Solar-Log: PV plant data loggers, feed-in management and monitoring portal

Overview

Solar-Log started as one person's monitoring device. Its company history says Jörg Karwath built the first Solar-Log in 2004, series production began in 2005, and Solare Datensysteme GmbH was founded with Thomas Preuhs Holding in 2007 to expand it. By 2011 the hardware was sold in more than 20 countries.

The company's position rests on being independent of inverter brands. A Solar-Log logger reads inverters and meters from many manufacturers through its own drivers, so an installer can monitor and control a plant, or a whole fleet of plants with different inverters, from one portal. In Germany it also became a practical way to meet feed-in rules: the same logger that records yield can cap export, respond to the grid operator's ripple control signals and pass direct-marketer commands to the inverters.

Swiss energy group BKW bought the company in 2015, and in 2021 it took the name of its product, becoming Solar-Log GmbH. Its timeline dates the WEB Enerest 4 portal to the same year, although the platform was first presented alongside the Base in 2019. In November 2024 Solarserver reported more than 415,000 plants and 17.6 GW on that portal, with products offered in more than 141 countries.

Offering

Solar-Log sells hardware, licences and a cloud portal, mostly through installers and wholesalers.

Solar-Log Base

The Base series, introduced in 2019, has three models sized by plant: Base 15 for up to 15 kWp, Base 100 for up to 100 kWp and Base 2000 for commercial plants up to 2 MWp, according to the 2019 launch announcement. Expansion licences raise the limits of the smaller models. The MOD I/O module adds potential-free contacts for ripple control receivers and the MOD 485 module adds RS-485 connections for more inverters. Licences activate free for 30 days after installation and are then bought from Solar-Log's online shop and activated remotely.

Feed-in management

Feed-in management covers the requirements of the German EEG and of VDE-AR-N 4110 for medium-voltage plants: fixed or dynamic percentage limits, limits that offset self-consumption, ripple control, reactive power control with an approved utility meter, and Modbus TCP telecontrol. The PM Pro licence covers the full power-management range; the interconnected control licence networks up to nine slave loggers and divides a plant into areas for separate direct marketers. Solar-Log also offers VDE commissioning support through to energy-supplier acceptance.

WEB Enerest and other services

The WEB Enerest portal provides dashboards, monitoring, task lists, fleet administration and billing. The company also lists Solar-Log WEB-4U, direct marketing, and smart energy and charging park management on its company page.

Technology

The Solar-Log Base is a DIN-rail logger. The Base manual for firmware 6.x and technical data sheet describe two 100 Mbit/s Ethernet ports, two RS-485 buses or one RS-422 bus, and one S0 pulse input, for indoor installation (IP20) from -20 to +50 °C. Inverters and meters connect through manufacturer-specific drivers in Solar-Log's component database, so the installed firmware and the device model decide what can be read on each bus.

Two Modbus TCP interfaces face outwards and do different jobs. The licensed power-management interface on the Base 2000 lets a telecontrol system send commands and receive feedback over Modbus TCP without analogue or floating contacts; IEC 60870-5-101 and -104 are reached through an external protocol converter. Separately, Solar-Log Modbus TCP Free (version 1.12, July 2026) exposes aggregated plant measurements read-only to an external monitoring or energy management system.

The Base includes VPN functionality, which the company says supports direct marketing. In the portal, a heat map of component communication helps find faulty inverter links, and the 2019 launch announced RS-485 signal-quality analysis for large plants. Solar-Log GmbH holds ISO 9001, ISO 14001 and ISO/IEC 27001 certification, and a VDE-AR-N 4110 component certificate for the Base.

Markets

Solar-Log's home market is Germany. When BKW bought the company in 2015, pv magazine reported that Germany made up about 70% of its customer base and Europe about 90%, with more than 230,000 plants and 9.9 GW in its portal. By November 2024 that had grown to more than 415,000 plants and 17.6 GW, and products were offered in more than 141 countries.

The German weighting follows from the product. Plants between 30 and 100 kWp need simplified feed-in management under the EEG, and medium-voltage plants must meet VDE-AR-N 4110, so installers of commercial rooftops and solar parks need a certified controller that the grid operator will accept. Direct marketing, in which a marketer sells a plant's output and may curtail it, adds a second command source that the logger must prioritise below the grid operator and log.

Customers are installers, wholesalers, plant operators and asset managers. Wholesalers such as BayWa r.e. list the Base range in their solar distribution catalogues alongside inverters from several manufacturers, which suits a logger whose value lies in working with whichever inverter the plant has.

Company

Solar-Log GmbH is registered at the Stuttgart local court under HRB 722895, at Fuhrmannstraße 9, Geislingen-Binsdorf, according to its legal notice, which names Jörg Niche as CEO and Marco Oesterlein as CPO.

The company was founded in 2007 as Solare Datensysteme GmbH with Thomas Preuhs Holding, building on Jörg Karwath's 2004 prototype. BKW, the Bern-based energy and infrastructure group, agreed to buy it in August 2015 for an undisclosed price, with all employees joining BKW, as part of its Renewables and Efficiency business. On 1 June 2021 Solare Datensysteme GmbH became Solar-Log GmbH.

Management has changed several times under BKW. Frank Schlichting was CEO at the 2019 Base launch. In 2022 BKW appointed Markus Eberhard to lead strategy. On 1 October 2024 Jörg Niche, until then chief sales officer responsible for global sales and service, became CEO (Solarserver), and Marco Oesterlein has since joined as chief product officer. Headcount and revenue are not published separately from BKW.