A 5 kW off-grid kit label packs a lot of data into a few lines. Read it right, and you can predict daily energy, check safety margins, and avoid mismatched parts. This case study decodes a real-world style label, line by line, and shows quick math to verify each claim.
What “5 kW off-grid kit” usually covers
“5 kW” on the front label often refers to the inverter’s AC continuous output, not only the PV array size. Kits may pair a 5 kW inverter with a PV array from 4.5 to 6.5 kW (STC). Read the fine print to see if 5 kW is DC array power, AC output rating, or both.
- AC side: 5 kW continuous, surge 2× for motor starts is common.
- PV side: Array power at STC can exceed inverter AC watts. That is normal due to derating and real irradiance patterns.
- Battery side: 48 V LiFePO4 is typical for this class. Usable kWh depends on capacity and depth of discharge.
Modern inverters are software-configurable. That flexibility mirrors utility-scale practice, where software sets many plant behaviors. As noted by the IEA, PV and wind plants are controlled through software, enabling tailored responses for stability (System Integration of Renewables).
Sample label — and how to read each line
Below is a typical off-grid kit label snapshot and what each line tells you. Values are representative, not brand-specific.
| Label line | Typical entry | What to look for |
|---|---|---|
| PV modules | 550 W mono x 10 (STC) | Total 5.5 kW at STC. STC = 1000 W/m², 25°C cell temp. Real output will be lower at heat and system losses. |
| String layout | 2 strings of 5 in series (2Sg x 5S) | Series count sets string voltage. Parallel strings add current. Verify with MPPT window and current limit. |
| Module Vmp / Imp | Vmp 41 V, Imp 13 A | Per module at STC. String Vmp ≈ 5 × 41 = 205 V. Two strings in parallel → array Imp ≈ 26 A. |
| Module Voc / Isc | Voc 49 V, Isc 13.8 A | Cold matters. String Voc_cold ≈ 5 × 49 × . At −10°C → ≈ 270 V. Check against max PV input voltage. |
| PV temp coeffs | Pmax −0.35%/°C; Voc −0.30%/°C | Power falls as cells heat. Expect summer derate. Use for NOCT estimates. |
| MPPT voltage window | 120–450 Vdc (max 500 Vdc) | String Vmp must sit inside the MPPT window in your climate. Cold Voc must stay below max PV input. |
| PV input current | 2 × 13 A per MPPT | Per tracker current cap. Do not exceed with parallel strings on a single tracker. |
| Inverter rating | 5 kW AC, 230 Vac, 50 Hz | Check continuous power, not only surge. Match local voltage and frequency. |
| Surge | 10 kVA for 5 s | Short bursts start pumps, fridges, tools. Confirm motor loads can start. |
| Efficiency | PV→AC 96%; Inverter 94% | Higher efficiency means less heat and more usable energy. |
| Battery | LiFePO4 48 V 200 Ah (9.6 kWh) | Usable energy ≈ capacity × DoD. At 80% DoD → ≈ 7.7 kWh. |
| BMS limits | Charge/Discharge 100 A | At 48 V, 100 A ≈ 4.8 kW. Pair BMS current with inverter power. |
| Cycle life | ≥ 6000 cycles @80% DoD | Estimate service years from daily cycles. LiFePO4 supports daily cycling well. |
| Charge rates | Max charge 100 A | Roughly 0.5 C for 200 Ah. Faster charge shortens life and strains wiring. |
| Combiner & fusing | 2-string combiner, 15 A fuses, SPD Type II | Protect against faults and surges. Match fuses to Isc × 1.25 rule of thumb. |
| Disconnects | PV DC isolator 600 V 32 A; Battery breaker 125 A | Safe service and emergency shutoff. Ratings must exceed operating limits. |
| Cables | PV 6 mm²; Battery 25–35 mm² | Size for current and voltage drop. Short runs waste less. |
| Certifications | IEC 61215/61730, UN38.3, IEC 62109, UL/EN equivalents | Confirms safety and reliability. Local codes may require specific marks. |
Reality-check the label with quick math
Check PV voltage against MPPT
String Vmp ≈ 5 × 41 V = 205 V (inside 120–450 V window). Cold Voc at −10°C: Voc_cold ≈ 5 × 49 × = 245 × 1.105 ≈ 270 V (under 500 V max). Pass.
Estimate daily energy
Array DC power at STC: 5.5 kW. Real output = PV kW × peak sun hours × system derate. A practical derate for off‑grid is 0.72–0.82 (module heat, wiring, MPPT, inverter, battery round trip).
| Location type | Peak sun hours | Expected AC kWh/day (5.5 kW, derate 0.78) |
|---|---|---|
| Low irradiance, winter | 2.5 | ≈ 5.5 × 2.5 × 0.78 ≈ 10.7 kWh |
| Temperate, average | 4.0 | ≈ 17.2 kWh |
| Sunny season | 5.5 | ≈ 23.6 kWh |
These ranges align with field reality. The U.S. DOE notes that real PV output depends on irradiance, temperature, and system losses (Energy.gov Solar Energy).
