Modular Solar Panel vs Fixed Solar Module Which to Choose

Choose modular for flexibility: add 1-2 panels yearly with 15% less rewiring. Pick fixed for cost efficiency—20% cheaper install, best if space/angle won’t shift. Match to long-term needs.

Conceptual Differences

When your roof has 20 square meters of usable area facing a solar system investment that can easily cost 30,000 to 50,000 RMB, the decision between "modular or fixed" is not an easy one.

Currently, over 80% of residential installations are still fixed systems, but the annual growth rate of modular products is as high as over 15%.

Fixed systems, with their over 25 years of technological precipitation and economies of scale, have driven the cost per watt down to a low of 4-6 RMB. In contrast, modular systems attract attention with their excellent performance of less than 5% power generation efficiency loss when dealing with shading (compared to potentially 20-30% for fixed series systems).

Fundamental Differences

Fixed systems are collective operations; modular systems are special forces teams.

1. Fixed System: A Fortified Concentration Camp

Its structural design goal is singular: remain immovable for 25 years. The mounting structure uses materials like aluminum alloy 6063-T5, with a typical thickness of 2.0-2.5 mm. The weight of the mounting structure for a 10kW system can exceed 350 kg. During installation, each connection point uses M8 stainless steel bolts tightened with a torque wrench to a preload of 16-20 Newton-meters, ensuring it won't fall apart even under extreme conditions with wind speeds of 60 m/s (equivalent to a Category 17 hurricane).

On the electrical side, 20 pieces of 500W panels connected in series can run DC voltages up to 600V-1000V. This high voltage is to reduce line loss, but it's a double-edged sword. If a tree's shadow falls on just one panel after 3 PM, causing that panel's output current to drop from 9 Amps to 2 Amps, the output current of the entire string of 20 panels will be pulled down to 2 Amps. The instantaneous power generation plummets from 10kW to 2kW, a loss of 80%. While you can remedy this by adding a power optimizer to each panel for about 250 RMB, the total investment immediately increases by 8%-10%.

2. Modular System: Flexible and Mobile Independent Units

A single panel is designed with a power of 300W-400W, weight controlled within 18-22 kg, so one person can carry it. The connection method heavily utilizes quick-connect plugs with an IP67 waterproof rating. Align and plug, a "click" sound indicates it's powered. This design makes it possible for non-professionals to install or remove a single panel within 15 minutes.

The revolutionary aspect of the circuit is that it completely abandons series connection. A microinverter is directly integrated behind each panel, converting DC electricity to AC as soon as it leaves the panel. Then, the AC electricity from all panels is connected in parallel to the grid. If one panel is completely shaded, its output drops to zero, but the other 19 panels continue to generate at full capacity with over 99% efficiency. The total system power only loses that one panel's share, about 5%, instead of the catastrophic collapse in a series system. Of course, the cost of microinverters is heat: an 800W microinverter costs about 1000 RMB and operates long-term at 60-70 degrees Celsius, which is a severe test for module lifespan.

3. Data Comparison: Real Performance Under Shading

On a typical roof where 15% of the area is shaded for 3 hours every afternoon:

l Fixed (No Optimizers): Annual average generation drops from 13,000 kWh to 10,000 kWh, a loss of 23%.

l Fixed (With Optimizers): Annual average generation maintains at 12,000 kWh, a loss of 7.7%, but the initial investment increases by 5,000 RMB.

l Modular System: Annual average generation is 12,500 kWh, with a loss of only 3.8%, and no additional hardware cost.

Performance Battle

A 10kW system can generate up to 13,000 kWh annually under ideal conditions. But in actual operation, due to temperature, shading, dust, and module degradation, the final electricity fed into the grid may only be around 11,000 kWh, a difference of over 15%.

Module power degradation is typically around 0.5% per year, but the time to first failure of the inverter may directly determine whether your returns after the 8-year payback period are stable or lost.

Rated Power and Actual Generation are Two Different Things

Standard Test Conditions (STC) in the laboratory measure power at 25°C panel temperature and 1000W per square meter irradiance. But your roof is not a laboratory.

1. Temperature is the "Invisible Killer" of Power Generation

The power temperature coefficient of solar panels is approximately -0.35% / °C. On a summer afternoon, the roof panel surface temperature can easily reach 65°C, which is 40°C higher than the standard temperature. This means that even with good sunlight, the actual output power of a 550W panel will decrease by: 550W × (-0.35%) × 40°C = 77W. The instantaneous power is only 473W, an efficiency loss of 14%. A 10kW system's peak power on a hot summer afternoon might only be 8.6kW. Due to relatively poor air circulation behind the panels, fixed systems typically have a temperature-related loss 1-2 percentage points higher than modular installations with gaps.

