Solar Panels vs Winter

Tech Talk – November 2019 – Solar Panels vs. Winter

As the days get shorter, many boaters wonder if they should put away or somehow protect their solar panels during the winter months.  Boaters often ask us if snow and freezing temperatures will affect the panels?   Can solar panels actually withstand months of inclement weather?   Let’s take a look at some of the options.

I am a big believer in leaving your solar panels on year-round.  On my own Catalina 36, I have a 450W solar array that has been mounted to the canvas with zippers .  Those solar panels have been out in the weather, 365 days a year for the last 7 years.  I use my boat during the shoulder season and on many clear, crisp winter days, I will still see some tangible input from the solar array. The main reason I recommend keeping your solar panels active on your boat is that if you are accidently disconnected from shore power or there is a power outage, your batteries will still be charged and therefore maintained.  Even if there is only a fraction of sun, a solar panel can float charge your batteries.  For example, flooded lead acid (FLA) batteries will discharge at a rate of 5 – 10-% per month without a charge.   Therefore, a 600Ah battery bank will lose approximately 30 - 60Ah per month or 1- 2Ah per day.  Even a modest 100W solar panel can keep up with that. 

If you don’t get to your boat as often as you would like or if you are away for the winter months, a solar array offers peace of mind.  Remember that the sun’s position changes throughout the year, and it takes a much lower path during the winter months.  If you are able to angle your panel, you will collect more energy and less snow.

Solar Belongs Outside.  Solar panels are designed for an outdoor installation because that is where they will receive the best direct exposure to sunlight.  High-end, marine-grade flexible panels, like those from Solbian or Gioco, use a techno polymer base on a thermoplastic poly matrix.  This allows the panels to be IEC 61701 (salty mist) certified.  This material also enables the panels to be manufactured without a frame because the water and humidity cannot pass through.  And the backing on the panels is made from plastic that is specifically designed for the marine environment, so it does not fade, yellow or crack.

If you have a snow build-up on your panel, carefully remove the snow leaving at least a centimeter or so on the panel.  This will ensure that the cells are not scratched by the brush, cloth or your glove.  Scratches create shadows and reduce the performance of the panel. Once the panel starts to warm from the sun, the balance of the snow will melt. If the snow starts to accumulate, the weight can cause flexible panels, and canvas, to bend excessively and break.  In this instance, if you are planning to be away for an extended period of time, it may make sense to remove the panels or have a backing plate install beneath the panels.  Panels that have been attached to canvas using zippers, Velcro or snaps can be taken off and stored away.

Maintenance.  Proper maintenance of your flexible solar panels is important to maximize the energy that the panels produce.  Flexible solar panels accumulate dirt primarily from wind-blown dust, sand, pollen and bird droppings.  When it rains, the water and dust can pile up on the corners or edges of the panel causing a decrease in output.

Try to clean the panels early in the morning or in the evening.  I find the morning is the best time as the dew that has settled on the panels will have softened the dirt. Do not clean your panels in full sun as the water will evaporate too quickly and smear the dirt.  Manufacturers recommend that they be washed regularly with a soft cloth, mild soap and fresh water.  It is important to rinse them completely as any dried soap will affect the performance of the panel.  Do not use any harsh abrasive cleaners or coarse cloths as they will scratch the panels and, again, the scratches will cast shadows which will affect the performance.  Denatured alcohol (methylated spirit) can be used to remove grease. When it comes to cleaning frequency, it is best to monitor changes in the power output of your panels before and after cleaning.  Even panels with a light dusting of dirt can lose up to 20% efficiency.

Some manufacturers recommend sealing the panels with a water-clear, thin film polymer coating that provides a high release surface, throughout the year. Products such as Plexus, Novus Plastic Cleaner #1, RejeX, Solar Shield and Repel claim to clean, shield and protect the panels however they can make the panels very slippery. 

MPPT Controller is a Must.  All solar panel installations should include an appropriately sized MPPT charge controller which protects your batteries from being overcharged.  It is important to also check the display and/or flashing lights as these controllers can fail.  If the controller has a display error or you suspect a failure, check all of your electrical connections between the panels, controllers and batteries. 

A solar array is a perfect compliment to boats in the Pacific Northwest.  With long hours of sun in the summer and, relatively low snowfall in the winter, solar panels offer another charging source for boaters.  This redundancy protects your batteries from draining due to a power failure at the marina or a disconnected shore power cord.  And, in both situations, you usually don’t find out until it is too late.

About the author: Jeff Cote is the owner of Pacific Yacht Systems, a full service shop delivering marine electrical and navigation solutions for recreational boats. Visit their website and blog for info and articles on marine electrical systems, projects and more: