Power System Transformation for Dummies
Power system transformation
understanding the challenges
Changing loads, flexibility and storage
System load will change in the next decades, just as a consequence of the energy transition. The illustrations of the phases do not reflect these changes by somehow adjusting the shape of the LDC. There are three reasons for this rude simplification:

Flexibility perspectives
Deploying flexibility potentials - regardless of load, generation or storage - it is essential to be explicit what perspective you have in mind: Attempts to combine these perspectives regularly reveal conflicts rather than synergies.

The illustration below is inspired by the methodology of the 'Flexibility Tracker' (see slide 8 of the presentation). It helps to understand potentials and structure of flexibility.


According to the 'Flexibility Tracker', flexibility providers are generation, loads and storage. However, these three groups are not completely flexible. In fact, they are quite diverse.


Much of the total load is inflexible because of its purpose. Digitalisation or smartness will not change this. Streetlights are needed during darkness and only during darkness. The schedule of trains preferably does not depend on prices at power exchanges.
Of course, you can decide to postpone the start of your washing machine or dishwasher or to iron your shirts later (if you iron them at all). Looking at your immediate living environment, you may realise that it is challenging to name many more of those examples.
Assessing flexibility of loads, it is important to be specific about the related time frames. Some applications, after appropriate preparation, allow shifting demand for a couple of minutes (electric arc furnaces), some for hours (cooling) but very few for days or even months. Nevertheless, these long timeframes are essential too when trying to match supply and demand.
Another aspect which deserves attention: once suspended, loads may ask for some extra power after being reconnected. If supply is still short, this may jeopardise the benefit of flexibility.

Because of the limitations of generation and load, scenarios with high vRES penetration always assume storage. Storage provides flexibility in time. Periods covered range from minutes to seasons. This is determined by technology, capacity and application.
Storage can be implemented as electricity storage like batteries. However, very often, it is attractive to deploy storage capacity in other forms of energy. Closely related to generation, this can be water reservoirs like hydro dams or pumped storage plants. Closer to loads, an elegant approach is using the inertia of the applications' final energy use. Examples are heat e.g. in case of electric arc furnaces or cooling appliances or buffer storages in drinking water supply. (In fact, these latter cases can be equally qualified as load flexibility. This is just a matter of definition.)
Dedicated electricity storage in the networks may also provide ancillary services.
In most countries far from the equator, seasonal storage is an inevitable precondition for realistically matching supply and demand. Electrochemical batteries are not an obvious choice for this purpose, even if they get extremely cheap. One single charge-discharge cycle per year does not justify putting huge amounts of materials in related equipment.

Export and import
In case of excess generation or a power deficit, export and import, respectively, may help to maintain the system balance. Let's interpret exports and import wider than just transmitting power via interconnectors to other regions.
The transformation process implies closer links of the power system with other economic sectors, like mobility or heating (power to heat) or cooling in the built environment. Excess generation may be converted into chemical energy carriers (power to fuel). These synthetic fuels may never be transformed back into electricity. Nevertheless - the fact that they can be stored easily adds flexibility to the system. On the other hand, some (zero-carbon) energy carriers need to be transformed back to power to cover deficits. This is the import in the graph. (Of course, in general, imports will not go directly to the load but will enter the system at the generation side.)

Exchanging power with other economic sectors can be considered as new load and generation, as storage or as export / import - this is just a matter of definition. Important is the extra flexibility offered by these concepts resulting in potential support for system balance.
Of course, synthetic fuels can also be physically exported, imported and traded between countries like coal, oil or natural gas nowadays. This is an efficient option for reducing the required volume of seasonal storage.

The 'Flexibility Tracker' characterises networks and power markets as flexibility enablers.
It is important to understand, that proper regulation is a precondition for unchaining existing flexibility potentials, but more networks or markets will not create them. Again: offering money for switching streetlights on during daytime in case of excess PV generation does not make this a sense-making application.

Networks and interconnection
While storage provides flexibility in time, networks and interconnection increase the spatial diversity and, hence, increase the deployable flexibility in space. Interconnection offers synergies like enabling vRES integration, increasing economic efficiency of supply and strengthening security and reliability of supply.

When planning networks for integrating vRES, there is one aspect which has to be understood: some limited curtailment is an intrinsic part of all power systems with high shares of vRES. - Why that? The peak output from PV plants or windfarms occurs only a few hours per year and, hence, peak output (in terms of power) is associated with a limited share of the annual yield (in terms of energy). It is economically efficient to chose the rating of the network assets lower than the nameplate capacity of the connected vRES projects and accept a very limited yield loss.
What are the consequences? For safe network operation, some monitoring and control infrastructure has to be implemented enabling the network operator to temporarily reduce vRES plant output during peak hours. (Alternatively, the output of individual projects can be capped statically at values lower than nameplate capacity.) From the perspective of vRES development it is crucial that the investors' risks associated with curtailment are manageable. Even if the total expected amount of yield loss will be low, for bankability and financing of projects it is important that regulation covers and reliably limits the financial risk to predictable levels.

Power markets
Economic incentives stimulate efficient use of existing flexibility. However, liberalised power markets do not create flexibility, neither are they a precondition for successful power system transformation. Important is adequate allocation of costs and benefits - otherwise nobody will be willing to provide the needed investments. Investments at the right spots: this is how markets - on the long run - can increase flexibility of power systems.

This website focuses on technical challenges. Elaborating on appropriate design of economic frameworks for vRES development (and power markets as one possible implementation) is another ambitious web-project. One day you may find a link here...

Phase X - no progress without cross sector coupling Overview Phases Phase 0 - vRES impact negligible