Yash
Like any other system, a solar power system’s output decreases due to the losses in the system.
Therefore, to design the right configuration, you must consider all the losses in the system.
Solar energy experiences many conversions and losses in your solar power system before giving the final output.
Let us discuss all such losses in this post.
1. Conversion losses in the solar power system
Although, the solar power received by the panel is much more than the energy we get as an output to run the electrical appliances.
Most of the energy in the solar power system is either gets lost as the conversion loss within the components or as a transferred loss through wires.
Take a simple example, when you speak, its intensity is maximum near your mouth and it fades away as the distance increases.
Similarly, when you throw a stone in the still water, the intensity of the ripples decreases with the increase in the circumference.
Both are examples of transfer loss with the increase in distance.
Can you convert all the chemical energy stored in the batteries of the car into mechanical energy?
or
Is it possible to convert all the mechanical energy of wind into electrical energy?
The answer is simply NO, you cannot convert an equal amount of one form into an equal amount of the other form. These are examples of conversion loss.
No system is fully efficient, that is it can convert a certain percentage of the input energy into usable energy and the remaining energy is lost in the surroundings.
We all know that the basic solar power system consists of the following components:
- The solar panels
- Charge controller
- Inverter and
- The solar batteries
The energy from the solar panels reaches the load and then to the batteries through the charge controller and then to the inverter.
It suffers attenuation in each process, whenever it passes through each component. We are going to discuss the effect on the energy when it passes through the above components.
a. Conversion losses in solar panels
The basic function of the solar panel is to convert the sunlight into DC electrical energy Not all the sunlight falling on the panels is converted into the DC electrical energy, some fraction of it is either reflected back or gets dissipated as heat into the surroundings.
In noontime and the clear sky, a solar panel of 1 m², lying flat on the earth’s surface receives around 1,000 watts of solar power.
It is able to convert a small percentage, say 18%, efficiency of solar panels, of the solar power into electrical power.
The remaining 82% of the energy is either reflected back or dissipated as heat into the surroundings.
This, I call the conversion loss of energy.
You can see that out of 1000 Watts of solar energy only 18% that is 180 watts gets converted into DC electrical energy.
The solar charge controller protects the battery from getting overcharged.
b. Batteries do experience conversion losses
When you are not using energy from the solar panels to run your electrical appliances, the energy gets stored in the solar batteries in the form of chemical energy which later on can be utilized to run the appliances, when there is no sunlight or during the night.
The battery provides energy by converting the stored chemical energy into DC electrical energy and there occurs a loss in this conversion.
If your battery is 85% efficient then it will convert 85% of its stored chemical energy into DC electrical energy.
c. DC to AC conversion by the Inverter
The energy after getting converted into DC electrical energy by the solar panels is passed through the inverter.
The basic function of the inverter is to convert DC electrical energy into AC electrical energy. This is a conversion of energy from one form into the other.
Suppose your inverter is 95% efficient, which means that it is able to convert 95% of the input DC electrical energy into AC electrical energy.
It will convert those 180 watts of DC electrical energy into 95% of 180 or 171 watts of AC electrical energy.
Those 9 watts are lost as conversion loss into the system.
2. Transfer losses in the solar power system
The energy that we receive as the output and which runs our electrical appliances needs a medium to travel from one point to the other point and this medium is provided through wires.
The different components of the solar power system are connected through copper wires. When the energy travels through a wire, some of it gets lost as heat into the surroundings.
The longer is the distance between the solar panel and your electrical appliance, the more is the wastage of energy as heat.
Therefore, one should try to keep minimum or optimum distance and the right sizing of the wires between the various components and the electrical load.
If I say that the wire losses are 1% of the DC electrical energy that is 1% of 180 watts or 1.8 watts are lost as heat.
I can summarize the above explanation in two lines:
There is conversion loss within the components and the transfer loss, through the wire running between the components.
3. Environmental losses in the solar power system
a) Shading loss
When your solar panels are placed under shade, they get less sunlight and in turn, they produce less current.
Try to install your panels with no nearby high structure or tree, I am calling it an obstacle.
