A methodology to study photovoltaics and storage system interactions

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Virginia Tech

A methodology is developed to study the interrelations between photovoltaics (PV) and storage systems in the context of demand side management. This study concentrates on the most prominent types of storage systems and photovoltaic technologies, which are lead acid batteries and single crystalline silicon cells and amorphous silicon cells, respectively. The methodology concentrates on the daily operating cost of the system. Only from a detailed comparison of alternatives can we develop a system that maximizes the benefits of photovoltaics and storage systems, while remaining cost competitive. This methodology consists of several steps that include; simulation runs to determine yearly energy production and consumption, life cycle costing, and analysis of daily cost graphs. During the analysis several items including photovoltaic and storage system technologies, different demand limits and demand charges, and different amounts of load control and purchased electricity as well as different PV and electricity costs are discussed, and the following conclusions are reached.

The type of photovoltaics used plays an important role in the system design. The amorphous cells seem to have a lower performance degradation in cloudy or hazy conditions, but single crystalline cells have a lower operating cost especially when there is high sunlight. The cost of photovoltaics also has a great effect on the daily operating cost. By keeping the cost of photovoltaics low (around $2.00/watt), the overall daily operating cost decreases while increasing the photovoltaic array size. This shows that photovoltaics can have a positive economic benefit. The effect of battery cost and on the daily operating cost is minimal. This is because its cost per day is a small part of the total daily operating cost. On the other hand, the demand limit and demand charge greatly effect the magnitude of the daily operating cost. The main component of the daily operating cost is purchased electricity. The daily operating cost increases as the cost of purchased electricity increases.