Solar system installation instructions
INSTALLATION OF AN OFF-GRID SOLAR PANEL SYSTEM
General: A solar panel system consists of three main components.
The solar panel converts the sun's radiation into electrical energy. The panel usually consists of several cells from which the desired voltage can be obtained by connecting them in series.
The battery is a store of energy. The energy produced by the panel is collected in the battery, from which the required amount is used. Suitable batteries for photovoltaic systems are AGM or gel batteries. The advantage of these is carelessness and a long service life.
The regulator's job is to take care of the battery. The controller cuts off the charging current when the battery is full. Some controller models also have a built-in battery guard that ensures that the battery does not get deeply discharged.
Placement and installation of solar panels
Solar panels should of course be installed in a place where the sun can shine on the panels as unhindered as possible. In summer cottages, such a place is usually on the roof of the building. With a permanently installed solar panel, the best annual yield is obtained in the conditions of Central Finland, when the panel is tilted approx. 45 degrees towards the south. Considering only the production of the summer months, the highest production is obtained with a gentler, approx. 30 degree, tilt. Solar panels should never be installed horizontally, also because the natural cleaning of the panels by rain requires that the panels are tilted at least ten degrees. A ventilation gap of at least 10 cm must be left between the solar panel and the roof.
When installing solar panels, the 30 to 50 year lifespan of the panels must be taken into account. For this reason, e.g. stainless screws and bolts must be used in the fastening, so that the fastening would have a sufficiently long life. The panels must be fastened sufficiently firmly so that the fastening structures can withstand the worst expected storm winds. The mechanical resistance of the panels themselves is good, as long as the panels cannot move or bend.
All roof penetrations must be sealed with Sikaflex or Silicone. It is good to ground the frame of the solar panels, in which case the grounding also acts as a lightning conductor for the building. The negative pole of the battery and the electrical system can be grounded to the same ground potential.
In series connection of solar panels, the same current flows through all panels. The voltage of the panel chain connected in series is the sum of the panel voltages. Solar panels consist of solar cells connected in series, so the same current passes through each cell. The production of a series-connected panel chain is determined by the worst producing cell.
When connecting solar panels in parallel, the panel voltage is the same as the voltage of one panel and the current is the sum of the solar panel currents. Shading of one panel does not interfere with the production of other panels connected in parallel. Similar panels can be connected both in parallel and in series. Panels with different voltage values (number of solar cells) can also be connected in series, if the current values of the panels are the same. Panels with different current values can be connected in parallel, if the voltage values of the panels are the same.
Connecting in parallel is justified if the solar panels are disturbed by occasional partial shading, because the shading on one panel does not disturb the production of the other panels. The panels connected in parallel do not have to be in the same position either, but can even be on different sides of the roof ridge (e.g. one panel to the east in the direction of the morning sun and the other panel to the west in the direction of the evening sun).
Connecting the panels in series is especially justified if the electricity transmission distance from the panels to the charging controller is long. You can see that doubling the voltage drops the transmission losses to a quarter. Panels connected in series must be in the same position.
The most common battery in cottage systems, both in wind and solar power systems, is a lead battery. Electrical systems usually use sealed, maintenance-free gel batteries that can be installed indoors. The most common voltage of the cabin system is 12 V, because DC devices are best available for that voltage, e.g. LED lamps. Lead-acid batteries are often 12-volt, so when using several batteries, they are connected in parallel. The parallel connection adds up the charging capacity of the batteries (indicated in ampere-hours). If the system uses an inverter and only alternating current devices, then it can be well justified to use 24 volt battery voltage, because then the electricity transmission losses on the direct current side are reduced. The 24 volt voltage is achieved by connecting two 12 volt batteries in series. In particular, the series connection of batteries requires that the batteries are very similar to each other. Namely, if, for example, the internal resistances of the batteries differ from each other, it leads to the voltage being distributed unevenly between the batteries when charging the batteries and it can lead to damage to the battery. Even when connected in parallel, it is desirable for the batteries to be the same, i.e. the batteries should be of the same type, from the same manufacturer and roughly the same age.
A fuse must be installed between the batteries and the system.
