Autonomous power plant for a farm building

«I need complete independence from energy suppliers» — said the owner of the building under construction. We at NENCOM love such tasks, so the conversation quickly turned into discussing technical solutions.

The building with an area of 200 m² is located in Varna region, on a large plot in a probing field, in which experimental types of wheat are grown. The electricity is temporarily produced by a generator. We need to create a heating system and an autonomous solar power plant. It was decided to divide the project into several stages.

First, even in the process of building, we installed a boiler and pellet Mudlark burner with Wi-Fi module, pellet hopper, radiators, 500 liter water heater, and a buffer tank with the same volume for the heating system. We also laid the cables for the future power plant from the roof to the technical room in advance, so as not to make unnecessary holes in the walls after the construction is completed.

We pre-assembled the small components of the future power plant in a metal cabinet 120×90×22 cm to speed up the installation on site.

Pre-assembly of power plants

As soon as the roof was ready, we proceeded to install the solar panels. For this project we chose monocrystalline Risen modules with power of 330 watts.

Risen RSM120-6-330M

The southern slope of the roof has an angle of 40° and the area is enough to fit 60 such modules. In the first phase we installed 20 modules with a total peak power of 6 600 Wp.

The solar panels are divided into 4 strings by 5 modules. In each string, the modules are connected in series, and the strings themselves are connected in parallel with each other. This allowed us to get the optimal operating voltage for the charger controller Victron Energy MPPT 250 | 100.

The first number in the controller name means the maximum allowed input voltage: not more than 250 volts. The second number — maximum output current: up to 100 amperes. The voltage at the output of the controller is determined by the battery. In our case, the battery voltage during charging is about 55 volts, so the maximum power of the charging controller in this configuration will be approximately 5 500 watts.

We installed lithium iron phosphate BYD Battery Box Premium LVL, in the technical room with a useful reserve of energy 15.36 kW·h.

BYD Battery Box Premium LVL

This is the first in Bulgaria BYD battery from the latest generation «Premium». Compared to the previous generation, the new battery has increased energy density and improved electronics.

On this stage, we installed one Victron Energy inverter MultiPlus-II with power of 4 kW, but we concerned the possibility of addding additional inverters to increase power. MultiPlus-II can work off-grid mode, as well as connectted to an external grid or generator.

Real time monitoring of the system

We launched the system at the end of May and the owner mmediately started actively using it. During the day, various electric motors were running and a 500 liter water heater was being heated, and in the evening — the usual consumption for the lighting and other small devices. We now have complete statistics for 4 months, from June to September.

As can be seen from the graphs, the total energy consumption during this period is 2 765 kW·h. Only 11 % of this energy is taken from the generator. In September, the need for irrigation decreased, so the generator was not used at all. Consumption of solar energy (directly and through battery) for 4 months was 2 457 kW·h.

On a typical summer day, you can count on a stable > 3 kW power from solar panels during 7-8 hours.

Solar generation on July 25

It takes just over three hours to heat water in a 500 liter water heater from 45 to 60 °C using a 3 kW heating element.

In summer, this is more than enough to save energy for other needs and charge the battery, but in winter there will be a shortage. Therefore, we plan to install additional solar modules in future.

The price of this solar power plant in May 2020 was 35 000 BGN (17 900 €) with delivery, installation and VAT.