the solar industry, including those involved in storage, as Dane Muldoon wrote for us a few months ago.

Note: We will have more on the solar guerrillas concept sometime soon.  

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  • Greg Cooper

    Could another option be to find a market for that spare energy that utilities have built themselves up to deliver. Would it not be sensible for the distributers to incorporate as part of their network the car charging stations around the country that will be needed to facilitate electric vehicles. This would then free up one of the current “roadblocks”, excuse the pun, for consumers in looking at purchasing an all electric vehicle and at same time increase the utilities potential market share significantly. It then has a dual win by removing polluting combustion engines from our community.

    • dylanpete

      Fully agree, every crisis is an opportunity…
      It just needs a little of proactive thinking from the ones like Energex to see this huge opportunity.
      That 1/4 of all houses in Energex’s corner of the world SEQ, already have a PV system installed and are prospective users of EVs. Part of this 1/4 do not have the best FIT and would be better off to charge their EVs with solar generated power instead of exporting it at a low FIT.
      For all new PV installations with low 8cts FIT it absolutely makes sense to use the excess generated solar power for driving EVs or powering up whatever electric garden tools.
      In SEQ Energex has all economical reasons to be at the forefront to promote usage of EVs and to install EV chargers, preferably including level 3 DC chargers.
      Prices of EVs have come down and newer models with increased driving range such as the Renault Zoe and the BMWi3 will become available in Australia in 2014. For Energex and the EV suppliers it’s a win-win to cooperate and build out the EV charging network in SEQ.

  • suthnsun

    On the one hand we hear that the network is currently very robust (previous RE article..) and that demand is falling with peaks not a problem and no new generation required because of excess generating capacity , on the other we hear that capital expenditure of 50 billion is planned for the next 5 years. If they are spending that money they should be taking all the risk themselves, not relying on regulatory help to claw the money back from anyone.
    I’m going the guerilla solar route, heating will be off grid and any other convenient to connect items. Previously all grid electric.Since I can buy raw energy from independent PV for 2-3c /kWh there is a payback of capital especially when compared to greenpower. If the utilities were providing an acceptable product (ultra low emissions power) I would probably have never started down this route..

  • Warwick

    This puts up an interesting social dilemma if people disconnect from the grid. If they’ve put in PV using SRES subsidies, these are only levied on grid connected customers on grids above 100MW. There is no obligation on a disconnected customer to buy SRES, so it basically could mean in future that a PV owner could be receiving a subsidy from network customers for their PV unit only from those customers still paying network charges.

    • Matthew Wright

      This already happens for off-grid customers at present. They get subsidies for their stand alone solar system solar panels. It has been the case for many years and is nothing new.

      • Warwick

        That’s true but the number of remote area power supplies and the amount of energy is not significant. The welfare issue moving forward is where customers have had networks built for them to their house, been upgraded to accommodate their air-conditioning, received generous subsidies through Feed In Tariffs through the network for PV, had their PV subsidised through SRES across all grid customers and now feel they want to disconnect from the grid at no cost. It’s not unlike having your university education subsidised through a HECS debt and then skipping the country without ever paying it back….

        • Matthew Wright

          The upgrade for their air-conditioner is the most generous subsidy they got. You seem to be emphasising the solar Feed-in-Tariff when those with old crappy and large (Input energy) air conditioners are the biggest receivers of middle class /rich welfare.

          A customer with a 30 or 60kW air conditioner using 35 or 70kVA of network capacity is paying the same sort of fee to access the network as a regular consumer or poor consumer.

          HECS is no correlation. There was never any agreement at the time to repay etc or do anything. While it’s pretty clear that HECS debt remains and is recouped in the earlier stages of someones working life.

          The simplest resolution is

          #1 kVAh charging and capacity charge based on 1,2,3…20kVA charging. Each kVA is $200-$250 per year.

          #2 Encourage customers to supersize there existing solar systems so that they create a tabletop output curve. (clipping throughout the middle of the day) ie PV300% or PV400%

          Solar at 5PM kills ‘super critical’ network peaks at 7PM.

          • Warwick

            It’s debatable whether the air-conditioner or the generous feed in tariff is the culprit for the largest case of subsidy largesse is not the point, rather that these are both cases where an individual’s sole benefit is smeared across the cost to all network users.

