How to Choose the Most Cost-Effective Solar Panel for Your Grid Parity PV Solar Plant

PVTIME - China’s National Development and Reform Commission (NDRC) has issued a consultation document to solicit advice for the 2020 policy on the prices of electricity generated by photovoltaic plants. According to the consultation paper, the tariffs of newly-built ground-mounted power stations in three resource areas of the country are set at 0.35 yuan/kWh, 0.4 yuan/kWh, and 0.49 yuan/kWh, respectively (unless indicated otherwise, tax is included in the tariffs). Meanwhile, the tariff of industrial and commercial distribution plants is set at 0.05 yuan/kWh, and the subsidy for household solar plant is 0.08 yuan/kWh. Although the tariff is higher than previously expected, grid parity for photovoltaics and price bidding remain key topics this year.

National Energy Administration (NEA) will continue to implement the
overall plan outlined in 2019 to support and prioritize the construction of unsubsidized
(grid-parity) projects. To reach grid parity, it’s important for photovoltaic
enterprises to choose modules with "low cost, high power, and high power
generation" as modules account for 47% of the system cost of a solar plant.

Starting from
early 2019, Jinko, JA Solar, Trina Solar, and Risen Energy have retrofitted their
production lines of 156.75mm wafers, cells and related modules to those of 158.75mm
products. The new production line significantly improves module power with
relatively low transformation cost and little retrofitting difficulty. Most tier-one
enterprises have completed the conversion to 158.75mm products, and have started
supplying the products to the market.

According to PVInfoLink,
the market share of 158.75mm silicon wafers is expected to reach 60% in 2020.
As for larger 166mm and 210mm products, most enterprises are still in the
wait-and-see stage.

To maximize the
advantages of 158.75mm products in energy yielding, producers choose to combine
158.75mm x 158.75mm cells with MBB and half-cell technology. The combination
has proved successful and is gaining market share. According to PVInfoLink,
suppliers including Jinko, JA Solar, Risen Energy, and Trina Solar are promoting
modules assembled with half-cut MBB 158.75mm cells.

Tested by some
Chinese producers as early as in 2016 to further improve cell efficiency, MBB
technology has been developed and applied on a large scale by leading module manufacturers
since 2019. The technology increases module power significantly with its round
busbar and closer busbar design.

Compared with conventional busbar design, the round busbar
design used in MBB cells reduces shading area and effectively reflects sunlight
to the cell to increase short-circuit current of the module. The “double” light
reflection of the round busbar boosts light absorption and utilization rate of
the cell by increasing the optical utilization rate of the busbar area from
less than 5% to over 40%.

MBB module is also
known for its high reliability. Closer busbar design reduces micro crack risk
by decreasing residual stress. Even in the case of micro-cracks or deformation,
the shorter distance between busbars decreases loss ratio of the cell and
enables it to keep generating electricity. Additionally, the latticed design of
busbars and fingers distributes inner stress evenly and reduces the risks of
micro-cracks. When dealing with micro-cracks, the structure maintains high
electricity-collecting capability and lowers thermal resistance risk caused by
micro crack under normal working conditions. Mechanical load test (5400 Pa)
shows that -micro-cracks could cause a degradation of 0.5% for conventional
modules, while only 0.1% for MBB modules.

Integrating the
advantages of high efficiency and reliability, the MBB technology can also
control the cost by reducing the amount of silver paste.

Because of its
advanced development and great efficiency improvement, half-cell technology has
been adopted by most photovoltaic enterprises. The so-called half-cell
technology is to cut the standard cell equally into two parts along the
direction perpendicular to the busbar with the laser cutting method. Through
this way, the current flowing through the busbar can be reduced to half the
amount as a full-sized cell.

When the
half-cut cells are connected in series, the resistance on the positive and
negative circuits remain the same, so the power loss will be reduced to one-fourth
of the previous level (Ploss=1/4*I2R), which ultimately reduces the power loss
of the module, and improves its packaging efficiency and fill factor.
Generally, half-cell module’s power can be 5-10W (1.6%-3.3%) or even higher
than traditional module of the same size. Little difficulty and investment in
retrofitting half-cell module production line and high yield make it a
differentiated product and highly sought by producers.

Relevant
experiments and projects also show that when the module is shaded, the special
structure design of half-cell module can reduce the power loss of the module
and perform better than regular modules.

The first-line producers’ average
mass production power of 72-cell 9BB half-cell PERC modules with 158.75mm cells
reaches 410W, and that of 78-cell module can reach 445W.

The combination of MBB and half-cell technology reduces the
micro crack influence area by 50% compared with regular cells.

MBB and half-cell structure also lowers the module’s hotspot
risk. Under the simulated condition of 1000W/m2 irradiation, 25 ℃
ambient temperature and 10W/m2·℃ convective heat transfer
coefficient on the front and back of the module (with good ventilation), the
heat dissipation effect of MBB half-cell module is better than that of the
conventional module (which has relatively lower effective heat density), and
the hotspot temperature is 27 ℃ lower than that of conventional module. In
addition, the working temperature of MBB half-cell module is 2-3 ℃ lower than
that of the regular module, and the power loss of working temperature is lower.
It effectively reduces soiling loss caused by snow, dust and dirt, and energy
loss caused by shielding, resulting in more stable power output.

After
the rigorous tests of loading, TC600 and dynamic loading with TC50 and HF10, the
EL of half-cell MBB large-CELL module remains normal.

With its lower
working temperature, better temperature coefficient and IAM, the half-cell MBB
module with 158.75mm cells demonstrates its advantage of electricity-generating
capability by increasing electricity by 1% during the testing period of one
month. With a slight increase in cost, the module can bring higher benefits to
users and achieve lower LCOE.

From the perspective
of solar plant investors, the size of 158.75mm is the most cost-effective size
in the entire industry at present. By combining with MBB and half-cell
technology, the module assembled with 158.75 cells strengthens its value
proposition, including (i) higher power and energy yield; (ii) greater reliability;
and (iii) lower BOS cost and LCOE. The broad application of the module can help
accelerate the launch of price bidding and grid parity projects, thus further promoting
the development of the solar industry.

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