5.5.2 Solar Components
The components of a solar system include the battery and the solar panel.
Battery
The DXM solar controller is designed to use a 12 V sealed lead acid (SLA) battery. The characteristics of a solar system
require the battery to be of a certain type. There are two types of lead acid batteries:
•
SLI batteries (Starting Lights Ignition) designed for quick bursts of energy, like starting engines
•
Deep Cycle batteries - greater long-term energy delivery. This is the best choice for a solar battery.
Since a solar system charges and discharges daily, a deep cycle battery is the best choice. There are different versions of a
lead acid battery: wet cell (flooded), gel cell, and an absorbed glass mat (AGM).
Wet cell batteries are the original type of rechargeable battery and come in two styles, serviceable and maintenance free.
Wet cell batteries typically require special attention to ventilation as well as periodic maintenance but are the lowest cost. The
gel cell and AGM battery are sealed batteries that cost more but store very well and do not tend to sulfate or degrade as
easily as a wet cell. Gel or AGM batteries are the safest lead acid batteries you can use.
Battery capacity
is a function of the ambient temperature and the rate of discharge. Depending upon the specific battery, a
battery operating at –30 °C can have as much as 40 percent less capacity than a battery operating at 20 °C. Choose enough
battery capacity based on your geographical location.
Table 7: Average voltage readings relative to battery charge
State of Charge (%)
Open Circuit Voltage
100
13.0 or higher
75
12.6
50
12.1
25
11.66
0
11.4 or less
A larger capacity battery typically lasts longer for a given solar application because lead-acid batteries do not like deep
cycling (discharging a large percentage of its capacity). Depending upon the battery, a battery discharging only 30 percent of
its capacity before recharging will have approximately 1100 charge/discharge cycles. The same battery discharging 50
percent of its capacity will have approximately 500 charge/discharge cycles. Discharging 100 percent leaves the battery with
only 200 charge/discharge cycles.
Use this information as a guide to the approximate state of charge and in determining when to apply conservation measures.
Batteries degrade over time based on discharge/charge cycles and environmental conditions. Always monitor the battery
system to obtain the best performance of the solar powered system.
Solar Panel
Banner solar panels come in two common sizes for the DXM: 5 Watt and 20 Watt. Both panels are designed to work with the
DXM but provide different charging characteristics. Use the 5 watt panel for light duty operation and use the 20 watt panel
when you require greater charging capabilities.
Solar Panel
Voltage
Current
Typical DXM Configurations
5 Watt
17 V
0.29 A
DXM Controller configured as a slave, ISM radio, I/O base board
20 Watt
21 V
1 A
DXM Controller with ISM radio and Cellular modem
Photovoltaic panels are very sensitive to shading. Unlike solar thermal panels, PV solar panels cannot tolerate shading from
a branch of a leafless tree or small amounts of snow in the corners of the panel. Because all cells are connected in a series
string, the weakest cell will bring down the other cells' power level.
Good quality solar panels will not degrade much from year to year, typically less than 1 percent .
To capture the maximum amount of solar radiation throughout the year, mount a fixed solar panel to optimize the sun's
energy. For the northern hemisphere, face the panel true south. For the southern hemisphere, face the panel true north. If
you are using a compass to orientate the panels, compensate for the difference between true north and magnetic north.
Magnetic declination varies across the globe.
A solar panel's average tilt from horizontal is at an angle equal to the latitude of the site location. For optimum performance,
adjust the tilt by plus 15 degrees in the winter or minus 15 degrees in the summer. For a fixed panel with a consistent power
requirement throughout the year, adjust the tilt angle to optimize for the winter months: latitude plus 15 degrees. Although in
the summer months the angle may not be the most efficient, there are more hours of solar energy available.
Sure Cross
®
DXM100-Sx Wireless Modbus Slave
www.bannerengineering.com - Tel: + 1 888 373 6767
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