Solar calculator: How many solar panels do I need

Going solar requires quite a lot of preparation. The first question that immediately arises is how many solar panels do I need? To make the task of answering this question simpler, we’ve composed a small guide on calculating your energy consumption and finding the right number of modules to match it. You’ll see that it’s actually not that complicated, especially if you make use of a solar power calculator.

How to calculate how many solar panels you need

Generally in the US 14 to 26 solar panels are enough to cover 100% electric needs of an average house. However, there are lots of factors to take into consideration, like your location, positioning of panels and their qualities when it comes to performance in low-light conditions, high temperatures, shading tolerance, etc. A solar panel calculator makes the task significantly easier and we recommend using it at least for extra info and to check your calculations.

Step 1. Determine your average monthly electricity consumption

The easiest way to figure out your monthly energy usage is to take a look at your bills. Your electric usage profile usually contains the kWh consumption records for each month of the year. If you have an electric meter, it also tracks down all your electricity usage. For example, a relatively small 1500 sq ft house needs around 650 kWh every month. A relatively large 2500 sq ft house requires over 1000 kWh.

If your bill doesn’t have such information and there is no meter, you can ask your utility for the data or try to get a very rough estimate by calculating everything manually. Basically, you just make a table of all the appliances in the house, their power rating and approximate number of hours in use per day. Then you multiply power ratings by hours and sum together the consumption of every appliance. This way you get a very rough estimate of your daily consumption and the next step can be skipped.

Step 2. Calculate daily kWh consumption

This one is easy. Once you’ve figured out your average monthly consumption, divide by 30 and you’ll get an average daily consumption. Again, a small house needs around 20-30 kWh daily whereas larger ones consume 30-50 kWh per day. What you’ll get is what your future solar system has to generate in one day to fully cover your electric needs.

Step 3. Estimate the amount of sunlight your solar panels will receive.

Let’s say that installation went smooth, you got the right side of the roof so that your panels face south and there is no shading. Your energy harvest is going to depend on the number of sun hours in the area that you live in.

Peak sun hours aren’t just your normal daylight hours — this is the time when your panels get maximum irradiance and therefore produce the most. For example, in California the average number of peak sun hours is around 5.6. Of course, it changes throughout the year.

To find out how much your array is going to produce daily, multiply the power of your modules by peak sun hours in the area. For example, a 300W panel in Los Angeles gives you around 1.68 kWh daily. The average system size in the US is around 6 kW — in California it gives you around 33.6 kWh daily.

Step 4. Consider the potential use of solar energy

What part of your energy needs you want your system to cover — all of them or just a little bit? The answer depends on the possibility of Net Metering and its terms. If you can sell your excess energy to the utility grid and there are no limits to it, that’s great. But if you go for an off-grid system or there are severe limits to Net Metering in your area, you won’t be able to do much with leftover solar energy. Besides, there might be legal limitations on the size of systems that are eligible for the Net Metering program.

Let’s say that you require 30 kWh daily, but you would prefer your system to cover only 80% of it. Then 30 kWh *0.8 = 24 kWh: that’s how much your installation should generate in a day.

Step 5. Determine how many solar panels you will need

Once you’ve figured out how much your future system has to produce, all that is left is to calculate the number of panels. You’ll have to take into consideration the amount of free room on your roof. A 6kW system needs around 300 sq ft of space. Going for higher power modules allows you to save space, but keep in mind that 72/144 cell modules are larger and it’s generally harder to fit them on the residential roof.

Solar experts have come up with all sorts of techniques and tools to simplify the process of calculating the size of a system. One of them is a solar calculator. Based on your location, a calculator analyzes utility rates, sun hours and prices for solar equipment in your area and tells you what system size should work best, what are the average savings that a system brings in and average payback time in your area.