**1. Introduction**

212 Renewable Energy – Trends and Applications

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During the last decades, human lifestyle and economic growth has had a profound effect on the energetic sector considerably changing the perspective on the energy issue (Ambros et al., 2004). The increasing energy demand and variable oil price, insecure energy resources and carbon dioxide emission have made us aware of the fact that energy is indeed a limited product (Awerbuch, 2002).

Regarding energy resources, the International Energy Agency estimates that oil resources will be over in 40 years, natural gas resources in 60 years and coil resources in 200 years. Renewable energy and coal are the fastest growing energy sources, with consumption increasing by 2.1 percent per year and 2.0 percent, respectively. A significant number of studies and scenarios have investigated the contribution of renewable energy to satisfy global needs in energy, indicating that during the first half of XXI century its contribution will increase from 20 to 50%.

Estimating the exploitable technical potential of renewable energy in Romania, it observed there is a high potential of our country, for the usage this type of renewable energy, and Romania's strategy in this area provides for 2012 a energy production of: 1860 MWh from photovoltaic (PV) sources, 314,000 MWh wind sources; 18,200,000 MWh hydroelectric sources and 1,134,000 MWh biomass. Total of 19,650,000 MWh should represent 30% of country`s electricity consumption (Vasile, 2009).

PV systems produce power in proportion to the intensity of sunlight striking the solar array surface. The intensity of light on a surface varies throughout a day, as well as day to day, so the actual output of a solar power system can vary substantialy. There are other factors that affect the output of a solar power system. These factors need to be understood so that the customer has realistic expectations of overall system output and economic benefits under variable environmental conditions over time. From this perspective, the development of photovoltaic systems is closely linked to development of measurement and monitoring techniques, built-in data acquisition systems.

Data acquisition systems (DAQ) can measure and store data collected from hundreds of channels simultaneously. The majority of systems contain from eight to 32 channels, typically in multiples of eight. An ideal data acquisition system uses a single ADC for each measurement channel. In this way, all data are captured in parallel and events in each channel can be compared in real time. But using a multiplexer that switches among the inputs of multiple channels and drives a single ADC can substantially reduce the cost of a system (Szekely, 1997).

Specialized data acquisition systems for PV installations require a study of sample rates and an optimal configuration of the measuring chain. This chapter brings informations regarding the structure of data acquisition systems used in the monitoring of photovoltaic installations. It shows the operating principles of building blocks and the operation is performed by simulations using LabVIEW™ - Laboratory Virtual Instrumentation Engineering Workbench.

An important part of the presentation is dedicated to current measurement and data acquisition systems dedicated for monitoring PV systems. Applied solutions and experimental results are discussed in terms of accuracy and optimization needs of the operation.
