Rooftop Solar Systems in Bangladesh: Net Metering Rules, Policy Targets, and Job Exam Questions Practice

Bangladesh is stepping into a new era of renewable energy. With rising electricity demand, the government has adopted the Renewable Energy Policy 2025, which sets ambitious targets:

• By 2030, 20% of total electricity demand will come from renewable sources.
• By 2040, this share will increase to 30%.

Among renewable options, rooftop solar PV systems play a central role. Supported by Net Energy Metering (NEM), rooftop solar enables households, industries, and commercial users to become prosumers.

🔹 Consumer vs Prosumer

Aspect	Consumer	Prosumer
Role	Only uses electricity supplied by the utility	Both produces and consumes electricity
Source of Power	100% from the grid (utility)	Partially from rooftop solar / renewable system, surplus exported to grid
Meter Type	Standard (single-direction) meter	Bi-directional Net Meter (records import & export)
Bill Payment	Pays full bill for consumed electricity	Pays bill on net import; can earn credits for surplus export
Example	A household connected to BPDB grid	A factory with rooftop solar exporting excess power

👉 In short:

• Consumer = Electricity taker only
• Prosumer = Electricity user + producer under net metering

🔹 What is a Rooftop Solar PV System?

A Rooftop Solar PV (Photovoltaic) System is a renewable energy generation system where solar panels are installed on rooftops, parking lots, garages, sheds, or other suitable open spaces under consumer premises.

• It produces electricity directly from sunlight using photovoltaic cells.
• Consumers first use the electricity for their own needs, and any surplus is exported to the grid.

Simple Rooftop Solar PV System with Net Metering

🔹What is Net Metering and How Does It Work?

Net Energy Metering (NEM) is a system where a prosumer or third-party investor connects their solar or renewable energy system to the distribution grid.

• In this system, a consumer uses renewable electricity for their own consumption, and any excess electricity is supplied to the national grid.
• Later, the consumer can draw electricity back from the grid at a predetermined rate.
• At the end of the month, the consumer pays the bill based on net imported electricity.
• If exported electricity is greater than imported electricity, the surplus is recorded as credit units.
• At the end of the settlement period, the consumer receives monetary payment from the distribution utility for the accumulated credits, as per government regulations.

A bi-directional meter (Net Meter) is used in the net metering system to properly record both import and export of electricity. This ensures:

• Accurate measurement of electricity taken from the grid by the consumer, and
• Accurate measurement of electricity supplied from the solar PV or renewable system to the grid.

The meter stores this data, which is then processed by the utility’s central billing server.

• In each billing cycle, the bill is calculated based on:
  1. Electricity imported from the grid
  2. Electricity exported to the grid
  3. Credit units carried forward (if any)
• If the imported electricity is more than the exported electricity, the consumer pays only for the net excess imported.
• If the exported electricity is more, the excess portion is carried forward as credit to the next billing period, and the consumer does not pay any energy charges for that month.

At the end of the settlement period (quarterly/annually as prescribed), all accumulated credits are settled in cash at the government-determined tariff rate, and the credits are reset to zero.

🔹Business Models in Net Metering

According to the guideline, two models exist for installing renewable systems under net metering:

1. CAPEX Model –
   The consumer invests in and owns the renewable system within their premises, and shares the benefits of net metering accordingly.
2. OPEX Model –
   A third-party organization (other than the utility and consumer) installs the renewable system under a commercial agreement with the utility and the consumer, and supplies electricity to the consumer.

Comparative Table (CAPEX vs OPEX)

Aspect	CAPEX Model	OPEX Model
Investor	Customer & Utility	Third Party + Utility & Customer (as service users)
Initial Cost	High (capital investment)	Low
Ownership	Utility/Customer	Third Party
Payment Type	One-time / heavy upfront	Monthly / contract-based recurring
Risk	On customer & utility	On the investor
Long-term Cost	Relatively lower	Can be higher over time

👉 Simply put, the CAPEX model is like “buy and use”, while the OPEX model is like “rent and use.”

