As old thermal generation assets retire and as the world moves towards a lower emissions future, we need to solve the ‘energy trilemma’. In other words, we need an energy future that is affordable, sustainable and reliable.

The role of renewable generation in achieving affordable and sustainable energy is clear. Wind and solar PV now offer the lowest cost of new energy development, have low ongoing operational costs, and near zero emissions – and therefore hold great potential for rapid decarbonisation of the energy sector.

However, replacing coal-fired power stations with wind and solar PV is not a like-for-like swap in terms of availability of power when it is needed by consumers. Coal-fired power stations produce firm baseload power, but generation from renewable resources varies due to the availability of the natural resource. Wind and solar PV vary according to the weather and the time of day.

So how can we achieve the third element of the ‘energy trilemma’: reliability? And how do we achieve reliability at the right cost?


Reliability means having stable, high-quality power available whenever it is needed. We know that renewables can produce energy, but is the power produced when it is needed? The variability in power from renewables – and its dependence on natural resources such as wind and sun– makes matching supply and demand a challenge. This challenge increases as more renewables enter the market.

With moderate amounts of renewables, it is still possible to maintain system reliability through clever solutions – in particular, targeted grid support designed through careful planning and study of generation profiles, and supported by solid communications, control, power systems studies and forecasting. However, there is a limit to such approaches.

Ultimately we will need storage solutions to enable renewable generation to be available whenever consumers require it and so that the grid can be stable and secure. At Entura, we call this ‘dispatchable renewables’, and we believe it is a critical component of solving the energy trilemma.


For generation to be dispatchable it needs to be available at the request of power grid operators or the plant owner according to the needs of the market. Dispatchable generators can be turned on or off, or can adjust their power output according to market need. If a generator is dispatchable it can be used to match load, meet peak demands, or fill the gap if another generator suddenly goes offline. Dispatchable generation is very valuable to the market because it can be used to match the profile of energy demand.

To make wind and solar PV dispatchable, storage solutions are needed, and these may vary depending on the particular project. The main contenders are large-scale batteries, pumped hydro, and modified use of traditional hydropower. All of these can ‘store’ energy (at times when wind or solar are generating more than the market requires), and release that stored energy again when the market needs more power than the weather-dependent renewables can supply. The choice of storage solution will depend on the particular circumstances of each project.

Effectively, baseload fossil fuel generation can be replaced by the combination of variable renewables, dispatchable renewables, change in use of existing hydropower, and smart high-voltage network support and planning to ensure sufficient transmission capacity.

The time to start planning for this transition, from thermal generation to fully dispatchable combinations of renewables and storage, is now.


The questions of when and how much dispatchable renewables we’ll need are complex. Future needs will be driven by a combination of commercial, regulatory and technical considerations as well as changing customer behaviour (all of which are in motion). Nevertheless, the trend towards increasing needs for dispatchable renewables is clear – so this is the time to get things moving.

There are already opportunities in which dispatchable renewables offer distinct advantages, and where business cases may stack up. With increasing wind and solar PV developments in the network without dispatchable capability, such opportunities will only expand. However, the lead time required to include large-scale storage in these ‘dispatchable renewables’ projects means that planning must begin well in advance.

About the author

Richard Herweynen is Entura’s Principal Consultant in Civil Engineering. Richard has 28 years of experience in dam and hydropower engineering, and has worked throughout the Asia-Pacific region on both dam and hydropower projects. Richard was the Project Director of the Kidston Pumped Storage Project Technical Feasibility Study and, in recent years, Richard has led the design of three roller-compacted-concrete dams within Australia and a number of significant dam upgrades. Richard was part of the ANCOLD working group which updated the guidelines for concrete gravity dams, and is the Chairman of the ICOLD Technical Committee on Engineering Activities in the Planning Process for Water Resources Projects. Richard has won many engineering excellence and innovation awards, and has published over 30 technical papers on dam engineering.