2. "Chronic Blood Loss" Caused by Shading and Dust

A wire lying across a panel might only shade 1% of the area, but if it happens to cover the starting part of a cell string, it could cause the entire panel's output power to drop by 30%. 

In low-rainfall areas, 30 days without cleaning can cause a 5-8% drop in generation efficiency; after 90 days, the loss may reach 12-15%. This means a system that should generate 1000 kWh per month might only produce 850 kWh if left uncleaned for half a year. Due to the independence of each panel in a modular system, the impact of local shading or dust is strictly limited and does not cause a chain reaction.

Power Degradation: The Slow Evaporation of Profit Behind the 0.5% Annual Rate

Modules leave the factory with a positive power tolerance. For example, a panel rated at 550W might actually be between 552W and 555W. But the first year sees the greatest degradation.

1. First-Year Degradation and Linear Degradation

Top-tier industry brands promise first-year degradation of ≤2%, and ≤0.45% per year thereafter. Second-tier brand parameters might be relaxed to first-year ≤3%, and ≤0.55% per year thereafter. This means:

l A top-tier panel's power at the end of Year 1 is approximately: 550W × 98% = 539W.

l Power at the end of Year 10 is approximately: 539W - (539W × 0.45% × 9) ≈ 517W, which is 94% of the initial power.

l Power at the end of Year 25 is approximately: 539W - (539W × 0.45% × 24) ≈ 480W, which is 87.3% of the initial power.

2. Non-Linear Degradation Risks: Potential Induced Degradation (PID) and Hot Spots

In high-temperature, high-humidity environments, excessively high system voltage can induce PID, causing abnormal panel degradation of over 5% within 2-3 years. Although high-quality inverters have anti-PID functions, it remains a potential risk. Hot spots occur when an individual cell in a panel is shaded or damaged, turning it from a power-generating unit into a power-consuming unit (a resistor). Local temperatures can exceed 100°C. Long-term exposure accelerates the aging and yellowing of encapsulation materials (like EVA), reducing light transmittance and causing irreversible additional power loss. Fixed systems, due to their high voltage and series structure, are more sensitive to PID and hot spots.

System Lifespan: The Shortest Plank Determines the Entire System's Life

The module's 25-year lifespan is a given; the inverter's lifespan is the critical node.

1. Inverter: The Module Most Likely to Fail First in the System

The design life is generally 10-12 years. In environments with poor ventilation or sustained high temperatures (internal enclosure >50°C), the lifespan may shorten to 8 years. The cost of a single replacement accounts for about 15-20% of the initial investment. Microinverters, due to their distributed installation, small individual size, and fanless design relying on natural heat dissipation, claim a lifespan of up to 25 years. However, their long-term operation at 60-70°C raises questions about the aging rate of internal modules (like magnetic core modules). There is a lack of large-scale data validating the failure rate after 15 years.

2. Durability of Supporting Modules

l Mounting Structure: Galvanized steel or aluminum alloy structures themselves have a long lifespan, but bolts and nuts at connection points may risk corrosion or loosening over 20 years of wind vibration and rain, requiring regular inspection (e.g., every 5 years).

l DC Cables and Connectors: The sheathing of DC cables exposed to UV rays will age and crack. MC4 connectors, if poorly crimped or made of substandard materials, may develop increased contact resistance after 5-8 years, leading to heating and even fire hazards.

Pros and Cons Comparison

Imagine you spent fifty or sixty thousand RMB installing solar panels, only to have your generation output discounted by 20% because of the shadow cast by your neighbor's tree every afternoon.

The emerging modular system is addressing this pain point with its "individual combat" capability. But don't rush; it's not a panacea either. Its cost per watt may be 15%-25% higher, meaning the upfront investment for the same 10-kilowatt system could be 10,000 to 20,000 RMB more.

Advantages Comparison

Imagine the solar system you invested 50,000 RMB in could lose over 600 RMB in electricity revenue annually due to shadows from a chimney or an afternoon tree. 

Modular systems, by equipping each panel with an independent microinverter, can reduce generation loss caused by shading from the common 20-40% in fixed systems to less than 3%. But its advantages go far beyond this. From the DIY design that can save nearly 10,000 RMB in installation fees to real-time monitoring down to each individual panel, modular solutions are redefining the home solar experience.

