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In the first part of this guide, we covered how to size the solar panel system itself. In this part, we will delve into sizing the other critical components of the system: the inverter, the batteries, and explain specific terms like MPPT (Maximum Power Point Tracking). For this example, we will assume an on-grid system with enough battery storage to cover a whole day with no sunshine.
Sizing the Inverter
Determine the system size: The inverter should be able to handle the total wattage generated by the solar panels. From our previous example, the system size is 7.5 kW.
Match the inverter to the system: Inverters are typically rated by their AC output in kilowatts (kW). Choose an inverter that matches or slightly exceeds the system size. In our case, a 7.5 kW inverter or slightly higher would be suitable.
Consider future expansion: If you plan to expand your solar array in the future, choose an inverter with a higher capacity.
Sizing the Batteries
Determine daily energy consumption: We previously calculated the household’s daily energy consumption to be 30 kWh.
Decide on battery storage: Since we want enough battery storage for a whole day with no sunshine, we need batteries that can store at least 30 kWh of energy.
Account for depth of discharge (DoD): Batteries should not be discharged completely. For this example, let’s assume a DoD of 80%:
Required Battery Capacity (kWh) = Daily Energy Consumption (kWh) / DoD
Required Battery Capacity (kWh) = 30 kWh / 0.80=37.5 kWh
Convert to Amp-Hours (Ah): If the battery capacity is given in amp-hours (Ah), convert the kWh to Ah using the system voltage (typically 48V for larger systems).
Capacity (Ah) = Capacity (kWh) × 1000 / System Voltage (V)
Capacity (Ah) = 37.5 kWh × 1000 / 48 V = 781.25 Ah
Select the number of batteries: If each battery has a capacity of 250 Ah, you would need: 781.25 Ah / 250 Ah per battery = 3.125 batteries, and since you can’t have a fraction of a battery, you would round up and use 3 or 4 batteries.
Sizing the Charge Controller
Calculate the maximum current: The charge controller must handle the maximum current from the solar panels. From our example, the system size is 7.5 kW, and the system voltage is 48V.
Maximum Current = System Size (W) / System Voltage (V)
Maximum Current = 7500 W / 48 V=156.25 A
Add a safety margin: It’s advisable to add a safety margin of about 25%.
Safe Maximum Current = 156.25 A × 1.25 = 195.31 A
Choose the charge controller: Select a charge controller that can handle at least 195.31A. It’s best to choose one rated slightly higher to ensure reliability.
Properly choosing the components of a solar panel system ensures optimal performance, efficiency, and reliability. By calculating the required capacity and matching it to your energy needs, you can design a system that provides continuous power, even during periods of low sunlight. With the right inverter, batteries, charge controller, and MPPT, your solar power system will be well-equipped to meet your household’s energy demands.
