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Types of Photovoltaic
Systems
Small Stand-Alone DC or AC System
The small stand-alone system is an excellent replacement for propane
or kerosene lights in a remote cabin, a recreational vehicle or a boat.
The size of the photovoltaic (PV) array and battery will depend upon individual
requirements. The actual sizing methods are discussed elsewhere. The PV
array charges the battery during daylight hours and the battery supplies
power to the loads as needed. The charge regulator terminates the charging
when the battery reaches full charge. The load center may contain meters
to monitor system operation and fuses to protect wiring in the event of
malfunction or short circuit in the house. You can add more panels
and an inverter to make this an AC Stand-Alone System.
PV
- Generator Combination
The PV - Generator Combination system may be an economical
alternative to a large stand-alone PV system, because the PV array
does not have to be sized large enough for worst case weather conditions.
A gasoline, propane, diesel, wind, or micro-hydro generator combined with
a battery charger can supply power when the PV array falls short. If the
PV array is sized for average conditions, then during extended overcast
situations or periods of increased load, the generator can be started.
When batteries are low, the generator will power the AC loads in the house
as well as a battery charger to help recharge the batteries. If the PV
array is sized much smaller than needed for normal use, the generator
can power peak loads such as doing laundry or pumping water and simultaneously
run the battery charger to charge the battery bank. In addition to allowing
for a smaller PV array, a back-up charging system may also allow use of
a smaller battery bank. Generator and battery bank size must be chosen
carefully for reliable system operation. See the system sizing section
for more details on equipment choice.
Utility Integrated System (Alternating
Current Solar System (not grid intertied))
For
areas that don't have utility Intertie easily available or if you want
backup power. Same as the Utility Intertie system below, but with battery
storage. If your PV array is large enough you will only need the Utility
(Grid) for backup power; i.e. extended cloudy periods.
Any
of the systems above can be made into a hybrid system with the addition
of a gas, wind, steam or micro-hydo generator.
Utility Intertie (Alternating
Current Solar System (grid tied))
The
utility intertie system is also used in a grid connected house. Instead
of storing power in batteries, it is sold to the utility company. The Utility
Intertie System employs a special type of inverter, which inverts DC power
from the PV array into low distortion AC, acceptable for purchase by the
local utility power company. Batteries are not required for storage. The
power is delivered through a kilowatt-hour (kWh) meter to the utility grid
as it is produced by the PV modules. A second kWh meter is used to measure
the power consumed by the loads in the house. The user of this system will
notice no difference from any utility system, except lower utility bills
or possibly payments from the power company for excess electricity that
is generated. This type of system tends to be an optimum configuration
from an
economic viewpoint because all the electricity is utilized by the owner
during the day and any surplus is exported to the grid. Meanwhile, the cost
of storage to meet night-time needs is avoided, because the owner simply
draws on the grid in the usual way. Also, with access to the grid, the system
does not need to be sized to meet peak loads.
AC Photovoltaic Module Intertie
At last ordinary home owners can begin to reduce their dependence
on utility power for their electricity. This type of utility sellback
system is comprised of PV modules with small inverters mounted on them.
This allows the output of the inverter-module combinations to be connected
directly to the AC line. The utility may require a second meter and disconnect.
The installation cost of this type of intertie system is much lower than
that of a large inverter system. A small system can be installed, and
as finances allow, additional AC PV modules can easily be added to the
system.
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