Diesel-PV Hybrid System Without Battery Storage

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The following article details the proceedings of the Micro Perspectives for Decentralized Energy Supply Conference - 2013.

Diesel-PV Hybrid System Without Battery Storage

In the presentations of Daniel Yamegueu and David Tsuanyo from the International Institute for Water and Environmental Engineering their “flexy energy” concept was presented. It consists of small solar systems with a single phase inverter and a number of small sized diesel generators, which can be switched on and off depending on the load and solar production. The generator(s) load is kept in the optimal load range of 70% to 80% by the management system. It can be stretched to 60-90%.

Technical data of the existing testing plant:

  • One Diesel generator 9.2 kW
  • PV modules with 2.85 kWp and a single phase inverter of 3.3kW
  • Two resistive load banks of 4kW each

Although the inverter is feeding into only one phase the voltage of this phase is kept in the tolerable range of plus 10% as in the norm stated. Also harmonic current and voltage distortions are not significantly higher. Current harmonic distortions are 0.8 percentage points higher, voltage distortion are maximum one percentage point higher.

Due to the PV system and load shifting of e.g. water pumping systems the generator size could be reduced from 13kW to 9kW. A challenge is the needed in time consumption. But dispatchable loads can be used as storage if there is more production than consumption.

The approach is made to lower the initial costs and avoid batteries due to the lack of battery recycling structures in Burkina Faso. In usual Diesel-PV-Battery system the battery costs are up to 40% of the system costs. As the system is flexible designed batteries can be added later if wished. Through load shifting of dispatchable huge consumers as water tower pumps the generator size was reduced from 13kW to 9.2kW. In the discussion was questioned if this system is lowering the costs of electricity compared to an optimized PV-battery-Diesel hybrid system. Overall an electricity price reduction of around 2.7% is achieved by the system.

Catherina Cader from the Reiner Lemoine Institute presented results of a study about the global cost advantages of stand-alone small-scale hybrid PV-Battery-Diesel Systems. The national diesel price is taken into account as well as transport costs via the remoteness of the places defined as travel time to the next major settlement. Together with further data a price optimized PV-Battery-Diesel system for each location is designed.

  • PV system: 2000€/kWp
  • Battery system: 120€/kWh
  • Interest rate: 8%
  • Generator efficiency: 0.33l/kWhel
  • Operational expenditure: 0.02kWhel

In the discussion was pointed out that the prices are significantly depending on the assumed size of the system. Larger systems has lower costs.

The electricity generation price is compared between this hybrid system and a pure diesel generator. Resulting is the price advantage of hybrid systems in areas with high diesel prices and/or high remoteness better and the share of renewables higher. In countries with high diesel subsidies there are no or only low cost savings by installing hybrid systems. That means diesel subsidies destroys business cases for renewable energies.

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