Mpfana Manu is a mechatronic engineer who's working in green energy electronics products.
Solar power is getting more popular by the day. Everyone is chasing it and the chase is worth it because the energy source is for free and it's clean. This demands more understanding about solar power and millions of bucks are being invested in photovoltaic technology and research experiments.
Here we're just going to explore the factors that affect photovoltaic system performance. Understanding how these factors affect the performance may help you become familiar with solar technology and also give you hints on how to handle your solar power system. These factors are listed below.
- Cell temperature
- Absorbed solar radiation
- Electrical load/resistance
Photovoltaic cells are the tiny wafers that make up a solar panel. There are several types of them but generally, they're all affected by the same factors. Now lets see how each of these factors affect a photovoltaic system.
This is the operating temperature of a photovoltaic cell. This might not seem like a big deal but it is huge. If your solar panel heats up, the efficiency of the photovoltaic cells drop significantly.
There's a term used by solar engineers which refers to how much a photovoltaic cell drops in efficiency as the cell temperature climbs. And the term is temperature coefficient.
Each type of photovoltaic cells has its own temperature coefficient depending on the material used to make the cell. Here's a table of the temperature coefficients of the most popular types of photovoltaic cells available.
|Type of photovoltaic cells||Temperature coefficient|
Monocrystalline silicon cells
Polycrystalline silicon cells
Amorphous silicon cells
Cadmium Telluride cells
Copper Indium Gallium Selenide cells
Temperatures can rise up to 70°C in the solar panel and there should be a way to dissipate all this heat. Most modern panels have in-built mechanical or thermal systems to get heat out of the panels. Some have coolant material at the back of the panel that will force a convectional heat transfer from the panel. But these mechanical or thermal means of dissipating heat become inefficient as the solar panel ages.
You might think that this heat comes directly from the sun but that's not the case. It comes from the photovoltaic cells themselves as they operate. When photons(sunlight) falls on the cell, not all the energy is converted into electricity. A huge deal of it is converted into heat energy which heats up the panel from the inside.
So how can you help your solar panel to cool down so that it can performs better and produce more electricity for you?
Here's what you can do.
This depends on the kind of solar panels that you have and the climate of where you live. If you live in a dry and hot land, and your photovoltaic system starts to deliver less electrical energy than what it was initially delivering ,perhaps in the morning, it would be very refreshing for the solar panels on your roof if you hose water them.
The water will drop the temperature and also remove dirt and dust that would end up blocking the light from getting to the photovoltaic cells in the panel. If your solar panel are those portable ones used to charge cellphones, you can just flap it around when it starts to boil up.
Heat dissipation naturally happens at night when temperatures drop. But if you live in hot areas where night temperatures are also high, then watering your panels would help them dissipate the heat off.
But if you live in a cool area with a rainy season, then nature will do the job for you. If your panels start to drop in performance, it wouldn't be the cell temperature causing the problem.
Absorbed solar radiation
This refers to the amount of photons that reach the photovoltaic cells. It is the sum of the beams, the diffuse and ground-reflected components of radiation. And it depends on three things. The air mass, the incident angle of the radiation on the panel and the intensity of the incident radiation.
There isn't much you can do about the air mass. That is totally environmental. The air mass accounts for the radiation that is caught up by air particles before reaching the photovoltaic cells.
The higher the air mass above the panels, the less radiation that reaches the cells. Air mass is greater in misty or smoky areas. If your solar power system is fixed, then you can't help your panels in this case. But if your solar power system is portable, you can help your panels perform better by mounting them where there's less smoke or less flying dust whenever possible.
The incident angle is the angle between the radiation and the normal of the solar panel. In this case, performance of the photovoltaic cells can be optimized by mounting the solar panels in a position where it is exposed to the sun from the time it dawns to the time it sets. This will insure a maximum incident angle of about 90° and a minimum of zero.
For instance, if your sun dawns from the east and sets in the west, and your solar panels are to be mounted on an inclined rooftop, it's best if they are inclined towards the north/south not east/west. All solar technicians are aware of this and that's why it's always a good idea to have a technician when installing solar panels. Even if you wish to install them yourself, at least consult a technician or follow a manual written by the technicians.
Then if your solar panels are to be mounted on top of a vehicle, perhaps an RV, it's best if they're mounted flat so that wherever the vehicle turns, the panels will not be shadowed(that is having an incident angle greater than 90°).
Intensity of the radiation
This one is straight forward. The more the intensity of the radiation, the greater the power output of the photovoltaic cells.
Photovoltaic cells perform the best during the day when the sun is overhead and perform the least at night when there's less light.
The performance of any solar power system is very dependent on the load it supplies. It should always be preferred to have a solar power system that delivers a maximum greater or equal to the possible maximum load at any time.
The load is the sum of all the electrical appliances the photovoltaic system supplies and the resistance of all the connecting wires.
If your solar power system is a grid-tied system, then the load will not be much of a big deal however your photovoltaic system performs. But when you have a stand-alone solar power system, the load is almost all that matters to judge how well your solar system performs.
The best wish for a stand-alone solar system is that it performs well enough to supply all the electrical appliances during the day and simultaneously charge the batteries with enough power to cater for the whole night.
It is therefore required to carry out an electrical power analysis in the initial stages of designing the system to see how much power the photovoltaic system is supposed to deliver. The main considerations of that power analysis should be as follows.
- What's the total electrical power required daily?
- What's the maximum electrical power required at any time?
- Is there any need for a backup system?
These considerations will result in making a more educated judgement in choosing the size of the photovoltaic system that will perform the best. It'll also help in deciding whether you need to install more solar panels or you need more batteries for your existing photovoltaic system.