Installing a solar PV system is a great way to power your home sustainably. To get the most out of your system, you need to pair it with the right battery size. This guide will help you choose the ideal battery capacity based on your electricity usage and solar PV generation. We'll simplify the process with an easy-to-understand equation.
Step 1: Understand Your Electricity Usage
Your electricity usage varies throughout the year. Typically, usage is higher in winter due to heating and lower in summer unless you use air conditioning or hot tubs.
Gather Your Electricity Bills: Collect your electricity bills for the past year. Note your annual usage in kilowatt-hours (kWh), this will usually be anywhere from 2000KWh - 13000KWh for residential depending on the size of the house.
Calculate Average Daily Usage: Annual Electricity Usage ÷ 365 (the amount of days in a year)
Step 2: Calculate or Estimate Your Solar PV Generation
Find out how much electricity your solar PV system generates in a year. If you already have a system, you can check the generation meter or use the app that comes with your system. If you don't have a system yet, your installer or solar electricians can estimate this based on your system size, location, and panel orientation.
For example, let's assume your system generates 3000 kWh annually.
Step 3: Calculate Battery Capacity
Determine Net Usage: Subtract your annual solar PV generation from your annual electricity usage.
Annual electricity usage: 5000kWh
Annual solar Generation 3000KWh
Net Annual usage: 5000kWh−3000kWh=2000KWh
Average Daily Net Usage: Divide the net usage by 365 ( the amount of days in a year).
2000kWh ÷ 365days = 5.4KWh
Battery Sizing Equation: Battery Capacity (kWh)= Net Annual Usage (KWh/year) ÷ 365=5.4KWh
Things to Consider
Daily Peak Output
If you have a smart meter or app, monitor your daily peak electricity output. This ensures your battery can handle your maximum daily load.
For instance, if your peak daily usage is 25 kWh, your battery should be able to handle this load.
Limitations
One limitation you might encounter with your battery output is the inverter. Even with the largest battery capacity, if your inverter is only 3.6 kW, the battery can only output 3.6 kW. This is why it's often better to oversize your inverter compared to your solar array, so it can handle the electricity peaks you may have throughout the day.
Conclusion
By following these steps, you can choose a battery capacity that matches your electricity usage and solar PV generation. Here's the process summarized in an equation:
Battery Capacity (kWh)=Annual Electricity Usage (kWh)−Annual Solar Generation (kWh) ÷ 365
By correctly sizing your battery, you'll maximize your solar PV system's efficiency and enjoy reliable solar PV battery storage, reducing your reliance on the grid and lowering your electricity bills year-round. If you're still struggling to work out what size battery is right for your system then give us a call at Capital Electrical & Solar and one of our solar electricians will be happy to help.
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