A guest blog by Victron Energy dealer Neosolar & Asolar, who are based in the Czech Republic.

This off-grid system was designed with high reliability and innovative functionality in mind – using Victron Energy products to assist in achieving these goals.

The system has proven itself operationally, having been originally commissioned on 12th February 2016.

Unique design

Czech companies Neosolar and Asolar implemented a unique off grid system for a family house in a permanently inhabited secluded newly built duplex. The building is not only a classic family house, but also the background for a small family farm. The main reason for building the system was the absence of a distribution network and high costs of its eventual construction. The investor’s requirement was straightforward: implement a sophisticated system with high operational reliability, low demands on operation and ease of use for all family members. It is a system with high operational reliability, minimum demands on operation and ease of use. It is a so-called DC-coupling with Victron MPPT solar controllers and hybrid Quattro and MultiPlus convertors and a lead-acid battery. The system is 230 V AC single-phase. Solar energy primarily powers appliances; the second priority is to recharge the battery, and the third is hot water.

Main DC circuits of the PV off-grid system.

Key:

PV segments and MPPT chargers

The PV array consists of 36 pieces of polycrystalline panels with a total output of 9.9 kWp. It uses two Victron BlueSolar MPPT solar chargers 150 V/85 A. Their data link optimises common operations, but can also work independently. There is a possibility of their easy functional inactivation (DC-manual bypass) with direct connection to panels, and a battery with solar emergency battery charging without MPPT controllers for non-standard situations.

Photovoltaic array of the island system consists of 36 modules with a total nominal output of 9.9 kWp.

Concept of two independent converters

Reliability is ensured by a pair of mutually independent converters. Main is the converter / charger Quattro 48 V DC/VA 10000/140-100/100 A. It is complemented by a converter/charger MultiPlus 48 V DC/5000 VA/70-100 A. That represents major converter when needed, and allows for reduction of operational energy during periods of low power consumption. Both converters can be output-united with a common power output of 13.5 kW in extraordinary consumptions. And that’s not all! The joint performance can be added to the main generator power of 5 kW (PowerAssist functionality). Permanent consumption can therefore be up to 18.5 kW. The “Select converter” option selector switch makes possible to manually select the converter (reduce operating power, fault), power their mutual affinity (increased consumptions), or shut down without the need for complicated parameterization.

Single-line diagram of the “Select converter” switch; the building powered by the main converter.

Key:

Two generators – backup power security in every situation (concept of two independent sources)

The main source of additional electricity is a single-phase generator with output power of 5 kW and automatic start controlled by the rate of battery discharge (lack of solar energy, protective charging of the battery). If necessary, there is a possibility of easy manual start by the switch regardless of the state of the system. The operation of the exchange is only allowed in the daytime to eliminate night time rush except in emergencies. The system is equipped with a backup generator with an output of 2 kW in case of failure of the main generator. It is started manually. Supplemental energy source is selected using the “Source selection” switch that allows you selection of the option “Off” – house wiring disconnected from both generators; options “Power by main generator” and “Backup generator power” are used for direct power supply of the house wiring from the generators in case the converter need to be disabled; options “Main generator + converter power” and “Backup generator + converter power” are standard options combining common functioning of the converter and the selected generator.

Main generator Kipor IG 6000 Sinemaster including automatic start (switchboard) and possibility of connecting backup generator Kipor Sinemaster ID 2600 (black cable).

Single-line diagram of the “Source selection ” switch.

Key:

Energy storage

Energy storage provides OPzS lead battery with a capacity of 1520 Ah/48 V with a total of 73 kWh of storable energy. Lead technology requires regular protective recharging to prevent battery degradation. SOC Manager in case when the battery is not sufficiently charged with solar energy for some time starts automatically forced charging from the generator.

Energy is stored in lead traction batteries with a total capacity of 73 kWh.

PowerGen function – maximum use of the generator

The system has exploitative feature to maximize the run of the main generator. The run of the generator is costly regardless of the degree of its energy utilization. Primarily, the generator charges the battery. In the final charging phase the absorption capacity of the battery is limited, and at that moment the surplus energy produced is redirected to water heating. The function is selectable via switch.

DC and AC water heating

After powering AC appliances and battery charging, the surplus solar energy is used to heat hot water. A unique direct-current 60VDC solution is used – connecting a heater directly to the main DC battery bus. Switching DC heating is governed by the current state of battery charge calculated by BMV700. If the battery charge rate is greater than 95%, DC water heating activates. If the battery charge rate drops to 94%, the heating switches off. If the current production of energy is higher than the common consumption of the AC appliances and the heater, the battery is charged to full state. If the production is lower than the consumption, including water heating, the battery is briefly discharged to 94% charge followed by turning off the DC water heating. The system is equipped with a selector switch that allows permanent shutdown of the DC water heating, or conversely activation of the heating even at the expense of deep discharge of the battery.

The advantage of water heating by DC current is zero wearing of the Quattro converter / charger and maintaining the power capacity for other AC household appliances. There are no energy losses by energy conversion from DC to AC. DC water heating engages MPPT solar chargers that maximize solar gains. The planned expansion of the system by a wind power plant will allow conversion of the excess wind power also to water heating.

The system is also equipped with supplemental AC water heating with a separate heating element. In case of lack of solar energy, a switch can be manually use to activate AC water heating at the power of 0.5 kW or 4 kW for heating part of the water volume. Energy is pumped through the converter from DC sources (PV array, battery) or from the main generator.

Compact design

The internal technology is housed in a compact electrical switchboard. Outside the cabinet there is all the above described control equipment + warning lights of the system operation for fast selection and controlling the functional status.

The precondition for reliability is also the clear visualization of the operational status, and the ease of operation (the “Select source” and “Select converter” switches).

The internal technology is housed in a compact electrical switchboard.

Detailed project preparation – precondition of reliability and future repairability of the system.

Credits

This guest blog and images are courtesy of Neosolar and Asolar.