## 1 Introduction
### Climatology and Microgrid Architectures at the Three Locations
#### 1.3.3 Skylmager in the Canary Islands  
Six insular power grids comprise the electrical network in the Canary Islands. Conventional generation costs more here than PV technologies, and savings can be shared between the PV system owners and the Spanish utility ENDESA. Penetration of renewables varies among these grids, from a high of 60% penetration of wind energy in El Hierro (after Gorona del Viento hydro-wind power plant is operational) to Lanzarote-Fuerteventura which achieves single-digit integration of renewables because of strong environmental regulations, a weak power grid, and an unstable regulatory environment in Spain for renewable energy infrastructure during the period 2011-15. However, new regulatory policies will provide a more attractive framework for investment. The Canary Islands Government plans to avoid ground-based renewable facilities with a large environmental footprint in favor of smaller rooftop plants close to electricity users. As in Hawaii, the existing distribution grid is not prepared for a large penetration of residential PV systems with resulting reverse flows, voltage and frequency instabilities, and drops at the end of long lines. ENDESA has built a testbed smart grid in a village at the north end of the Fuerteventura-Lanzarote insular power system (La Graciosa). La Graciosa is the smallest island in the Canary Archipelago with a surface area of 29 km\({}^{2}\). It is in a marine nature reserve north of Lanzarote and home to about 700 people in the island capital of Caleta de Sebo. Average global irradiation is 5.157 kWh/ kW-day (1883 kWh/kW-yr) while the average monthly high temperature is 20.8 \({}^{\circ}\)C. Located a few kilometers away from the African coast, its proximity to the Sahara Desert gives to La Graciosa particularly stable atmospheric characteristics due to a quasi-permanent subsidence thermal inversion. Constant north trade winds, along with the high content of aerosols and dust in the atmosphere, have a large influence over the cloud dynamics and therefore, the irradiance in the region. As shown in Figure 9, the La Graciosa grid is supplied by three 20/0.4 kV transformers (600, 400, and 400 kVA) and tied by a 20 kV seabed cable to Lanzarote. The island has two PV generation plants (5 kW and 30 kW), but recently La Graciosa PV capacity was increased, enhancing the attractiveness of a smart grid energy management system. Figure 8: (**a**) PV panels and Skylmager at UTSA; (**b**) Inverters & combiners, Engineering Bldg. One of the main differences between La Graciosa project and the prior two experiences in the USA, is that in the island, a system composed of two sky-imagers was installed, as can be seen in Figure 9. The reason behind this was to give the forecasting system the ability to estimate cloud base height (CBH) making use of stereoscopic techniques as in [46; 47]. This provides the system with added value in terms of functionality and gives extra data to incorporate in the next steps of the image processing and forecasting pipeline. A recent paper comparing the use of different instruments to measure the CBH concluded that using a pair of inexpensive cameras was the most cost-effective alternative in comparison with other methods such as a ceilometer or LIDAR [48]. In fact, cloud base height is quite important to estimate the position of the shadows if a ray tracing approach is taken and it can also be included as a feature if Machine Learning methods are preferred, as it correlates with the position of the clouds in the image and the recorded irradiance or PV production. In this case, the device falls away from the Internet of Things (IoT) concept, since two cameras are involved in the system, and some computation must be done either in one of the devices or (as it was done in the project) on a dedicated server. Of course, there are some advantages and drawbacks for using either method, but we found particularly easy the connection between the sky-imagers and the server, and we could exploit the higher computational capabilities of the dedicated server.