Electricity for cows

Photovoltaic system on a cow farm

Roman Rubanovich, NENCOM

Many agricultural facilities are not connected to power grids. Therefore, farmers use diesel generators to provide energy for the equipment they need.

Generators, which are expensive in themselves, constantly require additional costs associated with the purchase of fuel and regular maintenance: changing oil, filters, coolant, and so on. All of this is not cheap, but connecting to a grid is even more expensive.

The owners of a new cowshed, located near the village of Kalchevo, Yambol region, bought a three-phase diesel generator with a capacity of 22 kW. The farmers ran it twice a day to milk their cows.

Diesel generator

During operation, the generator made a lot of noise and stink, and sometimes the cow farm was left without electricity. The area around the generator was covered with soot for only several months. Of course, the farmers did not want to stay up with this state of affairs and turned to us.

Place for power plant installation

Important! Diesel engine exhaust is officially recognized as the first group carcinogen that causes lung cancer. Diesel exhaust negatively affects the ecosystem and agricultural efficiency.

Diesel exhaust carcinogenic

Diesel exhaust & Honeybees

Analysis of the situation

Dairy farming has a specific schedule of energy consumption, with two peaks during the day. The first milking takes place early in the morning, and the second — in the evening. This means that in the summer, cows give milk during sunrise and sunset, when most of the solar energy is absorbed by the atmosphere, and in winter — before sunrise and after sunset.

A typical day in September

In such a situation, the direct use of solar energy during milking is possible only partially. Batteries are needed to accumulate «extra» energy from solar panels during the day and release it during milking.

Dairy production requires strict adherence to sanitary standards, including immediate cooling of milk after milking. Therefore, the compressor of the cooling system and other equipment work together with the milking machine.

Milk cooling bath

The farm has 60 cows, milking is done in groups and takes more than five hours every day. The average power consumption during milking is about 5 kW. It is important to consider that this is the so-called «active» (useful) power, and during the operation of asynchronous electric motors (pumps, compressors), due to the phase shift between current and voltage, there is also a «reactive» power that does not do useful work.

«Apparent» power in alternating current circuits is measured in «Volt-Amperes» and consists of «active» and «reactive» components. Depending on the power factor of the electric motors, 5 kW active power can mean about 6 kV·A apparent power. In direct current grids (batteries, solar modules), reactive power does not arise: all power is active.

Therefore, in order for the inverter to be able to produce 5 kW of active power, required for the operation of milking equipment, it must take about 6 kW from the batteries, and taking into account the losses and consumption of the inverter itself — more than 6.5  kW. The capacity of batteries in such situations should be calculated with a margin.

If we assume that the batteries will deliver power of 6.5 kW for 2.5 hours, the energy consumption will be over 16 kW·h. Batteries are the most expensive part of an off-grid solar power plant, so the decision was made to make a small system first. This will shorten the running time of the diesel generator and collect detailed statistics.

Solar power plant

We have installed 32 photovoltaic Risen modules with 330 watts. The peak power of the solar panels was thus 10.56 kWp. We mounted twelve modules on the fucking southeast slope of the roof, twenty — in the southwest.

Risen solar modules

To conserve solar energy, we used eight 12 volt AGM batteries Victron Energy of the Super Cycle serie with a capacity of 230 A·h each. With a discharge depth of 80% admissible for these batteries, the useful energy reserve is 17.6 kW·h.

The batteries are charged using two solar MPPTs Victron Energy controllers with a total power of 9.24 kW.

Most of the equipment on the farm — three-phase. To convert the direct current from controllers and batteries to alternating current, we installed three MultiPlus-II Victron Energy inverters, one for each phase. The total power of the inverters is 12 kW or 15 kV·A.

Victron Energy Inverters

We connected the diesel generator to a solar power plant and set it up so that it automatically turns on when the batteries are low.

Automatic generator start

During operation, the generator not only supplies energy to the cowshed equipment, but also charges the batteries and then switches off automatically. You can control the generator operation and change its start-up settings remotely from a phone or computer.

Now the cowshed and the farmers house are provided with electricity all day long. Mostly — in complete silence. Fuel consumption has dropped significantly. Detailed statistics of energy production and consumption, as well as all technical parameters of the solar power plant, are automatically collected.

Update 21.12.2020

The system was put into operation on July 31, 2020. Now, on the day of the winter solstice, we decided to take stock of the power plant work for four full months: August, September, October and November.

VRM-Portal allows you to observe the operation of the power plant in real time, as well as analyze the statistics of various parameters with resolution by minutes, hours, days, weeks or months. For example, in this graph, we see the total consumption by month with the division of energy sources: generator, batteries and solar modules.

In yellow, the graph shows direct solar energy consumption during daylight hours. Green color — direct energy consumption from the generator during its operation. Blue color — energy consumption from batteries, which in turn are charged from both the sun and the generator.

It is important for us to evaluate the overall contribution of the photovoltaic system to the operation of the cowshed. This can be done by comparing different charts on the portal, but for deeper analysis it is better to download the data in spreadsheet format.

Therefore, the total electrical energy production for this period was 6 637 kW·h. Of these, 3 204 kW·h (48 %) were obtained from a photovoltaic system, 3 433 kW·h (52 %) — from a diesel generator.

The farm consumption during these months amounted to 4 979 kW·h, that is, 75 % of the total energy produced. The rest — these are natural losses in the process of charging and discharging batteries and reactive energy.

We expect that on average the solar power plant will provide about half of all consumption per year. The system can be enlarged, but in our opinion, it is first necessary to optimize the energy consumption of the farm. For example, to accumulate cold during the day using excess solar energy, so that the compressor of the cooling system is not turned on during milking.

Ice bank for milk cooling

Sometimes, biogas plants are used to generate electrical energy on livestock farms. These are expensive and complex systems that require special attention during operation. We are not fans of such solutions and do not like to burn anything to generate electricity.

Next year, after collecting more statistics, we are planning to optimize and expand the system to minimize the involvement of the diesel generator. We will increase the capacity of solar panels and the capacity of storage batteries. Perhaps we will additionally install a small wind generator.