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PV Batteries |
Batteries accumulate excess energy created by your PV system and store it to be used at night or when there is no other energy input. Batteries can discharge rapidly and yield more current that the charging source can produce by itself, so pumps or motors can be run intermittently.
The battery's capacity for holding energy is rated in amp-hours: 1 amp delivered for 1 hour = 1-amp hour
Battery capacity is listed in amp hours at a given voltage, e.g. 220 amp-hours at 6 volts. Manufacturer's typically rate storage batteries at a 20-hour rate:
220 amp-hour battery will deliver 11 amps for 20 hrs
This rating is designed only as a means to compare different batteries to the same standard and is not to be taken as a performance guarantee. Batteries are electrochemical devices sensitive to climate, charge/discharge cycle history, temperature, and age. The performance of your battery depends on climate, location and usage patterns. For every 1.0 amp-hour you remove from your battery, you will need to pump about 1.25 amp-hours back in to return the battery to the same charge state of charge. This figure also varies with temperature, battery type and age.
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Battery Types |
Different chemicals can be combined to make batteries. Some combinations are low cost but low power also, others can store huge power at huge prices. Lead-acid batteries offer the best balance of capacity per dollar and it's a common battery used in stand-alone power systems. In this section we will cover lead-acid batteries, for information on other type of batteries, please visit the FAQ link above.
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Lead-Acid Batteries - How They work |
The lead-acid battery cell consists of positive and negative lead plates of different composition suspended in a sulfuric acid solution called electrolyte. When cells discharge, sulfur molecules from the electrolyte bond with the lead plates and releases electrons. When the cell recharges, excess electrons go back to the electrolyte. A battery develops voltage from this chemical reaction. Electricity is the flow of electrons.
In a typical lead-acid battery, the voltage is approximately 2 volts per cell regardless of cell size. Electricity flows from the battery as soon as there is a circuit between the positive and negative terminals. This happens when any load (appliance) that needs electricity is connected to the battery.
Good care and caution should be used at all times when handling a battery. Improper battery use can result in explosion. Read all documentation included with your battery in its entirety.
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Wattage, Volts, Amps, etc. |
Most electrical appliances in the United States are rated with wattage, a measure of energy consumption per unit of time. One watt delivered for one hour equals one watt-hour. Wattage is the product of current (amps) multiplied by voltage.
watt = amps x volt
One amp delivered at 120 volts is the same amount of wattage as 10 amps delivered 12 volts:
1 amp at 120 volts = 10 amps at 12 volts
Wattage is independent of voltage:
1 watt at 120 volts = 1 watt at 12 volts
To convert a battery's amp-hour capacity to watt-hours, multiply the amp-hours times the voltage. The product is watt-hours.
To figure out how much battery capacity it will require to run an appliance for a given time, multiply the appliance wattage times the number of hours it will run to yield the total watt-hours. Then divide by the battery voltage to get the amp hours.
For example, running a 60-watt lightbulb for one hour uses 60 watt-hours. If a 12-volt battery is running the light it will consume 5 amp-hours (60 watt-hours divided by 12 volts equals 5 amp-hours)
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How big a battery do I need for a PV System? |
Ideally, a battery bank should be sized to be able to store power for 5 days of autonomy during cloudy weather. If the battery bank is smaller than 3 day capacity, it is going to cycle deeply on a regular basis and the battery will have a shorter life. System size, individual needs and expectations will determine the best battery size for your system.
Please contact us and our engineers and consultants will be happy to assist you.
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Battery Cycles |
Batteries are rated according to their "cycles". Batteries can have shallow cycles between 10% to 15% of the battery's total capacity, or deep cycles up to 50% to 80%. Shallow-cycle batteries, as those for starting a car, are designed to deliver several hundred amperes for a few seconds, then the alternator takes over and the battery is quickly recharged. Deep-cycle batteries or the other hand, deliver a few amperes for hundreds of hours between charges. These two types of batteries are designed for different applications and should not be interchanged. Deep-cycle batteries are capable of many repeated deep cycles and are best suited for PV power systems.
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Lead-Acid Battery Types |
Starting Batteries - Shallow cycle automotive battery not suitable for Photovoltaic Systems.
RV or Marine "Deep-Cycle" - 12 volt batteries usually 80 and 160-amp hour capacity. A compromise between shallow and true deep cycle batteries. Life expectancy is about 2 to 3 years.
Lead-Calcium Batteries -Occasionally these shallow-cycle batteries recycled from the telephone company are used in remote power systems. At 400 pounds per 2 volt cell and cycle limited to 15% - 20%, these batteries are not recommended.
Sealed Batteries - These are liquid-tight batteries that can operate in any position without leaking acid. Because of the seal construction, you cannot check cell conditions with a hydrometer. Vents prevent pressure build-up in case of gassing. Recommended only for situations where hydrogen gassing during charging cannot be tolerated, or the battery is going to be moved a great deal, or to be fit in tight spaces. Require lower voltage charge controls. Most AGM batteries (absorbed glass mat) have a life expectancy of 2-5 years, and 5-10 years for higher quality Gel cell batteries. Most sealed batteries are AGM.
True Deep-Cycle Batteries - True deep-cycle batteries are specifically designed for energy storage and deep-cycle service. They tend to have larger and thicker plates as shown in the image above. Ideal for renewable energy systems, deep-cycle batteries withstand having a majority of their capacity used before being recharged and survive hundreds and even thousands of 80% cycles. It is recommended to use 50% as the normal maximum discharge and leave 30% for emergencies. Do not use the bottom 20%, the less deeply you cycle your battery, they longer it will last. Available in many sizes and types.
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Products |
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SunXTender
PV System Battery
Deep-Cycle w/ backup power
Made by Concorde Corporation |
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