Multi-Site Commercial Solar Programme Delivery: Operational Discipline for Solar PV Installers

Winning a framework agreement to deliver solar PV across several commercial sites changes the nature of the job. A single-site residential or small commercial installation follows a linear sequence: survey, G99 application, procurement, installation, commissioning, invoice. Add five, eight, or ten sites under a single programme, and those steps multiply across parallel workstreams - each with its own structural assessment, DNO timeline, procurement schedule, sub-contractor allocation, and payment milestone. The sites will not be at the same stage at the same time. DNO approvals will clear at different dates. Equipment deliveries will land when they land. Snagging will surface at different points on each roof. The commercial solar installer who navigates this successfully runs a tight programme across all sites from day one, not a collection of individual jobs that happen to share a contract number.

Site Selection, Survey Sequencing, and Programme Scoping

When a facilities manager, property company, or multi-site operator awards a solar framework, the first operational test is whether the installer can assess all sites efficiently and build a credible delivery programme before mobilisation. Residential solar experience helps, but commercial site surveys are different in kind, not just in scale.

A commercial site survey for rooftop solar typically covers: roof age, condition, and material (profiled steel, flat felt, concrete, or EPDM membrane); structural load capacity for the proposed panel configuration; roof access provisions for installation and future maintenance; shading analysis across different seasons; electrical service capacity and distribution board location; and existing plant or rooftop equipment that constrains panel layout. On a 200kWp warehouse installation, the survey report informs the structural engineer's load calculations, the electrical design, and the G99 application documentation. The survey is not a pre-sales estimate - it is an engineering document that every subsequent step depends on.

For a multi-site programme, the sequencing decision matters. Survey all sites before procurement, or survey the most straightforward sites and begin ordering while others are still being scoped? The risk of surveying before ordering is lead time: panels and inverters for commercial systems from European and Asian distributors typically ship on extended lead times that can materially delay a programme if procurement is held until every site is fully confirmed. The risk of ordering before full survey sign-off is misspecification - discovering mid-programme that one site requires a different panel format, or that a structural engineer has reduced the permitted panel count on a constrained roof area.

Most experienced commercial solar contractors use a phased survey approach: complete structural and electrical surveys for all sites within the first four to six weeks, issue preliminary single-line designs for G99 submission across all sites simultaneously, and place procurement orders site by site as structural calculations are confirmed. This approach gets all sites into the DNO queue at roughly the same time, which matters because G99 processing - not the physical installation - is typically the longest single item on the project programme.

G99 and DNO Management Across Multiple Sites

For any commercial solar system above 16 amperes per phase - which covers virtually every commercial installation above around 11kWp on three-phase supply - a G99 application must be submitted to and approved by the Distribution Network Operator before the system can be energised. This is a non-negotiable regulatory step, and on a multi-site programme it is typically the single biggest source of programme delay.

A standard G99 application for a system up to 250kWp takes 8-16 weeks from submission to connection offer. Sites requiring full capacity studies - typically above 250kWp - extend to 16-26 weeks. Sites in constrained network areas or where the DNO identifies reinforcement requirements can take 6-12 months, well beyond what any programme schedule can absorb without restructuring the delivery sequence. Budget £3,000-£8,000 in DNO-related costs for a typical 100-500kWp commercial project, covering application fees, witness testing for systems above 50kWp, and capacity study charges where required.

For multi-site work, three G99 management principles determine whether the programme delivers on time.

Submit all G99 applications simultaneously, as soon as single-line diagrams, inverter datasheets, and protection settings are confirmed. A multi-site rollout where applications are submitted sequentially - as each site's survey completes - will finish months later than one where all sites enter the DNO queue on the same day. If an eight-site programme submits applications staggered over eight weeks, and each application takes ten weeks to clear, the last site is ready for commissioning nearly five months after the first. Batch submission compresses that window to a single ten-week span.

Map sites by DNO region at the outset. A ten-site programme spanning Yorkshire, the South West, and central Scotland covers three separate operators: Northern Powergrid, Western Power Distribution, and Scottish & Southern Electricity Networks. Each has its own portal, fee schedule, contact team, and response pattern. Assuming one application process handles all sites is an early-programme mistake that surfaces at exactly the wrong moment.

Manage the export limit risk explicitly. The DNO assesses local network capacity and may impose an export limit below the system's nameplate rating. On warehouse and distribution centre sites - where daytime loads are significant but weekend demand drops sharply - a 50% export curtailment can materially affect the client's projected return. Identify potentially constrained sites during the pre-application enquiry phase and address them before the contract programme is agreed with the client.

Three failure patterns cause approximately 80% of G99 application problems: incomplete documentation at submission, adding 2-4 weeks per application; network capacity rejection requiring renegotiation or system resizing; and inverters that lack valid G99 type-test certification - a risk when specifying non-mainstream brands or sourcing outside established distribution channels. Confirm G99 type-test certification for every inverter before specifying at programme scale.

Procurement, Equipment Scheduling, and Materials Planning

Commercial solar procurement at programme scale differs from sourcing equipment site by site. A 400kWp rollout across four sites requires several hundred panels, multiple string or central inverters, mounting hardware, cabling, and switchgear. The procurement discipline is whether to consolidate all of this against a single purchase order or to stage deliveries to match site readiness.

Buying in a consolidated batch has cost advantages. Volume pricing from distributors is better than individual site orders. Standardising the panel and inverter specification across all programme sites simplifies design, reduces G99 documentation variation, and makes future O&M straightforward. At portfolio scale - 50 or more sites - the cost-per-watt reduction from framework procurement and standardisation can reach 15-30% compared with equivalent single-site purchasing. For a 5-10 site SMB-scale programme the saving is proportionally smaller, but negotiating a framework price with a specialist distributor against the total programme volume is still materially better than site-by-site purchasing.

