PHOTON International The Photovoltaic Magazine

Module-integrated inverter from NKF

NKF Electronics, based in Gouda, the Netherlands, has rescheduled the sales launch for its new OK5-LV on-grid inverter for September.

	© NKF Electronics
Endless modularity: As many OK5-Wechselrichter as wanted can be connected with a very simple connnection mechanism.

The OK5-LV is a successor to the OK4, an AC-module inverter of which more than 50,000 have been sold worldwide. The new inverter will have a nominal power of 280 W and a MPP range between 14 and 25 V (LV stands for low voltage). For higher voltages, NKF will offer the OK5-MV (medium voltage), a device with the same nominal power but a MPP range between 56 and 100 V; it is slated to hit the market by the end of 2002. Originally, NKF had planned a market introduction last year, but »development took longer than anticipated,« admits company employee Diederik Jaspers.

Both inverter models are modular-expandable; Jaspers says the modularity is »endless,« limited only by the capacity of NKF's optional OK5 Energy Monitor data logger, which can store the data of up to 40 inverters at once. However, with additional management software and a PC, it should be possible to monitor and manage up to 640 OK5 inverters.

While the LV version is considered a semi AC-module inverter, which can be attached to the back of multiple 12 V modules connected in parallel, the MV version is designed for series-connected mini-module strings with each string (with a maximum module voltage of 48 V) making use of one inverter.

NKF's philosophy is to keep the number of modules per string on the DC side of the inverter as small as possible, so that the MPP tracker of each inverter needs to manage only a few modules to keep mismatch as low as possible

The OK5-LV, which is said to have a European efficiency of 93 percent, makes use of a passive anti-islanding system and features galvanic separation between the DC and AC sides.

A very interesting feature of the OK5 is that connection to other inverters on the AC side can be performed in only a few seconds, since the use of a special cable renders such tasks as skinning the wire and bolting unnecessary. Instead, this rectangular cable is placed in a special groove of the inverter with two metal spikes; as soon as the cable is fixed in place with the cover, it is spiked and thus electrically connected.

The OK5 also has a totally redesigned electronic concept: With the exception of three capacitors on the DC side, the interior is based only on surface mounted devices (SMDs). Even for inductivities, which often need to be winded laboriously onto transformers, NKF uses SMDs. Here, the windings are printed in spiral form on the circuit board and then enclosed by a ferrite block. Thus, all mounting works on the circuit board can be processed automatically, which greatly reduces costs. NKF claims it can sell the inverters for about €0.50 ($0.49) per watt once it reaches mass production. But they will start at a price before taxes of about €324 ($290) or €1.20 ($1.10) per watt, which is still quite cheap compared to other models in the same power class. The Energy Monitor costs an extra €308 ($280).

datasheet

NKF Electronics
Zuidelijk Halfrond 4
2801 DD Gouda, The Netherlands
phone +31/18259-2333, fax -2123
electronics@nkf.nl
www.nkfelectronics.com