Journal of Engineering Science and Technology Review 5 (4) (2012) 35 -37 Special Issue on Renewable Energy Systems Research Article The Wireless Albedometer D. T. Cotfas* and P. A. Cotfas Transilvania University of Brasov, Romania Received 5 August 2012; Revised 25 September 2012; Accepted 10 October 2012 ___________________________________________________________________________________________ Abstract The wireless albedemeter as a new solution for the measurement of the albedo is presented in this paper. The classica pyranometers which are used to build the albedometers were replaced with two small monocrystalline silicon photovoltaic cells. The mobility and applicability of the albedometer increase using the device called Tag4m instead of the classical acquisition board. Keywords: Albedometer, photovoltaic cells, wireless, Tag4m, router. ___________________________________________________________________________________________ 1. Introduction The solar radiation has several components. The global horizontal solar radiation is composed of the diffuse horizontal solar radiation and the direct solar radiation. If the surface is tilted the third component appears - the reflected solar radiation. The reflected solar radiation is very important for the energy balance. A new size - albedo has to be introduced if this type of solar radiation is taken into account. There are many definitions for the albedo in function of the reflecting surface and the research domain: ground albedo, crop albedo, etc. In general the definition for the albedo is the ratio between the reflected radiation of surface R and the global horizontal solar radiation G, see Eq. 1. G R a = (1) The albedo is an important parameter for different research domains, such as: the atmospheric sciences, the agriculture, the bio-geo engineering, the photovoltaic domain, climatology, the forestry and the building energy science. Taking into account the climatic changes and not only, albedo becomes a crucial parameter [1]. There are many researchers who claim that by controlling the crop canopy albedo, the warming can be averted. Increasing the crop albedo with ~ 0.04 can lead to a cooling effect with ~1oC for Europe in summer [2-5]. 2. Methodology There are three methods to measure the albedo: from the top of the atmosphere using planes, meteorological balloons or satellites [6,7], in the lab [8] and in the field conditions [9]. The first method is suitable to measure the albedo for the large area and homogenous surfaces. This method is not recommended for small surfaces. The influence of the atmospheric factors should be taken into account in this case. In the lab the albedo can be measured only for small samples. In this case the light source can be a problem. In the lab the light source must be a solar simulator to assure a very good matching between the spectrum of the light source and the solar spectrum. The price of the solar simulator is very high and it grows with the increase of the illuminated area. Another problem for the lab measurement is the area of the albedometer. The area of classical pyranometers which are used for albedometers is high and the shadow can cover the entire illuminated area. A good solution can be using the two small photovoltaic cells. The third method is the most widely used because the measurements are performed in the real conditions. The albedometers can be realized using one or two back to back pyranometers. In the first case the cost is lower than in the second when two pyranometers should be used. The measurements for the albedometer with one pyranometer are performed step by step. The reflected radiation of the target surface is measured first, and the global horizontal solar radiation is measured after the pyranometer rotation with 180o. There is a big disadvantage; the two radiations are not measured simultaneously. If the level of radiation is changed due to the clouds, the measurements are not accurate. In this case the measurements should be performed in clear sky conditions. Using the two pyranometers positioned back to back can eliminate the disadvantages above raising the measurements’ accuracy but the costs become considerably higher. To reduce costs pyranometers of inferior class can be chosen if the measurements accuracy allows it [1]. Jestr JOURNAL OF Engineering Science and Technology Review www.jestr.org ______________ * E-mail address: dtcotgas@unitbv.ro ISSN: 1791-2377 © 2012 Kavala Institute of Technology. All rights reserved.