As a general rule solar panels work best in full sunshine when there is maximum insolation, which is the amount of solar radiation hitting a horizontal surface. Standard practice is to assume 1000 watts per square meter when estimating the output of a solar panel, but this depends on several other factors.
Rule of thumb based on insolation conditions in U.S.A. tells us that a typical store-bought solar panel exposed to the standard 1,000 W/m2 sunlight will generate about 200 watts during peak sunshine periods. However, the average power produced over the year is about 38 W/m2, due to cloud cover, low insolation and night time.
Where Do Solar Panels Work Best?
Solar Panel Insolation And Orientation For the Best Output
Insolation is fixed for the area you live in, so if you intend to mount solar panels in a fixed location, such as your house roof, the best you can do is to point them towards South as much as possible at an angle of 60%.
It’s the best way to harvest the sun’s rays without spending money on a moving system which tracks the sun’s movement.
Do solar panels work without sun? Not too well!
Unfortunately, the sun doesn’t shine too much at the times of day that we need the most power. The chart below shows a very rough guide to generation and consumption of a fixed solar panel installation over 24 hours.
Power Generated %
Power Consumed % Rate
Seasonal Variations In insolation And Panel Output
The chart below shows irradiation over the year, month by month, for London, UK. OK, it isn’t the sunniest place in the world, but it gives you the general idea that in most places there is a huge difference between solar panel output between Summer and Winter. In this case, summer output is 6 to 7 times that of Winter.
Solar panel output vs time of day
What Time Of Day Do Solar Panels Work Best?
From the 24 hour Power Consumption Chart we can see that the watts fall off rapidly either side of the peak hours around midday. This is because the orientation, or the angle at which the sun’s rays hit the solar panels, becomes more oblique.
The solar panels are mounted in the best possible position, which is at an angle of 60 degrees facing South, but the movement of the sun changes the angle as it moves across the sky. This is the best you can do for a fixed solar array.
How many hours a day do solar panels work?
The graph below shows the power generation for solar panels mounted on a moving pedestal which automatically tracks the sun across the sky, thereby maintaining the best possible orientation between the sun’s rays and the surface of the solar cells.
The best dual-tracking systems improve power generation by up to 80% in locations with high insolation levels throughout the day. However, solar panel tracking systems are expensive and may not be worthwhile for smaller installations.
5 Main Factors Affecting Solar Panel Efficiency
Solar Panel Temperature
Solar cells are generally rated at 25 degrees C, but in high summer in the middle of the day the temperature can easily reach 50 degrees C. For each degree over 25 solar cell efficiency reduces by 0.5%, so it isn’t negligible.
It’s important to mount rigid solar panels with a space between the frames and the roof, so that air can circulate freely. Normally overheating isn’t an issue, but can be a factor at midday in high summer in some locations.
Many RV enthusiasts often glue flexible solar panels to the roof of their camper vans, with no space for air to pass underneath. In the hottest times of the year the output would be severely reduced because of high temperatures.
Maintenance Helps Best Results
Clean solar panels give their best performance when they are new, but do they need to be cleaned?
Experiments have shown that domestic solar panel installations in ordinary environmental conditions lose around 2.5% of their power output due to to dust collecting on the panel surfaces. In a large installation this can be a significant amount of power.
Shading – do solar panels work in cloudy weather?
Partial shading from passing clouds or overgrown trees reduces power output. Obviously, solar panels work best when the sun’s rays are not blocked. Commercial installations have electronic circuitry fitted to minimize the power loss due to partial shading.
The prudent home-owner should clean the glass surface of the panel frames 3 or 4 times a year to ensure optimum performance.
Solar panel quality affects output
Modern solar panels supplied by a reputable manufacturer have a working life-time of 25 years. It’s important to check the guarantees before purchase or DIY installation.
Solar panels give their best output during their 25 year working life, but that’s not to say that they suddenly stop working! The output slowly reduces and the manufacturer’s technical specs should tell you by how much over how many years.
Manufacturing quality is also a factor in determining how well solar panels stand up to the elements. Materials used should be robust, corrosion resistant and strong enough to resist wind forces.
Solar panel Orientation – What’s the best angle?
Monocrystalline Vs Polycrystalline Solar Panels
The type of solar panels chosen for a particular job depend on factors such as space limitations, budget, portability and power requirements.
Most larger domestic installations use monocrystalline solar cell panels as these are the most efficient at 20% conversion of sunlight into electricity. They can also be found on flexible form, which give comparable outputs and are much light. Flexible solar panels are best for mobile situations and for fixing over irregular surfaces.
Polycrystalline solar panels are best for DIY installations on a budget, as they are less expensive. The difference between cost is reducing all the time, and also the difference in efficiencies. Generally, polycrystalline panels are about 15% efficient.
What time of day do solar panels work best?
In any location, 4 or 5 hours around mid-day is always the best time for maximum solar panel output. Tests show that panels still work while there is daylight but towards evening and in the early morning the output is greatly reduced.
What angle is best for solar panels?
The best angle for mounting solar panels of any type is 60 degrees with the panel array facing perpendicular to the sun’s arc across the sky. For fixed locations this is not always possible and is often a compromise. Larger systems may benefit from a movable solar panel array with automatic tracking.
What type of solar panels are most efficient?
Monocrystalline solar panels are the most efficient at up to 20% conversion of sunlight into usable electric power. The efficiency of polycrystalline solar panels currently stands at 15%,due to the manufacturing process used to produce them.