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Prepping to Survive: The Nautical Series: Pt. 3 Solar Power

Learn, in depth how one prepper has equipped his yacht with solar energy as a means to thrive during a long-term emergency, as well as understand how we can all utilitize and harness the sun’s energy.

Editor’s Note: While we are sitting in stand still traffic for hours on end, Capt. Mike and his wife will be setting there sails toward a remote island to sit out a SHTF emergency in quiet solitude. This article will discuss, in depth how they have equipped their yacht with solar energy as a means to thrive during a long-term emergency. Click here to read Part 1 and Part 2.

In a recent article Tess Pennington wrote “So, what happens if and when the grid goes down for an extended period of time? Aside from the aggravation of not being able to determine what is happening through traditional media channels, for the Average Joe, his problems have only just begun. Our dependency to the grid doesn’t just stop at lack of electricity in our homes to power our appliances or an inability to charge our cell phones; it is much broader and affects every aspect of our lives”.

Oh how true that statement is; most people could not survive a day without computers, refrigeration, cell phones and TV. Most people have never had to live off the grid unless they were primitive camping; and even then it was probably only for a weekend. But for some of us people planning to use our yachts as a refuge for when the SHTF, using solar is already being practiced. Some of us have already taken the steps necessary to keep the power flowing; we have built our own power grid. We have tested it in the actual real world environment and have been using it when we are away from the dock for pleasure, so we know the application and technology works.

What Is a Solar Panel and How Do They Work?

Solar panels are in theory any panel that uses the sun’s thermal energy to produce electricity. A solar panel can be described as a photovoltaic panel, the term used in the industry, for panels designed to produce electricity from the rays of the sun. Despite the category of solar panel being discussed, almost all solar panels are flat. This is because the face of the panel needs to be at a 90 degree angle from the sun’s rays for the most favorable angle to absorb the sun’s rays. Solar panels are able to take in energy from the sun through an array of solar cells on their surface. Much like how a plant is able to soak up energy from the sun for photosynthesis, solar cells perform in a comparable manner. As the sun’s rays hit the solar cells on a photovoltaic panel, the power is transferred to a silicon semiconductor. The power is then changed into (dc) direct current electricity and then passed through connecting wires to finally enter a storage battery.

Types of Solar Panels

Types of panels most normally used in boating applications have either multicrystalline or amorphous thin-film cells. Multicrystalline panels are the oldest technology available and also the most powerful. When sized appropriately and matched to suitable batteries, these are the panels to use for operating large loads such as refrigeration. Amorphous thin film solar panels are only about 50% as effective as multicrystalline panels, but can be bought in flexible forms so they can roll or fold, or correspond to the shape of a yacht cabin top or bimini. They don’t normally have enough output for significant energy replenishment, but can be used to trickle charge a battery bank.

How Much Power Do Solar Cells Make?

Generally, we measure solar panels by wattage and that is how we buy them. You can buy solar panels for boats as small as 10 watts to as large as 200 watts or even larger. But it is easier to understand when we convert watts to amperage. We arrive at these values by multiplying the number of hours the panel spends in full sun (usually defined as 8 per day in Florida) times the panel’s wattage. For a 195 watt solar panel the output would be 195 x 8 hrs = 1,560 watts/day. Taking it step further, 1,560 watts/12 volts = 130 amps per day. Keep in mind that solar panels produce DC power which means that you will need a deep cycle battery bank to hold the charge. Batteries are rated by the amp hours they hold.

So what is Needed in a Solar Panel Setup?

Obviously, one or more solar panels are necessary to make the system work. In addition, you will need:

  • a large bank of deep cycle batteries, the bigger the bank the better
  • an inverter, choose between pure sin or modified (to be discussed in another article)
  • a controller and
  • proper wiring and fuses to wire the parts together.

Energy Consumption – A

My guiding principle on how many panels to buy is simple; buy as many panels as your budget and mounting location will allow. You cannot have too many. But you should complete an energy audit to make sure you are buying enough for your needs. Example, if you have 3 interior lights that draw 2 amps each and you leave them on for 4 hours per day, your consumption would be 3 x 2 x 4 = 24 AH/Day. You can generally find the amp load for appliances on a label inside a door etc.

Amps Hours AH/Day
House Lighting

Inverter Loads – B

An inverter is a device that coverts battery DC power to household AC power; without an inverter, unlike on a yacht, your solar panel will have little value if used at a home. But with an inverter you can use your hair dryer.

Inverter loads use DC power but they are powering AC appliances and equipment. If you need to convert watts to amps use (12watts/12 volts = 1amp).

