While
designing a solar photovoltaic off-grid system, you need to determine required
batteries. A little math is necessary to size batteries. An
off-grid battery bank should be designed in such a way that the system is
not only sufficient enough to supply necessary power during cloudy days but also
small enough to be charged by your solar panels. First of all, you need to decide how much storage you want to provide by
your battery bank. It is familiar as “days of autonomy" which is based on your expected number of days power provided by the system without receiving an input charge from the solar
array. Beside determining days of autonomy, you also need to consider the critical situation and usage pattern of your application. If you decide to install a system for a weekend home, you need to consider a
larger battery bank for charging
and storing energy all week. But, if you want to add a photovoltaic array to a generator-based system as supplement, then you need to undersized your battery bank slightly as the generator can be operated based on recharging needed.
Rated Capacity of Battery
Basically, the capacity of a battery is specified as Ampere-Hour (AH) along with some specific standard hour reference like twenty or ten hours. For example, you have a battery which is rated at 200 Ampere-Hours and specified as a 20 hour reference. This means the
battery is fully charged and will deliver a current of 10 amperes for 20
hours. If the discharge current decreases then the capacity will increase.
Depth of Discharge
The percentage of the rated battery capacity
that is withdrawn from the battery is called depth of discharge. The withstand discharge capability of a battery depends on its construction. Batteries are specified by two commonly use terms. They are deep cycle and shallow cycle. Shallow-cycle batteries are comparatively cheap, lighter and have a short
lifetime. Stand-alone photovoltaic systems should use deep cycle battery. Deep cycle batteries contain thicker plates and withstand up to 80% daily discharges of their rated capacity. These type of batteries are
flooded electrolyte. That is the plates of batteries are covered with the
electrolyte. In order to keep the plates fully covered, it is required to monitor the level of fluid and add distilled water
added periodically.
Effect of Temperature
Batteries are very temperature sensitive. You cannot expect as
much energy out of a cold battery as a warm one. Though, you can get more than rated capacity from a hot battery, operation at
hot temperatures will decrease the lifetime of battery. It is recommended to keep your batteries
near room temperature. In order to optimize the charging cycle at
various temperatures and increase the lifetime of your battery, charge controllers can be purchased with a
temperature compensation option.
Lifetime of Battery
It is quite difficult to predict the lifetime of any battery absolutely. Because it depends on various factors like depth of discharge, charging and discharging rate, number of cycles and operating at extreme temperature. It is quite exceptional for a lead-acid battery to last longer than fifteen
years in a photovoltaic system. But, usually it can last up to eight years.
Maintenance of Battery
Periodic maintenance is required for batteries. In order to ensure that connections are tight and there is no indication
of overcharging, it is necessary to check sealed battery periodically. For flooded batteries, it is required to maintain the plates well above the electrolyte level, check the voltage and specific gravity
of the cells for consistent values. If the reading shows a large variation, then it may indicate cell problems. It is necessary to check the specific gravity of the
cells by a hydrometer before the onset
of winter particularly. The electrolyte in lead-acid batteries
may freeze in cold environment. The freezing temperature is a function of a battery state
of charge. The electrolyte becomes water and battery may freeze if it is completely discharged.
Sizing the Battery
The recommended battery type for using in solar photovoltaic system is deep cycle battery. Deep
cycle battery can discharge to low
energy level. It also can be recharged rapidly. In order to operate at night and cloudy days, the battery should be large enough to store
sufficient energy. The size of battery is determined as follows:
- Determine the total Watt-Hours/day consumed by appliances.
- Divide the total Watt-Hours/day consumed by the battery loss factor (typically, it is 0.85).
- Divide the answer you got in item 2 by the depth of discharge of battery (typically it is 0.6).
- Divide the answer you got in item 3 by the Nominal Battery Voltage.
- Multiply the answer you got in item 4 with days of autonomy (the number of days required for the system to operate by solar panels when there is no power generated) to get the required capacity of the deep-cycle battery in Ampere-Hour (AH).
This is really an important blog with many helpful information. I have been searching for a long time for this types of content. Keep up posting more and thanks for your great staff.
ReplyDeleteBattery Operated Ultrasonic Level Sensor
Thanks for reading the post and commenting.
DeleteGreeting!
ReplyDeleteYour blog is really very informative. Solar energy for home is an absolute need of the hour because it is time for a sustainable energy policy which puts consumers, environments, human health and peace first.
Thanks Karia for your comment and sharing your opinion.
DeleteI am realy happy for this post.i think i will get a good result for this
ReplyDeleterated best green product
Thanks Hiedi for reading the post and commenting.
Deletebatteries for solar storage
ReplyDeleteLithium Battery Store is the best Batteries provider company in affordable cost we sell every type of Batteries like solar energy
storage batteries, solar panel batteries and lithium ion batteries. More about all types of batteries near me
Thanks for sharing the information.
Delete