Calculating Power Output for Solar Energy Projects

Cách tính toán sản lượng điện cho dự án điện năng lượng mặt trời

In previous shared articles, VREnergy has guided you through the first tasks before implementing a small-scale household solar power project to a  large-scale solar power EPC general contractor project.

Previous VREnergy articles, you can refer to:

Today, we will go to the next step, directly related to the value of the solar power project you will deploy, which is the step of calculating the electricity output for the solar power project.

Solar Energy

Currently, solar energy is understood as a combination of the number of hours of sunshine received in your locality and the intensity of sunshine. This energy will change according to the time of year and where you live.

du an tong thau dien met troi emivest feedmill 1 min

The combination of hours and intensity of sunlight is called exposure or insolation. This quantity is called the average radiant power, calculated in the unit W/m and for solar energy, this quantity is calculated in terms of kWh falling on one square meter of the ground during one day (kWh /m /day). One square meter is equivalent to 9.9 square feet.

Meaning of sunlight

Solar photovoltaic cells give the number of watts of power they can be expected to produce, based on an insolation of 1000 W/m . This number is usually the watt-peak (Wp) value, which indicates how much power the solar panel can produce under ideal conditions.

An insolation of 1000 W/m2 is what you can get at midday in summer at the equator. This is not an average value based on a daily basis.

However, when you know your local insolation, in terms of average daily value (kWh/m2/day), you can multiply this number by the number of watts of the solar battery to estimate the energy level. that your solar battery can provide.

Calculate electricity output based on sunlight exposure

Insolation depends on the locality (longitude – latitude) and changes according to the time of year (due to the tilt of the earth’s axis). To be able to estimate reasonably, you need to know the insolation value of each month in the locality where you reside. Thanks to PVsyst software, calculating sunlight illuminance for each locality becomes relatively simple. The computing system continuously monitors solar illuminance on the earth’s surface. These values ​​are used in calculating upper atmospheric conditions, average cloud cover and surface temperature and are the basis for sampling at 3-hourly intervals. 

Harvest solar energy

The tilt angle of the solar panel increases the amount of sunlight received: if you place the panel vertically or horizontally above the ground, you will receive less sunlight throughout the day than if you place the panel vertically or horizontally above the ground. When tilting this panel, always face the sun.

If you place your solar panels at an angle toward the sun, you will receive more sunlight, thus generating more electricity. This is very evident during the winter months, when the sun is slightly low in the sky.

The reason is simple: when the sun is high in the sky, the intensity of sunlight is also high. When the sun is low, sunlight spreads over a wider area.

Effect of tilt angle according to sun position

If the panel is tilted towards the sun, more solar energy will be collected, so the converted power will also be greater. In general, this tilt angle is determined according to the existing roof angle. However, each locality always has optimal angles for installing solar power systems , allowing to capture the maximum possible sunlight.

Calculate the optimal tilt angle

Because the earth’s axis is tilted 23°30′ relative to the sun, the optimal tilt angle of solar panels varies throughout the year, depending on the season.

Some systems can adjust the tilt angle of solar batteries (solar tracking system)  on a monthly basis, but there are also systems that install solar batteries at a fixed tilt angle.

you and dien with troi long and min

To calculate the optimal tilt angle, you can use the formula:

90° – latitude (where you live) = optimal constant tilt angle all year round

This is the optimal tilt angle for fixed panels used to generate electricity year-round. This doesn’t mean you’ll get peak power every month, instead, you’ll get optimal power throughout the year.

Optimal tilt angle according to time of year

Depending on the time period you want to use solar energy, you can choose the appropriate solar battery tilt angle for each time of year. Each month of the year, the sun’s angle in the sky changes about 7.8° – rising in the summer and lowering in the winter. By adjusting the solar panel angle according to the sun, you can increase the efficiency of the solar power system accordingly. You will see the optimal monthly tilt angle (rounded to the nearest whole number)/

Reasons to do this:

  • For an independent solar power system, not connected to the grid, you need to produce maximum power in the winter months to balance the decline in natural light.
  • When installing a grid-connected system in cold climates where the focus is on reducing carbon emissions, you should increase system capacity in the winter to compensate for the amount of electricity you need to buy when demand increases.
  • When installing a system connected to the grid to profit by selling electricity, you can adjust the tilt angle of the solar cells in the summer to get the highest power output.

Optimal winter corner

Below is an example of adjusting a solar power system. Solar power system performance is lowest in winter. However, by tilting your panels to capture optimal sunlight during the winter, you can significantly improve output during this time.

In the Northern Hemisphere, the optimal winter tilt angle for solar cells is the angle corresponding to November and January. In the Southern Hemisphere, the optimal winter angle corresponds to May and July.

90° – latitude (where you live) – 15.6° = optimal winter tilt angle

Optimal summer corner

If you want your solar power system to provide the highest power output, you can receive more power (during the year) by tilting the panels at the optimal angle during the summer.

Hot climates often consume a lot of electricity when the weather is hot, tilting the panels at the optimal angle to receive maximum sunlight in the summer is a good solution, both financially and environmentally.

The formula for calculating the optimal angle for winter will be:

90° – latitude (where you live) + 15.6° = optimal summer tilt angle

Positioning the solar battery

No matter where you live, the sun always rises in the East and sets in the West. If in the Northern Hemisphere, solar panels will always work best if they face south. In the Southern Hemisphere, panels will work well if facing north.

