Solar powered boat. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Alternative energy sources

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The cognitive aspect in the design of such a boat is to get acquainted with the practical development of photovoltaics. The intermittent nature of sunlight dictates the need for many circuits to use a battery, and thus we have electrical energy when we need it, and not when the sun is shining. One of the main problems when using batteries is the management of the charging current: overcharging the battery can lead to battery failure.

Until now, to ensure reliability and long battery life, a charge regulator was used or the output current of the solar array was limited. In this chapter, you will get acquainted with a new mode of operation of solar panels, namely with their self-regulation. When using them, no regulators of the charging current of the batteries are required.

Lead Acid Batteries

The self-regulating mode of a solar battery is greatly influenced by the characteristics of a lead-acid battery, so it seems to me that it is necessary to briefly familiarize yourself with their principle of operation.

A lead-acid battery consists of two lead plates immersed in a weak solution of sulfuric acid. In this case, a reversible electrochemical reaction takes place, as a result of which an electric charge can be stored. We will be interested only in the charging process.

During discharge, the sulfate ions of the acid residue are absorbed from the solution by the lead plates. When a charging current is passed through the plates, the electrical energy "pulls" the sulfate ions back into solution. After the battery receives about 80% of its original charge, the chemical balance inside the cell begins to change. Lead from salt is gradually reduced to a pure metal.

The result is similar to placing two metal rods in an aqueous solution, when excellent conditions are created for electrolysis. In fact, this is what happens. Electrolysis is accompanied by the release of oxygen and hydrogen bubbles, i.e., the so-called "boiling" effect of the battery cell. It is more correct to call this effect gas evolution.

It is the outgassing that leads to deterioration of the lead-acid battery. If no action is taken, the cell will eventually fail. To prevent damage, it is necessary to reduce the charging current at the very beginning of outgassing. Charge regulators serve this purpose.

You can reduce the charging current using a resistor connected in series with the battery. Part of the electrical energy is dissipated in this resistor in the form of heat, which leads to a decrease in the charging current.

Another, often used method: a constant voltage is maintained on the battery, and the current strength takes on different values. Since the amount of current depends on the difference between the voltage on the battery and the charging voltage, it is possible to adjust the charge rate by changing the voltage. Similarly, in a car's electrical system that uses a voltage regulator, the battery is kept charged.

Unfortunately, the use of a voltage regulator when the battery is fully charged requires an increase in charge time. With a limited number of hours of sunshine during the day, there is naturally little time for charging.

You probably already guessed that the ideal solution is to combine a current regulator and a voltage regulator in a single device. The charge starts with a large current without any voltage limitation. When the battery reaches the gassing stage, the device reduces current and switches to voltage regulation mode.

The battery stores the maximum amount of charge in the shortest time, while eliminating the possibility of overcharging the battery. Graphically, the ideal charge cycle is shown in Fig. 1.

Self-regulating solar panel

Now we can consider the characteristics of a silicon solar cell, shown in Fig. 1 (upper curve).

Ris.1

As you know, a silicon solar cell is a current generator. Regardless of the voltage before the curve bends, the current is always constant. The voltage across the element is determined by the load resistance.

As the load resistance decreases, there comes a point where the current is no longer the determining factor. This part of the curve is called the "knee". At high voltages across the load resistance, the laws of conservation of energy and quantum physics come into play, and the current decreases. Let us pay close attention to this fact, since it is the meaning of self-regulation of the solar battery.

This transition point on the characteristic of the solar cell is very important in the following consideration. In fact, it separates the two modes of operation of the solar battery. Above it, the solar generator acts as a current generator, and below it, it is equivalent to a voltage regulator.

If we compare the graph of an ideal charger with the current-voltage curve of a solar cell (Fig. 1), we can see that the two curves are very similar. In fact, they are almost congruent.

Therefore, it is quite natural to link both characteristics together. By coordinating the inflection point of the solar battery current-voltage curve with the moment the battery begins to outgassing, it is possible to achieve the effect of self-regulation.

Let's go back to a typical example. Let's assume that the process starts with a completely discharged lead-acid battery. Now let's connect it to a self-regulating solar generator.

When the solar panel is illuminated, the battery begins to charge. At the beginning of the process, the battery voltage is low (<10 V). In this case, the solar battery operates in the area above the "knee" in the current generator mode. In other words, the battery receives the maximum current that the solar panel can produce, which makes it possible to achieve the necessary fast charge.

