How Many Rainy Days Can a 30W Panel + 20Ah Battery Survive? Off-Grid Capacity Formulas
Keywords: solar system rainy-day autonomy, 30W 20AH capacity, off-grid power capacity design ｜ Target product: SQT-30W/20AH ｜ Suggested placement: Blog (EN site)
Search intent: How many consecutive overcast/rainy days can the system ride out? Design capacity with the generation-consumption-storage triangle, with a worked 30W/20AH example.
Quick Answer
SQT-30W/20AH (30W panel + 20Ah/12V battery) in a 4-sun-hour region supports about 2-2.5 consecutive overcast/rainy days at an 8W load; drop the load to 5W and it stretches to 3-4 days. Design principle: work backward from “worst-month” yield + target rainy days.
The Capacity Design Triangle
Premise: daily yield ≥ daily consumption — storage covers “night + rainy days”.
- Daily yield = panel wattage × effective sun hours × 0.8 (system efficiency)
- 30W × 4h × 0.8 = 96Wh
- Daily consumption = average load draw × 24h
- 8W × 24h = 192Wh ❌ Over? → note that low-power cameras average far below nameplate; a 4G bullet actually averages 4-6W
- At 6W: 6 × 24 = 144Wh
- Supported rainy days = usable battery capacity ÷ daily consumption
- 20Ah × 12V = 240Wh, usable 80% ≈ 192Wh
- 192 ÷ 144 ≈ 1.3 days (battery only) — but overcast days usually aren’t fully dark; low-light MPPT keeps charging, so realistically 2-2.5 days
Autonomy by Load (SQT-30W/20AH)
| Average load | Daily consumption | Theoretical autonomy | Real-world reference |
|---|---|---|---|
| 4W | 96Wh | 2 days | 2.5-3 days |
| 6W | 144Wh | 1.3 days | 2-2.5 days |
| 8W | 192Wh | 1 day | 1.5-2 days |
| 10W | 240Wh | 0.8 days | 1-1.5 days |
Capacity Short? Pick One of Three
- Bigger battery: 20Ah → 30Ah = +50% autonomy (SQT battery capacity is customizable)
- Bigger panel: 30W → 40W = +33% yield, faster recovery after overcast spells
- Lower the load: motion-triggered recording instead of 24/7 continuous, lower bitrate, fewer cruises — the highest ROI move of all
Hidden Factors That Affect Autonomy
- System self-consumption: low-quality controllers burn 1-2W on standby, eating half your budget; SQT <5mA — negligible
- MPPT vs PWM: MPPT charges 15-30% more in low light/overcast — longer autonomy under the same conditions
- Battery health: LiFePO4 lasts 2000+ cycles (5-8 years without degradation); lead-acid degrades noticeably in 2 years, so real autonomy shrinks
FAQ
Q: What about the southern rainy season (a week of drizzle)?
A: Effective sun during the monsoon may drop below 2h. Solutions: ① choose a larger capacity version (30Ah+); ② cut camera average draw; ③ if still short, consider dual panels in parallel or hybrid supply (solar + grid backup) — contact the factory for customization.
Q: How can I remotely check remaining power?
A: SQT systems offer optional charge monitoring / 4G remote modules: real-time battery voltage, charge/discharge status, history curves, and low-battery alerts — no site visits needed.
Q: How often must the battery be replaced?
A: LiFePO4 ≥2,000 cycles ≈ 5-8 years at one charge/discharge per day; SQT battery compartments are modular — replacement doesn’t require disassembling the unit.
All-in-One Systems vs. DIY Assembly: Why Choose the SQTlot Factory Solution?
| Comparison | DIY assembly (loose parts) | SQTlot all-in-one system |
|---|---|---|
| Parameter matching | Panel/battery/controller bought separately, poor matching | Jointly tuned to the load, maximum charge/discharge efficiency |
| Installation | On-site wiring and tuning, hard to troubleshoot | Factory pre-wired — mount and plug in |
| Protection | Weatherproofing depends on DIY skill, leak-prone | IP65 integrated design + full aging test |
| After-sales | Parts warrantied separately, finger-pointing | Whole-unit warranty + one-on-one factory support |
| Long-term cost | Higher failure rate, huge trip costs for unattended sites | Maintenance-free design, 10-year design life |
Core logic: Parking-lot retrofit projects are mostly existing points: trenching, cabling and approval processes create huge hidden costs. SQTlot all-in-one systems need no cabling or approvals — plug and play, with no dedicated electrician required.
Parking scenario: a single power outage on LPR/barrier cameras can lose entry/exit records and trigger billing disputes; the 30W panel + 20Ah lithium battery is designed exactly for these “charge by day, draw hard at night” loads.
B2B Procurement FAQ (MOQ / Lead Time / Certifications / Warranty)
Q: What is the MOQ?
A: Standard models start from 1 unit and sample orders are welcome; volume pricing is tiered by quantity.
Q: What is the lead time?
A: In-stock standard models ship in 3-5 days; customized configurations (special battery capacity/enclosure/connectors) take about 2-3 weeks after design confirmation.
Q: Which certifications do you hold?
A: CE / RoHS / FCC test reports and Declarations of Conformity are available; TÜV / UL certification can be evaluated in advance (lead time and cost apply).
Q: What is the warranty?
A: 2-year whole-unit warranty, 2-year lithium battery warranty and 5-year solar panel warranty; terms are written into the contract.
Q: What customization is supported?
A: Power, battery capacity, output voltage/connectors, enclosure color and printing can all be customized; load-matched panel-battery-controller design is offered free of charge.
Q: Trade terms and payment?
A: EXW / FOB (Shanghai) / CIF / DDP supported; standard terms are 30% deposit + 70% before shipment, with monthly settlement negotiable for long-term partners.
About Geningtech
Geningtech (SQTlot brand) offers capacity customization: submit “load draw + site region + target rainy days” and we’ll send a free sizing plan.
💡 Free sizing calculation: Send your load power, site sunlight hours and required rainy-day autonomy to our engineers (sales@sqtlot.com) — free one-on-one sizing, with a proposal & quotation returned within 10 minutes.
Related Reading (Internal Links)
Article provided by Geningtech, an IoT solar power system manufacturer. Product page: SQT-30W/20AH Solar Power System
