In an age when renewable technologies enable power plants to be built at virtually any size, how do you calculate the optimum size based on a vast range of economic and other factors?

This post is one of the articles published by a small cohort within our UK team, including Dr Mahmoud Elkazaz, James Wilson, Dereck Dombo, Andrew Eviston and Lewis Feldon. This group meets regularly to collaborate on topical issues of the day, shares the researching and writing effort across the team, and presents internally before publishing. 

Sizing electrical generation and storage

In the past, a single massive coal power plant turbine made sense because – in the context of the centralized grid at that time – it was the most efficient size for the task. Most new and carbon-alleviating technologies are modular to some extent, so the power plant size is much more variable.  But how do you calculate the most appropriate size for any particular plant?

Consider photovoltaic (PV) solar panels. They convert light into direct current, which is converted to alternating current via an inverter. Each panel is small. So, for more power, you simply add more panels and inverters. Whether a solar farm is 300 watts or 300 megawatts (a million times bigger), the way it works is almost identical, with each individual inverter the same size for either a small or large solar farm.

This raises the question: how big a solar farm should be? The same question could be asked about other modular systems, such as wind farms and battery energy storage systems (BESS).

What we mean by ‘optimal’

As people will always need more electricity, it would be simplistic and easy to say that a power plant should be as big as you can fit into the space available. The real answer is more nuanced and needs to take into account a lot of factors that determine how big the power plant should be.

One major factor is the load. Clearly, it’s pointless to build a 1000 MW PV plant if the load that needs to be supplied is 10 MW. The shape of the load also has to be taken into consideration. If the load is mainly at night, this means that a small PV plant will be insufficient and you’ll need to build complementary energy storage so that availability of the generated energy can be shifted to night-time. In addition, there are almost always technical grid limitations – such as voltage constraints – that can restrict the size of a power plant.

Other key factors include the ever-changing cost of construction and maintenance, as well as the price at which the energy can be sold. The price factor may require market dispatch conditions to be predicted for many years in advance.

When you add other factors to the calculation, such as carbon-zero and off-grid goals or further financial and technical constraints, defining the optimal size for a power plant can be a complex task.

The optimization process

The most practical way to combine all these factors is to create an energy model. This is a mathematical process that uses linear (or mixed integer) optimization to determine a power plant’s size, incorporating as many factors as possible over the required timeframe.

These models simulate the energy supply from any number of generation sources to any number of loads. They can even include factors such as charging/discharging storage devices or weather patterns affecting solar farms and wind energy.

A good model will not only provide the optimal size for a power plant but also enable you to examine opportunities, risks and other data that could influence the final decision.

To arrive at a conclusion, a skilled engineer will analyze the results from the energy model. It’s also essential to re-run the model using a number of different scenarios.

Sizing the BESS

As well as sizing the power plant, any associated BESSs need to be optimally sized. Several factors, including technical requirements, location, capital costs, and operating costs can influence the size of the BESS.

Power losses that result from integrating the BESS are an important factor. Losses can be reduced by integrating the BESS close to the supply load or the generation asset used for recharging. This is important because lower power losses help to reduce operating costs. The optimization process will help to minimize capital and/or operating costs, although, as with any investment decision, the process may involve several trade-offs on factors that influence the final decision.

How PSC can help with energy modeling and size optimization

PSC has extensive energy modeling and optimization expertise and has developed in-house software solutions such as the ‘’BESS sizing optimization tool.‘’ This quickly and efficiently optimizes BESS sizing to ensure the right level of investment in the battery.

Find out more about our capabilities with Distributed Energy Resources and contact us to discuss the first steps.