Thursday, May 5, 2016

Solar Power: Part 7-Panels

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Solar panels make up the backbone of the solar charging system; they provide the energy that is delivered through the solar controller into the batteries. Solar technology is changing quickly. At the current time, there are three types of solar panels that fit the basic system ($3500-5000) we discussed in the first article of this series. The three types are monocrystalline, polycrystalline, and thin-film. Each as advantages and disadvantages.

Monocrystalline panels are made from crystals of silicon and have a characteristic uniform color. The individual cells are not square because of the growth form of the crystals; the cutting process of the crystal produces angled or rounded edges. Because the silicon is grown as a crystal, the efficiency is higher; however so is the cost. They are also the most space efficient and have the longest life. Monocystalline panels suffer more when partially shaded. However, new technology has partially solved this problem with the addition of diodes that allow the un-shaded portion of the panel to continue to produce energy.

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Monocrystalline panels will be more expensive than polycrystalline. Polycrystalline panels have uneven coloring and square cells because of the manufacturing process which consist of poured silicon, not crystals. They will be less expensive than the monocrystalline panels but also slightly less efficient. Because of this loss in efficient, polycrystalline panels of similar wattage will be larger than monocrystalline panels. Polycrystalline also have slightly lower heat tolerance but this is typically not a problem for most tiny home homeowners. If mounted on a black roof, the panels would suffer because of the increased heat.

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The third type is thin-film panels. These are the flexible panels. The manufacturing process consist of depositing multiple thin layers of photovoltaic material. There are multiple types of photovoltaic material but I will not detail these types. The reader is encouraged to research the different types if they desire this detailed knowledge. The primary advantage of thin-film panels is flexibility. If you have a bus tiny house and you want to contour the panels to the bus roof, thin-film would fit this application. However, thin-film have the lowest efficiency of the three types; panels of similar wattage to mono or polycrystalline will be larger. However, they are cheaper to manufacture and many times cheaper to purchase. They are also less sensitive to shading than mono or polycrystalline panels.

Solar panels are rated in watts. Panels with higher wattage will be larger. When choosing the panels, it is important to choose panels that will fit the space available. If you will be mounting the panels on an independent frame, then size will be less of an issue. Typically, higher wattage panels have a lower cost per watt than lower wattage panels.

Multiple panels can be combined in series to increase the wattage. For example, four 12V-100 watt panels combined in series will provide 400 watts of power at 12V. Remember to not exceed the capacity of your solar controller. A set of panels of 400 watts is feeding at least 33 amps of energy to the controller when in full sun (400 watts/12V=33.33 amps). However, panels will typically generate greater than their stamped efficiency in full sun so it is important to not overpower your controller. Controllers were discussed in part 6 of this series. A 40 amp controller will accept 40 amps (480 watts at 12V); 40 amps of solar panels could generate much more than 40 amps on a bright sunshiny day. This is the reason I am only using four 100 watt panels rated at 33.33 amps.

The next installment of this series will cover wiring. Wiring connects the batteries together; connects the inverter to the batteries, connects the panels to the solar controller and connects the solar controller to the batteries.

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