Solar Power: Part 7-Panels

Image from amazon.com website

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.

Image from amazon.com website

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.

Image from amazon.com

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.

Solar Power: Part 6-Solar charge controller

The purpose of a solar charge controller is to regulate the current from the solar panels so that you do not damage the batteries. There are many descriptions of charge controller types and their function; I will not attempt to describe them in this article but I will refer you to this article. Why reinvent the wheel when it has been done well by others with greater knowledge.

However, what is not covered well in most other articles is how to choose the proper size charge controller. It is important to match the controller to the output of your solar panels. Getting a charge controller larger than your needs will not cause any damage but choosing a charge controller of insufficient capacity could cause a fire by overheating the controller.

Of the two basic types of charge controllers (PWT and MPPT), I much prefer the MPPT because of better charge regulation and because more of the solar panel output is directed to the batteries. Reading the above referenced article will help decipher a bit of the fog about charge controller types. I also recommend the Solar Electric Handbook (see link at bottom).

Solar controllers have a rated amperage. For example, my Renogy MPPT solar controller is rated at 40 amps. This is the maximum input amperage. Solar panels are rated in watts. We are back in the United Nations where everyone is speaking a different language (amps, watts, volts, etc). However, we can convert watts to amps with the following formula: Amps = Watts/Voltage.

In part one of this series, I stated that we are designing a basic 12V solar charge system costing $3500-5000. You can build a larger or smaller system, this just gives us a starting point so I can restrict my discussion to components that fit this system.

So, how many solar panels can I add to my solar charge system if I have a 40 amp charge controller. Forty amps is 480 watts for a 12 volt system. However, you do not want to exceed the capacity of the charge controller, when the sun is high in the sky with clear blue skies,  your panels will frequently exceed their rated capacity. So, let's leave a 10% margin of error (480 watts - 10% = 432 watts). Therefore, we can safely add 432 watts of solar panels to our system.

Solar panels are cheaper per watt the larger the panel you purchase. Typically, one 200 watt panel will be cheaper than two 100 watt panels. You will also save on mounting hardware, wires, and such by purchasing higher capacity panels. Panels also come in various sizes and it is important to match the panel size to your available space. This image shows the various components of my solar charge system (except batteries and solar panels); it is important to place the charge controller in an area that will get some circulation, charge controllers have cooling fins and need air circulation.

I will cover solar panels in Part 7 of this series. For my system, I choose four 100 watt panels because this fit the space I had available for my unit and this did not exceed the capacity of my charge controller. At a future date, I will install a second charge controller and four additional 100 watt panels.

There are many choices for charge controllers and books, these are the ones I have purchased and had good luck using. I wish you all well.