The inverter is the brain of the solar system, converting DC from panels to AC for factory use. For C&I scale (100kW-5MW): string inverters suit 100-500kW (multiple MPPT channels, easy maintenance), central inverters are more cost-effective above 1MW with uniform roofs, and micro inverters are rarely used in C&I. Key decision factors: DC/AC ratio (1.1-1.3), efficiency (>98%), MPPT channels, and heat derating for Thailand's climate (40C+). CapSolar specifies Huawei/Sungrow for every factory project with full ERC grid code compliance.
C&I Inverter Fundamentals (100kW-5MW)
Inverters convert DC power from solar panels into 3-phase 400V AC for factory use. C&I systems (100kW-5MW) differ from residential (5-30kW) in key ways: higher voltage, 3-phase output, transformer coupling required, and ERC grid code compliance mandatory.
Inverters represent 8-12% of total system BOM cost.
Thai factories must use grid-tied systems per ERC regulations — not hybrid or off-grid.
Inverter lifespan: 10-15 years (vs 25-30yr panels). Budget for one replacement cycle within a 25-year project.
| Specification | Residential (5-30kW) | C&I Factory (100kW-5MW) |
|---|---|---|
| System Voltage | 220-380V, 1-phase | 400V, 3-phase |
| Inverter Capacity | 3-15 kW | 30-350 kW (string) / 500kW-5MW (central) |
| Inverter Cost (THB/Wp) | 2.5-5.0 | 0.6-2.5 |
| Grid Code | Basic standard | ERC VSPP + anti-islanding + PF control |
String vs Central vs Micro Inverter — Which Is Best?
Choosing the inverter type is the first and most critical decision in factory solar system design. Each type has distinct advantages and trade-offs.
| Dimension | String Inverter | Central Inverter | Micro Inverter |
|---|---|---|---|
| Capacity per unit | 30-350 kW | 500 kW - 5 MW | 200-500 W (per panel) |
| Best for | 100-500 kW factory | >1MW factory / Solar farm | Residential (rarely C&I) |
| MPPT | Multiple independent (2-12) | 1-2 shared | 1 per panel |
| Partial shading | Good (independent MPPT) | Poor (single MPPT) | Excellent |
| Maintenance | Replace one unit, rest runs | Entire system down | Panel-level swap |
| Cost (THB/Wp) | 1.0-2.5 | 0.6-1.5 | 3.0-5.0 |
| Thailand factory recommendation | Primary choice 100-500kW | Consider >1MW if uniform roof | Not recommended for C&I |
For factories with multiple roof types, a hybrid approach (String + Central on the same site) is possible. CapSolar designs hybrid topologies based on actual roof conditions.
Thai factory decision tree: complex/multi-direction roof → String | flat uniform roof >1MW → Central | expansion planned → String (easy to add) | budget-constrained >1MW → Central (lower cost/Wp).
Key Specifications to Evaluate When Choosing an Inverter
1. Efficiency
Peak vs weighted efficiency (European/CEC) — Tier-1 brands achieve ≥98%. Weighted efficiency matters more than peak because it reflects real-world operation across the day.
2. MPPT Channels
More MPPT (Maximum Power Point Tracking) channels = better handling of mixed roof orientations and shadows. Factories with complex roofs should choose inverters with ≥6 MPPT channels.
3. DC/AC Ratio
DC/AC ratio = DC panel capacity / AC inverter capacity. Recommended for Thailand: 1.1-1.3. Example: ratio 1.2 means 1MW DC panels with 833kW AC inverter — boosting morning/evening output 5-10% with minimal noon clipping. Below 1.1 wastes potential; above 1.3 causes excessive clipping.
4. THD (Total Harmonic Distortion)
ERC requires THD <5% (harmonics per IEC 61000-3-12). Some cheap inverter models fail this requirement.
5. Input Voltage Range
Must match string design: verify Voc at Thailand's lowest temperature (~15C early morning) does not exceed max input voltage.
6. IP Rating
Minimum IP65 for outdoor installation in Thailand. IP66 preferred for coastal areas (Samut Prakan, Rayong, Chonburi) due to salt and industrial dust.
7. Communication
RS485, WiFi, 4G, Modbus — for monitoring system integration. Verify compatibility with your desired monitoring platform.
8. Reactive Power Capability
Q(P), PF(P), Q@Night modes help maintain PF >0.85 and avoid kVar penalties of 56.07 THB/kVar. Critical for motor-heavy factories.
4-Brand Inverter Comparison for Thai Factories
Four leading brands in Thailand's C&I solar market: Huawei, Sungrow, SMA, GoodWe — each with distinct strengths and trade-offs.
| Specification | Huawei SUN2000 | Sungrow SG-series | SMA Sunny Tripower | GoodWe |
|---|---|---|---|---|
| Capacity | 100-330 kW | 110-350 kW | 60-110 kW | 50-250 kW |
| Peak Efficiency | 98.8% | 98.9% | 98.8% | 98.6% |
| MPPT Channels | 10-20 | 9-12 | 6 | 4-10 |
| IP Rating | IP66 | IP66 | IP65 | IP65 |
| Reactive Power | Q@Night, Q(P), PF(P) | Q@Night, Q(P) | Q(P), PF(P) | Q(P) |
| Smart PID Recovery | Yes (built-in) | Yes (built-in) | No (external) | Optional |
| Monitoring Platform | FusionSolar | iSolarCloud | Sunny Portal | SEMS |
| Thailand Presence | Bangkok office + local stock | Bangkok office + local stock | Distributor only | Distributor only |
| Warranty | 10 yr (ext. 25) | 10 yr (ext. 20) | 10 yr (ext. 20) | 10 yr (ext. 25) |
| Approx. Price (THB/Wp) | 1.2-2.0 | 1.0-1.8 | 1.5-2.5 | 0.8-1.5 |
CapSolar default spec: Huawei SUN2000 or Sungrow SG for EPC projects (local stock + support center). PPA projects use whichever brand best fits the financial model.
