Topic:Off-grid system&Off-grid system
Two main solar system
Off-grid solar system On-grid solar system
Off-grid PV systems
Standalone photovoltaic power generation system, also known as off-grid PV systems.
In the absence of the grid area, the use of solar modules emit DC, charged by solar battery
charge controller for the use of electrical appliances.
The DC(direct current) energy of battery can be supplied directly to the DC electrical
appliances and other uses, such a system can be called the DC off-grid photovoltaic systems;
Battery is connected to off-grid inverter, a solar inverter, or PV inverter, converts the
variable direct current (DC) output of a photovoltaic (PV) solar panel into a utility frequency
alternating current (AC) that can be fed into a commercial electrical grid or used by a local, off-
grid electrical network. It is a critical component in a photovoltaic system, allowing the use of
ordinary commercial appliances. Solar inverters have special functions adapted for use with
photovoltaic arrays, including maximum power point tracking and anti-islanding protection.
Advantage of off-grid PV systems
Off-grid PV system with its flexible and reliable features meet the
demand of grasslands, deserts, islands and other areas home use
electricity, and achieved good results.
Small decentralized off-grid PV systems, especially building
integrated photovoltaic power generation systems, because of the
advantage of small investment ,fast construction, small footprint,
policy support ,the off-grid PV systems gradually become the
System accessory - solar panels, controller
Solar panels: solar panel is the core part of the solar system, the most valuable
part of the whole system . Its role is to conver the sun's radiation to electrical
energy stored in batteries or supply for the electrial appliances’work.
Solar Controller: Solar controller's role is to control the working status of the
entire system, and protect the battery from discharging or over-discharging. In
the large temperature difference condition, the controller should be equiped
with temperature compensation function. Its additional features such as light
control switch, time control switch ,should be the options of controller.
System accessory - batteries, inverters
Battery: lead-acid batteries, small micro-system, can also use nickel metal
hydride batteries, nickel cadmium batteries or lithium batteries. Its role is to
store the energy when there is light emitted by the solar panels, and then
released when needed.
Inverter: Generally,the direct solar energy output are 12VDC, 24VDC,
48VDC. Providing energy for 220VAC electrical appliance, the DC energy
generated by solar power system should be coverted into AC power, so we
need to use the DC-AC inverter.
Factors need to consider
Off-grid Solar power system design factors to consider are below:
where Solar power system is supposed to install?
How is the solar radiation situation?
The load power of the system ?
What is the system output voltage?DC or AC?
How many hours the system need to work per day?
If there is no sunlight or in rainy weather, the longest days the system needs to
continuously supply the power for daily use ?
Load conditions, purely resistive, capacitive or inductive, starting current much?
Case: solar home systems
Generation capacity: 1000 watts
Target facilities: individual residentialUsage: lighting, TV, radio, lights
Advantages: simple structure,Very suitable for living in scattered villages,
it is more accurate, because the user is a single household
100 ~ 150Wp home solar power system
Type Load power
Light LED 11W 2 set 3/4 88Wh
25W 1set 3/4 100Wh
Color TV 21inch 70W 1set 3/4 280Wh
Total 117W 468Wh
Solar panel ： 100W~150Wp ；
Maintenance-free batteries ： 50~65AH/24V ；
Inverter ： 150W ； Charge Controller ： 6A ；
Installation: Easy self-installing Can★
work continuously for three rainy days★
Application of off-grid solar system
Living in remote areas without electricity, electricity lighting, television, washing
machines and other household electricity;
Photovoltaic pump without electricity .deep wells for drinking, irrigation
Traffic lights in the field beacon lights, traffic / rail lights, traffic warning / marker
lights, street lights
And auto ancillary solar car / electric car, battery charging equipment, car air
conditioners, ventilation fans, refrigerators, etc.
Aerospace instrument satellites, spacecraft, space solar power station
Communication / Tele communications field solar unattended microwave relay stations,
cable maintenance station, Radio / Communication / Paging power system
Petroleum, marine, meteorology oil pipelines and reservoirs gate cathodic protection
solar power systems, oil rigs Health
Live and emergency power, marine testing equipment, meteorological / hydrological
observation equipment, etc.
Other portable appliances, desalination equipment and power supply
On-grid Pv system
Grid-connected photovoltaic power systems are power systems energized
by photovoltaic panels which are connected to the utility grid.
