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Your Position: > Knowledge >> Solar Products Knowledge >>> Charging battery by using a Solar Panel&Charge Controller

Charging battery by using a Solar Panel&Charge Controller

blue-light / 2011-08-11
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How to place a solar panel to maximize solar harvest 
The energy harvest from a solar system depends on location. The following map gives average daily solar radiation anywhere in the USA.
In addition, in a particular location the energy harvest depends on the inclination of the roof as well as shadowing:
Shading affects the performance of PV Systems with lower energy yield. For example, a branch of a tree can cover a portion of solar panel with very significant drop in power output from the panel.
How to connect a basic system 
Grid-tied system with batteries can store power when you produce more electricity than you need. For example, you can use such a system to store additional energy, produced during a bright sunny day, in a battery for later use at night. You can also use this energy during a grid outage. One important consideration is to estimate typical length of grid-outages in your area. Then, it is necessary to match the battery capacity so that there is sufficient energy (ampere-hour capacity) to meet your power load needs for the estimated time of power outages.
The following diagram shows a basic PV solar system interconnection with a battery bank.
Off-Grid PV Solar System with Batteries 
A Off-grid (or standalone) PV system can operate independently and is often used in remote locations where there is no utility grid service. For example, one possible use of standalone PV systems is in “cottages” where it is prohibitively expensive to bring utility lines over a long distance or rough terrain. People like standalone PV systems because they enable independence from the utility. However, people must apply some discretion when and how to use (PV system generated) electricity – it may not be ample enough to meet your needs unless your investment is significantly high. Or, your energy consumption is altered to match with the capabilities of your PV generated energy.
Standalone PV systems provide DC (direct current) to operate DC loads, such as lights, and to charge PV battery banks. Through an inverter, DC is converted to AC (alternating current) to operate household AC appliances and other consumer electronic devices common to most residential homes. Standalone (Off-grid) systems use batteries to store power – to supply electricity at night or during periods of low or no sunlight.
If you’re planning to use a standalone PV system that includes batteries, as a homeowner, you need to follow some design considerations for your choice. For example, the battery cost can be very high for installing a large-capacity system (higher KWh) that is designed to meet electricity requirement for your worst-case scenario. A large system requires larger batteries in (Ah), increasing the cost of your PV system by a significant amount. Instead, for a standalone system, you can consider using a medium-sized PV system that can meet your regular or short-term electricity requirements.
Charge controllers have current ratings of 4.5 amps to 60 amps. If your system requires currents over 40 amps, two or more 20 to 40-amp units are wired in parallel. The most common controllers used for all battery-based systems are in the 6 to 40-amp range.
In a normal grid-tied operation, the charge controller requires to be closed (electrically connected) for charging purposes. The reason for this is that any excess power from the arrays is automatically sold to the utility and it is quite unlikely that the battery voltage level will go above the predetermined setting. But, if for any reason, the PV solar system is unable to deliver the power to the grid (for example, due to a non-functioning inverter or when the grid loses power); the charge controller must disconnect the arrays from charging the batteries as soon as the voltage level of the batteries go above the pre-determined setting.
The charge controller also referred to as regulator since it regulates the electrical charge from solar PV modules.
Note that a charge controller is not needed for a PV solar system that forgoes the use of batteries completely and feeds electricity from the PV panels to the inverter.
A charge controller performs the following:
1) Blocks reverse current
1) Prevents overcharge
2) Control set points versus temperature
3) Control set points versus battery type
4) Disconnect load at low voltages (i.e. LVD)
5) Overload protection
6) Displays and monitoring
*Not all charge controllers come standard with the above features.  Please refer to product descriptions and/or data sheet for a complete list of product functionality. Some of the above such as LVD and displays must be purchased as accessories.
A more sophisticated charge controller is available in the market today. This is called the MPPT or Maximum Power Point Tracking solar electric charge controller. This controller monitors the output of the panels and compares it to the battery voltage. It then figures out what is the best power that the panel can put out to charge the battery. It takes this and converts it to best voltage to get maximum Amp to the battery. Since it is the Amps into the battery that counts, most modern MPPTs are around 92-97% efficient in the conversion. You typically get a 20 to 45% power gain in winter and 10-15% in summer. Actual gain can vary widely depending weather, temperature.
How to Connect a Charge Controller
The following diagram shows the interconnection for charge controller, battery bank and solar panel array.
Common mistakes to avoid for charge controller installation
• Follow all safety precaution of the battery manufacturer
• Don’t exceed the unit’s voltage and current ratings
• Follow the appropriate wiring instructions (length and type of wire, AWG, distance round trip in meter)
• Don’t reverse battery (+ or –) connections to the controller.
• Don’t reverse the battery and solar array connections to the charge controller
Solar Harvest for a Sample Residential System
You know how much electricity you need per month: say 1000 kWh
Then daily need of electricity: 1000 kWh/30 = 33.3 kWh/day
Solar insolation: depends on location where you live:
Let us consider our sample system is located somewhere in the yellow region of the above map: 
We need a system of 33.3/5= 6.6 kWp (Kilowatt peak)
Assume 1) Solar insolation: 5 kWh/m2/day; 2) 5 hours of peak solar radiation per day
Multiply by a safety margin: 1.25 = 8.25 kWp
An alternative calculation: 
How much solar energy we can get from 10 solar panels, each of 270 Watts (at a location where the average peak solar radiation is for 4 hours/day), assume 0.8= efficiency factor:
2700 x 4 hours per day x 0.8 x 30 days = 259200 watt-hour or 260 kWh (per month).

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