Designing a home solar power system involves several important steps. Using a solar panel system at home is both economical and environmentally friendly. But how do you choose a suitable battery and inverter? Also, how to work out all the precise calculations of the solar panel, battery, inverter, as well as charge controller may bother you a lot. Calculating the appropriate battery and inverter sizes for a solar panel system involves several steps and some basic information about your energy consumption and system specifications. This guide will walk you through the process, from assessing your energy needs to installing the solar power system for home.
Step 1: Determine Your Energy Needs
Calculate Daily Energy Consumption
- List all the appliances and devices you intend to power.
- Note the wattage of each device and estimate the number of hours each device runs per day.
- Multiply the wattage by the hours to get the daily watt-hour (Wh) consumption for each device.
- Sum the watt-hours for all devices to get the total daily energy consumption.
Take example:
| Device | Power (W) | Hours per day | Energy (Wh/day) |
| LED Light Bulb | 10 | 5 | 50 |
| Refrigerator | 150 | 8 | 1200 |
| Laptop | 60 | 4 | 240 |
| TV | 100 | 3 | 300 |
| Total | 1790 Wh/day |
But if you are a layman of such math issues, there are more specific calculations:
(1) Work out the maximum wattage or peak load of your house. You need to estimate the total wattage of your needed devices and appliances ranging from refrigerators and lights to laptops and hairdryers. And some of them may work at the same time.
Example: A room has two 50-watt light bulbs and a 200-watt laptop. The total wattage is:
50 watts x 2 + 200watts = 300 watts
(2) you need to figure out how many hours every device will operate each day. Then you simply multiply every wattage by its working time (hours) and get the needed power (watt-hour) per day. Next, you just add up all these values to work out the sum of energy in your house.
Example: The above-mentioned light bulbs need to run for 6 hours per day, and the average computer use time is 3 hours every day. The total value is:
50 watts x 2 x 6 + 200 x 3 = 1200 Wh
Step 2: Calculate Battery Capacity
Calculate Battery Amp-Hours
- Decide on the number of days of autonomy (days you want the system to run without sun, typically 1-3 days).
- Decide on the Depth of Discharge (DoD) for your batteries (usually 50% for lead-acid batteries and up to 80% for lithium-ion batteries).
Formula:
Battery Capacity (Ah) = [Total Daily Energy Consumption (Wh/day) * Days of Autonomy ] / [Battery Voltage (V) * Depth of Discharge (DoD)]
Example (for 1 day of autonomy, 12V battery, 50% DoD):
Battery Capacity (Ah) = [1790 Wh/day * 1 day ] / [12V * 50%] = 1790 / 6 ≈ 300 Ah
Battery capacity is important for you to make sure that the solar panel system operates smoothly and effectively. If you can’t access the grid, or you simply want to store the solar energy in a battery as a power backup for emergencies.
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Step 3: Calculate Solar Panel Size
Determine Solar Panel Size
- Calculate the peak sunlight hours in your location (average number of hours per day with peak sunlight).
- Calculate the total solar panel wattage required.
Formula:
Total Solar Panel Wattage (W)=Total Daily Energy Consumption (Wh/day) / Peak Sunlight Hours (hours/day)
Example (assuming 5 peak sunlight hours per day):
Total Solar Panel Wattage (W)= 1790 Wh/day / 5 hours/day = 358 W
If using multiple panels, divide the total wattage by the wattage of each panel to determine the number of panels needed. You can see 9 Steps for Installing Solar Panels on Roof.
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Step 4: Calculate Inverter Size
1. Inverter specification
- Add up the wattage of all the devices you want to run simultaneously to get the peak load.
- Add a safety margin (typically 20-25%).
Example:
Total Peak Load=150 W (Refrigerator)+60 W (Laptop)+100 W (TV)=310 W
Inverter Size=310 W×1.25≈388 W
Round up to the nearest standard inverter size, e.g., 500W 12VDC or 600W 12VDC.
You can read more details, Choosing the Best Power Inverter for Home Use
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2. Charge controller specification
You may ignore a component like a charge controller, but it is also significant to help your solar system perform perfectly.
A charge controller is used to prevent your model from overcharging. It interfaces the solar panels and the batteries. Thus it plays an important role in regulating solar power from solar panels to batteries.
Related MPPT Solar Charge Controller
You need the already figured out results from the above example to calculate how big your satisfying charge controller needs to be.
Formula:
Total Charge Controller Charging Current (A) = Battery Capacity (Ah) / Peak Sunlight Hours (hours)
Example:
Total Charge Controller Charging Current (A) = 300Ah / 5 Hours = 60A
Here we will talk about two common sorts of charge controllers: PWM and MPPT.
Pulse-Width Modulation (PWM) controllers are more economical compared to Maximum Power Point Tracking (MPPT) controllers but can result in significant power losses, up to 60% during conversion. This is because PWM controllers can’t optimize the voltage going to the batteries, making them inefficient for large solar power systems but suitable for smaller ones.
MPPT controllers, on the other hand, effectively optimize the voltage from solar panels, transferring energy to the battery bank at a maximum rate. They achieve an efficiency of 93%-97% by automatically adjusting to the peak power point. This high efficiency makes MPPT controllers a cost-effective choice despite their higher price.
Step 5: Install the Solar Power System
Once you have all the necessary permits, your installer will begin the installation process. This typically involves mounting the solar panels on your roof, connecting the inverter, and setting up the electrical components. The installation process can take a few days to a few weeks, depending on the complexity of the solar power system and the weather conditions.
By following these steps, you can design and implement a home solar power system that meets your energy needs and contributes to a more sustainable future.