Matching Electricity Supply with Demand Part 2

Energy Issues: 1. Matching Electricity Supply With Demand Part 2

Details, Details

The Duck Curve: An example is shown in the picture.  System load on the lefthand axis refers to net demand for electricity, that is gross demand minus supply, effectively the deficit to be plugged.  Australia has a lot of sunshine, so as solar supply increases in the morning, net demand goes down rapidly.  Net demand then rises to a big peak in the evening as solar supply disappears.   We can also see that the evening peak in demand has been increasing year-on-year, as population increases and uses more electricity per capita.  On the other hand, because more solar power has been installed each year, net demand has actually decreased in the middle of the day.  The duck’s belly has become plumper!  A somewhat comparable Duck Curve can be seen in the UK, except that low carbon electricity from wind, which is blowing 24/7, plays a much bigger role.  One thing to note is that total load includes business factories and offices.  These are going full tilt at midday, yet paradoxically net demand is minimal.  The duck’s belly tends to be plumper in service economies, such as Australia and the UK. In contrast, it sags less in manufacturing economies such as China and Germany, where companies generally consume much larger amounts of electricity.

The Duck Curve. This was generated from data in Western Australia (see :  https://www.synergy.net.au/Blog/2021/10/Everything-you-need-to-know-about-the-Duck-Curve#).

The Duck Curve clearly illustrates a mismatch between demand and supply of electricity, at several different times throughout the day.  Clearly, it would be smart to smooth out the net demand curve, in effect raising the belly and lowering the head of the waddling duck, and creating what wistfully could be called ‘the flying duck’.  How to do this is a problem of massive proportions, and mismatch between supply and demand will only get worse in the future as we increase our demand for low carbon electricity due to the triple threat of:

  • moving buildings off gas and oil boilers onto electric heat pumps
  • transitioning from petrol and diesel vehicles to EVs, and
  • generation of green hydrogen and carbon capture

Meanwhile, on the supply side, while solar and wind are eminently expansible, the electricity generated is intermittent.  Another issue is that natural gas and coal supplies can be stored physically on site close to where they are used, and in the case of gas there are always some residual hours of supply already sitting within the distribution network (so-called Line Pack).  In contrast, electricity is much harder to store, and so peaks in demand must be matched by instantaneous expansion of supply.  This has traditionally been achieved by firing up rapid response gas power plants – termed ‘peakers’, or at a pinch coal-fired plants.  When needed, these supplemented baseline generation by constantly on hydrocarbon-powered plants – so-called ‘base load generators’.  This approach cannot continue if we are ever to achieve Net Zero.  Quite the opposite, we have to cut out fossil fuels and substitute low carbon electricity, and possibly other green fuels such as hydrogen gas.  In the interim while build-out of low carbon electricity catches up and fills in the looming hole in supply, the vexed question is how to balance supply and demand?  From first principles, the options are to expand sources of supply, and to manage demand more actively.

Move Supply Towards Peak Demand:  One means of managing supply is to press electric batteries into service.  These can soak up spare electricity during period of excess supply, and then release it at peak demand, effectively time-shifting a chunk of supply from the duck’s belly to its head.  On paper, this is a no brainer.   However, although the price of batteries is coming down, at the current state of development they remain cumbersome in both size and weight.  What battery capacity is actually available?  Some third-party commercial battery facilities are now beginning to appear, and one recently-commissioned one in Yorkshire currently offers a storage capacity of 198 MWh, among the largest in Europe.  There is also a growing array of batteries in public buildings, churches, schools, and also private businesses.

