The amount of power needed while cruising depends on many factors including the energy used by appliances and lighting, the output of the engine alternator, the climate and the length of time away from shore power. These and other factors will determine the amount of solar power and thus size of the solar panel(s) you may need.   Working with Ed Foster of foster-wills.com, we have developed a worksheet to assist you in inventorying your on board power generation and consumption and estimating you solar power requirement.  Print out our Solar Power Calculation Worksheet and use it as a guide to figuring out your power generation requirement.  From this you can get an idea of what your solar panel options might be.  Hope it helps!
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We spent the month of July in the North Channel in Northern Lake Huron north of the 45th parallel.  We logged the output of our top-of-pole mounted 85 watt Kyocera solar panel and our daily power consumption.  It was an unusually cloudy July.  Here are some statistics.

Weather
Mostly cloudy      7 days
Partly cloudy       8 days
Partly sunny        8 days
Mostly sunny       7 days

Power Generation
Maximum power produced in a day was 38 amp-hours
Minimum power produced in a day was 12 amp-hours
Average power produced per day for the 30 day period was 25 amp-hours

Power Consumption
Average power consumed for the 30 day period was 46 amp-hours

Our travel pattern was to stay at anchor for 2-3 days and then motor/sail to another anchorage.  We connected to shore power one night.  While we ran a power deficit of 21 amp-hours per day while at anchor, our high output 75 watt alternator quickly replenished our batteries on our travel days.

We ran our refrigeration/freezer every day as well as our computer (chart plotting) and autopilot when underway.  We found the combination of our 85 watt panel and our 75 watt alternator provided us with ample power for the trip.
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Solar panels provide an excellent solution for obtaining the electrical power needed  to support on-board electrical systems.  They are quiet, require little maintenance and are reliable.

While cruising, we take a very conservative approach to using electricity on board our 38 foot sailboat.  Even so, when considering the solar option, I concluded that  using solar panels to supply all our electrical needs would be expensive and would require considerable panel surface area.  With this in mind,  I set out to use solar power to augment the generation of power with the goal that we could be at anchor for three days without running the diesel to charge the batteries.

The 85 watt Kyocera KC85T is rated at 5 amps (17 volts) and measures about 26" by 40".  We can generate about 35 amp-hours on a sunny day on the Great Lakes by adjusting the angle 3-4 times a day for optimum efficiency.  Our energy usage is roughly 55amp-hrs a day at anchor.  Thus we run a deficite of about 20 amp-hours per day.

Here is how we calculated our energy usage per day at anchor.
Equipment            Amps            Amp-hours/day
Refrigeration          5                        20
Instruments            1                         4
Computer               4                         6
Lighting                  2 (avg)                10
Pumps                    5                         5
Other                     1                       10
 (propane monitor, etc.)
                                                ________
Total amp-hours                                55

When under sail we have an additional current draw of 20 amp-hours from our auto-pilot and instruments.

We have a 75 watt alternator on board and a 360 amp-hour battery bank.  Because we typically run the engine several hours on the days we are moving, the battery bank gets charged on those days.  This system works out well for us.

Each cruising boat has different patterns of energy usage and different requirements.  Calculate your usage, consider your sources of power generation and select the size of the solar array you will need.  Based on this, you can determine whether a single panel or multiple panels will be required to meet your needs.

Contact us if you would like assistance in determining the size of panel that will be required to meet your needs.



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