1. Do the rooftop solar systems affect the factory roof? 

Answer: INPOS is well-known as a professional developer for rooftop solar PV systems. THE CURRENT ROOFTOP SYSTEM IS NOT AFFECTED BY PV INSTALLATION AT ALL, it is even better than current conditions. The reason is that:

1.1: If the workshop roof is the standard screwing roof: INPOS’s roof construction method shall not drill any additional hole into the available roof. It shall replace the available corrugate sheet metal screw with inox 304 screws and drill at the current borehole on the roof. Moreover, a newly complete waterproof shall be applied for the new screw system without any impacts on the old roof.

If the corrugated sheet roof is not screwed (seam lock or clip lock): The applicable construction method statement is that no screw is put on the available roofing to ensure no risk of water penetration. Method statement of clamping with hard reinforced shaping aluminum shall be employed by INPOS.

1.2: Upon PV installation, the corrugated sheet shall become an indoor activity (not be affected by weather conditions). Hence, the roof’s useful life shall be enhanced and free from damages

2. Do the rooftop solar systems affect the steel structure of the Factory?

Answer: The plant’s structure is not affected by the rooftop PV system at all because:

2.1: PV force is evenly distributed on entire roof purlins. Each PV is supported by 4 points on the purlin. The weight of a PV with accessories is 28 kg/2m2. That is why the force on 1m2 is just 14 kg and is also supported by 4 positions linked on the purlin. Hence, each purlin point is only subject to a force of 28/4 = 7kg (such force is too low)

2.2: Before installation, the structure of the factory shall be recalculated by the actual steel structure. When the structure worksheet is appraised and certified that it is qualified with load-bearing capacity under TCVN, then it may be deployed and submitted to the Plant for review before implementation. Such a worksheet shall ensure the Plant’s post-installation structure is qualified to bear the ever-strongest storm in the history of the site.

2.3 If PV installation on the workshop is not structurally qualified upon structure calculations, INPOS shall, at its own cost, reinforce the workshop frame to ensure that PV installation is complied with structure standard and found no impact on post-reinforcement workshop structure.

3. Do the installation of rooftop solar systems affect the Factory’s operation?

Answer: The method statement ensures absolute safety without affecting the plant’s production. The construction control procedure shall not cause any impacts on production and noise during installation through a sound-proof construction method.

Method statement:

A dedicated operation path is used as a separate walkway for workers and supervisors without directly walking on the corrugated sheet roof to ensure that force is evenly distributed on the roof upon traveling. The movement sound-proof measures are taken.

4. What if the rooftop is damaged or penetrated with water during the solar power system is operated (for example after 10 years of rooftop solar power system operation, it is damaged or penetrated with water, etc.)?

Answer: After rooftop PVs are installed on a corrugated sheet roof, the roof shall be subject to indoor operation (without weather impact). Hence, the roof cannot be damaged by any impacts (except for impacts beneath the plant).

If the roof is damaged by the PV system for some reasons whatsoever, the investor (INPOS) shall be responsible for repair and replacement at its own costs.

5. How long does it take to construct the rooftop solar system?

Answer: Equipment installation, acceptance, and commissioning at site, etc., lasts 30-45 days.

While the period of design, procurement of materials, and transportation to the site is 20-30 days

The total project construction period is 50-75 days

6. What are documents to be provided to INPOS?


  1. Certificate of Business Registration or investment license
  2. Construction Permit, Certificate of Land Use Rights of the plant
  3. Audited Financial Statements in 3 recent years
  4. Daily load profile, monthly power consumption output in 6 recent months (the factory may be supported to work with the local power authority to acquire this data by INPOS)

7. Is the factory’s power quality affected by solar power?

Answer: Solar power system invested by INPOS is the grid-connected solar power system. It means that the solar power system shall be connected with the national power grid. Upon grid connection, the plant shall collect such connected power and use it in the plant. Hence, the plant’s power quality shall not be changed.

8. Is solar power output sufficient to energize the plant? Is the plant subject to insufficient power? What happened if the solar power capacity is lower than the plant’s consumption load?

Answer: Solar power system invested by INPOS is known as a grid-connected solar power system. It means that the solar power system shall be connected with the national grid through the LV cabinet at the plant. When the solar power output is lower than the plant’s load upon connection with the national electrical system, then the grid power shall compensate for the inadequacy so that the plant capacity is always satisfied. When it is higher than the plant’s load, such surplus shall be automatically put into the grid (selling the surplus to power authority). Hence, the plant capacity is always guaranteed even when no power output is generated by solar power.

9. Is the plant still energized by the solar power system in case of a power failure?

Answer: In case of power failure, the inverter (AC generator) of the solar power system shall switch off power from the solar system. As grid power failure is found and solar power continues energization, it shall energize the grid. Then, the grid shall be live, resulting in non-safety for the grid. Therefore, when grid power failure is recognized, the solar power shall be automatically deactivated as per safety requirements by the power authority. That is why the plant shall not be energized by solar power in case of power failure.

10. Is the factory’s power system is affected if the solar power system failure?

Answer: Solar power system is characterized by a series of security levels. It aims to ensure that when solar power system fails (the probability is extremely low as the solar power system is static, failure probability is extremely low), the plant’s power system shall not be affected, including:

 Level 1 Protection system is located within Inverter: Comprising of fuse for overcurrent protection, lightning protection, overvoltage protection devices, phase balancer, DC and AC voltage loss protection devices, etc.

Level 2 Protection by MCCB/ACB and lightning arrester in LV cabinet behind inverter: Behind the inverter, an LV cabinet system shall be provided for overcurrent, surge, and lightning protection purposes once

Level 3: Protection by MCCB/ACB at master LV cabinet before it is connected with the plant’s master electric cabinet: Before it is connected to the plant’s master LV cabinet, an MCCB/ACB system shall be provided to further protect before the plant’s power system is connected.

11. What are plant operations affected by the maintenance and service of rooftop solar power systems?

Answer: Absolute safety is guaranteed by maintenance and service of the rooftop solar power system. Hence, the plant operations shall not be affected as the rooftop solar power system is fully monitored in offsite mode. The maintenance activity shall be launched in the afternoon or early morning when the power generation is not triggered by the system for safety reasons. The maintenance is carried out once every 2-3 months and only rooftop PVs are conducted with a built-in water system to ensure that the plant is not affected.

12. What is the head of terms of PPAs between INPOS and the Plant?

Answer: Head of terms in PPAs includes:

  1. The contract term is at least 20 years.
  2. The plant commits to buying the power output generated by the solar power system, corresponding to the plant’s consumption output calculated by INPOS by the plant’s load profile.

For example, 100 kWh is daily consumed by the plant (from 7 a.m to 5 p.m). INPOS shall calculate to install so that respective solar power output of 90-95 kWh is obtained. It shall be completely consumed by the plant. On non-working days (Saturday, Sunday, and Public Holidays), solar power output that is not consumed by the plant shall be sold to EVN under separate PPA made and entered by and between INPOS and EVN.

  1. The solar power selling price offered to the plant shall be 4-5% lower than that purchased from the EVN for the Northern projects and 15-25% for the Southern projects.
  2. According to the credit ratings (on the plant’s financial statement basis), the payment guarantee for solar power may or may not be required.
  3. INPOS shall be responsible for dismantling and restore the site when the PPA is terminated (20 years)
  4. INPOS shall cover the corrugated sheet roof maintenance and service if it is affected by the solar power system.
  5. INPOS shall fulfill any procedures with the concerned industries and agencies to ensure that the solar power system complies with all Vietnam and international standards. The plant is not required to do any procedure.