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Kristanov – Water Treatment Facility Energy Back-Up

Realization: 2021

Location: Český Krumlov District, South Bohemia Region

Implemented services: In cooperation with GWL and Asolar, installed Amvolt Battery Pack 11 kWh, complete system of Victron Energy inverters, solar power plant 6.5 kWp

Costs: Amvolt Battery Pack 42 kWh, price: 19.500 EUR w/o VAT (PV panels and inverters not included)

Municipal batteries with photovoltaics or "a house full of treasures"

Křišťanov is located in the heart of the protected landscape area and the local stream is home to one of the largest Central European populations of pearl mussels, which need clean water at the level of baby water to live. The purification plant in our small village is therefore not just any purification plant: it is equipped with special membrane technology, which is also used on spacecraft and the ISS. You can practically drink the water coming out of it. So any power failure in the water treatment plant here could result in dangers far beyond the horizon of the small village.

The investor's task was to back up the existing treatment plants against power failure for at least 24 hours. Furthermore, the requirement was to make maximum use of the roof of the plant for the installation of solar panels: this will not only reduce electricity consumption but also extend the functionality of the backup in the event of a potential black-out. In addition, a publicly accessible charging station for electric bikes and small electronics powered by solar panels is located in front of the treatment plant.

Batteries from the electric bus get a second life

The implemented Amvolt Battery Pack system consists of 64 pieces of originally 300 Ah LFP cells (lithium iron phosphate battery, or LiFePO4) with a total original capacity of 63 kWh (64 × 300 Ah × 3.3 V). Why original? Because these lithium cells powered an electric bus for nine years and covered 270,000 km. Their current average capacity is therefore "only" 240 Ah, which is still 80 % of the original. The real current capacity in kilowatt-hours is thus at least 200 Ah × 64 pcs × 3.3 V = 42 kWh. By that, we gave the batteries a second life and they will last at least another 10 years in their new location, but rather more. We like LFP technology for these properties.

There are 10 panels with a nominal power of 300 Wp installed on the roof, i.e. a total of 3 kWp system. Due to the complex bureaucracy and technical requirements of the electricity distributor, we configured the inverters of the system to a mode without power overflows to the grid. They only power the plant's own consumption and charging stations, or help to recharge the batteries. In its current configuration, it saves the investor about 30 % of energy costs per year. We will further improve the efficiency of the system by using the PV Forecast service from the Czech Technical University to predict the number of sun hours and the savings will be higher.

The cost of this installation without batteries, but including all related equipment, structural elements, safety protection and installation was 310,000 CZK. In addition, the municipality rented the aforementioned "second life" batteries in the Amvolt Battery Pack with a capacity of more than 42 kWh for a price of 100 EUR/month.

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