Charging with Solar Power - SailNet Community
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Charging with Solar Power

Where space isn't an issue, solar panels easily provide all the power almost any vessel needs.

What part can solar power play in your boat's charging system? I tell cruising sailors that before they look at other charging sources for their boats, they should install as much solar power as their space and budget allows. Chances are they'll run out of one of those before having too much electricity on board.

Why am I so adamant about solar? It's simple. Solar electricity is one of the miracles of  modern technology. Solar panels currently on the market are up to 16 percent efficient at changing sunlight directly into electricity. Compare that to incandescent light bulbs in your home or boat, which are only 10 percent efficient at converting electricity into light!

They perform their job silently and with no moving parts, day after day, for decades. Standard solar panels come with a 25-year guarantee against power loss, and in fact have no finite life as far as we know.  What other marine products can make this type of claim?

A small solar panel will provide the power for a simple 12-volt system.
I think you begin to understand why I feel so strongly that solar should be a major part in your battery charging mix. But how exactly does it fit into your electrical power system? Think of your DC-power system as having three major components: electrical generation (your charging sources), electrical storage (your batteries), and electrical loads (your appliances). The charging sources must keep up the appliance loads in order to maintain system balance (i.e. avoid dead batteries). Once you get a handle on what your average daily loads are, you can select charging sources to supply at least this much power on an average daily basis, and you should probably look first to solar.

Solar panels can supply all or part of your average daily load, depending on several factors:

  • The size of your average daily load
  • The space on board for solar panels
  • Your overall budget for electrical power gear.

"If we had added refrigeration, we would have needed an additional 150 to 200 watts of solar power to handle all of our electrical loads."
On our first cruising catamaran a single 35-watt solar panel supplied all of our electrical needs, but then we kept the portable panel facing the sun and we only had some fluorescent lights, a VHF, a small radio, occasional use of navigation lights, and an efficient low-drain anchor light.

On our second catamaran we required two of these panels to supply our needs. If we had added refrigeration, we would have needed an additional 150 to 200 watts of solar power to handle all of our electrical loads. Many boats can accommodate multiple large solar panels mounted on hardtops, biminis, stern arches, or davits; other boats simply don't have the space, and their owners must be content with installing a modest amount of solar power and supplementing it with other power sources.

Sizing solar panels must be done with reference to your total energy demands on board.
Sizing Panels    Let's try to establish what solar power can do on your boat. A typical average daily electrical load on a cruising boat with refrigeration is 100 amp-hours per day. How much of this daily load can you take care of with solar power? Solar panels are rated in terms of watts and amps. The watts rating reflects peak power at higher voltages than you'll normally see at the battery bank; the amps rating is more realistic and, therefore, useful. An 80-watt solar panel produces about 4.5 amps of current in bright sunshine, or roughly 20 to 25 amp-hours per day in most cruising grounds. You can see that if you can find mounting locations for four 80-watt panels with a total area of roughly 27 square feet (easy to do on a catamaran or beamy monohull; not so easy on most other boats), you'll come very close to supplying all your electrical needs with solar. This is an ideal situation. The less mounting locations you can find for solar, the more you'll depend on other charging sources.

Thin film panels are available with rigid or flexible frames.
Flexible solar panels use thin-film solar cell technology, which has advantages and disadvantages. They are lightweight, can be mounted on soft surfaces such as biminis and dodgers, and are not as affected by shadows as standard panels. On the other hand they are more expensive per watt, and with their polymer covers instead of glass they have much shorter warranty periods.

Go for as much solar power as you can on your boat, and I guarantee you won't be disappointed. There is no better piece of marine gear on the market, and making their purchase even more attractive, solar panels will eventually pay for themselves in fuel savings and reduced engine wear.

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