Managing standalone renewable generation: guidance

This guidance note is for public sector and community organisations who already own standalone renewable generating stations or are developing standalone renewable generating stations. These stations either export power to the grid, or to an off-taker via a private wire.

Owners of building-integrated renewables, such as rooftop solar panels, should instead refer to the guidance created specifically for rooftop solar management.

To socialise the importance of performance management of renewable generating stations.

To provide high-level guidance on how to manage and improve the performance of renewable generating stations.

Many public sector and community organisations own, or are developing, standalone renewable generation stations (e.g. wind, solar, hydro).

Successful operation of electricity generating stations is enabled when performance is managed by the owner on a daily basis. This is true for all sizes and types of generating stations, from rooftop solar to offshore wind.

Performance management, sometimes called ‘asset management’ or ‘operational management’, is essential to maximise generation and minimise downtime. The role of a performance manager is distinct from the services carried out by an Operation, Monitoring and Maintenance contractor.

A performance manager will;

• monitor, record and validate key data,
• ensure contractors meet or surpass their terms of service,
• supervise compliance with contracts and permits,
• manage supply and purchase contracts
• evidence insurance claims,
• keep an operational diary.

These tasks are proven to significantly increase the amount of electricity generated.

If you can measure it, you can manage it.

The operation of the UK electricity network and market is founded upon half-hourly data. Electricity is measured, bought and sold in kilowatt hours (kWhs) quantified at half-hourly intervals using industry-compliant meters. It is not possible to actively manage an electricity generating station effectively without direct access to the half-hourly meter data, via a data collector service.

Remote monitoring systems, used by contractors to operate the plant, may provide useful insight for a performance manager into the operation of a generating station. However, the platforms don’t usually provide direct access to the half-hourly meter data, which is essential to verify revenue and costs, manage generator performance, contractor performance, and compliance with operating permits, such as planning conditions.

Half-hourly data needs to be processed by the performance manager to make it useful for analysis. The simplest way to do this is by creating an Excel tool.
An Excel workbook/s is prepared in a grid format. Each row is a calendar date, and each column is one of the 48 half-hour periods of time in a day. Conditional Formatting can be applied to the value range to provide a visual indication of adherence to key performance benchmarks.

Half-hourly generation meter data is sourced (at Day+1*) direct from the data collector web portal, in a csv or Excel format. The half-hourly generation data values are copied and pasted into the pre-prepared worksheet. The Conditional Formatting appears.

(*Day+1 = the day immediately following a day of electricity generation.)

Key performance benchmarks, specific to the generating station, such as megawatt installed capacity, are coded into the Conditional Formatting by the performance manager. For example;

• a missing half-hourly data value, (meaning no data available) may be coded to appear in red typeface
• a half-hourly data value of zero, (meaning no generation) may appear in a blue fill
• a half-hourly data value above or below a specified number of kilowatts (allowing actual performance to be benchmarked against expected performance) may appear in an orange typeface

If tariff information is also added, an Excel tool may also calculate the value of generation or the cost of downtime for each half-hour period. This is useful for validating invoices and understanding revenue loss during downtime.

Analysing the meter data daily in this way enables the performance manager to immediately understand how well the generating station is performing against expectation. It is then possible to take rapid action to resolve any issues, thereby minimising loss of generation or periods of non-compliance with operating permits. The actions taken will vary but will typically involve contacting a contractor to resolve a data issue or a performance issue. Once performance management processes and analysis tools are set up, managing performance will take just a few minutes each day.

An Operation and Maintenance (O&M) contract will guarantee the percentage of a year that a generating station will be available to generate power. For example, 95% ‘Availability’ to generate per year.

A (half-hour) time period when a generating station is not available to generate power is called downtime and will likely result in a loss of revenue for the owner. Downtime is categorised as either planned or unplanned. The responsibility for planned downtime (e.g. scheduled maintenance) and unplanned downtime (e.g. unscheduled maintenance, grid outages, etc) will be attributed to either the owner or to the O&M contractor. Periods of downtime beyond the O&M contractor’s control will be removed from the Availability calculation.

However, as Availability is monitored by the O&M contractor then reported to the performance manager, it is vital the performance manager validates reported downtime allocation, rather than allowing an O&M contractor to ‘mark their own homework’. This can be achieved by analysing half-hourly data.

If the performance manager is to challenge the O&M contractor’s Availability calculation, they will need to evidence their claim with half-hourly data and an operational diary. An operational diary is a desktop calendar where the performance manager records periods of scheduled and unscheduled downtime and their causes, as well as time-sensitive events such as safety testing, contract renewal, material planning conditions and civils works.

Building a good relationship with the O&M contractor’s engineers can prove advantageous for smaller, non-utility clients, such as community groups and local authorities. This is because contractors favour clients with multiple, large generating stations over independent clients with (relatively) small generating station/s.

Most O&M contractors have multiple generating stations to monitor and maintain on behalf of clients: their motivation is to meet contractual terms, such as Availability, rather than maximise generation. But a performance manager will want to maximise the time their own station is available to generate electricity, and the amount of power generated.

Two actions which will encourage an O&M contractor to meet or surpass contractual terms are;

• Receiving a prompt call from a performance manager when generation performance drops, to ask for a resolution.
• Knowing that monthly performance reports will be verified in detail by a performance manager.

There may also be a separate High Voltage engineering contractor, responsible for the grid connection. This ‘Senior Authorised Person’ (SAP) may be separately contracted, and it is just as important to build a relationship with them and monitor their adherence to contractual terms.

Measuring the technical performance of a solar, wind or hydro generation plant is complex. A large number of variables need to be considered and the data to consider these is usually captured on monitoring systems, such as SCADA (Supervisory Control and Data Acquisition). Half-hourly meter data is a useful indicator, but a deeper investigation by the O&M contractor may be required.

If a performance manager is concerned plant is not meeting its design specification, and the plant supplier or O&M contractor are unable to provide a reasonable explanation, it is possible to have plant performance reviewed by an independent specialist. It is important contractual terms and conditions contain a mechanism for this to take place.

Generating stations increasingly operate under grid constraints. For instance, the network operator may ask output to be reduced at a particular time of day. Half-hourly data can evidence compliance or non-compliance with such operating restrictions.

Wind turbines may operate under noise constraints, meaning power output must be reduced under specified environmental conditions. Adherence to planning conditions is evidenced using SCADA data recorded at each turbine. Potential non-compliance may be visible to the performance manager in the half-hourly generation meter data at Day+1, particularly for single wind turbine sites. This knowledge, along with effective O&M terms, enables fast remedial action. It is often a permitting requirement to maintain electronic records of half-hourly meter data, and other monitoring data. This data proves compliance with operating terms and conditions. Loss of data, caused by a meter fault, a communications fault or an unpaid communications invoice, is soon noticed and resolved by a performance manager analysing half-hourly meter data on a daily basis.

Note

Non-compliance with operating permits can cause a generating station to be shut down.

Validation of electricity subsidies, power purchase and supply invoices is carried out by cross-referencing tariffs and half-hourly meter data. This cross-referencing will also evidence losses in revenue due to unplanned downtime.

Owners of generating stations are usually insured against long periods of unexpected loss in generation. It is important losses are quantified and evidenced.
This is done using long-term, historical half-hourly data to estimate generator output under similar environmental conditions. Therefore, it is vital the performance manager keeps records of historical half-hourly meter data to use alongside historical environmental data such as anemometer, irradiance or flow data.