As shown in the figure below, a household photovoltaic system generally
includes ① battery components, ② lightning protection box, ③ cables, ④
grid-connected inverter, and ⑤ metering instruments. But how do ordinary people
build a distributed photovoltaic grid-connected power generation system that
suits them?
1. How to apply to build your own home photovoltaic system
State Grid promises: State Grid will provide distributed photovoltaic power
generation project owners with full-process services such as access system
solution formulation, energy metering device installation, grid connection
acceptance and commissioning, etc., without charging any fees; it will support
distributed photovoltaic power generation decentralized access to low voltage
Distribution networks purchase surplus electricity in full in accordance with
national policies; system reserve capacity fees are waived for all distributed
photovoltaic power generation projects. The part of the project connected to the
public power grid is also paid for by the power grid. Users only need to invest
in photovoltaic power generation equipment and a small amount of cable lines for
their own use. So how do we apply?
The first step is for residents to have an independent site (such as a
roof) for installation. If it is a public roof, they need to seek consent from
their neighbors.
In the second step, residents need to seek permission from the property
owners committee or neighborhood committee of the community where they build
their own power station.
In the third step, residents go to the power company business hall to apply
for grid connection of distributed photovoltaic power generation projects. The
power supply department will conduct on-site inspections in the future and
organize the review of 380V (220V) volt access plans.
In the fourth step, if there are problems with the designed access plan and
equipment, the power supply department will provide an access plan and a letter
of opinion on the connection to the power grid, and residents will modify the
facilities based on the plan and opinion letter.
The fifth step is to install it yourself or find a professional company to
install the grid-connected system.
Step 6: After installation, notify the power company to come over for
acceptance. They will install the metering device in the residents' homes, sign
a power purchase agreement, and complete the final grid connection process.
2. Solar power generation system capacity design
Capacity is the power generation of the photovoltaic power generation
system, which is generally designed based on the buildable area of the
residents. An area of 1 square meter can currently generate about 150W of
electricity. The average resident can build a 3kw-5kw power station, which
requires an installation space of more than 20 square meters, and so on. The
installation space can be a sloped roof or a flat roof.
3. Selection of solar cell modules
Battery components are divided into monocrystalline silicon battery
components, polycrystalline silicon battery components and amorphous battery
components. Monocrystalline has the highest power generation efficiency and can
generate more electricity in the same area. For small installation areas,
monocrystalline is the most suitable choice, but the unit price will be higher.
The efficiency of polycrystalline silicon is second. For those with a relatively
large installation area, polycrystalline silicon is more cost-effective and the
price is relatively low. Amorphous silicon has the lowest efficiency and is
generally not recommended for use. (Tips: Monocrystalline cells generally have
rounded corners, while polycrystalline cells generally have square corners)
The five major parameters of battery components are peak power, open
circuit voltage, short circuit current, working voltage, and working current.
The selection of these parameters is very important.
Battery components are divided into different sizes according to their
power. The power of a single component ranges from 10W to 300W. The power of a
single component is directly proportional to the area, so when selecting the
power, you should also choose the battery component of the most appropriate size
to meet your installation space requirements. For example, if your space of 20
square meters is 2 meters * 10 meters, there are two installation methods you
can choose as shown in the figure below.
When the battery panel is exposed to sunlight (1000w/m2) ① the voltage
measured without load is the open circuit voltage, ② the current measured by
directly short-circuiting the positive and negative poles of the battery
component is the short-circuit current, ③ when the load is added In this case,
the voltage measured is the working voltage, and the current measured is the
working current. The operating voltage is generally proportional to the open
circuit voltage, and the operating current is proportional to the short circuit
current. The selection of these four parameters has a great relationship with
the inverter to be selected later. Generally speaking, the open circuit voltage
of grid-connected battery components is generally around 45 volts, and the
operating voltage is generally around 35 volts. Operating current and open
circuit current vary with component power.
Series and parallel connection of battery components: Multiple battery
components can be used in series or parallel, or a mixture of series and
parallel can be used. For grid-connected systems, series connection is to obtain
a voltage suitable for the operation of the grid-connected inverter, and
parallel connection is to increase the output power at the same voltage
level.
4. Selection of grid-connected solar inverter
As an interface device between photovoltaic cell components and the grid,
the grid-connected solar inverter converts the DC power of the photovoltaic
cells into AC power and transmits it to the grid. It plays a vital role in the
photovoltaic grid-connected power generation system.