Unique Advantages of Modular Systems

1. Shading? Not Even a Problem

Measured data shows that shading just 5% of the area can cause a 30% loss in overall system generation.

Modular systems completely solve this problem. Each panel operates independently. If one is shaded, the others continue working at full capacity with nearly 98% efficiency. For homes with chimneys, skylights, or surrounding trees, this means modular systems can generate 15%-25% more electricity than fixed systems during winter when light is poor, equivalent to an extra 300-500 kWh per year.

2. Installation is Like Building with LEGO, and You Can Add More Anytime

Fixed systems require professional teams for mounting, cable laying, and electrical connections. A 5 kW system typically requires 2-3 workers busy for a full day, with installation costs between 3,000-5,000 RMB.

Modular systems use a plug-and-play design with pre-assembled snap-on mounts and waterproof connectors, allowing users with basic DIY skills to install a 4 kW system in a weekend afternoon, saving all installation fees. More importantly is scalability: install 8 panels this year to meet basic needs; next year, if electricity use increases (e.g., a new child), just spend half an hour to add 4 more panels. The system will automatically recognize the new capacity. Expanding a fixed system often requires replacing the inverter and rewiring, with additional costs potentially exceeding 10,000 RMB.

3. Every Panel Works Under Your Watchful Eye

Through a mobile app, you can see the generation power of each panel accurately down to the single digit (Watt). When panel #7 in the southeast corner suddenly generates 18 watts less than its neighbor after 2 PM, you can immediately check if bird droppings have accumulated. This granular monitoring allows you to detect and solve 90% of common problems within 24 hours, avoiding sustained generation loss.

Fixed systems typically only show total system generation. When a 10% drop is noticed, it may require a professional to spend half a day testing panel by panel to locate the problematic one, during which the lost electricity is a fait accompli.

Core Advantages of Fixed Systems

1. Every Penny is Spent on Generation, Clear Cost Advantage

Modular systems require a microinverter costing 400-800 RMB for each panel, while fixed systems only need one centralized string inverter. This means that with the same module quality, the comprehensive cost per watt (panels + inverter + mounting) of a fixed system is 0.3-0.5 RMB lower than a modular system.

For a 10 kW system, this means a direct saving of 6,000-8,000 RMB in initial investment. Under ideal roof conditions with no shading, this saved money might be equivalent to the electricity revenue from 2-3 extra years of system operation.

2. The Simplicity of the Great Way, Reliability Verified Over Decades

Although a string inverter is a single point of failure, this technology has been developed for over 25 years, with an Mean Time Between Failures (MTBF) exceeding 100,000 hours (approx. 11.4 years). Major brands offer 10-12 year warranties, and extended warranties up to 20+ years are available for a fee.

The entire system is simple: solar panels are solid-state devices with no moving parts, first-year degradation does not exceed 2%, and subsequent annual degradation is only 0.55%. After 25 years, they can still maintain over 85% of their initial generation capacity.

3. Under Perfect Conditions, Slightly Better Peak Efficiency

In ideal laboratory environments, top-tier string inverters can achieve peak conversion efficiencies of over 99%, while microinverters are typically in the 96.5%-97.5% range. Although in real-world home scenarios, modular systems often have higher "global efficiency" due to various inconsistencies, for large commercial/industrial roofs with consistent orientation and no shading, fixed systems can convert 1%-2% more electricity during peak sun hours. For a 100 kW system, this means generating an extra 20-40 kWh per day.

Disadvantages Comparison

If that microinverter priced at 650 RMB in a modular system fails in the eighth year, you're not just paying for the part; you also have to pay a 600 RMB service call fee. Fixed systems seem cost-effective, but an afternoon shadow can instantly evaporate 30% of your generation, equivalent to losing hundreds of RMB per year.

Modular systems distribute the risk of failure across dozens of nodes, while fixed systems bet everything on one central inverter.

Weaknesses and Hidden Costs of Modular Systems

1. Every Penny of Upfront Investment Takes Longer to Recoup

A mainstream brand microinverter procurement price is 500-800 RMB. For 20 panels, you need 20 of them. This single item is 6,000-10,000 RMB more expensive than buying a single high-quality string inverter of the same power. This results in the total cost of a 5 kW modular system being about 20% higher than a fixed system. Under ideal light conditions, this extra investment requires 3-5 more years to be recouped through its slightly higher generation efficiency. 

