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Solar tracking is not worth it for domestic installations under 6kW, but a cost analysis of each installation is needed to determine the system payback period. It makes more sense to simply add more solar panels for extra power – it would be cheaper than a tracking system.
Sadly, solar panels are inherently inefficient. The most efficient are the monocrystalline type, which can reach 21% efficiency.
This means that for every 1000 watts of the sun’s energy falling onto a solar panel, only 210 watts of electricity is produced.
The Holy Grail of PV electric production is to improve solar panel output and there are several ways of achieving this, some better than others.
There are two types of solar tracking, single axis which tracks the sun’s horizontal movement across the sky and dual axis, which tracks both horizontal and vertical movement.
- When do solar panels work best?
- How To Find Out If Solar Tracking Is Worth It Or Not
- Fixed Solar Panels Vs Sun Tracker Cost Analysis Calculation
- Install a residential solar tracker or add more solar panels?
The vast majority of domestic and large-scale solar PV farms consist of arrays of big solar panels fastened to a frame and fixed in place on a roof or other angled structure.
The amount of sunshine falling on solar panels varies according to the season and also throughout any day in that season.
Not only does the horizontal position in the sky change but also the vertical. The angle of incidence determines the efficiency and a solar panel’s maximum output happens when its surface is at 90 degrees to the sun.
When do solar panels work best?
- irradiance – the power in watts falling on a surface at any instant in time
- insolation – the power falling on a surface over time (determines energy produced in kWh)
- temperature – solar panels most efficient at 77 degrees F (26 degrees C)
- orientation – direction pointing – due South for Northern hemisphere, due North for Southern
- tilt angle – location latitude +15 degrees in Winter and -15 degrees in Summer
Chart showing the effect of solar panel tilt angle on solar panel power output in USA:
Tilt angle in degrees
Percentage increase in production - Southern USA
Percentage increase in production - Northern USA
Assume 100 comparison only
108 - 8% increase
109 - 9% increase
113 - 13% increase
115 - 15% increase
115 - 14% increase
118 - 18% increase
114 - 14% increase
117 - 17% increase
110 - 10% increase
116 - 16% increase
We can’t do much about irradiance or insolation, except to keep the panels clean and make sure that they are not shaded.
Temperature is a definite enemy as power output falls by between 0.3% and 0.5%. Standard panel specifications given by manufacturers state a panel rating in watts based on a temperature of 25 degrees C. Unfortunately, panel surface temperatures can easily reach 65 degrees C in summer.
Orientation and tilt angle are definitely things we can adjust and some owners of fixed arrays adjust them en masse between seasons so the tilt angle is optimum. What about orientation? Does geographic direction affect output much?
Back-Yard Tests To Measure Fixed Solar Panel Production Compared To Tracked
I might seem a stupid question, but why should the angle at which the sun’s rays hit the surface of a solar panel affect its output so much?
The answer lies not in the chemistry of the crystals forming the solar cells but in simple geometry and physics of radiated energy. If the solar panel surface is tilted, then the area covered by the same energy is larger, so energy intensity is less because it is spread out.
When a solar panel is mounted perpendicular to the sun’s rays, we can say for example that 1000 watts of energy is falling on 1 square meter of the surface. When at an angle, the same 1000 watts will be activating solar cells over a much greater area, but at a lesser intensity.
How To Find Out If Solar Tracking Is Worth It Or Not
Once we know some variables then we can apply a simple formula to analyse cost vs payback. We need to know:
- The installation cost of an auto-tracking system
- Total annual energy generated by a fixed solar panel array
- Total annual energy generated by solar panel array using auto-tracking
- The cost per unit (kWh) of electricity in the locality
We can then calculate how many years it will take to pay back the installation costs. It’s then a personal choice if it’s worth while.
Step 1. Auto-tracking installation costs
On average, an auto-tracking system costs about 30% of the installation cost of the fixed solar panel array, which comes in at approximately $3 per watt.
The average domestic solar system in the US is 5kW = installation cost of $15000.
