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Balance Of System Components for Solar PV and Wind Turbines

   

Solar PV & Wind Turbine - Balance of System Components

Be it a nice sized solar array or wind turbine high upon a tower, you still need to get that renewable power into a usable format. That means cabling/wiring, fuses, batteries, controllers, inverters, switches, disconnects, meters, etc.

Cabling/Wiring

It is important to avoid excessive loss of power from voltage drop in the wire, from the source (wind generator or solar panels) to the controller/inverter. It is not necessary to use a wire size that minimizes voltage drop for the maximum generator output as this thick cable could be very expensive. Better to choose a wire size that gives a 2% voltage drop, for the average generator output. If the cost of wiring is excessive, you may want to look at turbines that output power in AC. You then convert it to DC just before connecting to the battery controller. Sending the AC power directly to the grid may also be an option of you have a feed-in tariff or net-metering arrangement with your electrical power provider.

Batteries
deep discharge batteries

One of the most important terms related to your battery bank is Depth of Discharge. This is the amount of energy you can take from a battery and still have it charge up again. If you drain 90%-100% of a battery's power, you radically shorten the life of that battery. Batteries made to work in your wind or solar system are designed to allow for a fairly deep discharge, usually 50%, and still recharge. Car batteries do NOT have a deep discharge and will fail prematurely if used. Capacity is rated in Amp Hours; number of amps multiplied by the hours of load supplied. Batteries located inside a building need to be properly vented. Types of batteries include:

Flooded Cell

- most common. Have removable caps for adding distilled water. Lower in cost. Have a long life. Will withstand overcharging.

Sealed Flooded Cell

- are maintenance free. Do not require water. Can be damaged by overcharging.

Recombinant Flooded Cell

- do not require water. Tend to be expensive. Can be damaged by overcharging.

Gelled Electrolyte Cells

- do not require water. Tend to be expensive. Can be damaged by overcharging. Can be mounted in various positions and will not spill acid.

Controllers/Charge Regulators

Charge regulators control the amount of charge that is sent to the battery bank, to protect it from overcharging and completely discharging. Some controllers include a maximum power point tracker (MPPT) for PV modules, in order to get the maximum amount of power out of the array. An MPPT controller can get 10% more power out of your array in the summer and 30% more power in winter. These gains are generally higher for panels with high voltage peak (Vp) values.

Inverters

Converts DC power into AC power. About 5% of the energy is lost in the conversion process.

Central Inverters

The input voltages range from 12, 24, 48 and up. Smaller units (under 1000 watts) may have only one input voltage and may produce a modified sine wave. AC produced using a modified sine wave may not power sensitive electronic equipment such as computers or laser printers. Higher end inverters usually produce a true sine wave version of AC. Higher end inverters also come with a range of additional features including remote meters, automatic generator start-up, built-in charge controllers, etc. Inverters are also designed specifically for GRID connection or for off-grid use. Grid connection inverters have the ability to synchronize with the utility (grid) power and will have automatic shut-off should the grid power be interrupted.

Balance of PV System

The Sunny Boy inverter I have connected to my grid-tie system, has an input range of up to 600 VDC.

Micro-Inverters

Solar micro-inverters converter the DC power from one or two solar panels, into AC power. The output from the micro-inverters is fused and combined and then connected to the grid via a disconnect box/unit.

Combiner Boxes

Combines the PV strings into a single output which then feeds the inverter for central inverters. For micro-inverters, the combination point is after the inverter, combining the AC outputs. Each individual string or micro-inverter is fused. This also provides a testing point for each string/micro-inverter should issues arise with the solar array.

Disconnect Unit

Provides a switched disconnect point, to disconnect the local energy source (inverter) from the grid. The local power company usually controls access to the disconnect unit via locks they provide.

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