The 1500 Volt modus operandi

The “next generation of PV power plants” is underway with system changes being made to increase DC system voltage to 1,500. As IHS’s Cormac Gilligan predicted in pv magazine (05/2015), it is the natural evolution of utility-scale PV to go 1,500 V. IHS anticipates this trend will arrive by the end of this year. And so do suppliers through the PV chain. With suitable products now emerging, the 1,500 V solar plant architecture seems to be the future.

Perks of going 1,500

The higher the voltage, the lower the current and thereby the loss at the time of power transmission. Mahesh Morjaria, Vice President, Systems Development, First Solar says, “A key advantage of higher voltage is that for the same power, the current in the conductor is reduced which in turn reduces the size of the conductor and losses in the conductor.” With a higher voltage plant, the system can be designed with longer string lengths and hence reduce the number of balance of system (BoS) components. More modules can be added to the source circuit and there are fewer source circuits for the same array capacity. Morjaria adds, “In case of the First Solar CdTe modules (Series 4), 15 modules are normally connected in series per string as opposed to 10 in the case of 1,000 VDC. This reduces the number of strings for the same amount of power. 1,500 VDC also enables increases in the power of the inverter (which is typically current limited). Therefore, an increase in DC voltage and the use of large-scale 4 MVA inverters leads to a significant increase in the DC array size. The typical 1,500 VDC system design will incorporate between 5 and 5.3 MWp DC of PV capacity, corresponding to a DC/AC ratio between 1.25 to 1.33.” In March 2014, First Solar announced the collaboration with GE on utilizing its thin-film CdTe modules with the ProSolar 1500 V inverter/transformer system. With the integration of new technology into the CdTe modules and the combination with GE’s ProSolar stations, the size of the PV array served by individual inverters increased and hence reduced the total number of inverter and/or transformer stations needed by a plant.

Cost cuts

Greater scale efficiencies and cost reductions are reaped by enabling higher power throughput for the same ampacity of DC components. Günter Arens from Hirschmann Renewable Energy concurs, “The trend to 1,500 VDC is driven by the possibility to further reduce the installation cost of PV systems. Primarily this is true for utility-scale PV projects.” How much exactly of a reduction in costs are we talking about? GTM Research has analyzed the current cost changes for 1,500 VDC systems compared to 1,000 VDC (see Table, p. 53). Scott Moskowitz, solar analyst for GTM Research states, “According to our research, installing 1,500 VDC systems in place of now-standard 1,000 VDC can lower costs by as much as $0.05 per watt.” Trina’s Pierre Verlinden sees costs falling for combiner boxes, cables, DC breakers and so on by more than 30%. He also additionally sees labor costs falling. This in turn decreases BoS costs and the LCOE.

Product certification

It gets a bit tricky with certification. Only recently were UL standards and testing programs for module safety modified to include 1,500 V module evaluations. As IEC already classifies 1,500 VDC in the Low Voltage Directive, the standards are not too difficult to meet. Morjaria adds, “IEC 61215 (for c-Si) and IEC 61646 (for thin film) govern up to 1,500 V module type approvals. IEC 61730 governs module safety up to 1,500 V. These standards establish materials, construction, and testing requirements that promote safe and reliable 1,500 V operation in the U.S. and other IEC PV countries.” Modules: CSUN, First Solar, Hanwha SolarOne, JA Solar, S-Energy, Suntech, Trina Solar and Yingli – to name a few – have developed modules suited for 1,500 V system installation. Trina Solar claim to be the first to receive the UL1500V certification for their polycrystalline modules. Moskowitz explains that the module testing standard UL 1703 was recently updated to enable certifications of 1,500 VDC modules. Prior to this, UL 1703 voltage limitations were the primary barrier preventing both adoption of 1,500 VDC technologies and further product introductions in this space.
First Solar got an extra perk during the development of its thin film CdTe modules (Series 4). An unintended benefit was derived during the development of these in that additional conversion efficiencies were realized. Effectively, modules optimized for 1,500 VDC offer better performance with respect to efficiency and maximum output power compared to their 1,000 VDC predecessors.
Inverters: GE has been proactive, partnering with Belectric (see Box on left) to work on the bigger project, supplying outdoor central inverters manufactured by Power Conversion. Other major inverter manufacturers like ABB (PVS980) and SMA (Sunny Central 2500) also offer central inverters tuned to such capacities. Moskowitz states, “Changes to UL 1703 will be followed by alterations to connector standards and harmonization of inverter standards (which already enable 1,500 VDC certification) to international standards.” He adds that as regulatory barriers dissolve, manufacturers will begin to introduce 1,500 VDC products in volume. “We expect this to begin in mid-2015 and continue into 2016. The market will initially target large utility projects with central inverters, but we expect three-phase string inverters to follow soon after. This will be further enabled by the implementation of next-generation silicon carbide devices that allow for higher switching frequencies and greater power densities,” he adds.
Components: Cables and connectors are plentiful in this range. Most players in the PV cable sector like Lapp, Huber+Suhner, Leoni and Multi-Contact have products that suit the new trend.
What is essential is having the certification done to enable implementation. “With the introduction of EN50618, the 1,500 V cable subject is covered. The present TÜV variants 2PfG 1169 and 2PfG 1990 will expire after a transitional period of 2 years,” adds Lapp’s Reinhard Probst.
Hirschmann’s Arens says that to his understanding there can not be any UL qualified junction box nor PV connector since there is no current UL standard available for these components. pv magazine will be covering this aspect in more depth subsequent issues of the magazine.
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Getting projects approved