🔹 Technical Rules for Grid Integration in Bangladesh

To ensure grid stability and safety, rooftop solar systems must follow strict technical standards:

• Frequency Synchronization:
  • Grid operates at 50 Hz ±1%.
  • Inverter must support ±4% frequency variation.
• Voltage Disturbance Limits (Table 4):
  • Continuous operation between 85%–110% of nominal voltage.
  • Quick disconnection when voltage <50% or ≥135%.
• Anti-Islanding Protection:
  • PV systems must disconnect from the grid within 2 seconds of grid failure.
• Power Quality:
  • DC injection ≤1% of inverter output.
  • Total Harmonic Distortion (THD) ≤5%.
  • Power factor ≥0.85 (lagging/leading).
• Reactive Power:
• If required, reactive power must be imported from the grid.
• OPEX agreements must clearly state reactive power obligations.

🔹 Benefits of Rooftop Solar in Bangladesh

• Cuts electricity bills for households and industries.
• Reduces load on fossil-fuel power plants.
• Helps Bangladesh meet renewable energy targets.
• Promotes sustainable development.

📘 Job Exam Practice Section

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✅ Multiple Choice Questions (MCQ)

1. What is the renewable energy target for Bangladesh by 2030?
a) 10%
b) 15%
c) 20%
d) 25%
✅ Answer: c) 20%

2. What is the renewable energy target for Bangladesh by 2040?
a) 25%
b) 30%
c) 35%
d) 40%
✅ Answer: b) 30%

3. What is the settlement period under Net Metering in Bangladesh?
a) 1 month
b) 3 months
c) 6 months
d) 12 months
✅ Answer: b) 3 months

4. In the CAPEX model of rooftop solar, who owns the system?
a) Utility
b) Third-party investor
c) Consumer
d) Government
✅ Answer: c) Consumer

5. In the OPEX model, who installs and owns the rooftop solar system?
a) Consumer
b) Government
c) Third-party investor
d) Utility company
✅ Answer: c) Third-party investor

6. What does COD stand for in renewable energy projects?
a) Certificate of Development
b) Commercial Operation Date
c) Commissioning of Distribution
d) Central Operation Division
✅ Answer: b) Commercial Operation Date

7. What is LCOE?
a) Levelized Cost of Energy
b) Local Current of Electricity
c) Load Control of Energy
d) Line Current Operating Efficiency
✅ Answer: a) Levelized Cost of Energy

8. Which type of meter is required for net metering?
a) Prepaid meter
b) Smart prepaid meter
c) Bi-directional meter
d) Single-phase analog meter
✅ Answer: c) Bi-directional meter

9. What does “Net Zero” mean in energy context?
a) Producing exactly zero energy
b) Consuming as much energy as produced from renewable sources
c) No losses in transmission
d) Zero energy bill regardless of use
✅ Answer: b) Consuming as much as produced

10. What is Anti-Islanding in solar PV systems?
a) Protection against voltage drop
b) Ensuring PV disconnects when the grid fails
c) Backup power mode
d) Export limitation method
✅ Answer: b) Ensuring PV disconnects when grid fails

11. Within how many seconds must a PV system disconnect after grid failure?
a) 0.5 seconds
b) 2 seconds
c) 5 seconds
d) 10 seconds
✅ Answer: b) 2 seconds

12. The inverter must operate continuously within what voltage range of nominal?
a) 90%–110%
b) 85%–110%
c) 95%–120%
d) 80%–125%
✅ Answer: b) 85%–110%

13. What is the maximum Total Harmonic Distortion (THD) allowed for inverters?
a) 2%
b) 5%
c) 8%
d) 10%
✅ Answer: b) 5%

14. What is the maximum DC injection allowed into the grid by an inverter?
a) 0.5%
b) 1%
c) 2%
d) 5%
✅ Answer: b) 1%

15. What is the minimum acceptable power factor (leading/lagging) for PV systems?
a) 0.80
b) 0.85
c) 0.90
d) 1.00
✅ Answer: b) 0.85

16. Which standards define inverter short-circuit current limits?
a) IEC 60269
b) IEC 61727 / IEEE 1547
c) IEEE 519
d) IEC 60364
✅ Answer: b) IEC 61727 / IEEE 1547

