Energy Reliability - Availability Factor and Reserve Margin

Availability Factor and Reserve Margin

Contents

1. Introduction

2. What Is Availability Factor

3. What Is Reserve Margin

4. Concluding Remarks

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Bitesize Edition

• With the world of geopolitics so busy recently, I’ve neglected my work on energy for a while. Today, I return to the topic, specifically discussing energy reliability.

• By exploring operating time, downtime, peak demand, and total capacity, we can calculate and analyse the metrics of availability factor and reserve margin.

• Both metrics are valuable for ensuring the importance of stable power. Hence, let’s explore these metrics with example calculations and discuss the advantages and disadvantages of utilising each metric.

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Introduction

As I return to the topic of energy, I’m going to dive into energy reliability. This refers to the ability of a power system to withstand instability, uncontrolled events, or failures. Today, I’ll explore energy reliability through the metrics of availability factor and reserve margin.

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What Is Availability Factor?

An availability factor of an electricity production method is a measurement of the amount of time over a certain period in which said production method can produce electricity. The higher the availability factor, the more active the production method is, and it spends less time dormant.

The formula for the availability factor is as follows:

\(\text{Availability Factor} = \frac{\text{Operating Time}}{\text{Operating Time + Downtime}}\)

Let’s use an example:

• We will take a total period of one year. This is equal to 8760 hours.

• Let’s say the plant we’re exploring had 120 hours of maintenance time and 30 hours of unplanned downtime. Hence, the downtime of the plant would be 150 hours. Operating time would be the total hours in the year, minus downtime.

\(\text{Availability Factor} = \frac{8610}{8760} * 100 = 98.29\%\)

This means during the year, the power plant in question produced power 98.29% of the time.

Some power plants achieve higher availability factors, such as nuclear, coal, and gas-fired power plants, typically all having an availability factor of over 80%. The solar availability factor falls around 15-30%, and wind turbines at 20-40%. The intermittency of the weather contributes heavily to this dramatic decrease. Older geothermal plants can suffer a decrease in availability factor due to scaling, resource depletion, and equipment wear, and hydropower plants often experience seasonality of water flows, thus affecting the availability factor.

On the surface, this highlights the availability factor as a great metric for baseload power plants, but the metric becomes weaker when intermittency enters the picture. Luckily, another metric that allows us to better frame renewables in this context is the capacity factor. I’ve discussed the capacity factor here, but as a reminder, the metric measures how much electricity a plant produces versus its maximum potential output, but it assumes the plant is operated at full capacity all the time. It is a measure of efficiency. Even when introducing this metric, renewables typically also find themselves at the lower end of the capacity factor range.

Since the capacity factor compares the output of a method versus its theoretical maximum output over the same period, it never exceeds the availability factor, but the difference between the two can demonstrate a plant that is being run at less than capacity.

There are some downsides to the metric of availability factor. Firstly, if a plant is available, but not producing power due to a lack of demand, then this would present itself negatively in the availability factor. It also excludes the reasoning behind any downtime. Upgrades could help to improve the reliability of a plant, but would once again be reflected negatively in the availability factor.

Now let’s move on to our second metric, the reserve margin.