A step-by-step guide to determining the right size solar panel system for residential, commercial, or mobile applications
Planning the sizing of your solar system is an essential first step to energy independence. It’s important to get it right because if you go too small, you won’t have enough energy for your needs; on the other hand, if you go too big, you’ll end up paying for equipment you don’t need. So what size solar panel system do you need? The answer depends on a few key factors:
- How much energy does your home, RV, or off-grid structure need?
- Do you want to store energy
- What’s your budget?
In this article, we’ll talk about how to answer those questions so you can design the perfect system for your needs.
Want some one-on-one help getting started? Set up a design appointment with one of our solar application engineers today!
Step 1: Estimate Your Energy Usage
To determine the energy usage of the structure you’re wanting to power, you’ll need to collect the last twelve months’ worth of utility bills. Add up the total kWH and divide by 12 to determine your monthly average.
Total Monthly kWH ÷12 Months = Monthly Average
Note this number, because it’s your baseline, and you’ll be using it in all your other calculations.
Step 2: Determine Peak Sun Hours
Peak sun hours are how solar production is measured. They are the equivalent hours per day when sunlight is strong enough to produce maximum power. You can find peak sun hours by accessing the National Renewable Energy Laboratory solar maps to find your local average.
Step 3: Calculate Your Initial Solar System Array Size
You’ll be looking for how many kilowatts you need your solar array to produce. To calculate this, divide your daily usage from step 1 by your areas average peak sun hours in step 2.
Daily Usage in kW ÷Peak Sun Hours = kW Solar Array
This calculation would give you the solar array you would need under ideal circumstances, but there are other considerations to take into account.
Step 4: Compensate for Solar Panel Degradation
Solar panels are tested in lab environments under perfect conditions, but the real world doesn’t have perfect conditions. Factors like heat, dust, shading, and normal wear mean production is never 100% of the rated wattage. Additionally, solar panels degrade on average .8% per year.
To compensate for these factors, add about 20% “headroom” to your calculations. For example, if your calculation in step 3 yielded a wattage of 5.45 kW, you would add 20% to determine the wattage you need your solar array to produce.
Example:
5.45 kW x 1.2 = 6.54 kW Solar Array
This would be the total wattage you would need to offset your energy consumption.
Step 5: Choose Between Full or Partial Energy Offset
Most solar users are looking to offset 100% of their energy usage, but there are a variety of reasons, including budget, that you may want to aim for partial offset. To do this, determine what percentage of usage you want to offset and multiply your solar array wattage by that percentage. For example, if you only wanted to offset half the power from the example in step 5:
6.54 x .5 = 3.27 kW Solar Array
Partial offsets are a good way to ease into solar as you can always expand on them later.
Step 6: Determine How Many Solar Panels You Need
Once you know your total array size, choose the panels you’ll be using and identify how many watts they use. Then divide your total array size by the panel wattage to get the number of panels needed.
Total Array Size ÷Panel Wattage = Number of Panels Needed
Additional Considerations in Solar System Design
By following the steps outlined in this article, you’re off to a solid start determining how much you’re going to need to invest in your solar power system. However, there are many other factors to consider that depend on whether you’re going for a grid-tied, off-grid, or hybrid system. These factors include:
- Whether your system will be powering battery backup
- Shading from a chimneyLocal net metering rule
- Future energy plans
- Code compliance and safety
- Equipment compatibility
- Financial planning
And there are many more things to take into account. A professional solar power system design will ensure your system is optimized for cost, performance, and flexibility, taking all the guesswork out of the process and matching the right system and components to your needs.
Watch the Video
Get a Free System Design Consultation
At Naz Solar Electric, our application engineers are here to provide system design for your complete residential or commercial project. Combined with exceptional, cutting-edge products from our manufacturing partners, and our network of top-tier solar installers, we’re your one-stop shop for getting your project designed, supplied, and executed.
Reach out with any questions or to talk to an application engineer.
