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The application of Appropriate Technology

Articles for Keyword "solar power systems"

A Guide To Lead-Acid Battries

Posted on Jun 4, 2011

General information about lead-acid batteries, charging practice, determining the state of charge and safety tips.

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Part 4: PV Panel Arrays and Wiring

Posted on May 27, 2011

When the panel angles are connected together they are known as an array. The voltage of the array must be matched to the voltage of the battery bank (if one is being used). Typically the bulk charging of a 12V battery bank will be done at about 15V. It is clear from figures 10 and 11 that both the 85W and 160W panels of 15V will deliver about 5A at 25°C therefore paying for 160W panels would be a waist of money. When panels are connected together in parallel, shown in figure 12a, they will operate at the same voltage: if a parallel array of 85W panels are charging a twelve volt battery bank all of the panel will be operating at the charging voltage (i.e. about 15V). The current from each panel in a parallel array are added together so that two 85W panels in series will produce (2 x 5) 10A at 15V giving (10×15) 150W. Note that the panels have not been down rated from the manufacturer’s specifications. Panels connected in series, as depicted in figure 12b, work the other way round so that the voltage will be the sum of the voltages across both panels but the same current will flow through both panels. Therefore, two 85W panels in series can comfortably operate at 30V charging a 24V battery bank with 5A, once again the total power is (5×30) 150W. However, if these two panels in series were connected to a 12V battery bank they would operate at 15V and still produce about 5A, thus the power produced would only be (15×5) 75W. Panels can be combined in series and parallel to get the desired current at the battery bank voltage (figure 12c). If batteries are not being used and the panels are connected to a electricity supply grid through an inverter the panels are usually connected in a long series string. This has the advantage of keeping the current small and thus losses can be kept to a minimum and thinner, cheaper wires can be used. This is not possible with a battery system because the voltage across each panel is summed so that the operating of voltage of a 20 panel series array may be about 300V. A moderately sized 12V system will require about ten 85W panels in parallel, producing about 50A. This is quite a large current therefore quite thick wires are needed to connect the panels together and to convert the panels to a battery charger. Wires with a large diameter cause a smaller voltage drop and will not burnout when substantial currents are fed through them. Another consideration when wiring PV panels is that at night or when in deep shade the cells tend to draw current from the batteries rather than sending current to them, this effect obviously causes the batteries to lose charge. Most charge modern controllers contain diodes to prevent the flowing of a reverse current however, if the charge controller does not take account of...

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