Why and how it make sense to go with higher DC system voltage?
As entire solar Industry across the globe is facing heat in competitive bid recent years that is because of drastically fall of overall project cost of Solar PV plant and alog with other factors i.e. Radiation, financing, creditworthyness of Offtaker etc. The drastically downfall of overall Solar PV system cost due to drastically change in Solar PV Module price (~0.80%-1.10%/Month since March 2015) and innovation ,optimization in BoS i.e. Solar Inverter, block size (smart block arrangement), optimized DC overloading, Structure design.
Lets checkout- How Solar Industry shifted in Higher voltage installation on DC side
Why did the industry move from 600 volt solar arrays to 1000 volt solar arrays? The answer is simple, to reduce system costs. The value of increased system voltages is realized in infrastructure savings, reduced installation costs, and end-to-end efficiency improvements. That is the same reason that the industry is now moving from 1000 volt systems to 1500 volt systems. Although 1000VDC-rated BOS equipment was generally more expensive than 600VDC equipment, those costs were more than offset by the cost reductions throughout the overall system. As the volume of the higher voltage rated components and wire increased, the installed costs were reduced even further. Again, the story is repeated with the move towards 1500VDC systems. The primary reason is the 31% to 37% decrease in DC current for the same power.
Lets talk about advantages first
- Lower DC Losses - Higher the system voltage lower the system current, for the same resistance ohmic losses will be lower
- Less Strings
- Reduced string cable length and Array cable length - Due to higher no. of module in series in case of 1500 V dc system compare to 1000 Vdc
- Reduction of String Combiner boxes
- Capex & Opex Saving
- Bigger Block Size - Concept of the bigger is better
Understand the challenge
One might ask why stop at 1500VDC? Why wasn’t it 2000V? The short answer is the solar panel, switchgear, fuse, and circuit breaker manufacturers weren’t ready to work with an increase of 1000V, so the acceptable challenge was a 500V step above the 1000VDC rating. 1500V rated wire is not the problem. Switchgear, fuses, surge protectors, circuit breakers and other BOS components are still being introduced and certified. The reduction of current is the advantage, but the corresponding disadvantage is the conductor spacing (creep). Spacing must be greater for the higher voltages so the equipment gets correspondingly bigger and takes up more room. Internal arcing becomes a bigger concern so the design standards for these components become more complex and costly.
Cooper Bussmann announced 1500VDC fuses in late 2012 and ABB announced their line of 1500VDC disconnect switches, molded case switches, contactors, surge protective devices and sensors in late 2014. Other manufacturers have joined in and the competition to supply the industry with the full range of 1500VDC rated components has both kept prices in check and increased the range of available product options. However, the list is still limited compared to those rated for 1000VDC.
The good news is that at any given power capacity, with the increase in voltage, the current is reduced. Inverters are power conditioning units that essentially, “push” current at a fixed voltage. The higher the current, the higher the heat and the higher the stress on current carrying components and switching devices. So a reduction in current is, in general, a good thing from the inverter’s perspective
Efficiency and cost considerations for 1500Vdc PV Systems
Higher output power levels can be obtained from essentially the same IGBT stacks if the current is reduced.The catch is that to work at the higher voltages, IGBTs have to be rated at the higher peak operating voltages. This means more expensive devices and higher switching losses. Some inverter manufacturers have had to accept lower efficiencies (usually .5% lower) compared to 1000VDC inverters. Sungrow has been able to maintain the same CEC energy conversion efficiencies in their line of 1500VDC inverters as they do in their line of central and string 1000VDC inverters (98.5%).
There are cost savings on the AC side of the inverter as well. With the increase in DC input voltage, the inverter can be designed for a higher AC output voltage. This reduces the AC current and allows for smaller gauge wire to be used for the wire runs from the inverters to the transformers. For example, a change from an output voltage of 480VAC to 600VAC reduces the current by 20%. For the same distance between the inverter and the point of connection to the transformer, this can mean a reduction of two wire sizes in most cases .
credit- Mr. Bhuwan Mehta, Gensol Consultants
Way forward- What does 1500 Vdc mean for Solar Industry in future
So where are the real savings?
If there is a premium for 1500VDC rated solar panels, and the 1500VDC rated BOS components have a premium, will that offset the savings in wire, labor, and other installation costs? If the inverter has a lower CEC weighted efficiency that results in a lower energy throughput, then the answer will be a resounding “maybe”. To some degree, the savings will be site specific, but with the high cost of wire and labor in the US, there will definitely be a reduction in the cost of the installed system. This is verified by the fact that virtually all utility scale project developers and EPCs are going with 1500VDC systems.
A recent survey by IHS showed that the over-all savings estimates for 1500VDC system installations by experienced EPCs were in the range of 20% to 25% compared to 1000VDC systems. The variables include the cost of the wire (changes with the market price of copper), the local labor rates, union or non-union, system architectures, use of trackers, and the choice of inverters
2. So where will the industry go from here?
It may move to even higher DC voltages, but the costs required to design and manufacture key components that can handle say, 2000VDC, may be too daunting. Most, if not all of the innovations and design changes have been incorporated based on their ability to reduce costs somewhere in the BOS components, installation, or O&M processes. Large volume orders and competition among 1500VDC component suppliers will continue to drive BOS costs down.