There are two types of household grid-connected inverters. One is a
centralized grid-connected photovoltaic inverter with a minimum power of 1kw and
an input voltage ranging from 150V-550V. The other is a micro grid-connected
photovoltaic inverter, which is generally used in the AC220V voltage level, with
power ranging from 200W to 500W, and the input voltage range is 12V~28VDC. The
usage of the two grid-connected inverters is very different, as shown in the
figure below. Centralized grid-connected inverters are generally large in size
and suitable for wall-mounted installation. Micro grid-connected photovoltaic
inverters are small and compact and are generally installed nearby with battery
modules (can be installed on the bracket below the battery module). Distributed
and distributed inverters are used for household use. Both grid photovoltaic
power generation systems can be chosen.
The main parameters of the grid-connected inverter are maximum input power,
maximum input voltage, rated input voltage, starting voltage, MPPT voltage
range, and output grid voltage. The maximum input power is a limit value, and
the peak power of the photovoltaic cell module must be about 90% of this value;
the maximum input voltage corresponds to the open circuit voltage of the cell
module, and the open circuit voltage of the module array connected in series
must be smaller than this value; The rated input voltage corresponds to the
working voltage of the photovoltaic cell module, which can have a certain range
of deviation; the starting voltage refers to the voltage point at which the
grid-connected inverter starts to work. The grid-connected inverter will not
work when the sunlight is too weak. The MPPT voltage range is a function of the
grid-connected inverter set according to the characteristics of the battery
panel. It will automatically adjust the input voltage and current of the
inverter so that the product of the voltage and current, that is, the power,
reaches the maximum value. This The voltage range is very wide, and inverter
panels with this function have higher utilization efficiency; the output grid
voltage refers to the voltage of the grid to be incorporated (single-phase
220V/three-phase 380V).
The choice of grid-connected inverter mainly depends on the rated power and
input and output voltage levels. Then users can easily determine the input
voltage range of the grid-connected inverter based on the voltage level and
series-parallel connection method of the selected battery components. They can
choose single-phase or three-phase according to the power consumption at home.
output. For example: the peak power of the battery panel is 200W, the open
circuit voltage is 45V, and the working voltage is 35V. To form a 2KW system, 10
battery cells need to be connected in series, then the maximum input voltage of
the grid-connected inverter must be greater than 45V/chip*10 Chip = 450V, rated
voltage is around 350V. The output voltage can be selected from single-phase
220V or three-phase 380V according to the specific power supply situation of the
home. As the most important component of the entire system, the grid-connected
inverter must choose products that have passed relevant national certifications
(such as Golden Sun Certification CQC).
5.Selection of other components
1) Cable. You can choose photovoltaic-specific cables, but they are
expensive and difficult to purchase in small quantities. For short distances, BV
cables are still used, and the safety current of 1 square millimeter is 6A. For
example, for a system with a power of 3kw, for photovoltaic input cables, the
rated input voltage of the inverter is DC350V, then the current is
3000W/350V=8≈.57A, and BV2.5 cables are selected. For the inverter output cable,
the rated output voltage of the inverter is AC220V, then the current is
3000W/220V≈13.63A. In theory, you can also choose BV2.5 cable, but for safety
reasons, it can be upgraded to a higher level. Choose BV4 cable.
2) Lightning protector. Lightning arresters are different from ordinary
lightning arresters. You must choose a high-voltage DC lightning arrester
dedicated to photovoltaics, because the continuous operating voltage of ordinary
lightning arresters is AC220V or AC380V, while the continuous operating voltage
of photovoltaic-specific lightning protectors can be as high as DC1000V.
3) Measuring instruments The electric power company will install two
electricity meters for users free of charge. One is an electricity meter that
measures photovoltaic power generation, and the other is a two-way meter, which
is a meter that measures electricity used by the user himself and sold to the
grid [2]. In this way, users can see their daily electricity consumption, power
generation and power output to the grid in real time.
6. Installation and debugging
Installation If you are not familiar with electrical systems, it is best to
ask qualified personnel to install them. It is best to complete the series and
parallel wiring after the panel is installed after the sun goes down to avoid
high-voltage electric shock. At the same time, lightning protection and
grounding should be done. In addition, attention should be paid to the wind
resistance level of the bracket, and northern users should also pay attention to
the snow resistance level. Debugging can be carried out in conjunction with the
personnel of the power company.
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