Inverter and PV System Technology
Industry Guide 2013

A photovoltaic plant (PV plant) that feeds all the power it generates into the grid essentially consists of the following components:

• PV generator (solar modules)
• support structure (mounting frame)
• generator junction box (GJB)
• inverter
• monitoring system
• feed-in meter
• grid connection
• direct current (DC) and alternating current (AC) cabling

Careful planning is critical to achieving the optimum balance between a plant’s components. These are continually undergoing further development to increase yield and efficiency. When integrating these components into a single system, the different module types available (modules with crystalline silicon solar cells or modules based on the various thin film technologies) must be given just as much consideration as the ever-increasing functions of the inverter.

Photovoltaic systems need to do more than simply feed energy into the grid if they are to make an adequate contribution to the power supply. Installations must also play a role in stabilizing the grids, for example by supplying reactive power, supporting grid frequency or keeping an installation on the grid when there are grid failures. This is why, as the systems’ intelligence centers, inverters are also increasingly required to perform grid services.

From purely feeding the maximum amount of energy into the grid through providing grid services, the inverter must now also develop itself into an energy manager that assesses the different options available for utilizing the solar power and then identifies the most profitable solution in each situation.

Private power supply is becoming increasingly distributed. Ever more PV system operators are themselves consuming the power generated on their roofs. PV systems technology is set to develop further as a result of this. This will particularly affect inverters, as they guide the solar power either into the household network, a power storage system or the public grid, depending on supply and demand.

Centralized and decentralized storage systems

Accumulators (batteries) offer a great option for storing surplus solar power and then feeding it into the domestic grid as required. This provides a new application for traditional lead-acid batteries, although new (e.g. lithium-based) storage systems are also being developed. New developments are still very expensive, meaning that initially their market is expected to grow slowly. If the necessary expansion of storage capacity is to keep up with the increasing amount of power being generated, the specific costs per stored kilowatt hour and per kilowatt hour withdrawn from storage (euros/kWh) must be reduced while the cycle life of batteries must be increased.

The market for storage systems is still too young, however, to foresee which technologies will secure a large foothold. A likely future scenario will involve a mixture of distributed, short-term storage systems and large, seasonal storage systems that are capable of storing surplus energy for several weeks or even months.

Off the grid

Photovoltaics is not just growing in importance in regions supplied by the public grid. In areas without grid connection – or where diesel generators are still the main power source – and where sufficient insolation is available, PV plants are able to generate electricity relatively cheaply. This is because off-grid supply is usually cheaper than connecting to a far-away grid. As a result, ever growing numbers of standalone PV systems are springing up in sparsely populated or technologically less developed regions in Asia and Africa. Hybridizing diesel power supply systems by combining them with a PV plant in order to reduce fuel costs is already cost-effective today. PV systems are also increasingly popular in areas with an unreliable public grid due to frequent grid failures and power fluctuations. Here they operate in parallel to the grid and support it when necessary. Off-grid and on-grid systems are growing together.