The number of installed batteries in homes is still somewhat limited, but costs are declining rapidly and there are strong arguments for buildings with solar to install batteries as well, to allow active management of the time of use.  More to the point, some of us already have the next best thing - the large battery sitting outside in our EVs, of which around a million have now been sold in the UK.  Attaching these to the grid through battery chargers is straightforward.  Moreover, if we add in batteries installed in businesses and public buildings, which are often much larger, total aggregate storage capacity available is potnetially considerable.  These batteries could collectively provide sufficient storage capacity for large amounts of buffer supply which could then be moved around on the grid, whenever, and to wherever, it is needed.  One word of caution is that current batteries have limitations on the rates that they can charge and discharge, in part to prevent damage.  This means slightly more batteries would be required for any given level of instantaneous supply than would be predicted from the sum of their total capacity.

The obvious next question then becomes, how do we encourage private battery owners to part with their spare electricity?  One emerging strategy is for providers to incentivise such households to share self-generated (aka micro-generated) electricity from their solar arrays and batteries, or for that matter to store surplus grid electricity in return for payments or reductions in tariffs.  One example is Octopus Flux, which has a special low tariff for charging a home battery, and a special high ‘feed-in’ tariff for power discharged to the grid.  Control of the process remains with the battery owner.  A newer version of this, Octopus’s Intelligent Flux, is similar, except that the battery owner gives up some control of charging and discharging to Octopus.  Note that most of these new, innovative tariffs require that the house have a smart meter installed that can broadcast download and upload readings to the supplier every half hour.

These kinds of tariffs could enable the coalescence of large virtual groups of micro-generators across multiple buildings, and potentially allow providers to instantaneously call up additional supply of electricity as needed.  Such virtual power plants could then function much as the gas-fired peaker generating stations have traditionally done. Equally, these virtual groups could also be pressed into service by providers to store electricity at times of excess supply, for example at night and/ or when wind power is especially strong. This could greatly assist more flexible matching of overall demand and supply of low carbon electricity – i.e., slimming down the Duck and making it waddle less.

In parallel, it also makes sense to increase baseload generation of low carbon electricity wherever possible.  Solar installations of photovoltaic panels (PV) on individual buildings are increasing rapidly, and some of these PV could be orientated to the West, rather than the South, in order to capture late afternoon sun, at the beginning of the evening demand peak.  At a national level, we need to build more large, commercial, solar and wind farms as quickly as possible.  One other theoretical notion would be to increase base load generation by importing solar power from farms in regions with intense sunshine, such as Morocco in North Africa. Some of these involve concentrated solar plants (CSP) with heated fluid and turbines, which can also achieve some time-shifting in the generation of electricity.  However, the costs and technical difficulties involved make this an improbable prospect, any time soon (see Energy Issues. 3. Will We Have Enough Electricity?).

Demand Response:  Traditional thinking has regarded total electricity demand as immutable.  It is what it is.  Deal with it!  The imperative then has been to instantaneously match it with supply. If this was unsuccessful, there were unpleasant consequences for consumers - brownouts and rolling blackouts.  A number of new strategies are now seeking to manage demand response more actively and flexibly, and to reduce peaks to more manageable proportions.

One obvious  approach is load shifting.  We domestic consumers could be encouraged to move use of energy hogs such as washers, dryers, dishwashers, and charging EVs from the evening peak hours (4-7PM) to some other time during the night, or even the middle of the day.  These are times when demand is generally low, and adequate supply not a problem. Load shifting can also work for hot water storage tanks, which will not drop more than a few degrees if temporarily turned off between 4-7PM.  Other less time-flexible appliances (e.g., ovens, electric showers, and combi-boilers) could still be operated if necessary.  In fact, there has been little incentive to engage in load shifting up until now.  Except for those of us on cheap night-time and other off-peak arrangements, tariffs don’t vary across the day.

The advent of smart meters has now allowed providers to put together smart time of use tariffs that do vary across the day.  One such is Octopus Agile, which adjusts the tariff every half hour across the day, tracking wholesale electricity prices.  It generally costs 10-20 p per kWh or less off-peak, but much more, up to 40 - 70 p per kWh, during the evening rush.  So, if we postpone use of the usual high energy suspects until off-peak times, we can save a fair amount of money.  In contrast, we will lose our shirt if we run these energy gluttons from 4-7PM.  Homes with solar and batteries can do even better, charging batteries when rates are low, and discharging them to the grid during peak times when tariffs are high.   Time of use tariffs will be especially important as the number of EVs charging continues to expand.  Energy suppliers also benefit, since this can be effective in getting people to shift demand away from their peak use habit, and make the Duck more aerodynamic!