            The point about HEC’s is that it is a subsidy by all taxpayers in the form of a low interest loan that is recouped over time and the society wide benefit it brings by a higher educated workforce pay more taxes in the long term…not unlike the proposed benefit from PV exports that are subsidised by a lower install cost thanks to the SRES credit. Disconnecting a PV from the grid breaks this nexus where some of the exports are shared across the community….as they have paid for it after all.

          • Matthew Wright

            You miss the point of subsidising solar. As with HECS you create a higher educated workforce so that you can get higher incomes and henceforth higher tax revenues in the future.

            With PV you drive innovation, scaling, learning through doing, research and development and more scaling – all this feeds back and everyone gets really cheap energy in the future. Which is the societal payback. The main payback is not through sharing the surplus power or merit order effect. The main payback is riding the cost curve.

          • Warwick

            So just how does everyone benefit when someones goes “off-grid” which was partly funded by the SRES across all network customers upon the anticipation that power would be fed into the grid for 15 years? Those who disconnect don’t get a FiT anymore so should they need to hand back the REC’s they received as a subsidy?

            Shouldn’t the homeowner who had network built for them at a lower price because it was expected that the asset would have a 30+ year investment horizon still be responsible for those costs?

            How exactly do you quantify the benefits of “riding the cost curve”?

          • Matthew Wright

            Simple to quantify.

            A system is installed in year 1 as a reference.

            A system is installed in year 3 at half the cost

            A system is installed in year 5 and 1/5 of the cost.

            And so on.

            I installed my first system 1.65kW in 2000 and it cost $25,000 (government pitched in an additional $7,000 or $7,500 (I can’t recall which)

            Now the same system costs $3300

            So that $8,000 and all the other ones contributed to the massive cost reduction. Get it?

          • Warwick

            No, I don’t get it… Cost reductions are brought about largely by the improvements in the supply side due to manufacturing improvement, economies of scale and competition (maybe dumping too?). If it was as simple as lumping a buyer’s subsidy to a market to reduce cost then the first homer owner’s grant would have brought about cheaper housing (it hasn’t).

            The main issue is not that solar is a good thing, it’s the subsidy arrangements that have existed and continue to exist (both explicitly and implicitly). Some people have been happy to receive the benefit of investments made on their behalf in the network or because of subsidies but if they go off-grid they pay no cost for these benefits they received in the past. “So long and thanks for all the FiT’s..”

            You need to consider the subsidies both visible and those less obvious, such as those for the fossil fueled plant that had mines and transmission lines built for them before we had competitive markets. Basically, any new generator be it renewable or not often has to bear the cost of building transmission infrastructure, whilst the existing generation stock had these costs washed through transmission charges.

          • Matthew Wright

            The structure of the German system tells the story better than the mish mash of Australian subsidies. (Though the Australian ones have contributed to the same outcome).

            Install volume goes up above the target. The subsidy is ratchetted down. Eventually the subsidy level is below retail self consumption (as it is today). And it continues to ratchet down until it is below wholesale. At that point subsdies can be lifted.

            Chart the German FiT to September 2013 and have a look at what is going on. You can do the same (with a very difficult to achieve) line of best fit for the mish mash of Australian support mechanisms.

            It doesn’t work for the first home buyers grant because property (land) is a finite resource. It has an artificial (political)constraint on it which is government zoning. So there is no relationship.

            Also if a technology does not respond to this kind of subsidy system then it should not be applied. Obviously solar does respond.

            Deployment results in Cost reduction, More Deployment results in More Cost Reduction

          • wideEyedPupil

            ” If it was as simple as lumping a buyer’s subsidy to a market to reduce cost then the first homer owner’s grant would have brought about cheaper housing (it hasn’t).”
            Very poor analogy. Supply of housing is limited by many (supply side) constraints which don’t apply to solar panel and inverter manufacturers. On demand side you have speculation bubble fueled by international investors with access to finance at very low interest rates (for e.g. Asian investors who can’t invest in Chinese property or who are hedging that bubble). This makes for a supply deficit much of the time leading to price rises and further speculation investment.

