We all know that it would be great to have unlimited power onboard while at sea or swinging on the hook but the limitations of our onboard power supply make it painfully clear that this cannot be the case for the average cruiser or boater. Even when we are not aboard and the boat is left vacant for any period of time, battery banks aboard can lose energy just from sitting. Firing up a generator or running the on-board engines can help to keep the battery banks topped up, but they can be noisy and burn ever more costly fuel. Wind generators and solar panels may offer another source of energy that can keep your batteries topped and even the possibility of running electrical components aboard without draining battery banks. Determining which of these options is better suited to your needs requires some research, planning and a good understanding of how each will perform on your vessel. In this issue we will look into solar panels and next month we will compare the capabilities of wind generators, with the hope that you can then determine which option would be best for your vessel.
Solar panels come in many sizes and forms and can be an excellent source of power for vessels of all types and sizes. Whether you just want a small panel to keep a battery topped off while in storage or at a mooring, or if you are a long range cruiser who needs a way to keep house banks at a usable level each day at sea, there is probably a panel out there for you. Technology and cost reduction are now making them a viable option aboard. Not all solar panels are created equally, however, and an understanding of the different types of panels and their limitations will help you make an informed selection. There are three basic groups of solar panels.
Mono-crystalline panels are the oldest technology. Due to its makeup this type of cell creates electricity efficiently in a small area (high conversion efficiency) and can take less space on deck per watt of power produced. These panels are an option for powering mid-range DC loads such as monitors, computers and other battery draining equipment. The mono-crystalline panels are made up of single silicone cells that are grown into larger cells and cut into wafers, chemically treated and then joined together. Cells are joined together in parallel to increase amperage and in series to increase voltage. This rigid type of panel can be susceptible to shade issues lowering or in some cases shutting off output unless they are wired with bypass diodes. They can also lose efficiency as they heat up in the direct sun.
The second group, known as multi-crystalline panels, is also made up of single cells but within those cells there are multiple amounts of crystals. This allows for very high conversion efficiency but can also be affected by shadowing and heat. These panels are rigid just like the mono-crystalline versions but can produce the highest levels of power for the footprint they occupy.
A newer technology is the amorphous thin film silicone panel. These panels are manufactured differently and less expensively from the panels above. As a result the cells are thinner and can even be manufactured to be flexible. They can be formed to fit curves and even attach to bimini tops, dodgers, boom and sail covers. Thinner size and flexibility does come at a cost however. These types of panels are only about 50% as efficient at creating power as the multi-crystalline variety of panel. Just like the mono and multi-crystalline versions they can usually be combined to create a higher output. Amorphous panels are however more efficient in low light or diffused light such as on a cloudy day and are generally shadow protected. One must keep in mind that most manufacturers rate their panels based on at least five hours of full sunlight. When the sunlight is not at full brightness efficiency can drop drastically. Another distinct advantage of these types of panels is that they are not as affected by heat and don’t drop drastically in efficiency when they get hot.
Whatever panel you choose, where they will be mounted should be a major consideration (and related cost of mounts factored in). Are they going to have a permanent home or will they be a temporary or movable energy source? Would a rigid panel mounted away from shadows and obstructions be possible or would a flexible panel that can be formed and mounted on a boom cover or fabric top be a better option? They need to be mounted in a way that they will not interfere with lines and rigging and in a place where they will not be impacted or stepped on (although there are models made that can be walked on). Even the location in which you will be boating is a factor. If you are in an area where there is little bright sunlight or one with high temperatures, these will all factor on what panel will work best for you.
No matter which solar panel you choose you must determine the output you need. A good rule of thumb is to take the stated output of the panels and divide by two. The resulting answer should match the Amp hours of the battery or battery bank you are trying to keep topped off. It is also recommended to add at least 20% to your determined power requirement to cover variances. When pricing a system it is important to also factor in a charge controller or regulator to any system especially if it is outputting more than 1.5% of a battery’s rated capacity.
With realistic expectations of their output and an accurate determination of your power requirements solar panels will allow you to enjoy a clean, silent power supply that will keep things running smoothly on any venture.