The Ultimate Beginner’s Guide to Sizing Your Solar System

Step 1: Audit Your Appliances and Consumption

• Find your latest energy bill for daily average use (kWh).

• List every appliance you plan to run off-grid; don’t forget water pumps, internet hardware, or essential tech.

• Use a free online calculator (Australia: Energy Made Easy, US: Energy Star, EU: OVACEN).​

• Add a 25% buffer to your estimate for real-world security.

Example:

• Efficient fridge: 40W x 24hrs = 960Wh

• Laptop: 60W x 6hrs = 360Wh

• LED lights: 20W x 8hrs = 160Wh

• Total: 1,480Wh → With buffer: 1,850Wh/day

Step 2: Consider Local Climate & Peak Sun Hours

• Australia: Sydney 4.5-5.5, Melbourne 7, Perth 9 hours/day (confirmed by BOM)

• UK: London ~2.8hrs, Manchester ~2.5hrs/day

• USA: Texas/California ~5-6hrs, Pacific NW ~3.5hrs, Arizona ~7+hrs

Formula:
Total daily usage (Wh) ÷ peak sun hours = required panel wattage
Sydney example: 1,850Wh ÷ 5 hours = 370W (recommend 450W for safety)

Step 3: Choose the Right Battery Storage

• Lithium-ion/LiFePO4 batteries are the global standard for safety and efficiency.

• Brands: FranklinWH and Tesla Powerwall are Clean Energy Council certified for Australian use; other reputable brands apply globally.​

• Rule of Thumb: Battery bank = 2–3 days of planned usage (for rainy/cloudy spells and overnight).

Step 4: Plan for Seasonal Changes and Expansion

• Winter means lower solar yields; size for worst-case scenarios, not summer peaks.

• If planning future appliances (AC, EV charger), add 15–25% extra capacity now.

Step 5: Compliance and Local Regulations

• Australia: All solar and battery systems must be installed by a Clean Energy Council (CEC) accredited electrician for safety and rebates.​

• Council approval: Most residential installs don't require council approval, but always check with local authorities for unique or large setups.

• Europe/UK/US: Local installer certification and grid connection rules apply—use government resources for updates.

• Portable setups for vans off-grid: Compliance matters for insurance and electrical safety everywhere.

Common and Costly Mistakes to Avoid

• Underestimating power needs (track everything!)

• Using non-certified/cheap gear; reliable brands mean safer, insurable systems

• Ignoring or misunderstanding local regulations

• Not including a backup option (small generator or portable power station is a must for critical loads)

Fast Sizing Cheat Sheet

Location Panel Size (W) Battery Bank (kWh)

Sydney, Australia 450 2–3

London, UK 600 3–4

Texas, USA 400 2–3

Berlin, Germany 550 3

Adjust for climate, shading, and future devices.

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References

1. Clean Energy Council. (2025). CEC Approved Batteries. https://cleanenergycouncil.org.au/industry/products/batteries

2. Bureau of Meteorology (Australia). (2025). Sunshine hours. http://www.bom.gov.au/climate/maps/averages/sunshine-hours/

3. European Commission Joint Research Centre. (2025). Photovoltaic Geographical Information System (PVGIS). https://re.jrc.ec.europa.eu/pvg_tools/en/

4. National Renewable Energy Laboratory (USA). (2025). Solar Radiation Data. https://nsrdb.nrel.gov