Solar Panel Size Calculator: What Size Panel Do I Need? Use our solar panel calculation https://www.renogy.com/calculators to find out what size solar panel you need to charge your battery. Calculator Assumptions The solar charge controller is the only load connected to the battery What Size Solar Panel Do I Need? To find out what size solar panel you need to charge your battery, you’ll need to enter the following info into our solar panel size calculator at the top of this page: Battery Voltage (V): What is your battery’s voltage? Battery Amp Hours (Ah): What is your battery’s capacity in amp hours? (If you only know its capacity in watt hours, first convert watt hours to amp hours) Battery Type: Is your battery a lead acid or lithium (LiFePO4) battery? Battery Depth of Discharge (DoD): What level of discharge is your battery at? 100% means fully discharged and 0% means fully charged. Solar Charge Controller Type: Will you be using a PWM or MPPT charge controller? Desired Charge Time (in peak sun hours): How quickly do you want your solar panel to charge your battery, in peak sun hours? Once you’ve entered the above info, click “Calculate Solar Panel Size” to get an estimate of what size panel you need to charge your battery at your desired speed. What Size Solar Panel to Charge 12V Battery? 12 volt batteries are the most common voltage I see people using in their solar power setups. Here is a chart showing what size solar panel you need to charge 12V batteries of various capacities in 5 peak sun hours with an MPPT charge controller. You need around 200-400 watts of solar panels to charge many common 12V lithium battery sizes from 100% depth of discharge in 5 peak sun hours with an MPPT charge controller. You need around 150-300 watts of solar panels to charge many common 12V lead acid battery sizes from 50% depth of discharge in 5 peak sun hours with an MPPT charge controller. Why Use Peak Sun Hours? Sunlight varies in intensity by location and time of day. The sun shines more intensely at 1pm in Arizona than it does at 8AM in Alaska. So if we were just to measure the length of time sun shines on a solar panel, it wouldn’t give us a very clear idea of how much energy that solar panel generated during that time. We need to know how intense that sunlight was. By measuring the sunlight in peak sun hours, we can quantify how much sunlight a solar panel receives. Then we can use that number to better estimate how much solar energy was generated during that time. Plus, we can use historical data to predict how many peak sun hours a location will get on an average day. These predictions help when picking what size solar panel or system to use.