Amps Hours AH/Day
Hair Dryer
*Calculate your total daily energy consumption
AH/per day

Solar Energy Production – C

Alternative sources of power such as solar panels can replace the amp/hrs drawn from the batteries. But like the energy budget that calculated your usage you will also need to calculate your re-supply of amp hours. Remember the formula – (12 watts/12 volts = 1 amp). But keep in mind, the formula is only a gage; absolute accuracy can only be where the panel output is constant and a solar panel may at times operate inefficiently due to shading by clouds.

Watts Amps X – Hours Sun Exposure = – AH Day
Solar Panel 1
Solar Panel 2
Total AMP Hours production:

Solar Panel Needs

Compare the daily energy consumption in AH/Day to the solar energy production. Your solar energy production ( C ) should be greater than the consumption ( A, B ). If not, select a larger wattage panel and recalculate. Always purchase more solar panel output than you will think you will need; some planners recommend at least 30% in excess. We bought our panel from Sun Electronics in Miami, www.sunelec.com as they had the best pricing I could find anywhere online. But remember, panels must be shipped via freight as they are heavily packed to reduce the chance of damage so be sure to calculate those costs in your purchase.

Mounting Your Solar Panel

Now that you have your solar panel, where do you mount it? As we said before, mounting the panel 90 degrees to the southern sun is optimum. You will get the best energy production this way. But on boats, finding a suitable location is tricky at best. I chose to mount our panel on the top of the trawler sundeck hardtop in a horizontal manner. Here it will get the best view of the sun and be clear from the radar arch shading as the trawler turns at anchor. The angle toward the sun in not exactly at 90 degrees but it will have to do. I chose a 195 watt panel so I have almost a 50% reserve capacity in my panel to make up for the slight inefficiency of the sun’s angle. If you choose to install a panel on land, consider mouthing it on rooftops or you may design and build a platform solely for that purpose.

Wiring Your Panel

Electrical wiring is very technical and hazardous; if you are not comfortable in doing this part of the task, please consult a qualified electrician. Your panel will be prewired for attaching to your boat/house but you will need to supply the connecting cables that will also be sold by your panel supplier; they are referred to as MC4 cables. The cables will come in different lengths suitable for your needs with a male and female connector attached; you cut one connector off. (The photo shows how we have our modified solar/wind turbine system wired.) . In addition, you will also need a controller. The controller regulates the electrical flow from the panel to your batteries keeping your batteries charged yet preventing over charging. Some controllers are simple but others have LED displays showing the rates of charge etc. The more whistles and bells the more expensive it will be. Your panel supplier will be able to recommend a controller that will meet your needs. I chose a controller made by Specialty Concepts. It is simple yet does the job. And the folks at the company are a big help in helping you choose the right model for your desired panel. When you contact them, the will need to know what size panel (wattage) you are buying and what the voltage is. Check them out at www.specialtyconcepts.com. I also bought my controller from the people at Sun Electronics in Miami. And lastly, you will need the appropriately sized cables to run from the controller to your batteries and a fuse to hook the controller to the battery bank. In selecting the correct fuse, you will need to find the short circuit current for your panel and rate the breaker at 125% of that number. The short circuit rating will be found on the panel specifications. This will give you the amperage of the breaker you will need. Your controller operating manual will have guidance on these too. Having a solar panel to maintain your batteries seems like a great idea but you’ll need to have a way to monitor your batteries. I chose to also install a Trimetric 2025RV Battery Monitor; www.bogartengineering.com.This smart device is wired into your battery bank to give a real time measurement of voltage going into the bank, amps being used by your boat, the percent full charge on the bank, and the amp hours used since the last charge.

Panel Operation

So we have now installed a 195 watt solar panel coupled with an 1800 watt inverter and a battery bank with 443 amp hours aboard our boat. We ran our tests at anchor with clear skies. Using the worksheets attached I concluded that our power consumption is 112.5 amp hours per 24 hours. The freezer alone is the biggest draw using 60 of the amp hours followed by the refrigerator. On a clear Florida summer day, the solar panel can supply 100% of the boats needs from sunup to sundown; we only lose approximately 40 amp hours overnight, but the panel will bring it back to full after a few hours of sunlight. When relying upon alternative energy, you must always be aware of your surroundings and how much energy you are consuming. For instance, our previous anchor light consumed 20 amp hours in a 10 hour period; replacing it with an LED light uses only .2 amp hours. When the SHTF, I think we’ll be able to maintain our lifestyles to a relative degree of normalcy. In future articles, I’ll discuss how to choose an inverter and how I have supplemented the solar panel with a wind turbine.

Fair winds,



Special thanks to Mike for taking the time to share his preparedness endeavors with us and helping us learn how being self reliant is possible, we just have show some initiative.

This article was originally published at Ready Nutrition™ on February 21st, 2012