According to many renewable energy experts, a stand-alone hybrid system that combines generation sources, such as wind and PV, offers several advantages over a single generation system.
In much of the United States, wind speeds are low in the summer when the sun shines brightest and longest. The wind is great in the winter when there is less sunlight. Since the greatest operating times for wind and PV occur at diverse times of the day and year, hybrid systems are more likely to yield energy once you need it. For the times when neither the wind generator nor the PV modules are producing electricity (for example, by night whilst the wind is not blowing), most stand-alone systems provide energy through batteries and/or an engine-generator powered by fossil fuels.
If the batteries run low, the engine-generator can be run by full power until the batteries are charged. Adding a fossil-fuel powered generator makes the system more complicated, but new electronic controllers can run these complicated systems without doubt. Adding an engine-generator can furthermore reduce the quantity of PV modules and batteries in the system. Keep in mind that the storage capability should be generous enough to supply electrical needs for the period of non-charging periods. Battery banks are typically sized for one to three days of function. An all-purpose rule is to design the renewable energy system to provide 80% of the energy and use fossil fuels for the residual 20%.
Balance-of-System (BOS) Equipment
In addition to wind turbines, PV modules, or a microhydropower generator, you should pay for BOS equipment. This could include battery charge controllers, batteries, inverters, wires, conduit, a grounding circuit, fuses, safety disconnects, outlets, metal structures for supporting the PV modules, and any other components that are part of the system.
In very little systems, DC appliances run directly off the batteries. If you like to use standard appliances that require normal household alternating current (AC), however, you should install an inverter to convert DC electricity to AC. Although the inverter to some extent lowers the overall efficiency of the system, it allows the home to be wired for AC, a definite plus with lenders, electrical code officials, and prospect home buyers. We’ll discuss BOS configurations initially for loads requiring direct current, then for loads needing alternating current. In grid-connected systems, the single extra equipment required is an inverter that makes the turbine output electrically compatible with the utility grid. No batteries are required. Work with the manufacturer and your regional utility on this process. When examining the expenses of wind turbines, PV modules, or microhydropower generators, remember that these expenses do not include the cost of BOS equipment.
Direct-Current System Equipment Battery.
In off-grid systems, the battery stores electricity for work at night or for meeting loads throughout the day as the generation source (wind turbines, PV, or microhydropower) is not creating enough electricity to endure load supplies. To provide electricity over lengthy periods, renewable systems require deep-cycle batteries. These batteries, commonly lead-acid, are designed to regularly discharge and recharge 80% of their capacity hundreds of times. Automotive batteries are shallow-cycle batteries and must not be used in renewable systems since they are planned to discharge just about 20% of their capacity. If drawn much under 20% capacity more than a few dozen times, the battery will be damaged and will no longer be able to take a charge.
The cost of deep-cycle batteries depends on the type, capacity (amperehours), the climatic conditions in which it will run, how frequently it will receive maintenance, and the types of chemicals it uses to store and make available electricity. An off-grid PV or wind system could have to be sized to save a sufficient amount of energy in the batteries to endure power demand during few days of gray weather or low winds. This is recognized as days of autonomy. Consult your dealer previous to selecting batteries for your system.
The charge controller regulates the flow of electricity from the generation source to the battery and the load. The controller keeps the battery fully charged with no overcharging it. When the load is drawing energy, the controller allows the charge to flow from the generation source into the battery, the load, or both. When the controller senses that the battery is full, it stops the flow of the charge from the generation source. Many controllers will also feel when loads have taken too much electricity from batteries and will bar the flow until enough charge is restored to the batteries. This last attribute can greatly enlarge the battery’s life span. The cost of controllers commonly depends on the ampere capacity at which your renewable system will run and the monitoring features you would like.
Alternating-Current System Equipment Inverter.
Alternating-current (AC) systems too require an inverter, which changes the DC electricity created by renewable systems and stored in batteries into AC electricity. Various types of inverters yield a diverse quality of electricity. For example, illumination, televisions, and power tools can run on lower-quality electricity, but computers and other sophisticated electronic equipment require the highest-quality electricity. So, you must match the electricity quality required by your loads with the power quality created by the inverter.
Inverters for most stand-alone applications (i.e., those systems not connected to the electricity grid) cost less than $1 per rated output watt. The cost is affected by few factors, including the quality of the electricity it needs to yield; whether the incoming DC voltage is 12, 24, 36, or 48 volts; the amount of AC watts your loads require when they are operating normally; the amount of additional surge energy your AC loads need for short periods; and whether the inverter has any additional features such as meters and indicator lights.