Just like in the initial stages of moving from 600 VDC to 1,000 VDC, the adoption of 1,500 VDC will still have to overcome hurdles. Modules and inverters – two major components – have not had a long run yet in the 1,500 VDC history. Some manufacturers have tested the field with projects, but the idea is still in its infancy. In Europe the IEC standards already address 1,500 VDC design and safety. But what about the U.S.?
GTM’s Moskowitz elaborates, “The NEC typically applies to domiciles, but many AHJs (Authorities Having Jurisdiction) do utilize the code. Others refer to the National Electrical Safety Codes, which have no voltage limitations. There are over 3,000 utility AHJs in the U.S., and so, this fragmentation means project requirements vary greatly. The 2014 version of the NEC does not provide clarity on voltages above 1,000 VDC, however it does require that system components be certified to UL by a nationally recognized testing laboratory (NRTL). As a result, in locations where this is the case, UL1500V certification limitations have been a significant bottleneck. Project owners often require UL certifications even when the code does not mandate UL as it makes it easier to finance and sell the project.” Morjaria opines, “Greater challenges are faced in the U.S., where the lack of established standards that address 1,500 VDC applications often make it challenging to obtain plant construction permits from AHJs. However, much like the earlier transition to 1,000 VDC architecture, these issues are addressable and no long-term barriers to adopting this architecture are expected.” The U.S. standards and codes community has been taking steps to address these issues. The announcement by UL to adopt ANSI/UL 62109-1 as the American National Standard for “Safety of Power Converters for Use in Photovoltaic Power Systems” enables U.S.-based certification of 1,500 VDC inverters, and is a step in the right direction, explains Morjaria.
He adds that UL is working towards the adoption of similar standards for modules and other DC BoS equipment, and in parallel, changes to the National Electrical Code (NEC) are anticipated that will better accommodate the unique aspects of design platforms utilized in large, utility-scale PV plants.
First Solar, in 2014, became the first to install a fully 1,500 VDC system with two pilot projects in Texas, getting the ball rolling in the U.S. But is the 1,500 VDC switch confined to the fields, literally?
Trina’s Verlinden sees the 1,000 V ceiling remaining in most countries for rooftop projects with the exception of the U.S. where 600 V could remain the norm (though Belectric proved rooftop 1,500 VDC is doable). This is for safety reasons, he asserts. On the utility-scale front, though permit acquisition might take a little longer, no other particular obstacle is in the way.

Watch this space

The economic benefits of 1,500 VDC power plants will drive market adoption – that can be said with certainty. Though high volume availability of such 1,500 VDC components may be somewhat constrained during this transition period there is movement, and product bottlenecks are unlikely to stop the 1,500 VDC takeoff.
In the coming months, pv magazine will continue exploring the 1,500 VDC trend and new products coming to market.