HYBRID AND STORAGE SYSTEM SOLUTIONS
The hybridization of solar energy with diesel units, storage or another renewable source is continually developing, because it makes it possible to supply a competitive kWh in areas that are far from the power grid. The operator’s aim is to manage these different sources more effectively so that he can reduce the cost per MWh produced. That necessarily implies a more efficient use of the solar production and therefore an excellent forecast of this production on different time horizons.
Our solution consists on the one hand of providing a very high quality day-ahead forecast, because it is adapted to the site’s specificities, and, on the other hand, a refined forecast of the next half hour’s production. This last point is essential for optimising management of the system. According to different situations, it will be SteadySat (forecasts using satellite images) or SteadyEye (forecasts using images taken from the plant) that will be implemented, in addition to SteadyMet (forecasts based on meteorological models). With certain of our customers, all of our technological building blocks have been deployed on sites that combine photovoltaic production and storage.
An hybrid energy system is generally constituted by classic energy sources (a fuel generator for example), by renewable energy sources (such as solar energy, biomass or wind turbines), a storage solution and an energy management system (EMS).They may be grid connected or not. These systems address perfectly the needs in energy of poorly connected areas such as islands, micro-grids, even completely off-grid areas like rural areas or some mining sites for instance. The largest possible PV implementation allows a significant drop of the average cost of the energy produced by such systems.
Solar energy, because of its meteorological dependency, may generate significant production variations. Storing the energy can partially tackle this issue but storage technology costs remain very high. As a consequence, an efficient forecasting solution is today the most economical solution to predict and manage these energy production variations. In the case of an hybrid system, the use of a ground based sky imager is the most suitable instrument to forecast at a high update rate on a very short term time horizon the expected power drops. This forecast is then taken into account by the EMS which will drive the associated resources (storage or fuel generator for example). This very short term forecasting solution allows to include more PV power in an hybrid system, to reduce the use of other more expensive resources (gensets) while maintaining and guaranteeing the stability of the whole system.
The SW-04 sky imager, deployed on site, is taking hemispherical photos of the sky up to every minute. These images are then processed with a forecasting algorithm developed by Steadysun, which predict the possible impact of the clouds on the PV production. This algorithm will generate very short term solar production forecasts (from 1 minute to 1 hour) which are transmitted to the management software of the hybrid system. The SteadyEye service solution allows, thereby, to obtain on the chosen time horizon a production forecast for one or several PV installations on a 10 km2 area. This forecast can be updated every minutes.
The issue is quite similar in the case of an off-grid site, like a rural area or mining site, but the solution must in addition operate taking into account the lack of telecommunications network as well. In this case, the steadyEye forecasting service may operate using a local PC which will run the forecasting software on-site and will send the forecast files to the site energy management system (EMS). A simple integration with a logic programmable controller or a SCADA system can be implemented. Besides operational cost-cutting (maintenance and fuel costs), SteadyEye solution allows an increase in the installed PV power and the share of the solar energy in the energetic mix of the system.