As the charge accumulates in the battery cells, the voltage begins to gradually increase. Remember how we took advantage of this increase in design charge regulator. We can do the same again.

If we match the gassing voltage, which starts at 12,6V in a 12V battery, with the knee voltage of the solar cell's V/A curve, we can get a reduction in charging current.

Assuming that the battery has reached the gassing stage, we observe that the solar panel exits the current stabilization mode. Now increasing the charge of the battery and the voltage on it will force the solar panel to work in the voltage regulator mode. As a result, the charging current will decrease.

The greater the charge on the battery, the greater the static voltage becomes and the further the operating point on the characteristic of the solar cell moves to the area below the "knee". An increase in voltage is followed by a corresponding decrease in the output current of the solar array.

By the time the batteries are fully charged, the operating point has shifted so far to the right in the characteristic that now only a small supply current flows from the solar battery. It is so small that the battery can remain in this state for as long as desired without fear of overcharging. At this point, the battery voltage is 13,2 V.

In this position, everything remains until we use up the energy stored in the battery. As the cells give off energy, the voltage across the battery decreases accordingly and the operating point shifts in the opposite direction along the volt-ampere curve. The strength of the charging current from the solar battery will depend on how much the voltage on the battery has decreased, that is, on the amount of energy consumed proportional to this value.

So we have reached the goal, now we have a self-regulating solar generator.

temperature effect

A self-regulating solar panel has a very unexpected property: it takes into account the influence of temperature. Few of the objects around us are not affected by temperature. Solar cells and batteries are no exception. Electrical charge is stored in a lead-acid battery through a chemical reaction that is highly sensitive to temperature changes. The higher the ambient temperature, the faster the reaction proceeds. In practice, this means that in colder weather conditions a higher charging voltage is required.

With conventional charge controllers, temperature tracking has always been a problem. It is not possible to solve it by simple means, and any more or less complex method will lead to a complication and increase in the cost of the design.

Ris.2

The temperature dependence of the current-voltage characteristic of a silicon solar cell compensates for the temperature properties of a lead-acid battery cell. Lowering the temperature actually causes the solar generator to work more efficiently.

Due to various influences on the volume of the semiconductor, the voltage component is most strongly affected. This is exactly what is required for the battery. When the outside temperature drops, the output voltage of the solar cells increases (precisely at the moment when the battery needs more charging voltage). Moreover, when operating in the usual temperature range, the temperature dependences of the characteristics of solar and storage batteries are so well consistent with each other (Fig. 2) that no additional measures are required for successful joint operation of these batteries in a common device.

оторная одка

It's time for the fun part of our story. Let the self-regulating solar array work* for us now. For this design, a small electric motor boat was chosen.

It is a rubber inflatable boat manufactured by Metzeler. Its length is 2,7 and its width is 1,2 m. The stability of the boat is ensured by two spaced pontoon-type cylinders, and the flat bottom serves as a spacious "cabin".

Ris.3

With a low water speed (9,4 km/h), this boat is perfect for fishing or just for a nice walk on a sunny day. Solar panels are installed on a canopy that protects passengers from the sun's rays (Fig. 3). In addition to powering a boat's electric motor, a photovoltaic system can also power a radio, lighting system, or water pump.

Design

We begin our description with a boat. Although there are many types of boats to choose from, I chose the inflatable pontoon boat for two reasons.

First, it's inflatable. This means that it is portable and deflated for easy storage. Secondly, an inflatable boat is a solid, stable vessel that can be used for a long time. In the following, I will explain in detail how the conversion of solar energy was carried out on this particular boat.

If you know more about boats than I do and want to mount a solar panel on a different type of boat, use the following recommendations nonetheless.

Solar panels are installed first. In this design, solar panels M-61 from ARCO Solar, Inc. were used. self-regulating type.

Each M-61 battery with a power of 25 W is structurally made in the form of a panel 120 cm long, 30 cm wide and 4 cm thick, containing 30 single-crystal round cells with a diameter of 10 cm. The battery is designed for a voltage of 14,1 V and a current of 1,75 A.

If you want to make a solar panel yourself, try to make sure that your battery has the same characteristics. Make sure that the solar panels are absolutely waterproof: there will be plenty of moisture!

For the movement of the boat, four solar panels with the specified characteristics will be required. Place them in a row on a 120x120 cm2 panel and connect them in parallel. The total current of four batteries connected in parallel is 7 A and the voltage is 14 V.