Since the wind turbines on which we depend for the majority of our low carbon electricity are spinning 24/7, there are times at night when energy companies have more supply on hand than there is demand, and they may or may not be able to store it (see above).  There are also practical limits on the amount of surplus wind power that Scotland can export to England.  This is due to choke points in the national grid, although new power lines such as the undersea Eastern Green link 2 are planned.  If excess electricity cannot be used or stored, it may then be necessary to temporarily turn wind turbines off, which is pretty silly after the massive costs involved in installing them.  So, some providers now announce ‘plunge pricing’ periods, usually when demand is minimal at night.  The price of electricity then actually goes negative. This means that people running their domestic electric gluttons during these periods, actually get paid for the privilege!  The good life also extends to battery owners, who get paid to charge them, and then paid again if they discharge them back onto the grid. Meanwhile, energy suppliers are happy because they can better smooth demand and match it with supply.

Another approach to creating flexibility of demand are the savings sessions offered by some suppliers. Consumers are paid to the extent that they turn things off and ‘save’ energy during defined savings sessions, usually during the 4-7PM evening peak.  As with time of use tariffs,  we can pick and choose which appliances to run during the savings session, and which later.  Octopus and Solar Edge have both run savings sessions.  Again, those households with batteries have the flexibility of charging them while demand and cost are low, and then living on them during saving sessions while avoiding use of grid electricity.

One exciting new prospect is the introduction of automated dynamic control of demand by ‘smart’ appliances e.g., fridges and heat pumps.  These can detect fluctuations in the frequency of grid electricity (held within 1% of 50 Hz) due to surpluses or deficits, and can turn themselves on and off accordingly. Ideas for the future are more radical.  They include mass interconnectivity of national grids across countries to balance supply and demand across multiple time zones, and smart grids where individual machines everywhere are connected and usage controlled on an Internet of Things (IOT).

What can we do?  While the build-out of low carbon electricity is catching up with rapidly-expanding need, we can as individuals make several real contributions to a better balance between available supply and demand:

Load Shifting: This simple trick involves being more deliberate in when we use electricity, moving use of energy where possible from peak periods to the middle of the day, or even better the middle of the night.  Those with solar and batteries also have the option of using their own self-generated electricity instead, during peaks of demand.  Load shifting can happen without changing to special time of use tariffs, in which case it does not yield any monetary benefit, unless done during a savings session.

Tariff Shopping:  This is the next layer, switching to a Time of Use electricity tariff that varies across the hours of the day. Effective load shifting can then bring a monetary benefit, from the reduced tariff applicable off peak.  As noted above, during periods of plunge pricing, we will actually be paid to use excess energy that could otherwise unbalance the grid.

 Solar and Battery Sharing:  For those with solar and battery, there is the further option of providing the grid with extra power during demand peaks, and storage capacity between peaks.  This requires specialised tariffs, and allocating the appropriate quantities of electricity to self and to the grid.

We can do our part by being more aware, and keeping a close eye on the various savings sessions and tariffs available.  They are changing rapidly at the moment, and it is worth regularly monitoring what is available, both online and through push notifications.  Energy suppliers can do their part by offering innovative tariffs and discounts that incentivise changes in patterns of usage that are effective and durable in the long term.  Making wider use of the virtual pool of electricity and storage across the installed base of solar array and batteries, and active management of demand, are both completely realistic. The prize will be a more flexible, dynamic balance between supply and demand, without needing gas peakers and even dirtier coal power plants.  We have to learn to keep the duck flying, on low carbon electricity alone, and as soon as possible.

 

Further Reading