What is TMEIC's '3rd-Generation PV Inverter'? (2)

With advantages of both central-, string-type PV inverters

2019/08/24 19:01
Kenji Kaneko, Nikkei BP Intelligence Group, CleanTech Labo

Continued from What is TMEIC's '3rd-Generation PV Inverter'? (1)

Can be carried by 2t truck

The advantages of the "modular system" are not limited to the above. Problems in construction and operation became prominent following the increase in the capacity of central-type PV inverters to mega-class levels. Trailers and heavy machinery are required for transportation and installation of the PV inverters due to the weight increase following the increase in the size. When one of the PV inverters stops operation during use, a wide range of solar panels are affected, increasing the power generation loss.

These problems were significantly decreased by incorporating the "modular system", according to TMEIC.

The module in the "Solar Ware U" was downsized to 2m in height, 1.1m in width and depth, and the weight is 1t or less. The installation area per capacity was reduced by 35% compared with conventional units (2.5MW) of TMEIC while the weight was reduced by 40%. Because of the light weight and compact size, the module can be transported easily by a 2t truck (Fig. 4).

Fig. 4: "Solar Ware U" (unit image) (source: TMEIC)

For weight reduction, materials were reviewed; resin covers were used instead of metal covers and aluminum frames were used instead of steel frames, in addition to incorporating the compact design.

The impact range of problems is minimized because failure of one module does not affect other modules when multi-connected PV inverter models are used. In the case where six units are connected and failure occurs in two of the units, for example, the remaining four remaining working units continue to generate power

Furthermore, MPPT (maximum power point tracking) for maximizing the output by controlling the power points (current value and voltage value) according to fluctuating sunlight, etc is performed by each module. So, the power generation amount could be higher compared with the case where the control is performed by a single large-capacity unit, when panels cannot be installed facing the same direction in mountains, for example.

When the output from some strings drops due to shading, MPPT is affected, and all PV inverters cannot be controlled to the optimum power points depending on the case. Such impact can be limited when MPPT is performed independently by each module.

This feature was said to be one of the advantages of string-type units. In this sense, the product is a central-type unit that features advantages of string-type units.

ABB, Schneider withdraw from market

From the start of the FIT scheme, solar power plants increased rapidly throughout Japan. However, the ratio of solar panels made in Japan among the solar panels installed in the country has been decreasing because many foreign manufacturers are entering the market. In the mega solar market, in particular, cost-competitive products made in China are the mainstream.

Conventionally, specialist manufacturers and major electric appliance manufacturers in advanced countries maintained high shares in the global market of PV inverters, which are the hearts of solar power generation equipment. Comparatively more advanced knowhow is required for production of PV inverters, compared with production of solar panels. And they cannot be manufactured simply by purchasing production equipment.

However, Chinese companies are beginning to manufacture PV inverters, and these companies are increasing their share with a focus on string-type PV inverters, which can be manufactured by utilizing mass production knowhow.

Under such circumstances, Schneider Electric SA, a major electric appliance manufacturer in France, decided to withdraw from the market of large PV inverters intended for mega solar power plants in January 2018 (Fig. 5). Meanwhile, ABB, a major heavy electric machinery manufacturer in Switzerland, announced in July this year that it will sell its solar power PV inverter business to FIMER of Italy.

Fig. 5: Schneider Electric SA of France announced its withdrawal from PV inverter business (source: Nikkei BP)

As for domestic manufacturers, Tabuchi Electric Co Ltd, which had a large share in compact PV inverters intended for low-voltage solar power generation equipment, recorded a decline in its business performance following shrinking of the low-voltage solar power market and inflow of PV inverters made abroad into Japan. The company has been making efforts to rebuild its business supported by Diamond Electric Mfg Co Ltd, utilizing the ADR (Alternative Dispute Resolution) system for business revitalization.

Price reduction is accelerating rapidly in the market of PV inverters intended for solar power generation, as is the case with solar panels, due to the trend of handling them as mass production products following the entry of Chinese manufacturers into the market that mainly manufacture string-type units. The withdrawal of major foreign companies from the PV inverter market and the decline in the business performance of domestic companies indicate that the profitability of the PV inverter business has been declining.

"The mega solar market is expected to grow steadily in North America and Asia in the future, and the needs for high-performance PV inverters are high," TMEIC Vice President Sawada said. "We will be able to realize sufficient differentiation by suggesting high-added-value products to customers."

TMEIC estimates that it can continue to grow by maintaining the profitability in the market, where price reductions are accelerating, because competitiveness will be enhanced in function and performance, as well as "delivery time and cost," by the "modular system" that it disclosed recently.

The production line for module production is simple. The delivery time of procured parts will be shortened while the lead time will be reduced significantly.

The cost will also be lower due to reduction of structural members following an increase in the integration degree, reduction of wires following downsizing and simplification of the system design. Based on the above, the company believes that it will be able to catch up with the price reduction that is in progress in the market of PV inverters for mega solar power plants.

Differentiation by 'integrated control'

TMEIC also plans to showcase the functions that cannot be realized by string-type units, in addition to introducing the "modular system," for differentiation. The company plans to use an integrated control system called the Main Site Controller (MSC) in combination.

The "integration" in this case means integration of multiple PV inverters for control. The MSC is an overall control system in the upstream process of each PV inverter.

Requirements of PV inverters will continue to increase in the future responding to introduction of solar power in large amounts. Reduction of load on power grids, satisfying the requirements for grid connection for stabilization of grid operation in the daytime when the demand for power is low, as well as output control by power companies, will be common in the future. Responding to these complicated requirements on control will be possible by introducing the MSC, according to the company.

It is also estimated that reduction of output fluctuations in "short cycles" of seconds and "long cycles" of hours by combined use of storage battery systems will be set as conditions for grid connection of renewable energies including solar power and wind power with output fluctuations in the future.

If the MSC is used, integrated control including PV inverters for storage batteries will be possible, also making it easy to equalize the renewable energy output in short cycles and long cycles.

Storage batteries are already used in combination with solar power plants in isolated islands, household power generation systems and so forth in Japan, and the company commercialized the TMBCS (TMEIC Battery Control System) for this purpose. In the TMBCS, the MSC is controlled in linkage with PV inverters for storage batteries and monitors the power generation amount of each grid connection point throughout the site in real time, controlling the batteries for charge and discharge (Fig. 6).

Fig. 6: "TMBCS (TMEIC Battery Control System)" introduced to a mega solar power plant equipped with storage batteries on Tokunoshima Island (source: Nikkei BP)

TMEIC expects that the combination of the "modular system" PV inverters and the MSC will contribute to the reduction of initial investments by power producers, as well as to operation power saving and improvement of income, responding to the needs of the time when renewable energies are introduced in large amounts.