Prices are indicative and vary with order volume, exchange rates, and specific model.
Solar Panel Brand ComparisonThailand Climate: Heat, Humidity, and Inverter Performance
Heat Derating
Tier-1 inverters run at full power up to 45-50C ambient. Above that, they derate 2-5% per degree. In April-May, Thai factory rooftops can reach 50-55C, reducing a 250kW inverter to 210-230kW output.
Temperature vs Output % (Typical 250kW String Inverter)
| Ambient Temp | % Output | Actual kW |
|---|---|---|
| ≤45C | 100% | 250 kW |
| 48C | 90-94% | 225-235 kW |
| 50C | 85-90% | 213-225 kW |
| 55C | 75-80% | 188-200 kW |
| >60C | Shutdown protection |
Heat Mitigation Solutions
1. Install under canopy or eaves, not in direct sunlight. 2. Maintain ≥30cm clearance on all sides. 3. Add forced ventilation fans. 4. Avoid west-facing wall installation (afternoon heat).
Humidity + Dust + Salt
IP65/IP66 for water + dust protection. Coastal areas (Samut Prakan, Rayong, Chonburi) require IP66 + conformal coating on PCBs. Monsoon season (Jun-Oct) requires regular seal inspection.
Lightning / Surge Protection
Thailand has one of the world's highest lightning densities. SPD (Surge Protection Device) Type 1+2 on DC side and Type 2 on AC side are mandatory.
Transformer Compatibility — Check Before Solar Installation
Thai factory transformer standard: 22kV/400V (PEA) or 24kV/400V (MEA), 3-phase. Inverter output 400V ±10% — verify transformer tap settings.
Check: can your existing transformer handle load + solar? If solar exceeds 50% of transformer capacity or the transformer is very old, get an engineering assessment.
Watch for reverse power flow on weekends/low-load periods — set protection relays accordingly.
Example: 1MW solar + 1.5MW factory load + 2MVA transformer — daytime grid import drops to 500kW, well within 2MVA capacity.
Verify impedance matching: avoid resonance between inverter output filter and transformer impedance.
Learn about demand charges and TOU/TOD ratesERC Grid Code + Anti-Islanding Requirements
Factory solar systems (<10MW) are classified as VSPP and must meet all ERC requirements. Tier-1 inverters pass all criteria, but protection relay settings must be configured correctly.
Anti-islanding: disconnect within 2 seconds (IEEE 1547 / IEC 62116) using both passive + active detection methods.
Voltage regulation: ±5% of nominal voltage.
Frequency: 50Hz ±0.5Hz.
THD: <5% (harmonics per IEC 61000-3-12).
Power Factor: 0.85 leading to 0.85 lagging capability required.
LVRT (Low Voltage Ride-Through): required for systems >1MW.
Required certificates: IEC 62109 (safety) + IEC 61727 (utility interconnection). Prepare type test report, single-line diagram, and protection settings for PEA/MEA application.
Inverter Sizing Methodology — 1MW Worked Example
8 steps to design a 1MW factory solar system in Thailand — from load analysis to monitoring setup.
Step 1: Determine Load Profile
Analyze factory peak demand, daytime base load, and weekend load to determine optimal system size.
Step 2: Size PV Array
1MW DC at Thailand average 1,500 kWh/kWp per year (PSH ~4.5 hours/day).
Step 3: Choose DC/AC Ratio
Recommended 1.2 for Thailand: 1MW DC / 833kW AC inverter = 1.2 DC/AC ratio.
Step 4: Select Inverter Topology
Option A: 4x Huawei SUN2000-215KTL (860kW AC total) or Option B: 1x Sungrow SG1000MX (1MW central).
Step 5: Design String Configuration
Calculate modules per string (Voc check at ~15C min temp) x strings per MPPT input.
Step 6: Verify Transformer Capacity
1MW solar on existing 2MVA transformer — check loading, voltage rise, protection coordination.
Step 7: Protection Coordination
Configure relay settings: anti-islanding, overcurrent, earth fault, SPD specification.
Step 8: Monitoring Setup
Install inverter-level monitoring + string-level MPPT tracking + weather station.
Cost Comparison: String vs Central for 1MW
String
String (4x 250kW): inverter ~1.0-1.5M THB + slightly higher BOS cost.
Central
Central (1x 1MW): inverter ~0.6-1.0M THB + lower BOS cost, but requires dedicated room.
Monitoring & Fault Detection for Factory Inverters
Inverter-level monitoring: real-time power, daily yield, efficiency tracking, alarm notifications. String-level MPPT tracking: detect underperforming strings (soiling, PID, hotspot, cable faults).
Thailand PR target: 75-85%. Inverter contributions to PR loss: heat derating, efficiency loss, downtime.
Common faults: insulation fault, grid fault, overtemperature, MPPT failure — good monitoring detects these before damage occurs.
Cloud platforms: FusionSolar (Huawei), iSolarCloud (Sungrow), Sunny Portal (SMA), SEMS (GoodWe) + local SCADA for large factories.
Predictive maintenance: replace fans every 5-7 years, check capacitor aging, update firmware on schedule.
Solar Monitoring & O&M Complete GuideRelated Articles
CapSolar Designs the Right Inverter System for Your Factory
We specify Huawei and Sungrow as standard with full ERC grid code compliance — every project is custom-designed for your actual roof and load profile.