Battery sizing and autonomy
48 V × 200 Ah = 9.6 kWh nameplate. Usable at 80% DoD ≈ 7.7 kWh. With 94–96% inverter efficiency and BMS overhead, plan for ≈ 7.2 kWh to loads. For 24-hour autonomy on 7 kWh of loads, this bank fits. For two cloudy days, either add capacity or run a generator input.
Match BMS current to inverter power
5 kW AC at 48 V DC needs roughly 110–120 A DC at full tilt after losses. A single 100 A battery cannot feed 5 kW continuously. Use a higher-current battery, parallel two 100 A modules, or limit inverter power. This prevents nuisance trips.
From label to loads: a quick sizing check
| Typical load | Power | Hours/day | Daily kWh |
|---|---|---|---|
| Fridge (A++ class) | 150 W | 8 h duty | 1.2 |
| LED lighting | 80 W | 6 h | 0.48 |
| Router + laptop | 60 W | 8 h | 0.48 |
| TV | 100 W | 3 h | 0.3 |
| Well pump (start 1.5 kW) | 600 W | 1 h | 0.6 |
| Misc. standby + losses | — | — | 0.6 |
| Total | — | — | 3.66 kWh |
Even in a modest-sun day (≈ 10–12 kWh), the 5 kW off-grid kit covers this load and charges the battery. Surge at 10 kVA starts the pump. If you plan power tools or larger HVAC, increase surge margin and battery current.
Safety, durability, and context from respected bodies
- The IEA highlights that inverter-based plants are software-driven, which allows tuned responses to events (System Integration of Renewables). That same flexibility helps off-grid inverters manage a stable microgrid frequency and voltage.
- Grid reports also stress temperature effects on conductors and capacity (Getting Wind and Solar onto the Grid). Heat reduces ampacity. Use cable sizes with headroom, especially near batteries and in roof runs.
- Distribution engineers rely on screening methods to prevent overloads and poor voltage profiles with distributed PV (China Power System Transformation). Apply the same spirit off grid: check power flow, voltage drop, and breaker ratings in your design.
- Advanced grid codes ask inverters to support system services (Next-Generation Wind and Solar Power). Off-grid gear can provide similar support locally: fast frequency response, soft starts, and programmable charge profiles.
- Global agencies maintain data and primers that help align expectations for output and costs (IRENA, EIA, Energy.gov).
Common label traps and how to avoid them
- STC vs NOCT: STC power overstates summer output. Expect 10–25% lower in heat. Ask for NOCT or PTC numbers.
- “5 kW” ambiguity: Confirm if it is inverter AC, PV DC, or both. A 5 kW inverter with 6 kW PV is fine if the MPPT allows it.
- BMS current bottleneck: A 5 kW inverter needs >100 A at 48 V. Ensure total battery discharge current covers it.
- MPPT window mismatch: Cold Voc must stay below max PV input. Hot Vmp must stay inside the lower MPPT limit.
- Undersized wiring: Check fuses, SPD, and wire gauges against Isc and continuous currents with margin.
Practical configuration tips
- Strings: 5S × 2P fits a 120–450 V MPPT with margin in most climates. In very cold sites, 4S may be safer.
- Battery: For power tools and pumps, pair at least 200–300 A discharge capability at 48 V with a 5 kW inverter.
- PV oversizing: 10–30% PV oversize improves cloudy-day harvest. Stay within max PV voltage and input current limits.
- Protection: Use a combiner with string fuses and Type II SPD. Add DC and AC disconnects for service safety.
These steps align with the engineering mindset advised in grid-integration handbooks: quantify power flow, voltage regulation, and component ratings upfront (China Power System Transformation).
What this kit delivers in plain numbers
- Daily energy: ≈ 11–24 kWh across typical seasons for a 5.5 kW array at a 0.78 derate.
- Power: 5 kW continuous, 10 kVA surge, enough to run fridge, lights, electronics, and a small pump.
- Storage: ≈ 7.2 kWh usable per full cycle from a 48 V 200 Ah LiFePO4 pack, with high round-trip efficiency.
- Scalability: Add a second battery string to double usable kWh and discharge current. Add more PV within MPPT limits.
We focus on LiFePO4 batteries, hybrid inverters, and complete off-grid solutions. The goal is reliable, scalable energy independence for homes, farms, and cabins.
Notes and disclaimer
Numbers here are illustrative. Always check the specific datasheets and local codes. Electrical work has risk. Use qualified installers and follow national standards. Non-legal advice.
FAQ
How do I know if the “5 kW” matches my loads?
Add up your simultaneous loads. Keep a 20–30% headroom for comfort. If you need 3.5–4 kW at once, a 5 kW inverter with 10 kVA surge is a good fit.
Is it safe to oversize PV beyond 5 kW on a 5 kW inverter?
Yes, within the MPPT current and voltage limits. Many systems run 10–30% PV oversizing to boost shoulder-hour energy.
How do I verify cold-weather Voc?
Use: Voc_cold ≈ Voc_STC × N_series × . Compare to the max PV input voltage on the inverter label.
How much battery do I need for two days?
Multiply your daily kWh by two and divide by usable DoD. Example: 6 kWh/day ÷ 0.8 × 2 ≈ 15 kWh nameplate at 48 V.
Why does my kit produce less than the STC sum?
Heat, dust, wiring, MPPT tracking, and conversion losses cut output. The DOE highlights these factors in PV performance basics.
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