Page 73 - North American Clean Energy March April 2016

To counteract a sudden increase
in irradiance, PV inverters can limit
their production by moving away from their maximum power point range and operating like a conventional power plant. However, when there is a drop in irradiance, the PV inverter is unable to control the energy produced, therefore requiring the use of ESS to provide power and to limit variations.
e integration of an ESS makes it possible to control the power ramps generated at the PV plant. Whenever a cloud passes over, with the subsequent loss of irradiance, the ESS provides the energy required to o set the energy shortfall. Once the cloud has gone, the available power increases sharply and this is used to charge the batteries whilst smoothly increasing
the power output at the same time.
Figure 3 shows an example of the system performance in the face of an 80%/min uctuation in irradiance (up and down), in accordance with the 10%/min output power variation currently imposed by some grid operators, such as PREPA in Puerto Rico.
In order to address this issue and to facilitate the greater integration of PV energy into the grid, a family of storage central inverters have been developed
with an output power ranging from 375 to 1,110 kVA, and are designed to integrate battery-based storage systems in PV plants. Moreover, it is possible to integrate the inverters and all the other electrical elements into a power station which can be supplied fully furnished on site, reducing capital expenditures (CapEx) and gaining cost-e ectiveness. us, this storage (or photovoltaic) power station can achieve up to 3,500 kVA power output.
is kind of utility-scale solution
has been developed by using the same technology applied to the medium-voltage photovoltaic power stations. e main reference is a 9,000 kWh storage system (with Li-ion batteries) coupled to a 9,000 kW PV plant.
Although there are several ways of integrating storage systems in PV plants, the engineers on this project believe the best one is to keep the ESS completely centralized, as if it was an independent installation coupled to the PV plant immediately before the point of connection with the medium voltage substation.
Figure 4 shows a typical connection diagram, with conventional grid-connected inverters for PV generation and dedicated storage inverters to connect the batteries to the electricity grid.
is option can be installed in PV
plants that are already operating. With this system it is also possible to provide reactive energy with the battery inverters, thereby avoiding the need to over-size
the PV inverters, should there be strict reactive power delivery requirements.
e power plant controller will manage
the energy ow between the grid and the batteries, adjusting the plant generation to a preestablished pattern.
In its annual ‘World Energy Outlook’ report, the International Energy Agency revealed that in 2014, renewables accounted for almost half of the new power generation capacity built worldwide and have now collectively become the second-largest generator of electricity after coal4. is clearly shows that we are now facing a global shift to low carbon energy sources.
Carlos Lezana is the marketing and communications director for Ingeteam’s Solar PV Energy Division.
1. Lux Research, 2014.
2. US Department of Energy. Grid energy storage.
3. According to BSW-Solar (German Solar Industry Association).
4. World Energy Outlook, November 2015. International Energy Agency.
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North American Clean Energy 73