Your guests are about to arrive when a terrible thought enters your mind. Did your solar panels charge the batteries all the way? They didn’t finish installing the solar panels on your dock until yesterday. Is that enough time to charge your battery bank?
You check the battery monitor and YES! They did charge the batteries.
The party goes on late into the night. The lights shine, the music plays, and the fridge keeps the drinks cold. In other words, you should have installed solar power on your dock years ago.
What are Solar Cells?
Solar cells, also known as Photovoltaic cells or PV cells, are made from semiconductor materials that absorb photons of light and turn it into electrical energy. Two types of semiconductor materials bonded together make up a solar cell. N-type, have extra electrons. P-type are missing electrons. As photons strike the n-type semiconductor they knock loose some of its extra electrons. These electrons jump to the p-type semiconductor creating an electric current. Metal contacts combine current from the cell with current from other cells.
Rated output in watts is used to group solar panels. But there are other things to look for.
- How the solar cells are made. Monocrystalline, Polycrystalline, or Thin-film.
- How many solar cells? Use a 36 cell panel when charging batteries with a PWM charge controller. Use solar panels with 60 cells or more when charging batteries with an MPPT charge controller. Likewise, grid-tie solar systems, that feed power into the electrical grid, normally have solar panels with 60 or more cells.
- Rated output in voltage. This is useful for comparing panels of the same wattage. A solar panel with a higher efficiency rating will make more voltage and current than one with a lower efficiency rating.
- Efficiency rating. The percentage of light hitting a solar cell that is turned into electricity is its efficiency rate. In other words, when you have two solar panels of the same wattage, the one with the highest efficiency rating will produce more voltage and amperage.
Types of Solar Panels
Solar panels are classified by the type of semiconductor material used to make the solar cells. Monocrystalline and polycrystalline solar panels have their solar cells mounted between a piece of glass and a backing panel inside a frame. The number of solar cells in the panel and the maximum wattage of the panel determine its size.
Monocrystalline solar cells, made from a single purified crystal of silicone, are the most efficient solar panels available. Some reaching over 20% efficiencies. Built using 36, 60, 72, or 96 solar cells, some with wattages over 400 watts. Because they are more expensive to manufacture, Monocrystalline panels are more expensive than polycrystalline panels. Therefore, they are best used in installations that need to produce a lot of electricity but have a limited amount of space.
To make polycrystalline solar cells, silicon is melted and poured into a mold. As a result, they are less expensive to manufacture than monocrystalline panels. Polycrystalline is the second most efficient solar panels with efficiency ratings between 15% and 17%. Built using 36, 60, or 72 solar cells, they come in wattages over 300 watts. Because of it’s lower efficiency, polycrystalline is best for installations with large areas for producing electricity.
Thin-film solar cells are made differently than Monocrystalline and Polycrystalline solar cells. First, the semiconductor materials bond directly to an underlying material such as plastic, metal, or glass. As a result, they are much thinner, lighter, and more flexible than monocrystalline or polycrystalline panels. This results in thin-film panels coming in non-standard sizes. Because of their low-efficiency, thin-film solar cells are best for boats, RVs or on large commercial buildings and solar farms.
Types of Thin-Film Solar Panels
Three different materials are used to make thin-film solar cells. CIGS, CdTe, or a-Si. They have efficiency ratings between 7% and 13% depending on the material used to make the cells.
CdTe (cadmium telluride) is the most common type of thin-film solar panels in use. They have an efficiency rating between 10% – 11%. There are environmental concerns with using the toxic chemical cadmium in manufacturing.
a-Si (Amorphous Silicon) is the next most popular type of thin-film solar panels. They do not have the environmental concerns associated with other thin-film panels. Unfortunately, they have an efficiency rating of only 7%.
CIGS (Copper Indium Gallium Selenide) have reached efficiencies exceeding 20% in a laboratory setting. However, manufacturers haven’t found a way to produce an efficient CIGS panel at a reasonable price. There are environmental concerns with using the toxic chemical cadmium in manufacturing. Some companies solve this problem by using zinc instead of cadmium.
Before choosing solar panels for your project you should think about a few things first.
How much space do you have to mount panels?
What type of charge controller will you use?
Will you be charging batteries, sending power directly to the grid, or both?
How much power do you need?
What is your budget?
The cost of solar has dropped to a point where it makes economic sense in many parts of the country. And you don’t have to tie into the power grid. Stand-alone systems allow you to add power to remote locations such as a dock or cabin for a reasonable cost.
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