Portfolio loss waterfall

Net budget (P50)

The P50 energy budget after the losses it allows for in each category. In this sample it is the gross P50 yield less each category's allowance.

Weather

The change in budget caused by the weather actually measured on site. It is not an operational loss, so it is shown in grey.

Budget at actual weather

The net budget re-run at measured conditions. Only the resource changes: the model and every loss allowance keep the percentages the budget was built on, applied to the energy the measured weather would have produced. This is the fair target for the period, and the starting point for judging operations.

Allowance and result

Each category's allowance is the share of expected energy the budget assumed it would lose. The bar is allowance less actual loss, so up means better than budget.

Expected energy

The site's own yield model, such as the PVsyst model behind the P50, run on measured conditions before any losses, and used in the absolute losses view. Solar uses measured plane of array irradiance and module temperature, before the inverter AC limit; IEC 61724-1 governs how those measurements are taken, but it does not validate the model itself. Wind uses measured free-stream wind speed through the warranted power curve, corrected for air density. Turbulence, shear and how representative the wind measurement is all affect how far that estimate can be defended, so a real assessment states the uncertainty.

Which losses apply where

Every technology: grid and curtailment, set point and export limit, balance of plant and unexplained. Solar only: trackers, inverters and strings offline, soiling, clipping, inverter thermal derating, row shading, snow, module underperformance and degradation. Wind only: turbine faults and scheduled maintenance, wake, icing, high wind hysteresis, power curve underperformance and yaw misalignment. CHP only: engine trips, failed starts, service overruns and spares, engines held at part load, heat-led control, gas supply pressure, cooling faults, ambient and gas quality derating, engine condition and turbocharger fouling. Categories with the same name hold different items for each technology, so compare them within a technology first.

CHP dispatch

A CHP plant is dispatched, not driven by the weather. Its expected electricity is what the engines should have produced in the hours they were called to run, at available capacity. The grey bar becomes dispatch: the plant ran more or fewer hours than budget because of heat demand or market prices, which is a commercial decision rather than a loss. In views that mix CHP with solar or wind it reads weather and dispatch.

CHP heat

Heat has its own waterfall in MWhth, metered at the energy centre export; losses on the network beyond it are out of scope. Budget heat moves with degree days to give the heat budget at actual demand. Engines not running is the heat lost while the engines were down for any electrical reason, at the guaranteed heat to power ratio. Recovery performance is heat the gas burned should have given at the guaranteed thermal efficiency but the exhaust and jacket water exchangers did not recover. Boilers covering is demand met by gas boilers while the CHP was available. Heat and electricity are never added together in MWh.

Heat dumped

Recovered heat rejected through the dump radiators because the network did not need it. It does not reduce heat delivered against demand, so it is not a bar in the heat waterfall. It does waste gas, so it is in the fuel view. Dumping while the boilers are firing shows up as boilers covering. Dump radiators are often unmetered, in which case the heat has to be calculated from radiator temperatures and fan speed.

Fuel view

Gas burned, measured on gross calorific value, split into electricity, useful heat, dumped heat, and exhaust and other losses, beside the engine maker's guaranteed split. In the UK the same electrical and heat efficiencies feed the CHPQA quality index.

Valuing CHP

A lost MWh of CHP electricity is valued at its margin: the power price less the gas it would have taken to make it at the guaranteed electrical efficiency, because the gas was not bought either. Heat is valued at the boiler gas it displaces.

Design and weather

Wake, clipping, inverter thermal derating, row shading, snow, icing and high wind hysteresis. Set by layout, equipment choice and climate rather than by operations, so shown in grey.

Grid and curtailment

Network outages and operator instructions, split into paid and unpaid.

Set point and export limit

Energy held back by the power plant controller beyond what the grid actually asked for. These losses usually sit with nobody, which is why they persist.

Balance of plant

ACB trips, protection relay trips (G99 in the UK), transformer derating and HV faults.

Equipment availability

Inverters, trackers, strings and turbines offline.

Performance

Losses operations can act on. For solar: soiling, degradation above the warranted rate and module underperformance. For wind: power curve underperformance and yaw misalignment.

Unexplained

Expected energy, less every counted loss, less metered export. The budget allows nothing for it. Keeping it small and honest is the real test of the data.

Counting each MWh once

In every interval, lost energy goes to the first cause that applies, in this order: grid and curtailment (the site could not export), balance of plant, equipment availability, set point and export limit, design and weather, then performance. Whatever remains between that and metered export is unexplained. The bars run in the same order. The sample data does not model overlaps. A real assessment applies the rule interval by interval, with the same exclusion rules as the O&M contract, and keeps the interval-level reconciliation so every MWh can be traced to its cause.

Curtailment and set points

Separating what the grid asked for from what the plant controller held back only stands up when the grid instruction and the controller's behaviour are both logged, time-aligned and kept as evidence.

Actionable

The sum, site by site, of every shortfall against allowance in set point and export limit, balance of plant, equipment availability and performance. A site that beats its allowance does not offset another that misses it.

Percentages

Every percentage is a share of expected energy before losses, so the bars add up.

Energy value view

Each MWh valued at the site's tariff. This is the value of the energy, not lost revenue or a recoverable sum: paid curtailment was compensated, so it cost the site nothing, and merchant sites earn the price at the time rather than a flat tariff. Paid curtailment stays in so the bridge closes, and the owner chart marks it as paid. A commercial impact figure would add compensation, merchant prices, contract penalties and what can actually be recovered.

Largest shortfall

The single site and category furthest below its budget allowance for the selected view and period, ranked on energy. It carries the spark in the waterfall, and its next step comes from a fixed rule for each category, not from a written opinion.

Events

Discrete losses, such as trips, faults, outages and curtailment instructions, are listed one event at a time. Each event carries its asset, first alarm, attendance, restoration, root cause, owner, contract position and evidence, and the events add up exactly to the item above them. In a real assessment they come from the SCADA alarm log, protection relay records, work orders and the instruction logs.

Continuous losses

Soiling, wake, degradation, derating and similar losses have no single event. They are shown by asset and by month, with the measurement behind them and what it found.

Response target

The time from the first alarm to someone on site, as the O&M or service agreement sets it: 4 hours for the solar sites, 12 hours for the wind farm and 8 hours for the CHP in this sample. Events reset remotely have no attendance.

Repeat events

Three or more events on the same asset in the period. The same breaker, inverter or engine failing again usually means the root cause was never fixed, only reset.

Data completeness

The share of intervals with a reading from the revenue meter, inverters and weather station, weighted by expected energy.

Completeness is not validity

A revenue meter can report every interval and still be wrong: scaled incorrectly, wired with reversed CT polarity, or out of step in time. A real assessment checks validity separately, reconciles the revenue meter against inverter and SCADA totals, and states how confident it is in the model, alongside completeness.

Sample data. The six sites, their names, tariffs, prices, allowances, efficiencies, events and every number on this page are fictional, generated to show how the waterfall behaves. Equipment models are named to make the sample realistic; the faults and figures attached to them are invented.