2. Failure Points Increase from 1 to 20, Making Repairs More Cumbersome

The main failure risk of a fixed system is concentrated on the inverter, a single device. Modular systems distribute this risk. With 20 panels corresponding to 20 microinverters, although the individual failure probability is low (annual failure rate ~0.05%), the combined failure probability increases. This means that over the system's 25-year lifespan, you will likely need to handle 1-2 inverter failures. The trouble is that replacing a damaged microinverter requires a technician to work on the roof. A single service call fee might be 500 RMB, and the material cost for a single inverter replacement is also around a thousand RMB. Although most modules have a 25-year warranty, the time cost of applying for a claim and waiting for replacement, plus potential service fees, need to be factored into the Total Cost of Ownership.

3. Rapid Technological Iteration May Lead to Compatibility Traps

Solar technology, especially power electronics, evolves quickly. If you install a modular system from Brand A this year, five years later when you want to expand, you might find that model has been discontinued. New microinverters may be incompatible with the old ones in communication protocols, mechanical interfaces, or voltage parameters. You could face the dilemma of being unable to simply expand, or needing to purchase an expensive adapter gateway to make old and new equipment work together. 

Those Annoying "Chronic Problems" of Fixed Systems

1. Shading is the "Number One Killer" of Generation, Losses are Beyond Imagination

Measured data shows that shading just 10% of the area of one panel can cause the generation of the entire string (typically 10-16 panels) to drop by 30%-50%. 

2. System Flexibility is Almost Zero, Late-Stage Modifications are Extremely Costly

Installing a fixed system is like cooking a dish that can't be changed later. Initially, you install a system matched to a 7 kW inverter based on your budget and roof area. Three years later, if you want to add 5 panels, you'll find the existing inverter has no capacity headroom. The choices are difficult: either endure the waste of not connecting the new panels, or spend 10,000-15,000 RMB to replace the inverter with a larger one, potentially involving grid capacity upgrade applications and full cable rewiring.

3. High-Voltage DC Arc Risk is an Invisible Hidden Danger

A typical fixed system can have DC-side voltages as high as 600V to 1000V. At such high DC voltages, if line connections loosen, have poor contact, or insulation is damaged, it's very easy to generate a DC arc. The center of a DC arc can reach 3000-4000 degrees Celsius and is difficult to self-extinguish, posing a potential fire hazard. Although modern inverters are equipped with Arc Fault Circuit Interrupters (AFCI), this is a protection mechanism that needs to be triggered. In contrast, modular systems convert DC to 240V AC at the roof end, fundamentally eliminating the risk of high-voltage DC arcs.

4. Troubleshooting is Like "Finding a Needle in a Haystack"

When a fixed system's generation drops by 15%, the troubleshooting process is very time-consuming and labor-intensive. Installers need professional equipment to measure each panel's voltage and current under the sun, checking connectors to locate whether a specific panel is degraded or a connector is oxidized. A single such on-site inspection service might cost between 300-800 RMB, and the generation lost during the inspection cannot be recovered.

How to Choose?

Data shows that in 2023, China's newly installed residential PV capacity exceeded 50 GW, but at least 30% of owners indicated within one year of installation that if they could choose again, they would place more emphasis on the system's flexibility or long-term returns.

Your roof may only have 20-30 square meters of effective area. Once you choose wrong, over the system's 25-year lifespan, the generation loss could be as high as 15-20%, equivalent to wasting thousands or even tens of thousands of RMB.

Residential Status

Installing solar is not a one-time consumption but a fixed asset investment with a term of up to 25 years. Data shows that the median length of residence for urban Chinese residents in the same home has exceeded 10 years, but still, 35% of households plan to change their primary residence within 5 years due to work, children's education, etc.

Nearly forty percent of households may not fully cover the solar system's average investment payback period of 6-8 years. If your house is just a "transit point" but you mistakenly install an immovable fixed system, then when moving, you will face a sunk cost loss of 40%-60% of the initial investment.

Situation 1: Renting or Planning to Move Within 5 Years

If you are a tenant or already plan to move in 3-5 years, your core demands are "investment preservation" and "asset mobility".

l Calculate a Clear Account: Assume you install a 5 kW solar system with a total investment of about 20,000 RMB. In an area with an electricity price of 0.6 RMB/kWh, it generates about 6,000 kWh annually, saving you 3,600 RMB in electricity bills.

l Choose a Fixed System: After living there for 3 years, you save about 10,000 RMB in electricity. But when moving, this system is almost impossible to dismantle and take. You can only try to transfer it to the next tenant or landlord, usually at a transfer price of only 30%-50% of the residual value, maybe recovering only 3,000-5,000 RMB.

l Choose a Modular System: Similarly, after 3 years, saving 10,000 RMB in electricity. When moving, you can use half a day and labor costs possibly under 500 RMB to completely dismantle and pack the entire system. In your new home, the system's remaining at least 22-year lifespan will continue to serve you. Your initial investment is fully preserved.

