Microinverter vs String Inverter Calculator

Compare editable inverter-side cost and simplified shade-value scenarios for microinverters and string inverters, with exact formulas and limitations.

Methodology reviewed August 25, 2026 by the Solar Calculator HQ editorial team. This is an editorial check, not professional engineering or tax certification. Review our formula, source and limitation standards.

Microinverter vs String Inverter Calculator

System size (kW) Number of panels Base annual yield (kWh/kWp) Assumed flat energy value ($/kWh) Shading scenario (%) Cost per microinverter ($) Micro balance-of-system per kW ($) Central string inverter cost ($) String BoS per kW ($)

Illustrative yield — string

1,356 kWh/kWp

Illustrative yield — micro

1,378 kWh/kWp

Illustrative upfront cost — string

$5,400

Illustrative upfront cost — micro

$3,600

Illustrative annual energy value — string

$1,391

Illustrative annual energy value — micro

$1,413

Micro minus string upfront cost

-$1,800

Micro minus string annual value

$22

Scenario assumptions

Illustrative only: each percentage point of shading reduces the entered base yield by 1.3% for string and 1.0% for micro. Every modelled kWh is valued at the entered flat rate. Costs include only the entered inverter and balance-of-system amounts; financing, maintenance, replacements, degradation, export/self-use differences and site constraints are excluded.

What this comparison models

The calculator compares two editable inverter-side cost allocations and values a simplified difference in annual output for 25 years. These costs are not complete installed PV-system prices.

The model calls energy value revenue, but mathematically it is:

system_kW × yield_kWh_per_kWp × tariff_per_kWh

That only represents avoided retail cost if every incremental kWh is actually worth the entered tariff. Exported energy, curtailment and time-varying value can make the correct rate lower or higher.

Inputs and defaults

Input	U.S. default	Interpretation
System size	6 kW	DC array size used in the value calculation
Panel count	15	Multiplier for per-micro cost
Baseline annual yield	1,450 kWh/kWp	Yield before this model’s shading deduction
Tariff	$0.171/kWh	Value assigned to every modeled kWh
Shading	5%	Input to the model’s two loss multipliers
Cost per microinverter	$200	Hardware or allocated cost entered by user
Micro balance of system	$100/kW	Added to panel-count micro cost
Central string inverter	$1,800	Added to string balance-of-system cost
String balance of system	$600/kW	Added to central-inverter cost

Do not enter a PVWatts result that already includes the same shade loss and then also enter shading here, or shade can be counted twice. PVWatts V8 exposes system losses and hourly output inputs.

Exact formulas

string_yield = baseline_yield × (1 − shading_percent × 1.3 / 100) micro_yield = baseline_yield × (1 − shading_percent × 1.0 / 100)

string_cost = system_kW × string_BoS_per_kW + central_inverter_cost micro_cost = panel_count × cost_per_micro + system_kW × micro_BoS_per_kW

string_value = system_kW × string_yield × tariff micro_value = system_kW × micro_yield × tariff micro_premium = micro_cost − string_cost annual_value_delta = micro_value − string_value net_25_year = annual_value_delta × 25 − micro_premium

The component recommends micro when net 25-year value is greater than zero; otherwise it recommends string. If the micro premium is zero or negative, displayed payback is zero. If premium is positive and annual delta is positive, simple payback is premium divided by annual delta.

The 1.3 string multiplier is an internal scenario assumption, not an NREL standard and not a physical shade model. NREL’s 2012 experiment reported approximately 4%, 8% and 12% relative improvement for its tested microinverter system under three defined shade protocols. The report also emphasizes that benefit depends on configuration and shade conditions. See NREL, Partial Shade Evaluation of Distributed Power Electronics for Photovoltaic Systems.

