Page 26 - North American Clean Energy May/June 2019 Issue

solar energy
Inverters that Boost LCOE in Extreme Weather & Terrain
OWNERS OF PV SYSTEMS WANT
the exibility to be able to build their projects in remote locations and harsh climates while still enjoying reliable, high performance production for the 35+ year life of their system. How these demands are met all comes down to the brains of any PV system - the inverter.
High performance under extremely high temperatures
One of the most important components for delivering solar power to the grid is the inverter. On hot summer days, when the temperature reaches the average high, cooling is required to maintain a certain level of power output. If the inverter
is not converting that power to its full potential, that lost e ciency translates into lost energy production. Regular operations and maintenance work (to keep the air ow at an adequate level) is another major key to maintaining inverter power output at a high e ciency. Refer to Graph A for an inverter power derating curve versus temperature.
Inverters are designed with di erent cooling mechanisms. Some of the most innovative ones are dual channel ventilation systems, with air forced and temperature
control to optimize the cooling process. An additional air-
air exchanger guarantees IP66 / NEMA4 for the electronic components, with an adequate air ow inside the inverter. e power stacks and electronics’ compartment are air cooled by a closed-loop heat exchange system (with no direct contact with the outside or with any other inverter cabinets - Image 1 and Image 2) is enhanced functionality makes it possible to increase the ambient operating temperature; thus, increasing the power output curve.
Graph A
Image 1
Image 2
by Nohra Nasr
reliable operation of equipment in these extreme operating conditions without performance losses.
A “sand trap” system can completely seal the ventilation circuit, for maximum protection against
the ingress of particles (which could cause serious technical problems in converters installed in the desert). ey may also be certi ed to the IEC 60068-2-68 international standard by an independent, external laboratory. is standard establishes the conditions to be met by electronic equipment in order to e ectively operate in environments with high concentrations of dust and sand.
In order to conduct the sand and dust test, a sealed chamber creates a controlled atmosphere with the humidity, wind velocity, and sand concentration conditions required by the IEC 60068-2-68 international standard. (Image 4)
In addition to the tests speci ed in the certi cation procedure, the equipment can be subjected to even more extreme conditions, such as those characteristic of a desert sandstorm - able to withstand situations with a high concentration of particles in the air (100 g/m3) and high wind speed (160 km/h). ese dust storms, or “haboobs”, have been witnessed in the southwestern states of the US, Abu Dhabi, UAE, and other desert environments around the world. (Image 6)
Enduring high humidity and corrosion
Other regions where solar energy makes incredible economic sense include islands and emerging countries in tropical environments. Many of these locations started out using high cost fossil fuels to generate electricity, which can cost over $200 per MWh. To combat this, many locales have begun to deploy solar plus storage. ese regions, as well as coastal cities, are marked by very high humidity and rain, which can shorten the life of the equipment.
Outdoor rated inverters, coupled with C5-M-H coating and stainless-steel hardware, help to overcome this environmental challenge and provide long operating lives. Many such inverters are already deployed worldwide, performing well on Islands like Hawaii, Puerto Rico, and Reunion Island.
Surviving arctic blasts
Solar photovoltaic cells convert sunlight into electricity. Cold winter temperatures do not impact production
as long as they are within the actual operating temperature range of the inverters. In fact, colder temperatures increase module e ciency, and can help improve the output of solar cells. Most PV inverters
in the market are designed to guarantee an operating temperature range of around -10oF to +140oF, with an option to add heating resistors kits for PV installations in cold regions. ese heating resistors are designed to guarantee operating at an ambient temperature of down to around -25oF.
Other e ective cooling systems include two separate ventilation circuits; outside air is drawn in to cool heat- producing components, while circulating warm air is cooled down in an internal ventilation circuit, on the inside of the inverter. e heat exchanger used in this process is operated by fresh-air supply.
Another cooling mechanism worth mentioning is an advanced hybrid cooling system using heat-pipe cooling technology, where the inverter runs without fan operation up to 50 percent load. Heat-pipe cooling simpli es thermal management because it uses fewer parts, and only a slow-speed fan with a heat pipe heat sink.
Standing up to sandstorms
Over the last few years, there has been a dramatic increase in the number of PV installations in desert environments. e bene ts include cheap land and excess sun, making it possible to generate solar energy for ~$20 per MWh. Market-led reduction in PV system costs has led to the use of outdoor inverter solutions that dispose of external enclosures to protect the inverters and other equipment at the transformer substations (transformers, medium voltage cells, etc.). is has driven the need for designs that guarantee the
Image 4: Sand and dust test chamber
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