          • Warwick

            There may be a better analogy in another market but the argument that throwing money at buyers will make the cost cheaper is still not persuasive. (It’s basic economics 101 to understand that giving a subsidy to buyers just moves the demand curve, not the supply curve) If this was the case, you could all argue that Kevin Rudd’s school bonus for laptops makes the price of IT cheaper as it’s “riding down the cost curve” too…yet I hear no-one saying we should continue to subsidise schoolkids’ laptops on the basis that it makes their iPad any cheaper.

          • wideEyedPupil

            You just went from a poor analogy to an even worse one. Increasing demand stimulates supply expansion/competition, as it did with SolarPV internationally. Eventually scale was big enough that meant mass market manufacturing China kicked into gear (subsidised by Chinese businesses that are effectively semi-SEOs due to generous lending practices). This all happened because a miniscule market was grown with demand side subsidies. You may have studied Economics 101 but you have not studied SolarPV cost curves and the political history around them.

            Kevin Rudd’s subsidies would have had zero influence on the marketing of one of the most mature and desirable product classes in the world because of the relative obscurity of the Australian school market in world wide sales. That is the opposite of the situation for solarPV in Germany three decades ago.

          • Matthew Wright

            Warwick,

            The school bonus for laptops will cause the cost of IT to be cheaper however because the market is so much bigger and the technology so much cheaper having already significantly ridden the cost curve the effect is less measurable and pronounced. The PV cost reductions through creating the market (as the Germans have mostly done) are evident. If you can’t see it then you’ve got blinkers on).

  • Matthew Wright

    We need to move to kVA charging on capacity. For the average punter 1kVA can be called 1kW.

    But the way it should be implemented is as a ‘critical peak’ small pipe. On days that are anticipated to be shaping or throttling days customers get a warning via there in-home display, an SMS or a mobile/landline telephone call. Radio and television news also mention it’s a critical peak day. Customers then no to curtail their instantaneous energy demand. In France they already have this system with Green, Orrange … etc days and customers who choose to know how to react.

    Some customers can opt for a soft cap and others a hard cap. Those with a soft cap will get charged a really high rate for exceeding that cap and it will be noted on their next bill. Customers who opt for a hard cap will have their meter remotely controlled to disconnect their electricity for 5 minutes. They will not suffer any bill shock but will get a small short interruption to their electricity service.

    The price of the service would be around $200 -250 per kVA and an average customer with 7200kWh/year usage would opt for 4-6kVA.

    I have detailed this in an article I wrote in August on the http://zeroemissions.org.au/ website in response to Colin Barnett having a go at solar customers http://zeroemissions.org.au/media/opinion/solution-barnett%E2%80%99s-unfair-fixed-charges-130826

    • Stuart

      I think charging by kVA is a great idea in theory but I think it brings up many perhaps unfair issues –

      I live somewhere that doesn’t get many hot days – Wollongong, and as a result I don’t have air con. Someone else however lives somewhere where it gets hot regularly – Western Sydney. They’ll already be paying a high bill due to increased consumption (assuming they have air con), is it fair to charge them an extra kVA charge because of where they live ?

      What if you rent a unit in Western Sydney and youve got no gas supply, you’re going to get stung with a massive kVA charge because your air con, oven and water heating use electricity instead of gas. Is this fair ?

      What about if you’re elderly or have an illness and you can’t deal with the heat. Should these people get stung with a bigger kVA charge too ? Or do you suggest we get bogged down in forms, exemptions ect based on location, age, health, gas/no gas ?

      • Matthew Wright

        Hi Stuart,

        I live in Melbourne and we goto 43/44C every summer and sometimes as high as 47C.

        A critical peak small pipe such that shaping is only applied during extreme events would not cause anyone pain.

        My house is all electric (in Melbourne where the heating season is much longer and more severe than Sydney) and I have 6 air conditioners (which I use predominately for heating). each air conditioner is capable of 800watts of impact on the grid for a total 4.8kVA (They are inverter air conditioners and do not cause signifcant power factor issues).

        I have never had them all running flat out, even when walking around in shorts and a t-shirt in winter. So why would a poor/disadvantaged person be any worse off if they could only run 2 or 3 air conditioners during a peak.

