Is More Solar Panels Better | Factors to Consider

Simply maximizing the number of solar panels is often counterproductive because system efficiency is physically bottlenecked by the inverter's rated AC output and local grid constraints rather than just available roof area.

If you install a solar array that exceeds the recommended 133% DC-to-AC ratio, the system will suffer from clipping during peak sunlight hours, meaning any power generation above the inverter's typical 5kW or 6kW limit is instantly lost as waste heat.

Additionally, since most distribution networks enforce a strict 5 kW export cap per phase, an oversized 13.2 kW system will produce significant surplus energy that cannot be exported, forcing the system's useful utilization rate to drop below 30% unless coupled with a large cell storage solution.

Electricity Consumption

Check Hourly

Just looking at the total monthly consumption on a bill is far from enough; you must request "Green Button" data or smart meter readings (Interval Data) at 15-minute intervals. A home with an annual consumption of 10,000 units consumes an average of 27.4 units per day, but if 70% of those 27.4 units occur between 18:00 and 23:00 after sunset, no amount of solar panels will cover this portion of demand.

When analyzing data, focus on "Base Load," which is the standby energy consumption when no one is home, usually between 200W and 500W (mainly from refrigerators, routers, security systems, etc.).

A standard 6.6 kW photovoltaic system can output up to 5000 W at 12:00 noon. If your daytime base load is only 300W, it means 4,700W of instantaneous power is flowing to the grid at a low price of 0.04-0.05 USD/unit, while you spend 0.35 USD/unit buying electricity after returning home at night.

Only when your daytime continuous Load Profile regularly breaks 2000W can expanding solar panels maintain the "self-consumption rate" at a healthy level of above 40%, otherwise the Return on Investment (ROI) will be stretched from 4.5 years to 8.2 years.

Air Conditioning is the Tiger

A 3-ton (36,000 BTU) central air conditioner typically has an operating power between 3.5 kW and 4.0 kW during cooling, consuming 0.6 units of electricity within 10 minutes.

If your roof is installed with 13.2 kW of solar panels paired with a 10 kW inverter, in the high temperature of 35 degrees Celsius at noon in summer, the efficiency drops due to the temperature coefficient (usually -0.35%/°C), and the actual output may only be 8.5 kW.

Turning on the AC at this time consumes 4 kW, leaving only 4.5 kW of available solar power for the home. If a 5 kW solar system was installed to save money, the Locked Rotor Amps (LRA) at the start of the AC might cause a voltage drop, and the system would have almost no surplus electricity for other devices while the AC is running, resulting in a continued need to purchase 20%-30% of electricity from the grid.

Data shows that for every 1 degree Celsius increase in the set temperature of the AC (e.g., from 22°C to 23°C), energy consumption can be reduced by 6%-8%, which improves the system's supply-demand balance more than blindly adding 2 pieces of 400W solar panels.

How to Charge EVs

Electric vehicles (EV) will completely change the home's energy consumption model. A Tesla Model Y traveling 20,000 km per year, calculated with a consumption of 160Wh/km, needs to consume 3200 units of electricity annually, equivalent to 35% of a typical home's annual consumption.

The power of a household Level 2 charger is usually 7.2 kW (32 A/240 V), which exceeds the output limit of most single-phase PV inverters (5 kW or 6 kW).

If you use solar charging during the day, even with a 10 kW solar system, during non-peak generation hours like 10:00 AM or 3:00 PM, solar power generation might only be 4-5 kW. This means for every 1 hour of charging, you still need to buy 2-3 units of expensive electricity from the grid.

To achieve 100% "Solar Charging," you need to configure at least a 10 kW+ solar array and pair it with a smart charger that supports "Solar-only" mode. This device can track surplus solar power at a variable rate from 1.4 kW (6 A) to 7.6 kW, preventing the loss of 0.30 USD in electricity costs per hour.

Huge Difference Between Winter and Summer

Seasonal variance is the core reason for photovoltaic system configuration errors. A 6.6 kW system in a 40-degree latitude region can have a daily average generation of 38-42 units in summer, while it might drop to 12-15 units in winter.

If you plan the system based on summer consumption (assume 30 units/day), you will face a 50% power shortage in winter; if configured based on winter demand (assume winter heating needs 50 units/day), you would need to install a giant 20 kW system (about 50 panels), which results in more than 100 units of surplus electricity per day in summer.

