By Thomas P. – Michael Pournaris

It is true that lately the inflatable boats have grown up to 50 feet in length. As a result, their equipment, such as refrigerators, freezers, heaters, microwaves, etc., have also increased, requiring thus greater need for more electricity than the onboard batteries can usually provide.

Solar panels

Especially when are used to anchoring in solitary coves for a weekend or more, the batteries need to be constantly recharged to meet our increased demands. This need is the main reason for the increasing use of solar panels in the boat, which can also charge our batteries daily when the boat is on the trailer.

How can a solar panel secure electricity on board?

A solar panel is basically a solar power generator. It absorbs the energy of the photons of the solar radiation which causes the electrons to move in one direction within the silicon of the panel and generate DC current. This current is afterwards transferred to the battery via the charging regulator which automatically interrupts the current flow once the battery is fully charged.

The solar panel is nothing but our solar battery charger. From the batteries, the electricity can be moved directly to the 12V devices (GPS, VHF, lights, pumps...) or to an inverter that converts the 12V DC derived from the batteries to 230V AC for use in television, air condition, microwave oven etc.

Advantages of using solar panels

  • We are self-sufficient in electricity, wherever we are
  • We keep the batteries charged and reliable at all times
  • We avoid using other sources of energy that disrupt both our own peace and our neighbors
  • We can charge our mobile devices, keep our drinks cool, cook or enjoy the music and lighting of the boat at night without having to run our engine every few hours or use diesel generators
  • We use absolutely clean energy without producing any additional pollutants while respecting the environment
  • Inexhaustible electricity that costs us nothing
  • Minimum maintenance

Solar panels

Types of solar panels

Monocrystalline - Polycrystalline:

The monocrystalline panel consists of high-purity silicon crystal and uniform chemical bonds, which gives it a uniform dark color, while the polycrystalline consisting of several silicon crystal structures give it a blue appearance which is different from one cell to another.
Their differences are relatively small, with monocrystalline panels outperforming the following:

  • They have slightly higher yields of about 0.5%
  • They can produce more power at high temperatures, which is particularly important for Mediterranean countries
  • They perform better in less sunshine (cloudy) conditions
  • They last longer

Flexible, semi-rigid and fixed:

The differences between them are in thickness and weight. The fixed ones are mounted on steady structures weighing from 8.5 kg or more, and they are about 3.5 cm thick. They obviously have a lot more durability due to their construction. The flexible and semi-rigid panels of the same power as the fixed ones weigh2 kgs or more while their thickness is almost 0.2 cm. They do not require fixed structures for mounting, they can be adapted to convex surfaces, allowing them to be stitched on the awning of the boat.

What we need to know so as to get maximum performance:

Suppose we have a 100 Watt solar panel on board. Many of us will wonder if its performance is in line with its rated power. We need to know that a panel can give us almost all its rated power only under ideal sunlight conditions and only when the sun is at its closest distance to the panel.This happens for 3 or 4 hours during a day. During the rest of the day the performance of the panel is significantly reduced.
The electricity generated by a solar panel is proportional to the amount of light reaching its surface.
Even thoughthe sun is above the horizon for 14 hours during the summer, it is prudent to calculate that a 100 Watt panel can produce up to 500 Wh per day. As we understand, this number corresponds only to the days with absolute sunshine.
But what if the sky is cloudy? It is clear that in this case the daily efficiency of the panel decreases even more and can reach only 300 Wh.

To get the most of the energy out of oursolar panel we must have:

  • Always keep it as perpendicular as possible to the sun's rays
  • Keep it as cool as possible, because the hotter the panel, the lower its output
  • Make sure that shadows (from antennas, radars, etc.) do not fall on its surface. Even a small shadow can dramatically reduce its performance
  • If it is not possible to adjust its inclination, it is wise to look southern.

Solar panels

Select the right panel according to our needs:

In order to be able to choose the right panel we need to know the power consumption of the electrical appliances we usually use during a day.
Each device has a label indicating its electrical consumption. For example, a 240 l/h bilge pump consumes 36 Watts per hour of operation and a radio-CD about 30 watts per hour. (Some devices do not list the watts but the Volts and the Ampere. For example, a 21-inch TV shows 230 volts and 0.5 Ampere. But knowing that W = VxA, we can calculate how much Watts the TV consumes per hour: 230 x 0.5 = 115 watt).

By summing the total energy consumption of all the appliances we use in one day, we can calculate the size of the solar panel we need.
In the table below we can see a typical consumption example when we are anchored in an isolated bay:

Operation time dailyConsumption Wh
Bilge pump 12v (36watts) x 12 minutes 7,2
Radio-cd (30-watt) x 3 hours 90
Led lights(30-watt) x 3 hours 90
Laptop(40-watt) x 2 hours 80
Heater 25L(200-watt) x 30 minutes 100
ΤV 21΄΄(110-watt) x 2 hours 220
Total 587,2

So we see that the total consumption of one day reaches 587.2 Wh. As a result, we need a solar panel that produces 587.2 Whdaily returning this power to our batteries so they are always fully charged.
Knowing that a 100 watt solar panel can give us up to 500 Wh in a sunshine day, it is easy to see that in the above example it is enough to install a single 100 watt panel to be self-sufficient. Of course, if the boat is equipped with more electrical appliances such as a refrigerator or coffee maker then it becomes clear that we need a larger power panel or a second one with 100 watt.

Recently, solar panels have become much cheaper and can produce even more power.
So let's make Ribbing more Eco-friendly!

...keep Ribbing!