Can I Charge Solar Lights Indoors? A Practical Guide for EPC Contractors and Buyers

Why Does This Question Matter for EPC Projects?

In many government and donor-financed solar projects, procurement officers often ask: “Can these solar lights be charged indoors before installation?” On paper, the idea sounds simple. In reality, indoor charging is rarely sufficient for large-scale street lighting.

As a project manager with 15 years of field experience in West and Central Africa, I’ve seen this misunderstanding cause shipment delays, rejected deliveries, and even contract penalties. For EPCs, knowing exactly when indoor charging works and when it fails is the difference between smooth handover and costly disputes.

How Do Solar Panels Generate Energy Indoors?

Solar modules are designed to convert photons from sunlight into electrical energy. Indoors, the available light is very different:

• Sunlight intensity (lux):
  • Direct noon sun: 100,000+ lux
  • Overcast sky: 10,000–25,000 lux
• Artificial light intensity (lux):
  • Fluorescent office light: 300–500 lux
  • LED household bulb: 100–150 lux
  • Halogen floodlight: 1,000–2,000 lux

In practice, a 40 W panel exposed outdoors may generate 200 Wh per day, enough to power a 60 W solar light for a full night. The same panel indoors under fluorescent tubes may only generate 10–20 Wh per day—barely enough for a small garden lamp.

This is why EPCs should never assume warehouse lighting is sufficient to charge street light systems.

What Happens If EPCs Depend on Indoor Charging?

From Nigeria to Burkina Faso, I have witnessed similar problems when contractors relied on indoor charging during staging:

1. Rejected FAT tests – In Senegal, a shipment of 1,000 units failed acceptance testing because the lights were only half-charged indoors. Runtime dropped to 2 hours instead of the specified 12 hours.
2. Warranty disputes – In Nigeria, a state government claimed “faulty batteries” when in reality the EPC had stored all lights in a warehouse for weeks without outdoor exposure.
3. Increased logistics costs – In Burkina Faso, EPC staff had to move 500 sets outdoors every morning just to meet delivery deadlines. Labor and transport costs increased by 15%.

These are preventable risks if EPCs educate buyers early and plan proper outdoor pre-charging.

Are There Cases Where Indoor Charging Works?

Yes, but only in limited situations:

• Small decorative solar lamps (1–5 W): Designed for gardens, balconies, or pathways. Low daily energy demand (2–10 Wh), so fluorescent lighting may be sufficient.
• Temporary indoor demonstrations: For exhibitions, donor presentations, or showroom displays, lights can be pre-charged under halogen floodlights (1,500+ lux).
• Hybrid models with USB/AC input: Some integrated solar lights now include USB-C or AC adapters. EPCs can top up batteries using generators or grid power before field deployment.

Outside of these scenarios, EPC-scale street lights require full-spectrum outdoor sunlight.

What Strategies Actually Work for EPC Contractors?

To avoid project delays, here are best practices I’ve implemented across different African markets:

• Outdoor staging before deployment: Keep lights in an open yard for at least 1–2 days of direct sunlight charging.
• Use LiFePO₄ batteries ≥6000 cycles: These hold charge longer during shipment and maintain ≥80% capacity after years of cycling.
• Select hybrid input models: Street lights with both solar + grid charging ensure runtime during rainy season or in dusty Sahel regions.
• Educate buyers clearly: Always state in tender documents that design autonomy (≥12 hours/night, ≥3 cloudy days) assumes outdoor charging.
• Track charge levels during shipment: Use smart BMS (Battery Management System) with SOC display. This prevents lights arriving with depleted batteries.

Comparison: Indoor vs Outdoor Charging

Technical Case: 60 W Solar Street Light

A standard 60 W all-in-one solar street light in Nigeria requires:

• Panel: 120 Wp
• Battery: 12.8 V, 40 Ah LiFePO₄ (512 Wh)
• Load demand: ~60 W × 12 h = 720 Wh

To fully charge the battery:

• Outdoors: 120 Wp × 5 peak sun hours = ~600 Wh/day → meets design.
• Indoors: 120 Wp × 5 h × 10% efficiency = ~60 Wh/day → only 8% of demand.

Result: Lights will fail after a few hours if charged indoors only.

Regional Example: West Africa Project Lessons

• Togo (7,000 units CIZO program): EPCs staged lights in an outdoor yard for 3 days before deployment, achieving >95% runtime compliance during handover.
• Mauritania (2,000 units): Units stored indoors for weeks arrived at site with depleted batteries. EPC had to delay installation by 10 days while re-charging outdoors.
• Nigeria (3,500 units in Borno State): Hybrid solar + AC input models allowed EPCs to guarantee performance during the rainy season, avoiding client complaints.

Buyer’s Checklist Before Accepting Solar Street Lights

1. Confirm outdoor pre-charging time (minimum 2 days in direct sunlight).
2. Check battery SOC (≥80%) before shipment.
3. Verify hybrid charging options (USB/AC) for backup.
4. Ensure LiFePO₄ cycle life ≥6000 cycles (tested to IEC 62620).
5. Request BMS monitoring data from supplier.
6. Test runtime on site: ≥12 h/night, ≥3 cloudy days autonomy.

This checklist saves procurement teams from disputes and EPCs from penalties.

Final Takeaway

Solar lights can charge indoors, but for EPC-scale projects the efficiency is too low to depend on. Indoor charging may work for small lamps or short demonstrations, but not for municipal or donor-financed installations.

For EPC contractors, the solution is simple: pre-charge outdoors, choose hybrid-capable lights, and communicate clearly with buyers. This guarantees smooth acceptance, reduces risk, and ensures compliance with tender specifications.

👉 Preparing a government tender? Choose Sunlurio solar street lights with ≥12-hour runtime, ≥6000-cycle LiFePO₄ batteries, and pre-charged delivery options.

Explore Sunlurio solar street light solutions