17. In Net Metering, if export > import, the excess is:
a) Written off
b) Added as credit units
c) Paid immediately in cash
d) Transferred to next consumer
✅ Answer: b) Added as credit units

18. At the end of the settlement period, credits are:
a) Expired
b) Carried forward indefinitely
c) Compensated in cash at tariff
d) Given as subsidy
✅ Answer: c) Compensated in cash at tariff

19. Rooftop solar system is mainly based on:
a) Wind energy
b) Photovoltaic cells
c) Thermal collectors
d) Hydropower turbines
✅ Answer: b) Photovoltaic cells

20. Loss of mains is indicated by voltage dropping below:
a) 70%
b) 60%
c) 50%
d) 40%
✅ Answer: c) 50%

21. Who is called a “prosumer”?
a) A consumer who only imports electricity
b) A producer who sells electricity
c) A consumer who both generates and consumes electricity
d) A government agency
✅ Answer: c) A consumer who both generates and consumes electricity

✅ Short Questions with Answers

Q1. Explain the difference between CAPEX and OPEX models of rooftop solar systems.

• CAPEX Model:
  The consumer invests their own money to install and own the rooftop solar system. The consumer bears the initial capital cost but enjoys long-term savings and full ownership benefits.
• OPEX Model:
  A third-party investor installs and owns the system under a commercial agreement. The consumer pays only for the electricity consumed, without bearing upfront costs. Ownership remains with the investor.

Q2. What is meant by “anti-islanding” in PV systems, and why is it important?

• Anti-Islanding:
  A safety feature in PV inverters that ensures the solar system automatically disconnects from the grid within 2 seconds if the utility grid goes down (loss of mains).
• Importance:
  Prevents backfeeding electricity into a dead grid, which could endanger distribution utility workers and damage equipment.

Q3. Write the technical limits of voltage disturbances (Table 4) for PV inverters.

Voltage at Interconnection	Max Trip Time (s)
V < 50%	0.10
50% ≤ V < 85%	2.00
85% ≤ V ≤ 110%	Continuous
110% < V < 135%	2.00
≥ 135%	0.05

👉 Inverters must continue operation between 85%–110% of nominal voltage, but must trip quickly outside this range.

Q4. How does a bi-directional meter work under net metering?

• A bi-directional meter (Net Meter) records:
• Import (from grid): Electricity taken from the utility when solar is insufficient.
• Export (to grid): Surplus electricity supplied to the grid when solar generation exceeds demand.

At the end of the billing cycle, the consumer is billed on the net difference (Import – Export). Excess export is carried forward as credit units.

Q5. Define LCOE and explain its importance in renewable energy projects.

• Definition: LCOE (Levelized Cost of Energy) is the average cost per unit (kWh) of electricity generated over the lifetime of a renewable energy system. It is calculated by dividing the total lifetime costs (installation, financing, operation, maintenance) by the total electricity generated.
• Importance: LCOE helps compare the cost-effectiveness of different energy sources and guides investment decisions in renewable projects. Lower LCOE means more affordable and efficient energy.

Q6. What is COD in renewable projects?

• Commercial Operation Date, when the system officially starts electricity supply after successful testing.

Q7. Why is reactive power important in rooftop solar integration?

• Reactive power ensures voltage stability; if the PV system cannot supply, it must import from the grid.

Q8. What is meant by Net Zero in energy?

• A condition where total energy consumed equals total energy generated from renewable sources.

Q9. Differentiate between Consumer and Prosumer.

• Consumer: Only uses grid electricity.
• Prosumer: Both generates (via solar/renewable) and consumes electricity, exporting surplus to grid.

Q10. Why is rooftop solar important for Bangladesh’s future?

• Helps meet 20% renewable target by 2030, 30% by 2040.
• Reduces fossil fuel dependency.
• Promotes energy security and sustainability.

Q11. What is Net Metering?

• Net Metering is a system where consumers with rooftop solar generate their own electricity, use what they need, and send excess to the grid. A bi-directional meter records both import and export, and bills are calculated on net usage.

Q12. What is a Net Meter?

• A Net Meter is a bi-directional meter that records both electricity imported from the grid and exported to the grid.