Before payment, require contractor identity and competency evidence, a site survey, load schedule, single-line diagram, exact bill of quantities, PV string calculation, battery power check, protection/cable schedule, written warranties, milestone payments and a signed commissioning/handover plan. Do not pay from a brand-and-kVA quotation alone.
The points that change the decision
- Verify the company, responsible engineer/technician and relevant NEMSA competency route.
- Make every major component identifiable by exact model and quantity.
- Tie payment to deliverables you can inspect, not promises or equipment arrival alone.
- Retain a final balance until testing, documentation and user handover are complete.
Checks before you request final pricing
Confirm the legal name, physical address, references for similar work and who will take responsibility for design and commissioning. NEMSA publishes competency certification schemes covering renewable-energy installation, solar home systems, inverter and battery storage work; ask for the relevant evidence and verify it through the agency's available channels.
A site survey should inspect distribution boards, supply phase, earthing, generator/changeover arrangement, roof structure and access, shading, cable routes, ventilation, equipment location, fire separation and mobile-network or Wi-Fi availability for monitoring.
- Company registration and traceable business address
- Named technical lead and relevant competency evidence
- Comparable installations with reachable clients
- Liability, safety and after-sales responsibility in writing
Documents required before a major deposit
| Document | What it must show | Why it matters |
|---|---|---|
| Load schedule | Quantity, watts, hours, essential status, simultaneity and motor surge | Prevents bedroom-count or guess-based sizing |
| Single-line diagram | Grid, generator, inverter, battery, PV, protection, earthing and changeover | Exposes unsafe or incomplete architecture |
| Itemised bill of quantities | Exact model, quantity, rating and unit scope | Stops silent substitution after payment |
| PV string calculation | Modules/string, Voc, Vmp, Isc, temperature and MPPT limits | Prevents over-voltage, clipping and poor harvest |
| Battery power check | kWh, continuous/peak BMS power, module count and protocol | Prevents a large battery that cannot support the inverter |
| Protection and cable schedule | Cable sizes, breakers, fuses, isolators, SPDs, busbars and earthing | Makes balance-of-system safety auditable |
| Warranty schedule | Product, installer, importer/seller, duration, exclusions and claim process | Clarifies who acts when a fault occurs |
A safer payment structure
Payment percentages depend on project and procurement risk, but every instalment should unlock after a defined, inspectable deliverable. Avoid turning almost the entire contract value into an unsecured advance.
- 1
Design acceptance
A limited first payment follows survey, agreed load schedule, drawings and exact specification.
- 2
Verified procurement
The next milestone follows invoices, model/serial evidence and inspection of genuine undamaged equipment.
- 3
Mechanical and electrical completion
Payment follows mounted modules/equipment, labelled protection, cable work and installation inspection—not simply delivery to site.
- 4
Commissioning
Release follows functional tests under grid, battery, solar and generator modes, plus monitoring access and defect list.
- 5
Retention / final balance
The final amount follows documentation, training, clean handover and correction of agreed defects.
Commissioning tests to witness
Do not accept a demonstration that only turns on a light. Test the system against the agreed operating modes and credible load combinations. Record settings and results so a later technician can distinguish design intent from accidental configuration.
For parallel or three-phase systems, confirm synchronized operation, phase allocation, communication, firmware compatibility and response if one unit is unavailable. For batteries, verify current limits, state-of-charge calibration, charge sources and safe shutdown thresholds.
- Grid loss and automatic transfer
- Solar charging and MPPT behaviour
- Generator input, charging and safe changeover
- Essential-load runtime and heavy-load interlocks
- Earth/neutral arrangement and protection tests
- Monitoring account ownership, alarms and data access
- Shutdown, isolation and emergency procedure
Red flags worth pausing the project
Pause if the quotation says only ‘10 kVA inverter, 15 kWh lithium, Tier 1 panels’ without model numbers and engineering basis. Also pause if the installer refuses drawings, claims protection is included but will not itemise it, promises every heavy appliance without a load study, or relies on a warranty whose responsible seller is unnamed.
Pressure to pay immediately because prices may rise is not a substitute for due diligence. Currency and inventory can change, so agree a quotation-validity period and substitution process: no equivalent product should be accepted without a revised datasheet, warranty and written approval.
What a credible final handover contains
The system is not complete when the panels begin charging. The owner should receive a technical and operational record.
Create an independent sizing brief
Bring a load-based inverter, battery and panel starting point into contractor conversations.
Primary sources used
Manufacturer and official Nigerian sources support technical or market claims. Worked examples remain SFP Technologies planning scenarios, not product guarantees.
NEMSA certification scheme
Official competency scope for renewable-energy, solar home, inverter and battery installation work.
Official source ↗NEMSA contractor directory and services
Official agency portal for certified electrical contractors and inspection guidance.
Official source ↗NEMSA competency certification process
Official application and competency-verification framework.
Frequently asked questions
How much deposit should I pay a solar contractor?＋
There is no universal safe percentage. Use staged payments tied to accepted design, verified procurement, installation completion, commissioning and handover. Avoid paying almost the entire contract before inspectable work exists.
What must be on a solar quotation?＋
Exact models and quantities, load/design basis, inverter topology, battery kWh and power, panel/string design, mounting, cables, protection, installation, commissioning, warranty responsibilities, exclusions, timeline and payment milestones.
Can an installer substitute an equivalent inverter or battery?＋
Only after supplying the new exact model's datasheet, compatibility, warranty and revised engineering impact for written approval. Brand or kVA equivalence alone is not enough.