However, it is not always possible to position solar panels correctly. For example, if you want to install solar cells on your roof and the roof faces east-west, it will be difficult or impossible to install solar cells facing the other direction.

The battery cools down for 5 min

In about 5 years VREnergy has been accompanying the solar power industry , solar battery design has improved significantly, so this problem is no longer as difficult to overcome as before. Depending on the manufacturer, the efficiency will be slightly different and depending on the seasons of the year, the average efficiency of solar batteries differs from the South (Northern Hemisphere) and the North (Southern Hemisphere) by approximately 1.1% in 5° increments .

This means that if the solar cell is facing east (or west), the efficiency loss is about 20% compared to the optimal position.

You could also point the power cells in the exact opposite direction – north in the Hemisphere and south in the Southern Hemisphere – the efficiency loss would be about 40%.

Use sunlight illuminance to calculate the power produced by solar cells

Based on the above data, you can calculate on a month-by-month basis the power generated by the solar cell per day, by multiplying the monthly sun illuminance value by the number of rated Watts of the solar cell.

Sunlight x Panel watts = Watt-hour/day

As you know, the sun illuminance value depends on the month and the tilt angle of the battery. Assuming the battery has a fixed rating of 550 W, the capacity of this panel battery in June and December will be:

JuneDecember
4.86 x 550 W  = 2.76 kWh0.6 x 550 W = 330 W

As you can see, there is a big difference in the power that can be generated between summer and mid-winter. In the example above, summer capacity is 8 times higher than winter capacity:

If the panel is tilted at an angle of 38 o, the optimal angle value for the whole year, the result will be:

JuneDecember
4.2 x 550 W  = 2.31 kWh1.05 x 550 W = 577.5 W

It is clear that the capacity is significantly improved in winter and slightly reduced in summer.

Use sunlight exposure to determine the capacity needed for the solar battery array

Similar to the daily capacity calculation method mentioned above, you can use the sunlight illuminance value to calculate the required capacity for the panel array.

This is only an approximate value, because the actual value depends on the following factors:

  • Characteristics of your locality.
  • Location and tilt angle of solar panels.
  • Obstructions block light at different times of the year.

In general, performing this calculation to create a preliminary cost table for a solar power system always achieves optimal performance. The calculation is relatively simple: take the calculated result for the total number of Wh/day and divide it by the insolation value of the month with the lowest value you want the system to operate.

3 screens in the house 1 min

For the example of a household with a daily power consumption demand of 695 kWh/day, we can give the lowest solar illuminance in December. Combined with the solar tilt angles, you can calculate the capacity according to the corresponding angle values.

Horizontal695 / 0.6 = 1.159 kWhIf the panel is placed horizontally, the panel array needs a capacity of 1159 W to meet the electricity demand of 695 kWh/day for household solar power .
Straight695 / 1.01 = 0.688 kWhIf placing the panel vertically, only use the 688 W range.
Tilt 38° (optimal all year round)695 / 1.05 = 643 WTowards the equator, just use the 661 W panel range.
Tilt 23° (optimal in winter)695 / 1.05 = 0.643 WFor the optimal winter angle, just use the 643 W panel array.
Tilt 53° (optimal summer)695 / 0.97 = 0.716 WFacing the summer sun, a 716 W panel array is needed to meet the electricity demand for December.
The tilt angle is adjusted monthly695 / 1.08 = 643 WWith the panel tilt angle adjusted each month, a 643 W panel range can be used (equivalent to the optimal winter angle).

Based on the table above, to provide enough electricity for your household, you will need a solar battery array with a capacity of between 643 – 1159 W, depending on the tilt angle of the panels.

So if the solar battery is blocked from light, its performance will be significantly reduced. Before installation, we need to survey the area where the solar power system will be installed to calculate in detail!

Factors affecting the electricity output of solar power systems

The performance of a solar battery system can be impacted by a number of important factors, including:

  • Sunlight: The level of direct sunlight affects the panel’s ability to absorb energy. When light is low, energy production decreases, reducing performance.
  • Temperature: High temperatures can increase resistance in the battery system and reduce performance. Some systems are designed to cool themselves, but if temperatures are too high performance can still be affected.
  • Dust and dirt: Dust and dirt on the panel can reduce its ability to absorb light, leading to reduced performance. Regular maintenance and cleaning are necessary to maintain optimal performance.
  • Installation direction and angle: The direction and installation angle of the solar panels also affect performance. If not placed in the best direction to receive sunlight, performance will decrease.
  • Covered: Any cover on the panel, such as shade from trees, buildings or panels, can also reduce performance by blocking light reception.
  • Battery panel quality and longevity: The quality of the panel and its lifespan directly affect performance. Poor quality or used panels may not produce energy effectively.
  • Electrical resistance: Any resistance in the electrical system, such as poor cables or connections, can reduce performance by reducing the current flowing through the system.
  • Power surges: Power surges or unwanted frequency variations can also affect performance by causing interruptions in power production.
  • Regular maintenance and testing : Regular maintenance and testing of the battery system also affects performance. If not properly maintained, the condition of the system can deteriorate over time.

In total, to maintain maximum performance of the solar battery system, it is necessary to pay attention to the above factors and perform periodic maintenance, inspection and monitoring of system operation.

By calculating the energy value of the solar power system, we can estimate the preliminary cost for the system, plan clear financial problems, and allow us to determine the area of ​​installation space.