Location is Everything

I had a conversation the other day with a friend who also lives with a renewable energy system. She is using her system to provide construction power while she builds her new home. At the moment the system is set up in a shed with the PV panels on portable racks so she can move them out of the way if she needs to.

She had been having trouble keeping her batteries fully charged last fall and asked me to check the system out. Her panels had always just barely kept her batteries full and sometimes after a cloudy stretch had trouble getting the batteries back to a full charge. But now, it seemed, they weren't producing the same power and her batteries were extremely low.

When I checked out her system I found that during the construction activity a wire from one of her panels had come loose. It turned out that she was getting a charge from only half her panels.

With the wire fixed her panels returned to producing the same amount of power they had before. But it was still just barely adequate. I had suggested that she might want more panels but she decided to wait until the house was finished to upgrade the system.

I didn't think much more about it until I stopped by to visit the other day. I asked her how her system was working and she told me she had discovered something amazing. She had just moved her panels a few days before to a spot about 20 feet east and 5 feet higher than they had been. Within a day of doing this she noticed she was getting much more power into her system.

"It's amazing!" she said, "My batteries are full up and working beautifully!"

By moving her system she had taken it out from under the shadow edge of a large tree to the west. In their original position the panels had begun to get shade around mid- afternoon. A PV panel will be adversely affected if even a part of it is in shade. By moving them further from the tree she increased the amount of time the panels received full sun. She added at least an hour of additional power production to her system and noticed the difference right away.

This little story illustrates perfectly the three things you need to make your renewable energy system work at its best. Location, location, location. This is true for all of the different ways of charging your system, PV panels, wind generators and small hydro power systems. Wind generators must be placed in an area free of trees and buildings that can block the wind. Small hydro generators must be placed where they get the most water at the highest possible pressure for maximum power production.

Because of the way they are constructed, PV panels must be placed where they will get little, or (ideally) no shade at any time during the day. Here's how solar panels work. The typical PV panel consists of 36 individual silicon wafer cells each of which produces 1/2 volt when exposed to the sun. When wired together inside the panel in series (the positive lead of one cell connected to the negative lead of the next cell), the entire panel will produce in the neighborhood of 18 volts.

As long as the panel is exposed to the sun it will produce its full voltage. But remember back to our discussion of electricity? Voltage is pressure, and if the voltage drops in even a part of the panel the rest of the panel will try to compensate for it. Whenever an individual solar cell in a panel is shaded it stops producing voltage. This drops the power output of the entire panel and the charge to the batteries drops off.

This is what happened to my friend. By mid-afternoon the shadow of the tree would cover the edge of the panels. Even though the majority of the panels were in sun, the shaded portion degraded the power output enough that it reduced the output of the panels. She didn't realize what she was missing until she happened to move the panels.

This illustrates very well the importance of proper location of your PV panels. Putting your panels in the optimum location is literally found money. Increasing the amount of sun by just an hour a day will mean you don't have to buy as many panels to get the same amount of power. At around $450-$550 per panel that can make a significant difference in your initial outlay.

All Contents © 1997
Wagonmaker Press
Thomas W. Elliot


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