In 2022, most solar panels on the market generated between 250 and 400 watts of power. "245W", "300W", or "335W" will commonly appear next to the panel's name on an estimate for solar installation. They are all related to a solar panel's wattage, capacity, and power output.

How to determine the amount of electricity produced by a solar panel
Under conventional test settings, all solar panels are assessed by the quantity of DC (direct current) power they generate. The output of a solar panel is measured in watts (W) and represents the panel's theoretical power output under perfect sunshine and temperature conditions. Wattage is computed by multiplying volts by amps, where volts represent the electrical force and amperes (amps) represent the total energy used.

Most residential solar panels today have power output ratings ranging from 250 to 400 watts, with greater power ratings commonly preferred. Solar pricing is commonly defined in dollars per watt ($/W), and your solar panels' total wattage considerably impacts your solar system's total cost.

For instance, if you live in a sunny state like California and receive five hours of direct sunlight every day, you may compute the output of your solar panels as follows: 5 hours multiplied by 290 watts (an example of the wattage of a premium solar panel) equals 1,450 watt-hours, or approximately 1.5 kilowatt-hours (kWh). Thus, each solar panel in your array would generate approximately 500-550 kWh of energy per year.

What factors determine the output of solar panels?
Before calculating the quantity of energy a solar panel can generate, it is essential to comprehend the two primary parameters that govern its power output: cell efficiency and solar panel size.

Let's evaluate each aspect separately to gain a better understanding of them.

Solar panel efficiency
When purchasing solar panels, efficiency is one of the most crucial variables. The greater a panel's efficiency, the more energy it can generate. Currently, most silicon-based solar cells can convert 18 and 22 percent of the sunlight that strikes them into usable solar energy, resulting in solar panels with a power output greater than 400 watts. Higher efficiency equals more energy. Thus, solar panels with high efficiency will create more electricity for your home. 

Number of solar cells and size of the solar panel
Solar panels can be divided into two size categories: 60-cell solar panels and 72-cell solar panels. Typically, 60-cell solar panels are around 5.4 feet tall by 3.25 feet wide and generate between 270 and 300 watts. In contrast, 72-cell solar panels are larger due to an additional row of cells, and their typical output ranges from 350 to 400 watts. 72-cell solar panels are typically employed on larger buildings and commercial solar projects instead of private residences.

Environmental variables: shade, direction, and sunlight hours
Solar panel-rated power is directly affected by sun panel efficiency and the number/size of solar cells in a solar panel. In the real world, a panel's actual power output is impacted by a few additional factors:

• The shading of your solar panels will reduce their output. The wattage ratings of solar panels do not account for the decreased output of a panel caused by shade.
• The orientation of your solar panels affects production that is not captured by a panel's output rating. Ideally, your solar panels will face the sun directly. Roof planes are nearly never properly oriented for maximum productivity in practise.
• The length of time your solar panels are exposed to sunshine per day (or year). The greater your productivity, the longer you spend in the sun.

How much energy can a complete solar panel system generate?
Knowing how much energy a single solar panel produces is useful, but it is vital to know how much solar power your roof can create. Calculate the sums below:

Using solar panels rated at 290 W, you receive an average of five hours of direct sunlight per day (the typical amount of sunlight for most locations in California) and an average of five hours of direct sunlight each day. Supposing you install 30 of these premium solar panels on your roof, you would have an 8.7 kW solar panel system comparable to the average system size purchased on the QuestGreens. Multiplying the five expected hours of direct sunlight by 8.7 kW yields approximately 43.5 kWh of daily electricity production. And for one final conversion, if we multiply 43.5 by 365 days in a year, we get around 15,800 kWh of power produced in a calendar year from a rooftop array of 30 premium, 290 W solar panels. The average annual electricity consumption in the United States is approximately 10,600 kWh, which is likely more than enough to power your home.

This estimate is likely on the higher end for most solar purchasers, presumably due to our estimation of the amount of sunlight the system will receive (known as sun hours). 

Solar panel efficiency and cost
The cost of a solar panel is significantly affected by its output. With data, we can know how much 3kW, 4kW, 5kW, 6kW, 7kW, 8kW, and 10kW solar systems could cost on average. This cost can vary depending on where you reside and your needs. To figure out how much this could be for you, determine your location's average cost per watt and multiply that by the solar panel output you have in mind.

Why does solar panel output matter?
The power output of any residential or business solar panel system is a crucial measure. When purchasing or installing a solar photovoltaic (PV) energy system, the pricing is often based on the system's solar panel output (expressed in watts or kilowatts).

The watts of a solar panel show its theoretical power output under optimal sunlight and temperature conditions. Wattage is computed by multiplying volts by amps, where volts represent the electrical force and amperes (amps) represent the total energy used. Open-circuit voltage and the voltage of your system may not be as important of concern for grid-connected systems. However, it is an essential component of your PV system if you are off-grid or intend to utilize battery storage. The savings you obtain from your solar system result from the electricity it generates over time (expressed in kilowatt-hours).

What effect do size and quantity have on output?
Power output alone is not a sufficient indicator of a solar panel's quality and performance attributes. Some panels' greater power output rating is attributable to their larger physical size rather than their higher efficiency or technological superiority.

For example, if two solar panels have 15 percent efficiency ratings, but one has a power output rating of 250 watts. At the same time, the other is certified at 300 watts, which means that the 300-watt panel is around 20 percent physically larger than the 250-watt panel. Because of this, QuestGreens and other industry experts consider panel efficiency to be a more representative measure of solar panel performance than solar capacity alone.

A solar panel system with a total rated capacity of 5kW (kilowatts) might be constructed with either 20 250-Watt panels or 16 300-Watt panels. Both systems will produce the same amount of electricity in the same geographic area. Even though a 5kW system may generate 6,000 kilowatt-hours (kWh) of power per year in Boston, the same system will generate 8,000 kWh annually in Los Angeles due to the quantity of solar each site receives annually.

The impact of materials on production
Solar panels can be constructed from either monocrystalline or polycrystalline cells - monocrystalline cells are more efficient and can generate more power than polycrystalline cells. In contrast, polycrystalline solar panels are considerably more inexpensive. A team of researchers at NREL is also striving to improve solar cell technology to increase efficiency and reduce production costs.

The amount of electricity generated by a solar PV system is determined by its rated power output, as well as other factors such as panel efficiency and temperature sensitivity, as well as the amount of shading the system experiences, and the tilt angle and azimuth of the roof on which it is installed. As a general rule of thumb, it makes sensible financial sense to build a solar system with as much power output as you can afford (or that your roof can accommodate) (or that your roof will accommodate). This will optimize your savings and accelerate the payback period of your solar energy installation.

Explore your solar possibilities with QuestGreens right now
Suppose you're beginning your solar research and would like a rough estimate for an installation. In that case, you can use our Solar Calculator, which provides upfront cost and savings estimates based on your location and roof type. Check out the QuestGreens if you want to obtain and compare estimates from local contractors.