Solar Battery Sizing Calculator
Planning to installsolar panels with a battery Start with the energy you want to use at night or during an outage. Panel size alone cannot tell you how many battery kilowatt-hours you need. Your household load, backup duration and available solar energy all matter.
The solar battery sizing calculatorbelow estimates installed battery capacity, module count, a starting solar array size and power ratings to check before buying. You can begin with your monthly bill, then improve the estimate with meter readings and actual equipment specifications.
Table of Contents
What do you need to size a solar battery?
- Daytime electricity use (kWh/day): The energy the solar array should supply to your home while the sun is up. Entering zero excludes that demand from the solar array estimate.
- Energy to shift into the night (kWh/night): Enter only the energy you want the battery to supply, not every unit on your electricity bill. If you only have a monthly bill, use the built-in day/night split as a first approximation.
- Essential outage loads: Enter each appliance's running watts, quantity and duty factor, plus your target backup hours. A fridge, for example, does not draw full running power all the time. Check motor and air conditioner startup demand as well.
- Battery specifications: Capacity per module, allowable depth of discharge (DoD), design state of health (SoH), charge and discharge efficiency, and power per module. Use the candidate product's datasheet and warranty.
- Solar information: Existing panels in kWp and expected yield in kWh/kWp/day. The calculator's default is illustrative. Review location-specific monthly estimates usin PVWatts or output from your existing installation.
โซลาร์เซลล์พร้อมแบตเตอรี่ ควรติดตั้งขนาดเท่าไร?
เริ่มจากพฤติกรรมใช้ไฟและโหลดที่ต้องสำรอง แล้วตรวจว่าขนาดแผงผลิตพอสำหรับใช้งานและชาร์จแบตกลับหรือไม่
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โหมดทั้งสองอย่างจะกันความจุสำรองไฟไว้แม้ผ่านคืนที่ใช้ไฟตามปกติแล้ว จึงบวกพลังงานสองส่วนเข้าด้วยกัน
กรอกพลังงานที่ต้องใช้
ใช้ข้อมูลมิเตอร์หรือสเปกเครื่องใช้ไฟฟ้าจริงจะช่วยให้ผลใกล้เคียงขึ้น
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เครื่องใช้ไฟฟ้าที่ต้องทำงานตอนไฟดับ
กดตัวอย่างเพื่อเริ่ม แล้วแก้ W, จำนวน และสัดส่วนเวลาที่เครื่องทำงานตามเครื่องจริง; อุปกรณ์สำคัญต้องต่อเข้าวงจรสำรองด้วย
ระบุสเปกแบตเตอรี่และแผง
ค่าที่มีให้เป็นสมมติฐานตั้งต้น กรุณาแทนด้วยข้อมูลจากรุ่นที่สนใจ
ปรับสมมติฐานด้านประสิทธิภาพและการติดตั้ง
ขนาดระบบจากข้อมูลที่คุณกรอก
รายละเอียดสำหรับคุยกับผู้ติดตั้ง
ผลนี้ใช้สมมติฐานพลังงานเฉลี่ยและคืนที่ไม่มีแดด ไม่รับประกันชั่วโมงสำรองจริงหรือการคืนทุน ก่อนติดตั้งต้องตรวจวงจร EPS/backup, กำลังสตาร์ต, BMS, การระบายอากาศ, พื้นที่แผง, เงา, การเชื่อมต่อกับการไฟฟ้า และ datasheet ของรุ่นที่จะใช้ ตรวจผลผลิตแผงด้วย PVWatts
How to read your solar battery calculation
1. Installed capacity and usable AC energy
Installed battery capacity is the combined nameplate kWh after rounding up to whole modules. Usable AC energy accounts for your DoD, design SoH and discharge efficiency. It is therefore lower than nameplate capacity and can be compared with your stated night energy and outage reserve.
For a quick check, minimum battery kWh = required AC kWh ÷ (DoD × SoH × discharge efficiency), with percentages entered as decimal fractions. Then round up to available module sizes. The calculator does not prescribe a battery voltage or series/parallel wiring: use only configurations approved for the actual equipment.
2. Minimum panels for your stated energy goal
The array estimate includes daytime demand, energy to recharge the battery for nighttime use and extra generation to restore the outage reserve over your chosen sunny days. Charging efficiency applies to recharging; discharge efficiency is accounted for on the energy delivery path. Existing panels are compared with this target. The result does not establish roof fit, panel count or inverter size.
3. Power demand and checks before installation
Read simultaneous load in kW separately from energy in kWh. Compare it with the continuous power ratings of the inverter, battery and BMS; check startup surge for motors and compressors. Review any warnings about insufficient existing panels, three-phase circuits or missing equipment ratings.
Worked example: solar panels and a home battery
Assume a home uses 8 kWh/day while the sun is up and needs 6 kWh/night from its battery. Its critical backup loads average 0.5 kW for 8 hours , or another 4 kWh. Select “Both” to hold 10 kWh of total AC energy for these two purposes.
With 5 kWh modules, 90% DoD, 90% design SoH, 92% discharge efficiency, 95% charge efficiency, a solar yield of 3.5 kWh/kWp/day and a two-sunny-day backup recovery target, the calculator returnsthree modules (15 kWh installed), about 11.18 kWh usable AC energy and approximately 5.0 kWp of panels when rounded to one decimal place. These are example inputs, not a recommendation for every home.
What else should you check before installing solar with a battery?
- Backup wiring: Confirm the inverter and backup/EPS circuit can run essential loads when the grid goes down. Ordinary grid-connected solar does not automatically provide outage backup.
- Power and phases: Verify simultaneous demand, startup surge, battery/BMS limits and the placement of backup loads in a three-phase property.
- Roof and generation: Assess shade, orientation, tilt, available area, monthly production and equipment compatibility at the site.
- Installed price and value: Request a complete quotation covering the battery, inverter, protection, backup circuits, installation and warranty. This tool does not estimate cost, bill savings or payback. For a broader panel and bill estimate, use our Solar Panel Calculator .
Frequently asked questions
How much battery storage do I need for a 5 kW solar system?
You cannot determine battery size from the panel rating alone. Size storage from the kWh needed at night, essential outage loads and backup hours, then check whether the panels can recharge it. Enter those loads in the calculator.
How long can a 5 kWh solar battery run my home?
At 90% DoD, 90% design SoH and 92% discharge efficiency, a nominal 5 kWh module provides about 3.73 kWh of AC energy. At a constant average load of 0.5 kW with no solar input, that is about 7.5 hours before allowing for changes in real consumption. Verify battery and inverter power ratings as well.
Will my solar battery power the whole home in an outage?
That depends on the inverter, backup switching and which circuits are connected to the backup/EPS output. Start with the loads that matter most, such as the fridge, lights and internet, then have the wiring assessed on site.
Does this calculator estimate battery price or payback?
No. Accurate comparisons need an actual installed quote, time-of-use consumption, charging strategy and warranty terms. Use these results to review packages and request a site assessment ; compare solar alone with solar plus storage using the same assumptions.
Next step: Use “Copy summary” to share your night kWh, critical backup loads and hours, peak kW, proposed solar kWp and candidate battery specifications with an installer. Confirm the electrical design and roof conditions before choosing equipment.
Further reading: DOE: Solar Energy and Storage Basics · DOE: Inverters and Grid Services · PVWatts: Solar Production Estimate
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