How do you know whether a factory solar installation is delivering the savings promised in its business case? A dashboard showing solar generation is useful, but it is not the same as proof of reduced electricity expenditure. For UK manufacturers, meaningful solar monitoring brings together generation, site electricity use, grid imports and exports, tariffs and changes in production activity.
This guide explains how factory finance directors, operations managers and energy teams can build a practical measurement and verification (M&V) process from project design through to ongoing reporting. It complements our solar panels for factories UK guide, which covers the wider investment decision.
1. Separate solar generation from electricity savings
A solar inverter may report how many kilowatt-hours (kWh) the system has produced. That figure alone does not show how much electricity the factory avoided purchasing, what was exported or how much money was saved.
At a typical grid-connected factory, three measurements matter: solar generation (output from the PV system), grid import (electricity bought from the supplier) and grid export (electricity sent back to the network). Site consumption is a separate quantity. If there is no battery, and metering boundaries and losses are handled consistently, solar used onsite can be estimated as solar generation less solar export.
Where a factory has battery storage, multiple generation systems, private-wire connections or unusual metering arrangements, a qualified engineer should document the energy flows and adapt the calculation. See our factory solar self-consumption guide for the relationship between daytime demand and onsite use.
2. Establish the baseline before the panels go live
Before installation, retain representative half-hourly electricity import data, the electricity contract and tariff schedule, production-shift patterns, planned changes to machinery and any existing energy-efficiency projects. These records make later comparisons more meaningful.
A factory’s electricity use may change because of new production lines, seasonal demand, shutdowns or changes in operating hours. Comparing one post-installation bill with a bill from a different production period can therefore be misleading.
The International Performance Measurement and Verification Protocol (IPMVP) provides a recognised framework for defining a measurement boundary, establishing a baseline and making suitable adjustments. An M&V plan should be proportionate to the investment and agreed before results are reported as verified savings.
For project sizing before installation, read our half-hourly electricity data guide.
3. Agree which meters provide the evidence
Ask the installer and energy supplier to identify the authoritative source for each metric. Inverter monitoring, dedicated generation meters, building-management-system readings and supplier settlement meters do not always measure at the same point or on the same time interval.
- Generation: inverter portal or suitable AC generation meter, with agreed treatment of inverter and auxiliary losses.
- Grid import: supplier or approved boundary meter readings, preferably in half-hourly intervals.
- Grid export: separate export register or meter, with the appropriate commercial export agreement.
- Site operations: production hours, output volumes and relevant process changes to explain demand variation.
- Costs: actual import tariffs, export revenue, demand-related charges, standing charges and agreed service fees.
Check meter accuracy, time synchronisation, missing-data handling and who can access the raw records. A visually attractive dashboard is not a substitute for auditable data.
4. Understand export payments and contract eligibility
Export revenue must be modelled separately from avoided grid purchases. The UK’s Smart Export Guarantee applies to eligible solar PV installations up to 5 MW, subject to scheme requirements. Larger projects and some commercial arrangements need different export contracts. Do not assume that every factory installation qualifies for a particular export tariff.
The UK government’s SEG guidance explains qualifying arrangements and export metering requirements. Discuss the export MPAN, metering configuration, agreed tariff and settlement process with the relevant supplier or offtaker before commissioning.
Our factory surplus electricity guide explores what happens when generation exceeds onsite demand.
5. Illustrative calculation: what the numbers really mean
Consider an illustrative factory solar system generating 400,000 kWh in a year, of which 60,000 kWh is exported. Assuming no battery and consistent measurement boundaries, approximately 340,000 kWh is used onsite.
If each onsite solar kWh avoids an illustrative 18p of variable import cost, that suggests £61,200 in avoided purchases. If exported electricity earns an illustrative 6p per kWh, export revenue would be £3,600. The combined illustrative annual gross electricity benefit is therefore £64,800.
These figures are examples, not a quote, customer result or guaranteed return. Actual value depends on half-hourly prices, contractual terms, losses, any export restrictions, changes in demand and charges that solar does not avoid. The gross benefit is also before finance costs, maintenance, insurance, taxes and future equipment replacement.
6. Agree performance KPIs before handover
A factory monitoring plan should distinguish between the health of the solar equipment and the commercial outcome for the business. Useful monthly KPIs include generated kWh, generation versus the agreed weather-adjusted forecast, onsite-use proportion, exported kWh, avoided import costs, export income, inverter availability and fault response times.
Record the assumptions behind the original proposal. A lower-than-forecast generation month may reflect weather rather than equipment failure; conversely, strong generation does not necessarily mean the factory captured the forecast financial benefit if shifts or tariffs changed.
Agree how often results are reviewed, who investigates anomalies, and what data will be retained for finance, ESG reporting and warranty claims. Where a performance guarantee exists, check its exact definition, exclusions, measurement methodology and remedies.
7. Use monitoring to find operational improvements
Solar data becomes more valuable when reviewed alongside the factory’s operating schedule. A manufacturer might discover that a planned cleaning, charging or compressed-air process can be moved into a period of higher onsite solar generation without harming production. Other factories may need a different strategy because their demand is already high throughout the day.
Any changes should be justified by real half-hourly data, labour requirements and process constraints. Avoid moving critical production solely to chase an assumed solar saving. Our factory solar battery-storage guide explains when storage merits separate financial analysis.
8. Factory solar monitoring checklist for procurement teams
- Keep a documented pre-installation electricity and production baseline.
- Confirm generation, import and export measurement points and meter responsibilities.
- Agree raw-data access, retention, time intervals and fault notifications.
- Set a method for adjusting comparisons when production volumes or shifts change.
- Separate avoided import costs from export revenue and fixed charges.
- Define generation, availability and commercial KPIs with named owners.
- Include commissioning records, monitoring training and warranty procedures in handover.
- Review actual results at agreed intervals and investigate unexplained differences.
9. Questions factory finance directors should ask
Does solar generation equal the reduction in my electricity bill?
Not necessarily. Generation may be used onsite or exported; the financial value depends on when electricity is used, import and export tariffs, fixed charges and other contractual terms.
Can we simply compare bills before and after installation?
Bill comparisons can be a starting point, but changes in production volumes, shifts, weather and tariffs may distort the conclusion. Use a documented baseline and a proportionate adjustment method.
Who should own the monitoring dashboard?
Operations should review equipment availability and alarms; finance should reconcile measured energy flows with the tariff and project business case. A named owner should coordinate the combined report.
Conclusion: prove the factory solar business case
A successful solar project is not measured only by the panels installed or the kWh shown on an app. For manufacturers, it should be assessed against actual site consumption, reliable meter data, relevant tariff terms and an agreed baseline. A proportionate monitoring and verification plan makes the investment case more transparent and helps protect long-term value.
Considering a factory solar project? Contact Commercial Solar Systems to discuss a site-specific assessment.
