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advantages are long cycle life, low internal resistance, making them suitable for high
power applications, and easy determination of the state of charge, which is directly
related to the voltage.
Super capacitors are unsuited to long- or medium-term storage because of their high
rate of self-discharge. However, they may find application where peak power demand
is high, such as during starting of pumps or in smoothing power fluctuations (Sauer,
2003).

6.7 POWER CONDITIONING AND REGULATION

6.7.1 Diodes
Blocking diodes protect the battery from short circuits in the solar array, as well as
preventing the batteries from discharging through the solar cells when they are not
illuminated. Their function is often satisfied by charge regulators.
Diode voltage droppers can also be used to ensure the batteries do not supply excess
voltages to the load.
6.7.2 Regulators

Battery voltage regulators, also known as charge controllers, are needed in PV-based
power systems to protect batteries by limiting discharge levels and overcharging
(Roberts, 1991; Preiser, 2003; Schmid & Schmidt, 2003; von Aichberger, 2004).
Regulators are not specified in detail by any Australian Standard but guidelines for
regulators in small solar home systems intended for rural areas (see Section 8.9) are
included in the Universal Technical Standard for Solar Home Systems (UPM, 2003)
and by Usher and Ross (1998). Four set points are commonly specified (Watts et al.,
1984), namely:
1. Regulation set point (VR)—the maximum allowable voltage. On reaching
VR, the controller either discontinues charging or regulates the current
delivered to the battery. Temperature compensation is needed for VR unless
battery temperatures vary by less than ±5°C.
2. Regulation hysteresis (VRH)—the difference between VR and the voltage at
which maximum array charging current is restored. If VRH is set too large,
there will be long interruptions to charging. If VRH is set too small there will
be frequent oscillations, possibly with noise and with the potential to damage
the switching elements. The voltage level VR – VRH is called VRR (Usher &
Ross, 1998).
3. Low voltage disconnect (LVD)—defines the voltage at which the load is
disconnected and hence the maximum depth-of-discharge and available
battery capacity. LVD prevents over-discharge.

4. Low voltage disconnect hysteresis (LVDH)—the voltage span between the
LVD and the voltage at which load reconnection is allowable following
disconnection. If LVDH is set too small, the load cycles on and off rapidly at
low battery state of charge, possibly leading to controller and/or load damage.
If it is too high, the load will remain off for extended periods. The voltage

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