Under Net Energy Metering (NEM 3.0) policies, surplus summer electricity only earns meager credits of 0.03-0.05 USD, which usually cannot be carried over or cashed out across years, making 60%-70% of summer generation effectively a "free donation" to the power company.

Calculations show that the optimal capacity configuration is usually for the system to generate 10%-15% more electricity than consumed during spring and autumn, balancing the leverage between an additional hardware investment of 2500 USD to 4000 USD and electricity bill savings over the whole year.

Time Slots are Most Valuable

In mature markets like California or Australia, peak electricity prices (usually from 4:00 PM to 9:00 PM) can be as high as 0.50-0.60 USD/unit, while solar generation has decayed from peak to below 10% or even zero.

If you have a constant-temperature pool pump (power 1.5 kW) or an electric water heater (power 3.6 kW) at home, these "Shiftable Loads" must be set via a timer to run between 10:00 AM and 2:00 PM.

This single adjustment can shift 1500 units to 2000 units of electricity demand per year from an average cost zone of 0.35 USD to a solar self-consumption zone of 0 USD, directly generating a net profit of 500-700 USD.

In contrast, without adjusting usage habits, simply adding 3 kW of solar panels (costing about 2500 USD), generates an extra 4000 units per year, mostly sold at 0.04 USD during the day, with an annual return of only 160 USD. The payback period is as long as 15.6 years, far less cost-effective than buying a few smart plugs for 50 USD.

Data Core: When the ratio of the grid buy price to the Feed-in Tariff reaches 4:1 or 5:1, for every 10% increase in the self-consumption rate, the overall Internal Rate of Return (IRR) of the system increases by 2.5%-3.0%.

ROI

Calculate Initial Installation Costs

Installing a 3 kW micro-system involves fixed costs like labor, scaffolding (usually 500-800 USD), and grid connection application fees (about 200 USD), so the Price per Watt could be as high as 2.80 USD.

In comparison, the Price per Watt for a 6.6 kW system drops rapidly to 1.00-1.30 USD, with a total price around 3500-5000 USD.

When trying to further expand to 13.2 kW (about 32 panels), although the hardware cost per watt decreases slightly to 0.90 USD, the total budget will soar to 8000-10000 USD, and may trigger additional grid protection upgrade fees.

If your main switchboard is not only old but has no remaining space, upgrading to a switchboard meeting current safety standards (e.g., RCBO protection) requires an extra expenditure of 800-1500 USD.

If upgrading from single-phase to three-phase power is needed to accommodate an inverter output exceeding 5 kW, connection fees and underground cable relaying costs could be as high as 3000 USD. This extra expense will directly cause the first-year ROI to plummet from a healthy 20% to below 12%.

Payback depends on price gap

In a market environment where the grid purchase price is 0.30 USD/unit while the Feed-in Tariff (FiT) is only 0.05 USD/unit, every unit of solar power you consume directly is worth six times as much as selling it to the grid. Suppose a 10 kW system generates 14,000 units per year:

· Scenario A (High Self-Consumption): If you achieve 50% self-consumption (7000 units), you save 2100 USD on electricity bills, earn 350 USD from selling surplus, for a total annual profit of 2450 USD. If the system costs 9000 USD, the simple payback period is 3.67 years.

· Scenario B (Low Self-Consumption): If you blindly pursue a large system and the self-consumption rate is only 20% (2800 units), you save 840 USD, earn 560 USD from selling surplus, for a total annual profit of 1400 USD. For the same cost, the payback period is stretched to 6.42 years.

Under this price gap model, every additional solar panel beyond the home's base load produces electricity that is almost entirely reduced to cheap 0.05 USD export electricity. The marginal payback period for this portion usually exceeds 10 years, and may not even beat inflation.

Replace Once in Ten Years

Most photovoltaic modules (panels) offer a 25-year performance warranty, promising that the output power in the 25th year will be no less than 80-85% of the initial value, but the string inverter, the heart of the system, usually only has a 5-10 year standard warranty.

Statistics show that the Mean Time Between Failures (MTBF) of electronic modules, especially capacitors, in outdoor high-temperature environments (where internal temperatures often exceed 60°C) is about 10-12 years.

Over the full life cycle of a photovoltaic system, you will need to replace the inverter at your own expense at least once, with costs including 1200-2000 USD for hardware and 300-500 USD for labor.