Grid-connected photovoltaic power systems consist of Photovoltaic
panels, MPPT, solar inverters, power conditioning units and grid connection
Unlike Stand-alone photovoltaic power systems these systems seldom have
batteries. When conditions are right, the grid-connected PV system supplies the
excess power, beyond consumption by the connected load, to the utility grid
Solar energy gathered by photovoltaic solar panels, intended for delivery to a
power grid, must be conditioned, or processed for use, by a grid-connected
inverter. This inverter sits between the solar array and the grid, draws energy
from each, and may be a large stand-alone unit or may be a collection of small
inverters, each physically attached to individual solar panels. See AC Module.
The inverter must monitor grid voltage, waveform, and frequency. One reason
for monitoring is if the grid is dead or strays too far out of its nominal
specifications, the inverter must not pass along any solar energy. An inverter
connected to a malfunctioning power line will automatically disconnect in
accordance with safety rules,
Another reason for the inverter monitoring the grid is because for normal
operation the inverter must synchronize with the grid waveform, and produce
a voltage slightly higher than the grid itself, in order for energy to smoothly
flow outward from the solar array. For more details on inverter operation
System accessory -DC / AC inverter
DC / AC inverter
The device can Convert the DC power into AC power . Because the current the solar
system generate is direct current, and general loads are AC load, the inverter is
Grid inverter Is used in the on-grid solar power generation system ,It can feed the
electricity generated by the system into the national grid.
Islanding refers to the condition in
which a distributed generator continues
to power a location even though power
from the electric utilityis no longer
present. Islanding can be dangerous to
utility workers, who may not realize that
a circuit is still powered, even though
there's no power from the electrical grid.
For that reason, distributed generators
must detect islanding and immediately
stop producing power; this is referred to
In the case of a utility blackout in a grid-
connected PV system, the solar panels
will continue to deliver power as long as
the sun is shining. In this case, the
supply line becomes an "island" with
power surrounded by a "sea" of
unpowered lines. For this reason, solar
inverters that are designed to supply
power to the grid are generally required
to have automatic anti-islanding
circuitry in them.
A grid-connected photovoltaic power system will reduce the power bill as it is possible
to sell surplus electricity produced to the local electricity supplier.
Grid-connected PV systems are comparatively easier to install as they do not require a
Grid interconnection of photovoltaic (PV) power generation systems has the advantage
of effective utilization of generated power because there are no storage losses involved.
A photovoltaic power system is carbon negative over its lifespan, as any energy
produced over and above that to build the panel initially offsets the need for burning
fossil fuels. Even though the sun doesn't always shine, any installation gives a
reasonably predictable average reduction in carbon consumption.
Some applications of On-grid system
Photovoltaic power plants: 10KW-50MW independent photovoltaic power plants,
scenery (diesel) hybrid power plant, various large parking with charging stations.
solar building will combine solar power and building materials, making the future of
large-scale construction to achieve self-sufficiency in electricity is a major future
direction of development.
The difference of off-grid and on-grid system
1 Off-grid system can be used in every place,cause it has battery to back up,while on-grid system
should be get connected to national grid;
2Off-grid system is expensive than on-grid one because the battery cost a lot and also the battery
have a lifespan for 3-5 years mostly;
3An on-grid system ,the user can sell the additional electricity generated from the system to their
country ,this can make profits for users;
4When it is at night,the on-grid system can not supply power,user should trun to the national grid
for electricity,but in fact ,if you generate too much energy at day time,you sell to national
grid,when you need,you can get from them ,but when it is out of power ,it can not supply energy;
5When it is raining or at night,in a off-grid system,you can use the energy ,because the battery
can supply you energy no matter it is our of power of raining ;
Our suggestion for 250kw solar plant system
According to Pakistan’s national grid condition ,our suggestion is choosing off-grid
system ,as to 250kw plant ,it is better to choose distributed off-grid system,we can
devide the 250kw into three independent part,one is 100kw,another two are 100kw and
50kw or 5 unit 50 kw independent solar system.
Why we can not supple an off-grid system of 250kw plant:
As for as i know in our maket,generally the inverter capacity can reach to 50 kw
and the most biggest can be 100kw ,but the stability is said to be not good ;
often for solar plant like 250kw , usually do on-grid system ,but considering Pakistan’s
special condition of national grid,our suggestion is above:Three independent solar