Because at one point in a day, the obstacle comes in between the sun and the panel in such a way that its shadow covers a portion of the panels and block the sunlight.
b) Losses due to temperature rise
When I was new to this technology, I use to think like many others that the panel efficiency increases with the rise in temperature.
Oh! I was wrong.
On the contrary, its efficiency decreases with the increase in temperature.
If you got to see the backside of the panel, you can see the temperature coefficient as one of the characteristics written over there.
Let us assume that you have 200 watts of solar panel and its temperature coefficient which is written at the backside is -0.4%/°C.
It means that your panel will lose 0.4% of 200 watts for every degree rise in the temperature from the tested temperature of 25 degrees.
Let us say that the panel surface temperature is 60 degrees.
It means that the panel will lose 0.4% x (60 -25)
= 0.4% x 35
= 14%
14% of 200 watts or 28 watts at this temperature.
In other words,
you will get 200 – 28 = 172 watts for running your appliances.
c) The dirt loss in the system
The moving air takes away dirt from the ground and leaves it over your panels. These dust particles form the thin layer on the panels, preventing the sunlight from striking their surface.
If you clean dust more often from the panels. I can bet that you live in a high airspeed place.
The one very good advantage of living in a high wind speed region is that it keeps your panels cool which helps them to produce more current.
If you have the disadvantage of dirt accumulating on the surface then on another side the high airspeed keeps your panel cool.
You know the sides of the same coin.
Can you find the average wind speed in your area?
d) Design losses in the solar power system
The panels perform to their maximum when the sunlight is falling perpendicular to their surface.
But the sun rays cannot be every time normal to the surface because the earth and the sun are always in relative motion.
Also, we cannot always keep on changing the tilt of the panel in order to make sunlight fall normal to it.
Yes, we have solar trackers which keep on moving the panels from east to west in line with the sun’s motion to get the maximum sunlight.
But the solar trackers are costly if we are considering a small solar power system.
Therefore, it is good to find the most optimum tilt where you can fix the panels and get the maximum sunlight in the day.
The tilt and the orientation depending on the location of the region where you are living.
The right angle of the panels gives you a maximum current than any other.
e) Age of the system
Just like we work less as we grow old, our solar panels also degrade with time and produce less current.
In general, the output of the solar panels reduces to 80% of their rated power in the 25th year.
Assuming the life of the panel as 25 years.
For example, a solar panel of 200 watts will produce 80% of 200 = 160 watts in the 25th year from now due to degradation (reversible and irreversible degradation) with time.
Or in other words, 40 watts are lost with time.
So, on average, we are losing 40 watts / 25 years = 1.6 watts per year.
Conclusion
I can summarize the above explanation in two lines:
There is conversion loss within the components, the transfer loss through the wire running between the components, design losses, losses due to the age of the system, and the environmental losses
The sum of the input energy and the sum of the output energy remains the same; it is using energy that gets reduced with every conversion and while transferring from one component to the other.
Solar energy = AC electrical energy (usable energy) + conversion loss + Heat loss + energy reflected back to the surroundings + System degradation with time + Environment losses
If you closely notice, then you can find that the major conversion loss occurs at the first stage when solar panel converts solar energy into DC electrical energy.
Therefore, it is very important to include these losses and then calculate the overall efficiency of the system.
An example in the last
Okay let’s do it here
I have the following losses and efficiencies values of the solar power system with me:
- Panel efficiency: 18%
- Inverter efficiency: 95%
- Transmission efficiency: 98%
- Temperature derating factor: 0.95
- Dirt de-rating factor: 0.95
- Shade de-rating factor: 0.95
- Age de-rating factor: 0.99
Now, let’s calculate the overall efficiency of the system:
Simply, multiply all these parameters together, you get the efficiency of the complete system.
It is 14.2%
It means that you are able to utilize only 14.2% of the sunlight to run your electrical appliances.
In addition, this discounted efficiency gives you a real picture of the financial feasibility of the system.
Don’t worry guys!
Even with this efficiency, the residential solar power systems are financially rewarding and help in reducing the carbon content from the environment.