        Taking it a step further. Daikin now has a new model that is COP 5.95 in cooling mode. So it only uses 500watts to do 2.5kW of cooling. Why couldn’t somebody get by with that?

        I think it is gilding the lily to suggest that kVA charging would unfairly impact the poor. It would impact those who have huge old out of date air conditioners pulling 30kW. That’s who would be hit hard by it and they certainly aren’t the poor.

    • suthnsun

      Hi Matthew,
      This sounds eminently sensible to me, as long as it can be implemented with the low impacts you are suggesting. Have your group costed the widescale implementation of this and compared to other peak-shaving measures?

  • Bob_Wallace

    “Essentially, this is an idea that households would install rooftop solar
    PV to satisfy the needs of their greatest single energy demand – hot
    water. The panels, rather than being connected to the grid, would be
    used to heat the water. Elliston says there was nothing the grid
    operator could do prevent the installation. Indeed wouldn’t even know,
    apart from wondering what had caused a sudden reduction in demand.”

    If a homeowner installs storage of any kind, water or battery, how is the grid operator to know? If someone’s use drops will they send out the grid police with a warrant to search your house?

    • dwj

      This arrangement has no more or less an effect on the grid than installing an evacuated tube collector.
      However, it would be a shame if people started doing this, since if you have PV which is grid connected you can export surplus energy rather than just spilling it. For hot water, this could be a significant fraction of the panel output.

      • Matthew Wright

        When you choose evacuated tubes SHW you are spilling hot water (or at least hot water generating potential. If PV drops to 36cents a watt, why wouldn’t you do this instead of a SHW unit?

        Also grid operators are restricting connections to the grid ie <3kW in rural NSW. This allows you to max that out with 3kW of inverter and 3-9kW of panels (supersizing) and then running the hot water seperate to that again, only with the boost circuit kicking in if you are short.

        • dwj

          Mathew I am not saying that PV hot water is not a good idea, I am saying that it is a shame and a loss to the community if PV generated energy is wasted due to business self interest.

          • Matthew Wright

            Hi dwj,

            Clipping PV is likely to become the normal. ie oversizing and supersizing. Making solar arrays at 300% or 400% (or in extreme cases even 600%) of inverter rated capacity so that the capacity factor (over the daylight hours of the year ie 12hrs) can rise from 33% to 65, 72 and 80% respectively.

            Oversizing is cheaper than batteries and will likely be as solar costs are falling quickly towards 36cents a watt (2017)

          • taiyoo

            Most inverter manufacturers have some limit on supersizing – I believe SMA has a 135% limit (although this was a year or so ago). Beyond this you may void you warranty.

          • Matthew Wright

            That is not correct. I have a letter from SMA stating that inverter ratios <70% are acceptable as long as the technical documentation (Voltage VOC) limits are adhered to.

  • Jeremy

    Capacity charging (aka “thin pipe”) is a great idea and could include:

    – Unbundling bills to separate network charges from other charges
    – Eliminating consumption charges to pay for electricity networks
    – Introducing capacity charges to pay for electricity networks
    – Applying the same capacity charge (c/kVA/day) to all consumers (residential and commercial)
    – Allowing all consumers (residential and commercial) to select their required capacity (e.g. 4, 6, 8, 10 kVA) in 2 kVA steps
    – Allowing distributors to charge a penalty fee when consumers exceed their capacity
    – An independent regulator to determine the capacity charge (c/kVA/day) and penalty fees for each network in Australia

    This could be rolled out across the country by charging customers in accordance with the rating of their main breaker. Customers could opt for lower network charges by installing a smaller main breaker or paying for a smart meter and agreeing to penalty charges if they exceed their self-selected capacity.

    The winners will be the frugal households who do not contribute much to peak demand – the losers will be those consumers who will be forced to pay for their choice to use large amounts of electricity.

    • Matthew Wright

      1kVA steps would be better as most customers would initially opt for 5-6kVA. The option should be a hard or soft cap. Hard cap has a breaker go (or at least a virtual breaker via the smart meter) a soft cap is as above where you pay through the nose if you go over.

