Solar-use planning series · 6-minute read · Updated 5 October 2026

A factory roof can receive sunshine while production is stopped. What happens to that potential solar output depends on the loads still running, the approved connection arrangement and the system controls. Before comparing quotations, check whether each proposal accounts for those quiet days. A weekday-only assessment can miss an important part of the operating year.

These six checks help factory owners and facility teams prepare a weekend and shutdown brief for a commercial and industrial solar assessment. The regulatory references concern Peninsular Malaysia. They are not a substitute for a site-specific electrical design or confirmation of your approved scheme.

1. Count every type of closure day

List normal weekends, public holidays, maintenance shutdowns and longer festive closures. Separate a half-day Saturday from a fully closed Sunday. Also identify months when production changes substantially.

Give the designer the operating calendar rather than a statement that the factory “runs five days a week”. Two sites with the same annual consumption can have very different opportunities to use solar electricity during daylight.

2. Measure what remains on

A stopped production line does not necessarily mean zero demand. Refrigeration, security, servers or required environmental controls may continue running. Record the actual essential loads rather than assuming their combined consumption.

Where available, supply interval data covering operating and closure days. The interval is the time between readings. Ask your metering provider or electrical team what records are available and whether they represent the entire premises.

Illustrative example, without a battery: assume an array could deliver 300 kWh during daylight on each of two days. If coincident site demand absorbs 270 kWh on a working day but only 60 kWh on a closed day, the remaining potential is 30 kWh and 240 kWh respectively. That remainder may be exported where permitted or curtailed by controls. It is not automatically saleable electricity or lost revenue.

3. Confirm the approved destination for surplus

Check the actual approval and contract before modelling income or credit. Under Solar ATAP, eligible non-domestic exports are valued using Average System Marginal Price, subject to programme limits and billing-period treatment. Existing NEM customers need to use their own contract terms.

Grid-connected SELCO is different. The Energy Commission’s June 2026 revision does not allow power to flow into the utility supply system at any time. Do not treat SELCO as an export-credit arrangement.

For ATAP details, consult the official guideline. Ask the project team to document which route and limits apply to your premises.

4. Ask what the controls do when demand falls

Where export must be prevented or limited, the design needs to manage low-load conditions. Curtailment means deliberately reducing the solar output delivered. It can explain why recorded generation is lower than an unconstrained sunshine-based estimate.

Ask for the expected closure-day operating behaviour, the monitoring information available and who receives alerts. Confirm that the commissioning checks address the approved operating limits. Do not change inverter or export-control settings yourself.

A battery is not an unlimited destination for surplus. Its ability to accept energy depends on its capacity, charging power, current charge level and operating controls. First confirm whether storage is required under the current rules for your installation. Where it is optional, assess it separately rather than assuming it is financially justified simply because the factory closes.

5. Test operational changes without creating waste

Identify existing tasks that can safely move to daylight on low-load days. Consider staffing, process dependencies, maintenance requirements and product quality before changing a schedule.

Do not run unnecessary equipment to make the solar-use percentage look better. Compare the complete operating effect: energy, labour and any applicable demand charges. TNB’s current tariff information distinguishes tariff categories and time-of-use arrangements; a generic electricity rate is not enough for every factory.

Weekend surplus and maximum-demand reduction are different design questions; ask for each to be assessed on its own evidence.

6. Request a calendar-based operating summary

Before accepting an annual generation figure as the whole story, request a summary that distinguishes:

• Expected solar output on working and non-working days.
• Electricity used directly on site.
• Permitted exports and the assumptions behind their value.
• Expected curtailment or other operating limits.
• What changes during longer shutdowns.

For a fair quotation comparison, ask whether metering, export controls, any required storage and commissioning are included. Request exclusions and ongoing service charges in writing. A lower total alone does not show that two proposals cover the same operating requirements.

The figures remain estimates until supported by operating data. Weather, shading, equipment availability and production changes can affect the result. Use our post-installation monitoring checklist to check the assumptions once the system is running.

What happens when you send your records

Evolts’ contact page asks commercial customers for twelve months of bills and interval data where available. Add your shutdown calendar and explain which loads must remain on. If records are incomplete, identify the gaps so the team can explain what still needs measuring.

1. Send a recent TNB bill and a roof photo, plus twelve months of bills, interval data and your closure calendar if you have them.
2. An engineer reviews the records and replies within one working day with an indicative system size, cost band and payback estimate.
3. If it is worth pursuing, a site survey follows, usually within five working days and before any firm quotation. Ask for the closure-day assumptions to be explained before you compare quotations.

Questions facility teams ask before enquiring

Planning for a home as well? Use the separate household daytime-usage checklist rather than applying factory assumptions to it.