Auto-tracking system installation cost = $5000 ($5000 represents a lot of electricity!)
Step 2. Annual energy generated by 5kW fixed solar panel array
For this step we need to choose a location, so we can use a real irradiance value for calculating energy. The location chosen is South Bend, Indiana.
Using the site GlobalSolarAtlas and entering South Bend we see the annual Normal Direct Irradiation value is 1422 kWh/m2. Another way of expressing this value is as 1422 peak-sun-hours.
Multiplying 1422 x solar panel power will give us the annual energy production in kWh:
- 1422 x 5kW = 7110 kilowatt-hours (the average US home usage is actually over 10000 kWh)
Step 3. Annual energy generated by 5kW solar panel auto-tracker
Although gains of 65% have been claimed by some systems, this is likely quite rare, depending heavily on the location. It’s safest to assume a conservative estimate of about 30% improvement over a fixed panel array.
- Auto-tracker energy generated = 7110 kWh + (7110 kWh x 30/100) = 9243 kWh
The auto-tracking system will generate 2133 kWh more than the fixed.
Step 4. The cost of electricity per kilowatt hour
In Indiana the cost of electricity 10.53¢/kWh.
Fixed Solar Panels Vs Sun Tracker Cost Analysis Calculation
Case study: A 5 kW solar panel system in South Bend, Indiana
- Installation cost $15000 (-30% after government/state relief) = $10000
- Energy generated (saved) 7110 kWh = $748.68/annum
- Payback period = 10000kWh/$748 = 13.5 years
- Solar array + tracker Installation cost $20000 (-30% after government/state relief) = $14000
- Energy generated (saved) 9243 kWh = $973/annum
- Payback period = 14000kWh/$973 = 14.4 years
In our case study above the payback period is only slightly longer, so after this time the annual savings will be greater. The above calculation doesn’t take into account additional maintenance costs of the realistic life of the sun-tracker mechanism, which obviously has moving parts that wear out and need replacing.
The active life of the solar panel array will also be shorter due to the extra heat brought by the more focused irradiation. Each extra degree not only reduces solar cell output but also the effective life of the crystals. However, the effect is minor.
Install a residential solar tracker or add more solar panels?
Out of the total installation cost of about $3/watt, equipment purchase cost is $1.70. The actual cost of a solar panel per watt is falling every year until in most places in 2021 it’s less than $1/watt.
For many homeowners, it isn’t worth the hassle of installing a complex piece of equipment like a sun-tracker when they could simple add a few solar panels to get the same impact, particularly if they only have limited roof space for mounting.
The sun-tracker in our case study saved 2133 kWh/annum. The solar panel power needed to replace this gain in output would be the energy saving divided by the annual peak-sun-hours:
- 2133 / 1422 peak-sun-hours = 1.5kW
For perhaps $4000 an extra 1.5 kW of solar panels could be connected to give the same effect, with a longer life and less maintenance.
The diagram below shows the difference between dual-axis sun tracking and fixed solar panels over 24 hours. The array power is 100 kw, so considerably larger than the normal domestic system. In the case of large systems the savings are very worth while.
How much more efficient is solar tracking?
What is the solar panel temperature coefficient?
Solar panels are at their most efficient at a temperature of 77 degrees F (25 degrees C). For every degree C over that value the efficiency falls by a percentage between 0.3% and 0.5% on average. This percentage is known as the Panel Temperature Coefficient.
How can I increase my solar panel output?
PWM or MPPT regulator? Always use an MPPT solar controller – they are up to 30% more efficient than PWM type. Regular maintenance and cleaning helps maintain solar panel output. Ensure the solar panel array is in direct sunlight with no shading. Solar reflectors can help to boost output but care must be taken that the panels don’t overheat, which will reduce output.
Which solar panels are best poly or mono?
Monocrystalline solar panels are more efficient than polycrystalline, but they are also more expensive. However, the relative costs and efficiencies are moving closer and there is not a lot of difference.
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