Most of us think that the solar panel produces more current when the temperature soars.
But it is the opposite, the performance of the solar panel deteriorates with the increase in the temperature beyond 25 °C.
25 °C is not the ambient temperature, it is a cell temperature.
The cell temperature is always higher than the ambient temperature and the difference can be as high as 30 °C to 40 °C.
Let me make you understand the science behind this.
Assuming, you are sitting inside the car with all windows closed and your friend is standing outside beside your car.
The air temperature (surrounding temperature) is 30 °C. It is okay with your friend but you will feel more heat.
Because the glass of the windows traps the sunlight, leading to an increase in the temperature.
A similar phenomenon happens with the solar cells that are enclosed behind the glass coating.
In addition to this trapping effect, when sunlight falls on the solar cells, they produce electric current
The flow of electric current produces heat.
This dual phenomenon increases the overall resistance and now the solar cell produces less current and you get less power to run your electrical appliances.
Read: Solar Panel Specifications Explained: A Complete Guide
The Temperature Coefficient of Power
Now it is clear that the temperature increase harms the performance of any solar panel, and the profitability reduces.
The different panels lose different values of power with the increase in the cell temperature.
The amount of power any solar panel will lose is found by the Temperature Coefficient of Power.
It is in %/°C, and you will find the negative values of the Temperature coefficient of power.
Assuming, a solar panel with a P(max) of 400 watts is having a temperature coefficient of -0.4%/°C,
it means that it will lose 0.4% of 400 watts with every degree rise in the temperature beyond 25 °C.
The negative sign indicates a loss.
It can be calculated using the following formula:
Assuming the cell temperature of 45 °C
The power Loss = (45°C - 25°C) x -0.4%/°C
= 20 °C x -0.4 %/°C
The 400-watt solar panel will lose 8% of its P(max) when its cell temperature is 45°C.
The absolute loss in watts = 8% of 400 watts = 32 watts
The more is the value of these metrics, the more power your panel is going to lose.
People living in a hot climate and planning for the solar power installation, it is better to go for the solar panels having a low
Temperature coefficient of Power.
Read my post, ‘The best solar panels for home-owners living in the hot climate’.
You will get an idea about this.
The Power Loss
Okay, coming back to the point how much impact can the temperature coefficient of power have on the profitability of any solar power system.
You will find solar panels in the market having temperature coefficients of power are in the range of -0.26 %/°C to -0.5%/°C.
Assuming you live in a place where the average ambient temperature is 30 °C, it means that the solar cells might be performing at around 50 °C.
The power loss (%) when the cell temperature is 50 °C:
= (50 °C – 25 °C) * 0.26 to (50 °C – 25 °C) * 0.50
= - 6.5% to - 12.5%
The solar panel is going to lose in the range of 6.5% (when Temp Coefficient Power is -0.26 %/°C) to 12.5% (when it is -0.5%/°C)
How this loss is going to impact your Solar Savings?
Units produced when the cell temperature is 25°C
Assuming a standard 5 kW system is installed in a good sunlight region.
This system will produce around 22 units per day when its solar cells are performing at 25 °C, totaling around 2,00,000 units in its life time of 25 years.
Units produced in real conditions
We hardly see ideal conditions in real life. They are used to make a comparison or taken as a reference.
In real-world, the solar cells are performing at a much higher temperature than 25 °C
Assuming the cells are at 50 °C
In that case, the system will produce around 20 units per day when its temperature coefficient of power is -0.26%/°C, producing around 1,82,500 units in its lifetime.
Units lost = 2,00,000 – 1,82,250 = 17,500 units
18 units per day when it is -0.5 %/°C, a total of 1,64,250 in 25 years.
Units lost = 2,00,000 – 1,64,250 = 35,750 units
We can find the monetary value of the units lost if we know the grid rate where the system is installed.
For example, the average grid rate for residential electricity in the USA is 13 cents per unit.
In that case, my monetary value of the units lost would be:
17,500 x 13 cents to 35750 x 13 cents
Monetary Loss = $ 2275 to $ 4647
A 5-kW solar power system would lose $ 2275 to $ 4647 in its lifetime when its temperature coefficient of power is in the range of -0.26 %/°C to -0.5%/°C.
Similarly, the monetary loss of the 5-kW solar power system in India is:
The average grid rate is Rs. 6 per unit.
The loss would be Rs. 1,05,000 to Rs. 2,14,500
Monetary Loss due to Grid Escalation
I have assumed that the electricity rate would remain the same for the next 25 years.
Are you sure that the grid prices will remain the same in the future?
Look at the last ten years’ trend, the prices are increasing and, the same is most likely to happen in the future also.
In short, this monetary loss calculated above is not correct.
I have missed one thing that is the escalation in the grid prices.
Monetary loss with the escalation:
The average increase in the electricity cost in India is 8% per year.
It is around 3% in the USA.
When I consider these escalations, the monetary loss becomes significant. It is $ 3300 to $ 6700 for the USA
The monetary loss in India in 25 years after considering escalation is Rs. 3,00,000 to Rs. 6,25,000
Now you can see that it is a considerable amount of loss of your
When I see the monetary loss in the solar panels with -0.5 %/°C of temperature coefficient of power, this loss is almost double when you are using panels with -0.26 %/°C temp coefficient of power.
Price Benefit Analysis
The solar panels with a low temperature of power are indeed costlier, when you see the considerable amount of savings they can do in the future, they are worth buy.
It is recommended for people living in a tropical climate where the average temperature is around 30 °C.
Design and find the return of your solar power system, try Solar Feasibility Spreadsheet.