Battery voltages. When the sun shines directly on the panel, the charging voltage can rise up to 14.4V. The voltage after the sun sets is 12.7 – 12.8V. The voltage without charging is called the resting voltage. The resting voltage of a full battery is 12.74 and a completely empty battery is 11.88V. The difference between an empty and a full battery is therefore, regardless of size, 0.86V.
Modern solar panel charge controllers have a maximum power point tracking feature (MPPT, Maximum power point Tracking), which ensures that the solar panel connection works all the time at the voltage that gives the maximum possible power. Good charging controllers have temperature compensation for battery charging, which is necessary especially in the event that the batteries of the solar electric system are left in a cold cabin for the winter. A cold battery requires a higher charging voltage than a warm battery. Fully charged batteries can withstand frost well, but empty batteries are damaged by frost. Modern Charge Controllers allow solar panel switching to vary over a wide voltage range, e.g. 15 – 150 V, so they enable solar panels to be connected freely in an appropriate manner. The charging current of the charging controller and also the load current taken from the charging controller are limited. There are e.g. 10, 20 and 40 amp charging controllers available
Before the panels, connect the battery to the – and + terminals of the controller. Connect the panels to the – and + terminals. Connect all devices that consume more energy directly to the battery terminals.
Installation work of a low-voltage system
The system is low-voltage if its direct voltage is no more than 120 V and alternating voltage no more than 50 V. There is no essential difference in the amount of work and the prices of installation materials when installing a low-voltage and "normal" electrical system. A low-voltage system may be installed without professional qualifications and contracting rights in the electrical field. The basis is that you cannot get a dangerous electric shock from the low voltage. Even a low-voltage electrical system is not without danger: A short circuit can cause a fire, so fuses must be installed in all pairs of wires coming from the battery. Dropping a metal tool on top of the battery can also short-circuit the battery's terminals, as a result of which the battery discharges and the energy stored in the battery is released very quickly as heat in the battery's internal resistance. It is a good idea to cover the solar panels while connecting them, because the voltage produced by the panels can cause e.g. sparks when connecting the wires. However, shorting the panel will not damage the panel.
Consideration of transmission losses
Electric power is the product of current and voltage. Electricity transmission losses are proportional to the square of the electric current, i.e. inversely proportional to the square of the voltage. In a low-voltage (12 V) electrical system, the transmission loss in the conductor is approx. 400 times compared to a "normal" 240 V system, if the transmitted power and conductor thicknesses are the same. The most common installation cable in a 12 V system is a 2 x 2.5 mm2 cable - in a standard 240 V system, for example, a 16 A current can be conducted in a 2.5 mm2 copper cable for up to a hundred meters without significant transmission loss. - a rule of thumb: in a 12 V system, a current of 16 A can only be transferred the distance in meters that is the cross-sectional area of the conductor in square millimeters - if it is just LED lighting, the currents are small, on the order of one ampere, and transmission losses do not become a problem, even if the transmission distance would be tens of meters - e.g. the electricity needed by a 200 W and 12 V (approx. 16 A) coffee machine can be transferred in a 2.5 mm2 conductor only 2.5 m, a transmission distance of ten meters requires 10 mm2 conductors
Installing the inverter
Electrical equipment intended for direct current is less readily available than equipment intended for ordinary household alternating current. As a rule, direct current devices are more expensive than alternating current devices. 12 V LED lamps are fairly well available for lighting, so it is advisable to use direct voltage for lighting. The inverter converts 12 or 24 V direct voltage into 220 – 240 V alternating voltage. The inverter is connected directly to the battery terminals with short and thick wires. You can connect the inverter and also the extension cord from the inverter without having a professional qualification in the electrical field. Possible fixed installations for standard AC voltage require an installer with electrical contracting rights.
Low-voltage electrical system installation accessories
In the low-voltage electrical system, ordinary junction boxes and switches can be used, e.g. for lighting. The most common type of conductor is 2 x 2.5 mm2. Sockets and plugs are specially made, because the positive and negative poles have different meanings in direct current devices. If necessary, the frames of electrical devices can be grounded to the negative wire (the negative pole of the system is grounded).