The risk of bulk procurement is site dependency. If DNO approval is delayed on one site, equipment allocated to that site sits in a yard consuming capital. If a structural engineer reduces the permitted panel count after the order is placed, the programme has surplus stock that may not be returnable without a restocking charge. The practical approach for most SMB-scale commercial programmes is to procure shared infrastructure - inverters, cabling, switchgear, and mounting systems - against the programme once all sites are confirmed, and order panels site by site as structural calculations are signed off.

Purchase orders for programme-level commercial solar should capture: product specification including MCS-compliant panel and inverter references; confirmed delivery lead time; site-level allocation where equipment is being split across multiple delivery addresses; and a clear variation and returns provision for design changes that alter quantities mid-programme.

Sub-contractor and Crew Scheduling for Concurrent Site Delivery

Commercial rooftop solar installations involve more trades than residential work. On a complex roof or a large system, the principal contractor is coordinating: a scaffolding or MEWP access sub-contractor; a roofing contractor if membrane repairs or penetration works are required before panels are installed; a structural engineer for load calculations and sign-off; an electrical sub-contractor for distribution board connections, metering, and any three-phase supply upgrades; and the panel installation crew. On sites within the scope of CDM 2015, principal contractor duties apply, adding a further layer of method statement and coordination responsibility.

For a multi-site programme delivered in parallel, the scheduling problem compounds. Each site needs access scaffolding erected before installation begins, and that scaffolding needs to be struck after commissioning to release the access sub-contractor for the next site. If the scaffolding sub-contractor treats each site as a separate booking rather than a coordinated programme, their own scheduling pressures determine when they move between your sites - not your programme sequence.

The discipline that prevents this: issue sub-contractors with the full programme schedule at the outset, showing confirmed access dates and booking windows for all sites simultaneously. A scaffolding company with visibility of a six-site programme across ten weeks will resource and schedule accordingly. One receiving individual call-off bookings will treat each as a standalone job. The practical difference is whether scaffolding is available when your installation crew arrives, or whether the crew is standing on site waiting for access to be erected.

Labour time recording on multi-site commercial work is more complex than on single-site jobs. A crew working across three sites in one week needs to record time against each site separately. Hours entered against the wrong job distort site-level job costing and make it impossible to identify whether one site is over-running on installation labour while others remain on budget. This is particularly important where the programme includes any variation-priced elements - additional structural work on one site, additional cable runs on another - that need to be distinguished from the fixed-price scope.

Stage Invoicing, Cost Control, and Financial Reporting

Multi-site commercial solar contracts are invoiced in stages against programme milestones rather than as a single lump sum. The standard stage structure for a commercial solar framework is: a deposit on contract signing (typically 20-30% of contract value, to fund early materials procurement); a stage payment on G99 approval confirmation for each site; a payment on practical completion of installation per site; and a final payment on commissioning and handover of all MCS documentation, as-built drawings, and O&M packs.

For an eight-site programme this creates 20-30 invoicing events against a single contract, each needing to be tracked against the correct site, the correct milestone, and the costs committed to that site. A programme that is generating revenue on paper may have specific sites running at a loss due to unforeseen sub-contractor costs, additional structural work not initially scoped, or equipment substitutions after the order was placed. Without site-level job costing, those losses are invisible until the programme closes.

Cost control on multi-site commercial programmes requires three numbers per site, reviewed weekly. First: committed cost - what has been ordered but not yet invoiced by suppliers or sub-contractors. Second: incurred cost - what has been invoiced and approved for payment. Third: forecast-to-complete - the estimated remaining cost of installation, commissioning, and any outstanding snagging. The gap between committed-plus-incurred and the programme budget for each site is the real-time margin position. Catching a site running over budget at week four allows intervention. Finding it at final account does not.

Stage invoice timing also requires attention. Issuing a G99-stage invoice before the client has received the DNO connection offer creates a contractual dispute - the milestone has not occurred. Align invoice issuance to confirmed external events (DNO connection offer received, installation practical completion confirmed in writing, MCS certificate issued) rather than to internal progress estimates.

How Zigaflow Supports Commercial Solar Programme Delivery

Managing a six-site commercial solar programme across quotes, purchase orders, sub-contractor costs, delivery notes, and stage invoices in a spreadsheet creates exactly the information gaps that erode margin: costs allocated to the wrong site, stage invoices issued before the triggering milestone is confirmed, sub-contractor POs without a clear site allocation, and no real-time view of committed costs against remaining programme value.

Zigaflow brings all of these workstreams into one system. Each site runs as a separate job with its own cost lines, purchase orders, delivery confirmations, and invoicing schedule. When a supplier invoice arrives, it can be matched against the original PO and goods received confirmation before payment is approved. Stage invoices are raised against the correct job at the correct milestone. Sub-contractor costs are allocated site by site. The programme manager can see, at any point, how each site is tracking against its budget - not just the aggregate contract position.

For solar PV installers managing their first multi-site commercial framework, that site-level visibility is the operational foundation for everything else.

Multi-site commercial solar is where programme discipline earns its return. The technical skills that make a solar installer competent at single-site work - accurate surveys, clean electrical installation, MCS-compliant commissioning - do not automatically translate into the programme management, sub-contractor coordination, and financial control that a multi-site commercial contract demands. Installers who build those operational disciplines early - surveying across all sites before procurement, submitting G99 applications in a batch, scheduling sub-contractors against a published programme, and tracking costs site by site - find that multi-site commercial work becomes more repeatable with each programme. The margin comes from the system, not just from the installation.