If this inevitable mid-term expenditure of 2000 USD is ignored when calculating ROI, your expected Internal Rate of Return (IRR) will have an inflated bias of 2-3%.

If choosing micro-inverters, although the warranty can reach 25 years, the initial cost is usually 20-30% higher than string inverters, which requires a running cycle as long as 15 years to break even financially.

Value Declines Over Time

The power generation efficiency of solar panels is not constant but degrades linearly at a rate of 0.4%-0.6% per year.

A 400W panel's actual rated power in the 10th year is about 380W, dropping to 360W in the 20th year.

This means annual generation profits decrease year by year, while the grid's Daily Supply Charge (usually about 0.90-1.10 USD/day) often rises by 3-5% annually with inflation.

When performing a 20-year Discounted Cash Flow (DCF) analysis, future returns must be discounted.

Assuming a discount rate of 5%, the present value (PV) of 1 USD saved in the 10th year is only 0.61 USD.

Many overly optimistic ROI reports assume electricity prices rise by 5% annually and do not calculate system degradation and maintenance costs (such as a 200 USD professional cleaning fee every 2 years), eventually leading to an actual payback period 3-4 years later than expected.

Financial Red Line: When the total installation cost of a system exceeds 1.80 USD per watt (for 6 kW+ systems), or the expected self-consumption rate is below 30%, the Net Present Value (NPV) of the project is highly likely to be negative within 10 years.

Efficiency

Nominal Values are False

The 22.8% conversion efficiency or 440W maximum power seen on a datasheet are measured under "Standard Test Conditions" (STC).

STC assumes an irradiance of 1,000 W/m², a cell temperature constant at 25°C, and an air mass of AM 1.5.

In the real world, the cumulative duration of this perfect condition does not exceed 20 hours per year.

A more relevant metric is the "Nominal Module Operating Temperature" (NMOT/NOCT), which simulates a real scenario with an ambient temperature of 20°C, irradiance of 800 W/m², and wind speed of 1 m/s.

Typically, a panel with an STC rating of 415W can only output 310W to 315W under NMOT conditions.

This means the 10 kW system you purchased actually has its peak output hovering between 7.5 kW and 8.0 kW at noon on most sunny days.

If your installer did not explicitly inform you of the natural power drop of about 25% between STC and NMOT, you might mistakenly think the system is faulty.

For roofs with poor orientation (e.g., deviating 45 degrees from True North), an additional 3%-5% azimuth loss must be deducted.

Afraid of Heat, Not Sun

Voltage is inversely proportional to temperature. Every solar panel has a "Temperature Coefficient," usually Pmax -0.34%/°C (P-type) or -0.29%/°C (N-type).

The baseline here is a cell temperature of 25°C, not ambient temperature. In summer at noon, when the ambient temperature reaches 35°C, the surface temperature of black heat-absorbing panels often soars to 65°C or even 70°C.

Calculating based on this, the temperature rise difference is 40°C (65-25). For a panel with a coefficient of -0.34%, the power loss is 40 * 0.34% = 13.6%.

If you install a 6.6 kW system, just because of high temperatures, the instantaneous power will vanish into thin air by 900 W.

In contrast, panels using Heterojunction (HJT) technology have coefficients as low as -0.26%/°C, which can recover an extra 3%-4% of power generation under the same high temperatures.

This is why, in hot Arizona or Queensland, Australia, N-type TOPCon or HJT modules are still worthwhile even if they cost 0.05-0.08 USD/watt more than traditional PERC modules.

Must Connect in Series

In a typical String Inverter architecture, a string of 10 series-connected panels follows the "barrel effect."

If the current (Impp) of one panel drops by 20% due to bird droppings, shading, or manufacturing tolerances, the current of all 10 panels in the string will be pulled down to this level, causing the total string power to plummet by 20%, not just the loss from that one panel.

Although modern panels are equipped with 3 bypass diodes to isolate shaded areas, activating a diode requires a voltage drop and reduces the panel voltage by 1/3.

If a string of panels originally has a voltage of 300 V, and shading activates multiple diodes causing the total voltage to drop below the inverter's "Start-up Voltage" (usually 100 V-150 V) or the Min MPPT Voltage (usually 180 V), the entire string system will completely stop generating power.

In such complex shading scenarios, using Micro-inverters or Power Optimizers is mandatory. Although this increases costs by 0.15-0.20 USD/watt, it can recover 15%-25% of annual power generation.