Engineer checking how much energy a set of solar panels are producing

Each solar panel can be expected to produce between 400 and 600 kilowatt-hours per year. The exact electricity production depends on the panel specifications and the amount of sunshine received. Smart design decisions can also improve the productivity of a solar power system.

Assuming that sunshine does not change, there are two main ways to increase the amount of energy a solar panel produces:

  • Making the panel larger, to capture more sunlight.
  • Achieving a higher efficiency with an improved solar panel design.

Solar panel manufacturers prefer to work with standard sizes, since this simplifies fabrication. For this reason, you will find that most panels have either 60 or 72 solar cells. Current research focuses on improving cell efficiency to increase energy production with the same panel sizes.

How much energy a solar panel produces depends on several factors. Solar panel efficiency and size are important, since they determine how much sunlight is captured and converted into electricity. Solar productivity also depends on the local climate, since more sunshine translates into a higher energy output. Finally, the panel orientation affects the amount of sunlight hitting its surface. The best solar companies make sure that no panels are covered by shadows, while finding the orientation that captures the most sunlight.

What Is the Average Wattage of Solar Panels?

The power rating of solar panels is commonly misunderstood. All panels are tested under equivalent laboratory conditions, and the resulting wattage becomes their rated power. However, the operating conditions in actual projects differ from the ideal lab scenario, and energy production also varies.

Solar panels with 60 cells normally have a wattage in the range of 250 to 350 watts. Some 72-cell panels go above 400 watts, since they have 12 additional solar cells producing electricity.

The controlled laboratory conditions for panel wattage tests differ from those found in most project sites. However, the power rating gives an idea of how solar panels compare with each other. A 360-watt panel will tend to produce around 20% more energy than a 300-watt panel, even if they don’t operate at their rated wattage in actual projects.

Based on the efficiency of the average solar panel, you can expect to convert between 15% and 20% of sunshine into electricity. However, some of the most efficient solar panels available go above 22%.

How Solar Panel Specifications Affect Energy Production

The productivity of solar panels depends on site conditions and the properties of the panels themselves. Site conditions cannot be changed, but the panels can be positioned to get maximum sunshine. With respect to the panels themselves, energy production is strongly dependent on the following specifications:

Panel size

A 72-cell panel has 20% more area than a 60-cell panel, thanks to the 12 additional solar cells. They are more productive simply because they capture more sunlight.

Panel material

Assuming the same size, monocrystalline panels have the highest energy production, followed closely by polycrystalline panels. Thin-film panels produce the least energy per square foot.

Temperature coefficient

Solar panels lose wattage as temperature increases, and this is represented as a percentage loss per degree Celsius. Thin-film panels are the least affected, with losses under 0.30% per °C. On the other hand, mono and polycrystalline panels normally lose over 0.40% power per °C.

Consider that performance loss with temperature is a temporary effect, and it does not represent permanent damage. When the temperature drops, panels recover their lost wattage.

You will notice that 60-cell panels are rated at 20 volts, while 72-cell panels have 24 volts. This data is used by solar installers to design electrical connections, but wattage is the value that matters when estimating the amount of energy produced. Under equal conditions, a 20V 350W panel will have the same productivity as a 24V 350W panel.

close up of a 72 cell black solar panel

Solar panel specifications can change a lot from vendor to vendor, but the way they function stays the same. Installation costs are roughly equivalent for all types.

How Much Electricity Do Solar Panels Produce Each Year?

Solar panels are characterized by their versatility. They can be used in nearly all buildings and climate zones, as long as the following conditions are met:

  • Having a roof with enough structural capacity for the panels, or a large enough property for a ground installation.
  • The prospective area for solar panels should not have serious shading issues. Solar panels produce a lot more energy when there are no shadows.

How much electricity does a solar panel produce? An accurate answer is only possible if a solar company inspects your property, to then design a suitable solar power system. However, there are online solar calculators that provide a broad estimate of production based on your geographic location and electricity consumption.

When comparing sites, a very useful metric is the yearly kilowatt-hour production per kilowatt of installed capacity, or kWh / kW.

  • For example, if your home solar system has an installed capacity of 10 kilowatts, and the output in year was 14,500 kWh, you are getting 1450 kWh per kW.
  • This production rate increases in sunny locations, since there is more solar radiation that can be converted to electricity.

NASA and other scientific institutions have compiled solar productivity data based on location. The SOLARGIS website has solar productivity maps for over 180 countries, and you can check the expected kilowatt-hour production for every kilowatt of solar capacity.

Annual Productivity with Various Solar Panel Wattages and Sunshine Conditions

The following table estimates the kilowatt-hours a solar panel can produce per year, considering five panel wattages and five sunshine conditions:

Solar Panel

Wattage

At 1300

kWh/kW

At 1500

kWh/kW

At 1700

kWh/kW

At 1900

kWh/kW

At 2100

kWh/kW

240 W

312

360

408

456

504

270 W

351

405

459

513

567

300 W

390

450

510

570

630

330 W

429

495

561

627

693

360 W

468

540

612

684

756

This table provides an idea of what production to expect from a single solar panel, based on wattage and the local sunshine. However, only a solar company can provide an accurate estimate. A solar system design considers factors like rooftop orientation and the presence of shadows, which are unique for each site.

Solar productivity values in kWh per installed kilowatt normally include the conversion from direct current to alternating current. The DC power output from panels is not suitable for home appliances directly, and it must be converted to AC by an inverter. The best solar inverters have an efficiency of over 97%, but losses are unavoidable because no energy conversion system is perfect.

Since solar panels only operate at rated wattage in laboratory settings, you will find that the inverter is specified smaller than the total wattage of solar panels. For example, you may find that a 5-kW inverter is connected to panels that add up 5.5 or 6 kW of capacity. This may seem like a design mistake at first, but actually it is the best decision:

  • Solar panels operate below their rated wattage most of the time. A larger inverter would simply be wasting capacity while being more expensive.
  • Inverters can “clip” any solar production that exceeds their capacity. They will not be damaged if there is a sudden peak in the amount of power from panels.

How Much Electricity Does a Solar Panel Produce per Month and per Day?

The annual productivity of solar power systems is relatively constant. However, the monthly productivity is more variable due to the effect of the seasons. As you might expect, solar panels are more productive in summer and less productive in winter.

A set of solar panels on a roof that are covered in snow

Using an example from the table above, a 360W panel will produce around 684 kWh per year in a site that offers 1900 kWh/kW. On average, this is equivalent to 57 kWh per month and 1.87 kWh per day. However, the monthly and daily productivity will be above the average value during summer, and below the average value during winter.

Having a higher productivity during the summer months is actually useful, since that is when air conditioners operate at full capacity. The additional power consumption of air conditioners can be offset by the extra production from solar energy systems.

Solar offers from the best companies will normally include production estimates by month. These can give you a better idea of how the productivity of your solar panels will change throughout the year.

Why Solar Panel Output Matters

The productivity of panels is important when designing solar systems, since it determines how many are needed to reach a certain energy production target. When the square feet available are limited, getting the highest possible output from each panel is important.

The sufficient number of solar panels needed to power your home depends on your electricity consumption and savings goal. For example, reducing a power bill by 80% requires more panels that reducing it by 50%. If energy storage is added to use electricity from solar panels at night, the production calculations must also consider the kilowatt-hours required to charge batteries.

Solar shingle installations follow a completely different approach, since solar cells are embedded in roof shingles. This makes them worth installing in new homes, since there is no need to install a separate roof and solar energy system. Conventional solar panels are still the best option for existing homes. Solar shingles would require a complete roof removal in this case, which is very expensive.

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