Photovoltaic (PV) inverters are the
core equipment of the solar power generation system, therefore the reliability
of the inverters determines the reliability of the PV system. The heat
dissipation performance is the key factor influencing the reliability of PV
inverters. The power component, a core component of inverters, is sensitive to
temperature, which means change in temperature could impact
connection/disconnection process. In the case of high temperature, the power
switch may suffer poor performance or even break down. Therefore, inverter heat
dissipation is a key factor when it comes to inverter performance and quality.
PV power plants are generally situated
in deserts and plains in MENA, where the sunlight is abundant. However, these
areas also have extreme high temperatures and strong sand-wind weather. For
those that are close to the sea, the corrosion is severe. In these scenarios,
inverters are directly exposed to extreme environmental conditions, leading to
deteriorating exterior components. That is why the prime concern of inverters
becomes how to strike the right balance between environmental adaption and heat
dissipation.
In recent years, utility-scale power
plants around the world have widely adopted string inverters over central
inverters due to obvious advantages: higher yields, smaller footprint, no
equipment room, reliable operation, and simpler O&M (operation and
maintenance).
1.
Common Heat Dissipation Mode and Relevant Problems in Inverters
In general, inverters dissipate heat through natural or air
cooling. Normally, central inverters are installed in containers or equipment
rooms that often adopt direct ventilation. The heat dissipation capability of
string inverters is improved through external fans, but string inverters are
normally used in harsh environments, and this poses higher requirements on the
protection level of external fans. Fans wear out
quickly and
cannot be totally protected from dust. Harsh environment could accelerate the
deterioration of fans, resulting in frequent replacement. Fans need to be
replaced whenever they are faulty, which brings endless troubles to PV plants
that are supposed to run for 25 years.
Popular container-type equipment rooms are said to be
protected to IP54. However, as such equipment rooms usually use air-cooled heat
dissipation method, the actual Ingress Protection Rating can only reach IP44 if
not lower, and therefore the Ingress Protection Rating of the entire system
fails to reach IP65. What’s more, dust and corrosive gas cannot be blocked out
of the inverter. The accumulation of dust on the circuit board and terminal
block inside the inverter could shorten the creepage distance, and pose safety
risks such as discharge and fire. In addition, to protect fans from rain, the
air channel has to be designed in a complex manner while the air channel form
is limited. Once the fan fails to work, the heat dissipation capability is
badly impaired, causing the inverter output power to derate and energy yields
to decline, greatly affecting the benefits of customers. What’s worse, the lifespan
of fans could be tremendously shortened due to years of exposure to rain, dust
and other corrosive objects. Causing fans needing multiple replacement within
the lifespan of the inverter, resulting in high O&M cost.
On the other hand, high-power fan rotates at high speed
when the inverter works in the daytime and brings dust into the equipment room
from outside. Some particles accumulate on the equipment room floor, some block
the air filter, and some fine dust particles enter the cabinet. In the desert
region of MENA, the air filter needs to be replaced or cleaned every two to
three months. If the air filter is not maintained or cleaned in time, the blockage
will decrease the supplied air volume to the equipment room, thus exaggerating
heat dissipation and raising the temperature in the equipment room. The
inverter will then deliver derated output power or even shut down due to poor
heat dissipation. If the derating and protection mechanisms are not effective,
the inverter may be burnt or on fire.
Below figure shows a fan cooling
inverter used in a typical power plant. We can see that after a year of
operation, the fan is dusty and badly corroded.
A fan is damaged
mostly due to sandstorm, corrosion, and wear and tear, rather than temperature.
A large number of statistics from PV plants show that the external fans of central
inverters in a PV plant need to be all replaced after five to ten years. The
logistics cost, labor cost, and energy yield loss resulting from fan
replacement are very considerable. What is more important is that fan replacement
severely affects the O&M efficiency as O&M personnel have to do a large
quantity of valueless maintenance work.
2.
Solutions to Inverter Heat Dissipation Problems
At present, natural cooling design is
the advanced solution. Natural cooling technology allows the protection level of
inverters to reach IP65 with fully-sealed design while retaining a high
reliability in hot & moist environment. In addition, noise is reduced,
reliability is improved, power deration is eliminated, maintenance is simplified,
and cost is lowered.
As the
output power of the inverter increases and its size decreases, heat dissipation
becomes a major bottleneck. To address this issue, including copper and aluminum
composite, heat pipes, temperature equalization plate, may be employed to
reduce thermal resistance and improve the dissipation capability of radiators.
By
adopting the mentioned heat dissipation concept and employing the heat
equalization design, heat isolation and heat shield technologies, Huawei
SUN2000 string inverter is sealed completely and designed with natural cooling.
By taking the thermal isolation and thermal shielding technologies, heating
components and thermosensitive components are deployed in different compartments
to ensure no partial hot spots, improving the reliability of heat dissipation,
and ensuring that the inverter can operate properly outdoor under extreme high
temperature, without power derated. Whether it is in the desert of the Middle
East or in the coastal regions of Japan, Huawei string inverters withstand the
tests of sandstorms and corrosion, bringing high reliability, effective
protection, sound operation, and quality performance.
