We will experience some solar PV installations and technology while traveling, so I provide some more details about it below.
A few more terms that are important to know:
Recall that the rule of thumb is that the optimal tilt is "latitude tilt," and the ideal orientation in the Northern Hemisphere is due south (180º). This begs the question: what happens if the tilt and orientation are not optimal? The answer, as you might guess, is "it depends." This impact can be quantified by something that is called tilt and orientation factor (TOF). The tilt and orientation factor is a decimal that indicates what percent of the maximum solar output you would receive throughout the year at said tilt and orientation. So if you install an array and it has a TOF of 0.85, that means that it will only be able to output about 85% of the energy it would output if it were at the ideal tilt and orientation.
Wilmington, Delaware is at about 40º north. As it turns out, the ideal tilt is closer to 35º (rules of thumb are only rules of thumb, after all!). The tables below show the TOF at different tilts and azimuths. The first table illustrates the TOFs of different tilts, all with an orientation of 180º. The second table shows the TOFs at different azimuths, all at a tilt of 35º (the ideal tilt). (You can investigate the TOF for locations throughout the U.S. by going to the Solmetric website [3].)
Tilt (º) | Azimuth (º) | TOF |
---|---|---|
0 | 180 | 0.87 |
5 | 180 | 0.905 |
10 | 180 | 0.935 |
15 | 180 | 0.959 |
20 | 180 | 0.978 |
25 | 180 | 0.991 |
30 | 180 | 0.999 |
35 | 180 | 1.0 |
40 | 180 | 0.996 |
45 | 180 | 0.985 |
50 | 180 | 0.969 |
55 | 180 | 0.947 |
60 | 180 | 0.92 |
65 | 180 | 0.888 |
70 | 180 | 0.851 |
75 | 180 | 0.81 |
80 | 180 | 0.764 |
85 | 180 | 0.715 |
90 | 180 | 0.662 |
Tilt (º) | Azimuth (º) | TOF |
---|---|---|
35 | 90 | 0.797 |
35 | 100 | 0.833 |
35 | 110 | 0.897 |
35 | 120 | 0.898 |
35 | 130 | 0.926 |
35 | 140 | 0.951 |
35 | 150 | 0.972 |
35 | 160 | 0.986 |
35 | 170 | 0.996 |
35 | 180 | 1.0 |
35 | 190 | 0.997 |
35 | 200 | 0.989 |
35 | 210 | 0.976 |
35 | 220 | 0.956 |
35 | 230 | 0.932 |
35 | 240 | 0.905 |
35 | 250 | 0.874 |
35 | 260 | 0.839 |
35 | 270 | 0.803 |
Okay, now we're ready to calculate the solar output. There are a number of software programs and a formula or two that can do this, but the National Renewable Energy Laboratory (NREL) provides a free one that is well-regarded in the energy industry called PVWatts [4]. In the video below, I demonstrate how to calculate the annual output of the array in the images above, which has the following specs:
Hopefully, by now you have a relatively good grasp on some of the considerations that go into designing and calculating the output of solar PV. Solar PV really took off in the early- to mid-2000s, led by residential array installations, which generally had capacities of a few kW. The solar industry in the U.S. is not dominated by utility-scale solar, which is much cheaper per W to construct because of economies of scale. Utility-scale arrays can be thousands of watts (multiple MWs) in capacity!
Finally, there are a few ways that people can use and pay for solar PV:
Links
[1] http://www.pveducation.org/pvcdrom/properties-of-sunlight/motion-of-the-sun
[2] http://news.energysage.com/average-solar-panel-size-weight/
[3] http://www.solmetric.com/annualinsolation-us.html
[4] https://pvwatts.nrel.gov/
[5] http://www.seia.org/initiatives/community-solar
[6] http://www.nrel.gov/docs/fy15osti/63892.pdf