P/V CAPABILITY

We have at most 640 watt of solar generating power.

No.Watt
1-120
2- 80
1- 50
18- 15
8- 5

Solar tracking, the closer you manage to track the actual solar path across the sky, the more your panels are on “maximum” collection. Example, Yuma, AZ, is at 32.6 degrees N.

Only on the equinoxes does the sun rise “directly” east, and set “directly” west. Otherwise, rising/setting is (i.e. summer/winter solstice) either north or south of east/west, respectively. To maximize tracking, think that the primary axis for east/west rotation is tilted up toward the equator the latitude of the location. Then, on that axis, the panel can independently be adjusted up and down 23.5 degrees from parallel to the rotation axis.

To obtain a chart of the solar path in your area, see the University of Oregon website:

With the chart for your area you can estimate, for any time of the year, the true bearing where the sun will rise & set, the true bearing and altitude angle of the sun, how long in any given position your panels would receive useful power, etc.

A website to work right triangles is at:

Even with the greater amount of atmosphere due to the low angle, at 10 degrees above the horizon, there may be available up to 50% of the total solar power. If your panels are two feet wide, to not shade each other on the E/W axis when tilted to only 10 degrees up from the horizon, they must be spaced apart nearly twelve feet. If you limit your morning/evening aim to 30 degrees above the horizon the panels need to be spaced only four feet apart. Depending upon factors such as your latitude, time of the year, and physical barriers, the difference between ten and thirty degrees may be a lot of solar sky-time missed. Our limited number of panels may then best be arranged that they are all on the same North/South line. Remember that if a solar panel is partially shaded, most lose a significant portion of their power generating capability, well beyond the percent of the panel shaded.

Summer Solstice Equinox Winter Solstice

Start-Stop = Hours

100548-1812 = 12:24 : 0650-1710 = 10:20 : 0800-1600 = 08:00

150612-1748 = 11:36 : 0711-1649 = 09:38 : 0825-1535 = 07:10

200633-1727 = 10:54 : 0736-1624 = 08:48 : 0906-1454 = 05:48

250702-1458 = 09:56 : 0800-1600 = 08:00 : 0949-1411 = 04:22

300724-1634 = 09:12 : 0827-1533 = 07:36 : 1035-1325 = 02:50

For discussion purposes, I am not including losses in efficiency of components, therefore if we track to within 30 degrees vs 10 degrees, then:

- Summer solstice - we would be getting 9 hours and 10 minutes of useful power, vs 12 hours and 24 minutes if we track as far over as 10 degrees above the horizon. (5.86 KWH vs 7.93 KWH for a 26.0% loss)

- Equinox's - we would be getting only 6 hours and 6 minutes of useful power, vs 10 hours and 20 minutes of useful power if we track as far over as 10 degress above the horizon. (3.90 KWH vs 6.13 KWH for a 40.9% loss)

- Winter solstice - we would be getting only 2 hours and 50 minutes of useful power, vs 8 hours of useful power if we track as far over as 10 degress above the horizon. (1.81 KWH vs 6.12 KWY for a 64.5% loss)

YUMA CHART

If you do NOT track at all, a key selection is the angle of the panels. Are you going to align for maximum noontime collection for summer, winter, or the equinoxes? If you align for the noon equinoxes, noon at the summer and winter solstices will be off by 23.5 degrees (only receiving 92% of potential power). While someone with better math skills could calculate accurately, at a ballpark during the solstices when the sun is around 35 degrees east or west of the panel, you are only getting 50% or so of the available power. A significant aspect for the summer solstice is that the sun rises and sets North of an East/West line. Checking the Yuma Chart, optimistically it appears that the fixed panel would not even "see" the sun at due east until around 0840, and the sun would pass north of the panel at around 1520. (6 hours and 40 minutes exposure) During the summer solstice, due to the longer path of the sun across the sky, you are on "best" power only from about 11:30 AM to 12:30 PM.

During the winter solstice you are on "best" power from around 10:00 AM to 2:00 PM.

BATTERY DISCUSSION

Call our highest solar collection day 8.00 KWH. Using 12 volt batteries, it is almost 700 ampere/hours. To preserve battery life, a "rule of thumb" is do NOT discharge it below 80% of full charge capacity. If the summertime full input from the sun of 700 ampere/hours representing 20% of battery capacity is used each night, then total battery storage capacity of around 3,500 ampere/hours is required.

Call our shortest collection day 1.8 KWH. Our winter daily electrical demands must be kept to this level or lower.

Merely as an example, Sam's Club has golf cart batteries rated at 210 ampere/hours ($70.00 each). To store full summer generation we would need 18 of these batteries. ($1,260). If the full 8 KWH is not used each night, still more batteries are required.

640 watt at 12 volt means around a 60 ampere charge controller. Batteries need to be kept in a cool & dry place. Temperatures above 77 degrees F can cut battery life by 50%.

At this writing, the additional solar path charts applicable to us are Tucson & Willcox, presented below.

TUCSON CHART

WILLCOX CHART