Situation 2: Planning to Reside for 8-15 Years

If you are a newlywed couple or a family with school-age children planning to reside in the current property for 8+ years, this is the optimal timeframe for fixed solar systems to leverage their cost advantage.

l Unit Price Advantage from Economies of Scale: Fixed systems, due to standardized batch installation, can control their cost per watt between 1.5-2.0 RMB. A modular system of equivalent quality, incorporating more plug-and-play design and microinverters, may have a cost per watt as high as 2.2-2.8 RMB. For a 10 kW system, the total price difference could reach 7,000 to 13,000 RMB.

l Investment Payback Model: A 10 kW fixed system with a total investment of about 45,000 RMB, generating 12,000 kWh annually, saves about 7,200 RMB in electricity bills per year. Its simple payback period is approximately 6.25 years (Total Investment / Annual Return). From Year 7 until Year 25, the electricity revenue generated by the system is almost pure profit. If you reside for 15 years, the total return would be 7,200 RMB/year * 15 years = 108,000 RMB. Subtracting the initial investment, the net profit exceeds 60,000 RMB. This is a high-quality investment with an annualized return rate exceeding 10%.

Situation 3: Retirement Home or Permanent Residence

If you are 50 years old and living in a house planned for retirement, then your decision-making perspective is 25 years or even longer.

l Ultra-Long-Term Reliability Overwhelms Everything: The warranty for mainstream PV panels is typically 12 years product warranty and 25 years linear power warranty (guaranteeing end power at year 25 is not less than 80% of initial). 

l Asset Appreciation Attribute: For a permanent residence, a well-designed, adequately powered fixed PV system can directly increase the property's valuation. Property assessments show that a solar system capable of covering 80% of a household's electricity demand can increase the house value by 3%-5%. For a property worth 3 million RMB, this alone can increase its value by 90,000-150,000 RMB, far exceeding the system's installation cost.

Roof Conditions

Data shows that over 40% of owners have roofs with varying degrees of "non-standard" conditions when installing solar: about 25% of roofs have permanent obstructions (like chimneys, ventilation pipes), 15% of roofs are made of special materials with unknown load-bearing capacity (like color steel tiles, glazed tiles), and another 30% of roofs have insufficient effective usable area (less than 60%) due to varying orientations.

If you don't conduct a thorough "physical examination" of your own roof and blindly choose a system type, it may cause the initial installation cost to soar by 35%, or even lead to an annual generation loss of 20% or more.

Scenario 1: Flat Roof or Simple Large South-Facing Pitched Roof

If your roof is such a "standard test site": a flat cement surface, or a sloped roof with a pitch between 15-35 degrees, large area facing south (deviation east/west not exceeding 20 degrees), and no shadows from chimneys, trees, or parapet walls from 10 AM to 3 PM during the day.

l Fixed systems can perform at their maximum efficiency here. Professional installers can use aluminum alloy mounts to customize an tilt angle for your roof. For example, in Beijing (around 40°N latitude), they would install the array on a flat roof at a 35-degree tilt. This angle allows the panels to receive the most solar radiation throughout the year, increasing generation by 5%-8% compared to laying them flat.

l Costs are minimized. Under these ideal conditions, installation is standardized assembly-line work. A 10 kW system can be completed by two workers in 2-3 days. The installation cost per watt can be pressed below 1.6 RMB, with a total price around 16,000 RMB. This is the best quote you can get.

l Calculate the Generation Account: Such an unshaded 10 kW system can generate an average of 12,000 kWh annually (calculated based on an average of 3.3 hours of effective daily sunlight). If partial shading reduces effective generation time by 1 hour per day, it would generate over 1,000 kWh less per year, a loss exceeding 600 RMB.

