How To Choose The Right Solar Panel

If your sailboat’s battery runs out of a charge before you run out of the need for it, installing a solar panel might be a good option for you. It might be the only option for you to recharge the battery if you normally moor without access to shore power so that you can use a conventional charger. Solar technology has progressed a lot in recent years and you have more options than ever.

This is a guest post submitted by the folks at PowerScout,  a company that strives to bring the best solar technology within easy reach of the average homeowner. Their mission is to help people go solar, however they do it—in their homes, in their cars, or even in their sailboats. They don’t have a dog in the fight for your solar purchase so their advise can help you make a more informed decision, whatever products you choose.

Dead or depleted batteries make for some stressful moments as you try and figure out what to do. Equipping your boat with solar panels solves this problem. Taking advantage of the sun’s natural energy is an easy solution to power up while you’re out on the water.

There are a lot of different solar panels on the market right now so there’s something for boats big and small, and for all types of budgets. This post aims to help you navigate through the choices to find the panel that’s just right for your sailboat and your budget. Solar technology is a big subject so this post links to additional information if you want to dig a little deeper.

Solar cell types explained

The first choice you should make is the type of solar cells that the panel uses. A solar cell is the basic electricity generator in a solar panel. There are three primary types of cells based on the material that they are composed of. All panels are made of one or more of these types of cells and there are pros and cons to each type.

Monocrystalline panels are usually very efficient and take up less space as a result. One square meter of a monocrystalline cell usually pumps out about 190 watts of energy. Due to their efficiency, they’re usually more expensive than other options. On the other hand, polycrystalline panels are a bit cheaper up front, but they are less efficient and produce fewer watts of energy in the same area.

Another type of panel, amorphous silicon, works best in shaded situations. The panels are cheap to make and are not very energy efficient, but they can charge even if the cells are in a shadow, which can be a great advantage on a sailboat. These panels also can be quite useful since they can be attached to a non rigid surface.

Calculating capacity

You can calculate panel efficiency (the ability of a solar panel to convert sunlight into energy) by multiplying the amount of sun that hits the panel in your area times the area of your panel. Divide the maximum wattage on your panel by this number, then multiply it by 100 percent you’ll get an efficiency rating. Another important calculation for panels is energy output tested under Standard Test Conditions. Manufacturers are required to meet or exceed the wattage they put on their panels after they are tested under STC. STC looks into panel temperature, orientation, and light exposure.

It’s important to stay aware of STC because panels are tested at 25 degrees Celsius for the STC rating. Obviously, real world temperatures can vary a lot, and most panels are actually about 20 degrees Celsius hotter than the ambient temperature, which can make output a lot different. If you’re looking to install panels in places that don’t get a lot of sun, you’re going to want to invest in high efficiency panels. On the other hand, you might be able to get away with less efficient panels if they’re going to be placed in a sunny spot.

Overall, your solar panels should aim to exceed your basic energy requirements by about 20%. This allows them to be self sufficient and account for your power consumption. Of course, numbers might change based on your circumstances. Things might be different if you’re looking to just charge batteries as opposed to also powering things like pumps or refrigerators.

It’s important to keep in mind aspects like cloud cover and where the sun is during the day. Those sailing around the equator can usually expect about 12 hours of consistent sunlight per day. If you’re farther north (especially in the winter), there’s not going to be much sun to harness.

Those just trying to keep up with battery discharge can usually get away with 5 watts of panel power per 60 or 120Ah of battery (depending on the type). If you’re looking to power a fridge, 80 watts of power is recommended. A 100-watt panel is usually fine for most medium sized boats.

Mounting considerations

No matter how big or powerful your panel might be, its location and installation on your boat will determine a lot. Common spots to mount a panel include the aft or stern, a pole on a rail, or on an arch. A lot of owners will tilt their panels so they can be at a right angle to the sun. Your panels should try to tilt true south in the northern hemisphere, or true north in the southern hemisphere. True north and south are different than magnetic north and south.

Generally, placing solar panels more than a 45 percent angle respective to true south (or true north) is going to greatly decrease their productive output. The decline in production can potentially reach up to 30 percent.

There are several calculations that you can do to determine the best angle for your panels if you’re going to install fixed tilt ones, as opposed to adjusting them throughout the seasons of the year.

It’s important to carefully think this process through and to take into account the size of the boat and the panel. Keep in mind your panel might be completely ineffective in shade if it’s not amorphous silicon. Some companies offer mounting kits or other equipment that can safely secure a panel to your boat. If you’re mounting on the deck, make sure to let air circulate below by raising the panel.

The higher your panel’s efficiency is, the more sensitive it will be to a bad mounting job.

Install it right the first time

Any sort of wiring and charge controller should be chosen carefully. The marine environment can quickly destroy the conductivity of wires and wreck other equipment. Wires should only be marine grade, and you should consider installing a voltmeter if there is not one there already.

Once everything is set up, regular monitoring is necessary to make sure things keep running smoothly. Solar panels are a great way to quietly charge your batteries, but you must ensure wiring and other equipment are not corroding or breaking down in rough conditions. Many solar companies offer software packages that let you keep track of your panels, see the power they’re producing, and even check out weather conditions (all from your computer). A lot of these programs have smartphone apps.

Overall, adding a solar panel to your boat can be one of the best decisions you make. The days of being stranded are over once they are working.  Even better, new and cheaper solar panel technology keeps coming out each year, making upgrades nice and easy.

For helpful tips on mounting a solar panel on your sailboat, see Installing a Solar Panel by the Numbers. To learn how you can make your outboard motor do the job, see Upgrade Your Outboard Motor to Charge Your Battery. For wiring guidelines, see How to Completely Rewire Your Sailboat.


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