The solar panel is attached to the deck with a 4 cm diameter PVC plumbing pipe frame (Schedule-40). Plastic tubing is an excellent material for such purposes; it is tough, inexpensive, lightweight and, most importantly, does not corrode.

The pipe frame is made in accordance with the scheme shown in fig. 4. 90° connections are made with elbows and the top frame is attached with tees.

Ris.4

Four posts are required, each about 120 cm long. The lower ends of the two front pillars are connected by a coupler, which, as can be seen from Fig. 3, resting on the bottom of the boat directly in front of the front seat. The two rear pillars are connected in the same way and fixed at the rear seat.

Cut with a hacksaw pieces of plastic pipes of the required length and assemble the frame, adjusting the parts in place. Although in fig. 4 are exact dimensions (in cm) and should be used as a guide only. The final fitting is done on the boat itself. The supporting frame of the solar array must fit snugly between the pontoons when installed in place on the bottom of the boat.

When you are sure everything is done correctly, glue the parts together with a clean PVC adhesive containing plastic solvent. When two plastic parts are glued together, a bond is formed that is as strong as the original material itself. Tetrahydrofuran is used as a solvent for PVC. When working with it, it should be remembered that it is poisonous, as, indeed, most other solvents.

It is necessary to work with this glue quickly, it leaves no time for reflection. Therefore, before gluing, prepare and place all the details. Glue no more than two parts at once and wait for the glue to fully set before proceeding to the next connection.

Then bolt the solar arrays together into a single 1,5 m2 unit. For this purpose, there are special holes on the metal edging of the batteries.

A small gap must be left between the batteries in order to reduce the windage of the structure. Spacers can be used to separate the batteries.

The solar panel is then placed on a supporting frame and tied with string or rope at least four points on each side and where the batteries are screwed together. Better not skimp on the cord, otherwise your battery will fall into the water after a strong gust of wind.

An electric motor weighing about 13 kg is used as a boat engine. Similar electric motors are manufactured by various companies, such as Montgomery Ward and Sears.

The boat engine is supplied attached to a wooden yoke that will easily support a small electric motor, as the design is designed for low power up to 4 hp. With. (about 3 kW).

The electric motor is powered by a 12-volt lead-acid battery. This is a battery of gel cells, similar to that described in Chap. 14 type. Essentially, a gel cell is similar to a conventional lead-acid cell with a liquid electrolyte. However, not a liquid, but a thick Jell-O electrolyte, which has the consistency of jelly, is poured into the gel cell.

The use of a gel battery instead of a standard marine battery is due to the lack of electrolyte leakage. Even if the boat capsizes (which has never happened), the acid will not spill.

Since solar panels are self-regulating, the only thing required is to connect them to a storage battery, which in turn to an electric motor. Everything is very simple!

What is the purpose of solar self-regulating solar panels in this design? On the one hand, such batteries simplify the design and increase reliability. This is the main reason. On the other hand, this gave me the opportunity to demonstrate to you one more property of solar panels.

Boat capabilities

Do solar panels work well? Well, I confess: in Fig. 3 you see is not my boat, it belongs to Gary Zanstecher (sitting in it), to whom I leave the opportunity to explain whether it is good. Here is his opinion:

"This is a stable boat, easy to transport and assemble. The boat is usually moored in Marina del Rey. We use it on weekends and in our free time.

Due to its characteristics, the boat develops a speed of 9,4 km / h. When driving, the motor consumes 25 A, therefore, a battery with a capacity of 80 Ah is enough for approximately 3 hours of operation. However, it must be remembered that at the same time there is continuous recharging from the solar battery.

I have been boating for 4-5 hours in a row and have never experienced a lack of electricity. Of course, I only used the boat on sunny days.

The boat is berthed for at least a week between trips, so the solar panels have enough time to charge the batteries.

Look, solar panels are not oriented towards the sun. It is unwise to do this, since the boat is constantly changing its orientation and direction of movement. The batteries are mounted horizontally and, of course, do not generate full current most of the time. However, when the sun is high above the horizon, they function quite well.

The batteries are only attached to the panel, so they can be removed very quickly. They are quite expensive and I don't want to lose them in a storm. True, the boat withstood the effects of wind blowing at speeds up to 56 km / h without any problems.

In general, I must say that a boat with a solar battery is a very funny thing."

Author: Byers T.

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