Siemens: More Sitops join the fray

In order for an inverter to efficiently transform a solar generator's energy into alternating current, its power has to optimally match that of the generator. 

© Siemens AG (2) Sitop series: On the right, an indoor device with IP 21 protection type; at left, an outdoor version with an IP 65 housing.

But once the solar generator is designed, it can often be difficult to locate an inverter from a desired model range that adequately meets power requirements. Thus any truly good inverter model range does its best to limit the gaps in power specs between the various devices in the series. And that's exactly why Siemens AG has expanded its Sitop series – to minimize these product gaps. 

Siemens' inverters have consistently employed the master-slave concept. Generally, this means two or three inverters work together – that is, unless it's a very small system for which a single inverter's power would suffice. According to the master-slave concept, only one inverter remains active during periods of weak solar irradiation, while additional devices come on line if irradiation increases. This helps avoid operation in the adverse part-load range. 

Until now, the Sitop product range included two indoor models, the 1500 and 2300, with 1.5 kW and 2.3 kW nominal powers respectively. These two devices have been joined by the 1100 model with 1.1 kW and the 2000 with 2.0 kW. While the smallest one (as master only) comes at a list price before taxes of €1,133 ($1,460), the larger device (in both master and slave models) is offered at a net list price before taxes of €1,466 ($1,890) and €1,021($1,310) respectively. A clever combination of master and slave models allows operators to cover the entire area of 1.1 kW to 5.0 kW (on the alternating current side) in fine gradation. Different device combinations generally reduce power gaps to less than 300 W, if not lower. That means that customers can better match solar generators with inverter power, which results in higher system yields. 

Naturally, inverter efficiency is an essential part of achieving high system yields. Here the smallest device with a top efficiency of 93.5 percent can hold its own against a larger model in the series. The same holds true for the 2000 models: the 2300 model is the most efficient in this range of master-slave devices, with efficiencies of 94 percent (master) and 95 percent (slave) respectively. Despite all the differences in the devices' configurations, they generally look as alike as eggs in a basket. Hence combinations of different models will still produce a uniform aesthetic impression.

The IP65 series, which until now has consisted of just the 4600 model, is also being expanded. As the name implies, these devices have metal housings that adhere to IP 65 protection type requirements, which means they are suitable for unrestricted outdoor use. The 4600 is being joined by the 3000 IP65, with a nominal power of 3 kW and a list net price of €2,526 ($3,250), and the 4000 IP65, with 4 kW and a list net price at €2,818 ($3,630). In fact, these models, like the 4600 IP65, consist of two Sitop inverters in a common housing. That's why all the models in the IP65 series have two separate DC inputs each with its own MPP tracker. Apart from the power, the models do not significantly vary in any other way: they have the same dimensions and the same weight as the 4600 IP65 model.

All devices in the Sitop series use a single-phase feed-in and include an ENS for grid monitoring. Insulation monitoring and error current detection are also part of the general security package. A fan provides the necessary cooling. The master devices in the indoor series have an alphanumeric LC display. All devices are available off-the-shelf. Siemens offers a two-year guarantee, with the option of extending it to five years at additional cost. In the event of a failure, a replacement device is delivered to the customer within two days.

datasheet

Siemens AG
A&D SE PS1
Würzburger Strasse 121
90766 Fürth, Germany
phone +49/911/750-0, fax -2998
info@siemens.com
www.siemens.de/sitop/solar

Philippe Welter
© PHOTON International, June 2005