Scenario 2: Multi-Slope Roof, With Shading, Special Materials

This is the most common roof type in China's old urban areas and self-built houses. It's like an "obstacle course" with complex rules, but modular systems excel at "guerrilla warfare" in such places.

l Dealing with "Fragmented" Area: Your roof might have a 3 sq m empty space on the east side, 5 sq m on the west, but the best south-facing spot is occupied by an air conditioner outdoor unit. Fixed systems require at least 15-20 sq m of continuous space to be economical. Modular systems are different. You can place 1 panel (about 2 sq m) on the east, 2 panels on the west, starting with a small 1.5 kW system for a total investment of maybe just 6,000 RMB. Later, with more budget, move the AC unit and add 3 panels on the south side.

l Coping with "Stubborn Shadows": A chimney might cast a shadow 3 meters long on the roof on the winter solstice. In a fixed series system, this shadow covering just one-tenth of one panel can cause the power generation of the entire string (dozens of panels) to plummet by over 30%. Modular systems (especially those with microinverters) achieve "point defense": the shadow only affects the blocked panel, with a generation loss of only 5%, while other panels operate normally at 100%. All things considered, over a year, the total generation of a modular system might actually be 15% higher than a fixed system.

l Solving "Load-Bearing Anxiety": The load-bearing capacity of an old house's color steel tile roof might be only 15-20 kg/sq m. A fixed system, with mounts and panels, can weigh over 25 kg/sq m, posing a risk. Lightweight modular panels can be controlled to under 15 kg each.

Scenario 3: Peculiar Roofs (Dome, Glass Roof)

For some special roofs, like glass roofs on sunrooms or arched roofs on industrial factories, both systems may not be perfectly suitable.

l Creative solutions are needed then. For example, on a glass sunroom, you cannot drill holes for traditional mounts. A dedicated "rail-less adhesive" installation method can be used, which is essentially an extreme form of modularization. Each panel is directly glued to the glass with structural adhesive, forming its own system. Although the cost per watt may soar to over 3.5 RMB, it's the only feasible solution.

l Load-bearing is a hard metric. Before starting work, the roof's load-bearing data must be clarified.

Budget Model

The initial investment for installing solar is a significant expense for most families, with a budget range of 30,000 to 50,000 RMB being most common. Data shows that over 60% of potential users postpone installation plans because they cannot provide the full amount upfront, but they often overlook a key characteristic of solar investment: this is an expense where the larger the upfront investment, the lower the long-term unit cost.

A 10 kW system installed in two phases will ultimately cost 18%-25% more than a one-time installation, approximately 7,000 to 12,000 RMB. Your budget planning method – whether "One-step in place" or "phased construction" – will directly determine your total return level over the next 25 years.

Option 1: One-Time Investment

If you have idle funds of 50,000 RMB or more in your savings account and no larger consumption plans (like buying a car, renovation) in the next 5 years, then a one-time installation of a fixed system is the financially optimal choice.

The Gap Between "Wholesale Price" and "Retail Price": A significant portion of the solar system cost consists of fixed costs, such as the inverter, mounting structure, cables, distribution box, and the most expensive labor installation fee.

l Example: Installing a 10 kW fixed system has a total quote of 45,000 RMB, equivalent to 4.5 RMB/W. If you only install 5 kW, the total price might not be 22,500 RMB, but rather 28,000 RMB (5.6 RMB/W). The "missing" 5,500 RMB is the allocated fixed cost. When you decide to add another 5 kW later, you need to pay almost all the fixed costs again. The price for the second 5 kW system might still be around 28,000 RMB. Ultimately, for the 10 kW system, you actually spent 56,000 RMB, which is 11,000 RMB more than a one-time installation, a premium of 24%.

Significantly Shorter Investment Payback Period: A one-time investment of 45,000 RMB with an annual return of 7,200 RMB has a payback period of about 6.25 years. A two-phase investment of 56,000 RMB, due to the delayed generation of the second phase, will extend the overall payback period to 8-9 years.

Option 2: Phased Investment

If your family's liquid funds are tight, or you wish to spread the 50,000 RMB budget over 2-3 years, then the "installment savings" model of modular systems is tailor-made for you.

l Smoother Cash Flow, Easing Initial Pressure: You can use an initial budget of 15,000 RMB to first build a 3 kW modular system. This system can meet about 40%-50% of the household's basic electricity demand, saving you 2,500 RMB in electricity bills annually. The next year, you can use these saved 2,500 RMB, plus new budget, to easily add 2 kW.

l Leaving a Window for Technological Iteration: PV technology is still developing rapidly, with module efficiency increasing by about 0.5% annually and prices slowly declining. Phased investment means the modules you install later might be more efficient (e.g., from 21.5% to 22.5%) for the same price. Although the total price may be higher, you gain access to more advanced technology and more flexible cash flow.

l Extremely Low Trial-and-Error Cost: If you are skeptical about the actual effect of solar, investing 15,000 RMB first to install a small system as a "trial" is a very low-risk strategy.