Solar battery. What is it?
A solar cell is a combination of cells with semiconductors (most often silicon crystals) that convert solar energy into a constant electric current. Solar panel - the finished product. Namely - a certain number of these cells, interconnected, based on a solid or flexible basis of a given size. The more cells in the panel, the larger it is, the more powerful its characteristics.
Is it effective in our latitudes
Yes. The efficiency of the solar battery depends on the intensity of the solar best and on the correct angle of incidence of these rays on the panel (ideally, the angle should be straight). But even in cloudy conditions, as well as in horizontal planar basing, cells still produce charging current, albeit with less efficiency.
Types of solar panels
According to the structure of crystals in the cells, solar panels are divided into polycrystalline and single-crystal. Differences in different production technologies. In practice, there are many disputes, which is better. The most common opinion is that a single crystal works better in clear weather, but it is almost completely inactive in overcast. A polycrystal works worse than a single crystal in clear weather, but it gives out a weak, but charging current even in cloudy weather.
By structure, solar panels are divided into flexible and solid. In the first case, silicon crystals in the cells are made more flexible, which allows placing the panel on curved shapes. The flexibility of such a panel is still significantly inferior to a sheet of paper, so it can only be positioned on bends with a smooth, no large angle or rounding. Such panels are noticeably lighter than solid ones.
Solid panels are made of anodized aluminum frame, covered with hardened glass and polymer film on top. Such panels have much greater strength and durability, cool better and cost less.
Solar panel positioning
Ideally, the angle of inclination of the panel to the sun’s rays should approximately correspond to the latitude of the base. For Moscow - 53 °. It will be more effective to change the angle 2 times a year by 15 ° (upwards for the winter, this will allow the panel to self-clean from snow, to a smaller extent for summer).
In reality, the roof on motorhomes and caravans is flat; not everyone wants to raise and lower the panels every time they stop. The horizontal position is permissible, but at the same time the useful working time is lost in the morning and in the evening, when the sun's rays "slip" off the panel and are not converted into electricity in sufficient quantity. To eliminate this drawback, you can either a large number of panels or a smaller number of electricity consumption.
Controller. What is this for?
The voltage and charging current on a solar panel varies with the intensity of solar lighting. The controller levels the output voltage to “charger”, interrupts the charge, avoiding “overcharging” the battery, reconnecting the “charge” when the battery is “discharging”, and disconnecting consumers when the battery is “discharging”. There are 2 types of controllers: PWM and MPPT. They differ in different charge technologies. If you have one or two solar panels, you need to use a PWM controller, we connect the panels in parallel. If the number of panels is more than three, it will be more efficient to use the MPPT controller, the connection of the panels is consistent.
The flexible panel can be immediately mounted on the adhesive sealant. For mounting a solid panel, a special aerodynamic fastener is used, which provides a clearance (about 10 mm) between the panel frame and the roof of the motorhome for better cooling (the solar panel heats up very much and needs ventilation in order to maintain its performance). Aluminum corner from the nearest hardware store will also be a great fastener, though not so aesthetic. The frame of the panel with fasteners are connected with screws through drilling, fasteners with the roof through glue-sealant. Usually it is Sikaflex 252i, Sikaflex 552 or Decalin Decaseal 8936. When dismantling, the sealant is cut off by a string. The connection of the panels among themselves, as well as the wiring going to the controller, takes place with the help of special terminals. For hermetic cable laying through the roof, a plastic “passage” is used, which is also mounted to the roof on glue-sealant.
Any solar panel is designed to charge the battery, and he, in turn, distribute electricity to consumers (12V direct, 220V through the inverter). Preferences should be given to traction lead-acid batteries by AGM or GEL technology. These batteries can withstand a large number of charge-discharge cycles, sealed and safe. With a limited budget, liquid lead acid batteries are also suitable. For their safe use, it is necessary to ensure the discharge of harmful acid vapors released during charging to the street.
How many panels and batteries do I need in my motorhome?
The main question asked by each caravaner. To answer it, you must first calculate the power of all potential consumers and the frequency of their use for one day. Based on this, select the number and capacity of batteries, as well as the power of the inverter (if consumers will be at 220V), then the number and power of solar panels (taking into account the useful area and roof topography, as well as hatches, fungi and antennas that prevent the positioning of large panels ). If this issue is difficult, you can start with a classic starter caravan kit: a 150 W polycrystalline solar panel, a 100 A / h helium battery.
This kit will allow you to:
- Use 12 volt lighting;
- Use a water pump;
- Charge phones, tablets, laptops;
- Watch a small LCD TV;
- Use the blower system from 12V in your gas heater.
During daylight hours, the solar panel will charge the battery, in the evening and at night you will use it. Realizing that the power panel is not enough, that would charge the battery completely during the day, you can always add one or two panels at 100 W / 150 W, connecting them parallel to the first.