      Other important factor is to introduce kVAh charging. Zero Emissions Australia has researched this and the article about it is here http://zeroemissions.org.au/media/opinion/solution-barnett%E2%80%99s-unfair-fixed-charges-130826

  • Jeremy

    Is the “guerrilla solar” presentation publicly available? Does the water tank have two separate heating elements – one from the “guerrilla solar” and the other as a grid back up?

    Did the author (Barbara Elliston) also propose extending the concept to space heating – e.g. driving a reverse cycle A/C direct from solar PV?

    • Matthew Wright

      Hi Jeremy,

      There is a company in the US dong this http://www.securusair.com/ however their air-conditioner is only COP 3.0 So when it gets to nighttime and the A/C is driven from the grid it will only be achieving COP 3.0 while the Daikin FTXZ25N achieves COP 5.95 http://reg.energyrating.gov.au/comparator/product_types/64/search/?wrapper_search=&cycle_type=&installation_type=&output_range=&model_number=FTXZ25N&paginate_by=20

      So if someone (preferably Daikin) could offer a hybrid Solar PV version of the new 2014 Daikin 2.4kW split then it would be an amazing product.

      BTW: beware of solar thermal hybrid air conditioners which are being marketed in Australia – They are most likely scams as the laws of physics aren’t on their side.

      • taiyoo

        I’ve seen a basic schematic of a version of the guerilla solar and it seems to work by the use of an intelligent changeover switch – the hot water is on the house’s normal circuit then switches to the solar only circuit when the time is right (sun is shining and water is cold). It shouldn’t be too much of a stretch to add things like A/C to the solar only circuit.

        • Matthew Wright

          Hi Taiyoo,

          A DC inverter air conditioner goes from AC -> DC -> AC

          Some fancy electronics would be required to drive the DC side of the pump inverter air conditioner directly. The AC side that faces the grid would need a constant 240volts and enough power (Current + Volts) and this would not be possible to deliver without the unit failing.

          Whereas powering the DC part can vary the speed of the air conditioner or draw additional power requirements as a load on the grid.

          • taiyoo

            The guerilla solar I have seen uses a standard grid connected type inverter as DC powering hot water elements was considered likely to increase corrosion, so no need for fancy A/C electronics (beyond the changeover mechanism).

  • Motorshack

    Why use expensive, high-tech PV just to heat water?

    Solar thermal collectors will trap three or four times the energy that PV does, and the technology is something that anyone can build from scratch with simple tools and cheap materials.

    If you want free, well-tested plans, check out http://www.builditsolar.com. The guy who runs the site, Gary Reysa, is a retired engineer, and his stuff is painfully well documented. Also, he heats his house – in Montana – with the same technology, so he is definitely willing to eat his own cooking.

    Check it out.

  • Martin

    Amazing. A whole article and 17 comments about grid costs and capacity payments and not a single mention of electric vehicles.

    We have managed to limit our electricity use to less than 3kWh/day without compromising comfort. The only way for our electricity retailer to convince us to use more power, would be for them to make sure that the electric car models available in Europe would become available here at similar prices. With an electric car our daily consumption would increase fivefold.

    But if most makes and models of electric cars remain unavailable, or only become available at inflated prices, we are certain to go off-grid as soon as the solar FIT runs out.

  • Martin

    Sorry Greg Cooper, I overlooked your comment. 🙂

  • Sean

    This thin pipe idea is one step away from the most ideal proposition: Thin pipe (guaranteed supply at a fixed price) combined with a spot market price (the price of which is based on available supply headroom and the current generation spot price)

    This way households could buy supply at a fixed price for their “baseload” and then buy up their additional consumption on the spot market. The amount of each is up to the household.

  • igor

    If the peak demand is a real concern then networks can learn from internet providers. A thin pipe is similar to a download speed limit : we pay more to have a higher speed. Networks will then know the max power that can be consumed during peak periods.

  • Dissenter

    First a remark: as grids cost are fixed costs it makes sense to charge a fixed amount for the use of the grid, determined by the maximum connection capacity of the connection.

    As the issue seems strongly related to solar rooftop be aware that such a thin pipe model is only possible in areas where PV is delivering the whole year and preferably a bit more in the part of the year when demand is higher.