May 21, 2019

Autonomous holiday homes

Do not “give” any account!

The existence of a functional and reliable public electricity grid is not always self-evident and possible. Therefore, whether there is electricity from a public network such as PPC, but this is unreliable due to insufficient infrastructure or there is no reason at all, there can be an autonomous power generation system that exploits the inexhaustible renewable natural sources of energy, such as sun and air.

Fortunately, in our homeland both these sources hide ample energy that must be transformed reliably into electricity. Sun is the first source of energy to take advantage of since it is sunny in Greece for most days. The collection of this energy and its conversion to electricity is achieved with the photovoltaic systems. There are also cases where the energy produced by the sun through the PV modules is not enough. Where weather conditions allow, where there is enough wind potential, the PV system can be boosted by a small wind turbine.

However, as there may be periods of low solar and wind energy (for example night, clouds, low wind intensity), oil or gasoline or gas generators can also be used, and rarely, because of the high cost of hydrogen, in order to ensure a continuous and controlled supply of energy. Systems that use more than one source to generate electricity are commonly called “hybrids.”

Plenty of applications

Already in Greece there are hundreds of autonomous facilities in homes, business premises, tourist accommodation etc. One of them is the complex of small rented tourist houses on a small island of the Cyclades. The owners of the particular tourist unit, with respect to local architecture and ecological consciousness, decided not to feed the complex from the Public Electricity Network, avoiding the installation of many unsightly pylons, overhead cables and plug-in transformers but to install a small autonomous unit which fully meets the electricity needs of small residences. The tourist unit consists of five independent accommodation. Each accommodation has 5 energy-saving lamps, a small fridge, an electric oven, a ceiling fan, and can support a variety of small appliances (computer, mobile phone charger, etc.). In addition, there is outdoor lighting around the complex.

This system costs about 20,000 euros today, which can be increased according to the needs of each owner. Also, it should be stressed that the whole residential complex is fed by a system rather than separately, in order to limit the total cost. The owner can expand the capabilities of the standalone system at any time. For the installation and proper operation of an autonomous hybrid system, accurate and complete design is required by specialist engineers based on needs and operating areas, as well as the choice of branded and reliable equipment.

There are two standard equipment configurations that can be applied to the design of autonomous power supply systems. AC coupling device and DC coupling *. Both provisions can have equivalent effects, but the final choice lies with the designer of the system, who must assess the pros and cons of the case and make use of qualitative, appropriate and reliable equipment for each particular case.   * Ac-coupling is more expensive and this is why it is mainly used in large systems. Previously, it was also applied to smaller systems, due to better exploitation of PV energy. Plus, with modern MPPT chargers, this advantage does not exist. The type we will use depends, essentially, on the size of the system and on the distribution of consumption.

The materials used

After carefully planning and estimating the daily requirements of the complex in kWh the following basic equipment was used to implement the system:

  • 15 Centrosolar (Germany) photovoltaic panels totaling 2700 Wp with an annual output of approximately 4300 kWh or about 16 kWh per day on average in the summer
  • 2 autonomous Inductors / Chargers Victron Energy (Netherlands) Multiplus 48/5000 in parallel operation, total power 10 kVA
  • 1 Morningstar (USA) TS-MPPT-60 Maximum Power Point Charger
  • 1 Aerodyne Lakota (Spain) 900 W wind turbine with an annual output of about 2500 kWh or about 7 kWh per day on average in the summer
  • 24 Batteries Hoppecke (Germany) OPzS solar power 620
  • 1 Mase Generators (generator) diesel engine (generator) of 5.4 kW with Yanmar type PD 70

 Parts of an autonomous hybrid system

The basic equipment of a hybrid system consists of the following devices / units:

  • Photovoltaic Panels.
  • Independent Inverters / Chargers
  • Interconnected Inverters for AC coupling
  • Charge regulators for direct current coupling
  • Wind generators
  • Accumulators
  • Petroleum or gasoline generators
  • Various accessories, measuring and controlling the system