Worked verification using the displayed defaults

For 6 kW, 15 panels, 1,450 kWh/kWp, $0.171/kWh, 5% shade, $200/micro, $100/kW micro BoS, $1,800 central inverter and $600/kW string BoS:

String yield = 1,450 × (1 − 0.05 × 1.3) = 1,355.75 kWh/kWp, displayed 1,356
Micro yield = 1,450 × (1 − 0.05) = 1,377.50 kWh/kWp, displayed 1,378
String cost = 6 × $600 + $1,800 = $5,400
Micro cost = 15 × $200 + 6 × $100 = $3,600
Annual string value = 6 × 1,355.75 × $0.171 = $1,391
Annual micro value = 6 × 1,377.50 × $0.171 = $1,413
Rounded annual delta = $22
Micro premium = −$1,800
25-year net value = $2,358
Result = micro, with 0 years displayed payback because the modeled premium is negative

This default result is cost-driven. It should not be summarized as a general 5% shading break-even rule.

Sensitivity check

Change only cost per microinverter from $200 to $400:

Micro cost becomes 15 × $400 + 6 × $100 = $6,600
Micro premium becomes $1,200
The unrounded annual value delta remains about $22.32
Simple payback becomes about 53.8 years
25-year net becomes about −$642
Result changes to string

This demonstrates why current, comparable cost inputs matter more than a brand label.

Limitations that can reverse the recommendation

Hourly and panel-level shade geometry is not modeled.
An optimized string system is not a separate architecture choice.
Panel orientation, mismatch, snow and soiling are collapsed into one shade input.
Baseline yield is fixed; module and inverter degradation are absent.
Electricity value is constant and identical for every kWh.
Replacement, service labor, roof access and downtime are excluded.
Cash flows are undiscounted; inflation, financing and taxes are absent.
Equipment compatibility, clipping and DC/AC ratio are not checked.
Product warranty and installer-service risk are not priced.

Run site-specific production in the solar panel output calculator, screen the chosen ratio in the inverter size calculator, and keep full-system quote comparison separate in the solar cost calculator.

Decision checklist

Before selecting an architecture, obtain:

A shade study or hourly production model for each roof plane
Comparable bills of materials and labor scopes
Exact module-inverter compatibility and design documentation
Current manufacturer warranty terms and installer labor coverage
Replacement and roof-access assumptions
Utility valuation for self-consumed and exported energy
Review against the local adopted rules and interconnection requirements

Sources

NREL PVWatts Version 8 API documentation — system-loss and hourly-output inputs used to avoid double-counting shade
NREL: Partial Shade Evaluation of Distributed Power Electronics for Photovoltaic Systems — measured results and limits of the cited partial-shade experiment

Frequently asked questions

Are microinverters always better on a shaded roof?

No. Architecture, string layout, bypass diodes, shade pattern, module electronics and inverter behavior all matter. An NREL side-by-side study found a benefit for the tested microinverter system under its light, moderate and heavy shade protocols, but those results do not create a universal threshold or validate this calculator's 1.3 multiplier.

Why do the displayed defaults recommend microinverters?

Because the default modeled micro cost is $3,600 and the default modeled string cost is $5,400. The micro scenario therefore starts $1,800 cheaper before energy differences. A displayed zero-year payback means no positive micro premium under those inputs; it is not evidence that microinverters pay back instantly in the market.

Does a 25-year warranty prove 25 years of service life?

No. Warranty term, covered failures, labor, shipping, transfer, exclusions and remedy are different from expected life. Enter costs appropriate to the exact products and review their current warranty documents.

Does the calculator include inverter replacement?

No. It assumes fixed annual yield and tariff for 25 years and includes no degradation, replacement, maintenance, downtime, discount rate, tax, export-price difference or warranty recovery.

Does the result establish electrical-code compliance?

No. It does not evaluate product listings, approved equipment pairings, rapid shutdown, grounding, string voltage or current, service capacity, adopted code edition, utility rules or the authority having jurisdiction.

Microinverter vs String Inverter Calculator