Solar Energy System of the Month:

Award-winning photovoltaic system: solar power system as backup system offers protection against blackouts

The last large-scale power failure (blackout) in Europe affected about 10 million people: on 4 November 2006 at 22:09 pm parts of Germany, France, Belgium, Italy, Austria and Spain were without power for two hours. Even in Morocco the effects could be felt. In the event of a power failure or a network interruption, solar power systems are separated from the electricity network according to law. So far it was thus not possible to use one’s own solar power system as a backup for essential household appliances in the event of the public electricity network suffering a failure. This loophole has now been closed with the "Sunny Backup System" developed by SMA Technologie AG: in the event of a power failure the system fully automatically switches to “stand-alone power supply”. The Solarserver June 2007 wishes to present this innovative photovoltaic backup system as the “Solar System of the Month”. It maps the route to stand-alone supply safety with the help of network-coupled solar power systems.

Solar Energy System of the Month as PDF-Document

Solar power system PV emergency power system "Sunny Backup"
Solar power system; PV emergency power system "Sunny Backup": with very little effort photovoltaic systems can be expanded to become true backup systems. Source: SMA Technologie AG.

Innovative synthesis of solar power stand-alone PV system and connection to the network

Most of the approx. 330 000 photovoltaic systems in Germany that were installed up until the end of 2006 feed the direct current generated by solar modules on the own roof into the public network via an inverter. For alternating current that is compatible with the network, operators receive compensation in terms of the renewable energy law. Up to 54 cent per kWh is what network operators must pay for solar power from systems that are connected to the network in 2007. For economic and technical reasons solar power is not stored; to a certain extent the electricity network serves as storage. Also for private and industrial operators of solar power systems, electricity comes from the power sockets – provided the network is up and running.

By contrast, solar power systems that are not dependent on the network, also called stand-alone photovoltaic systems or solar home systems, provide consumers with power directly or from batteries if the sun is not shining. Such stand-alone PV systems can be found in cabins in the mountains or on holiday premises in Germany and, even more so, in rural regions of developing countries where no access to the electricity network is given. There the required supply of solar power is regulated by intelligent electronics around the clock and, depending on the need, direct or inverted current consumption devices are driven with power from the PV generator or from solar batteries.

In the past, blackout implied that solar power systems were off too

In the light of an increasing frequency of blackouts, solar power producers are asking themselves why their system linked to the network must be switched off for security reasons when the network is not supplying any electricity. And this is no longer a seldom experience: large-scale and long-term power failures occurred in Europe in November 2005, in November 2006 and, as a result of hurricane Cyrillos in January 2007. In the USA the centralised electricity network broke down almost completely on 15.08.2003. It is expected by experts that blackouts and temporary power failures will continue to increase. The result: no light, no heating, no electricity for the refrigerator and the computer – and all this in spite of the fact that solar modules on your own roof as a small decentralised power station could provide electricity for your own consumption needs.

Synthesis of stand-alone PV system and network connection closes supply loopholes

This is where the pioneering concept of the company SMA Technologie AG comes into play. The company was awarded the prize for the “Most Innovative Solar Product 2007” in March 2007 at the 22. Symposium of Photovoltaic Solar Energy in Bad Staffelstein. With the new Sunny Backup System owners can use their solar power systems even if the network is down and can supply essential electrical appliances with their own power. Within 30 milliseconds Sunny Backup will switch over to stand-alone power supply, even during the night or when the residents of the home are on holiday. The backup technology can be added to new as well as existing solar power systems easily and cost-efficiently without any negative impact on the photovoltaic degree of efficiency.

Solar power even when the network’s down

The solar backup system by SMA is based on over 25 years of experience in the development of network-linked photovoltaic systems and over 1 000 solar power stand-alone PV systems installed worldwide. Sunny Backup includes the first backup inverter certified in terms of DIN VDE 0126-1-1. The completely pre-configured sets including the automatic switching device and suitable batteries are available for three performance categories.

Simple, intelligent and reliable: the "Blackout Blocker" by SMA

During normal operation, solar power is fed into the public network through one or more inverters. Only when the network fails, the backup inverter supplies consumers inside the house directly, by forming a stand-alone network within split seconds. The central component of the solar emergency power system is the additional inverter “Sunny Backup 5000” that manages the entire system. Other components are the automatic switching device (AS box) that separates the photovoltaic generator from the network according to the respective standard in the event of a network failure, as well as a set of batteries. In the event of a network failure Sunny Backup co-ordinates all switching, e.g. the separation from the network and the switching of the PV system.

Graphic presentation of a solar power system with Sunny Backup System.
Graphic presentation of a solar power system with Sunny Backup System. Source: SMA Technologie AG [Wording:Network, Sunny Backup System, PV system (modules), SMA Sunny Boy, Consumer, Sunny Backup Switching device.

Solar power systems and batteries used in parallel

The newly developed stand-alone network together with the PV system will provide electricity for the most important household or business appliances. The solar modules are used for direct supply as well as for re-charging the batteries. Direct operation during times of sunshine allows the battery set to be small and thus cost-efficient because generally it will only have to bridge the hours of the night. The parallel operation of a solar power system and batteries will ensure that even during a long-term power failure, electricity will be available for a significant period. One of the conditions for this is the consistent utilisation of the AC coupling developed by SMA that will ensure a hassle-free operation of Sunny Backup with the solar inverters.

Sunny Backup 5000.

As soon as the public network is available again, the backup inverter will automatically and without any interruption switch back to network operation and will thus make the solar power system available for its solar “colleague”, for example a Sunny Boy.


Photo: Sunny Backup 5000. Source:SMA Technologie AG

Uncomplicated and rapid installation by professional fitters

With the Sunny Backup System virtually every PV system can be upgraded, SMA Technologie AG emphasises: no specialised knowledge, e.g. on standards, guidelines or battery technology, is required for the assembly of the various models (up to 5,7 Kilowatt peak performance, from 20 to 30 kW and from 30 to 110 kW). Both one- and three-phase systems are available; a modular extension based on an AC-coupling can be done at a later stage. Planning and logistical requirements have been minimised. As a first step the professional fitter assembles the Sunny Backup 5000 and the switching device, then the batteries and the cabling. As a third step the backup inverter, the Sunny Boys and the selected consumers are connected on the alternating current side to the switching device. This is in turn connected to the main distribution unit (metre board). Then the fitter adjusts the parameters of the Sunny Boys to the stand-alone network operation. Finally the system is tested, configured according to commissioning instructions and switched on.

Inverter (1), automatic Sunny Backup Switching device (2), Sunny Backup 5000 (3) and set of batteries (4).
Inverter (1), automatic Sunny Backup Switching device (2), Sunny Backup 5000 (3) and set of batteries (4). Source: SMA

Security of supply for private and industrial operators of solar systems

The importance of power supply is only felt when it is no longer available. Private households but also companies must suddenly cope without lights, heating no longer works because the electrical pumps are not functioning, even basic communication devices such as telephones and PC’s are no longer available. Particularly grave consequences of power failures are noted when chains of cold storage units are interrupted and food or even medication can no longer be used. In agricultural businesses, stable ventilation and infrared lamps cannot function.

With Sunny Backup a solar roof can become an emergency electricity supply for companies or agricultural businesses.
With Sunny Backup a solar roof can become an emergency electricity supply for companies or agricultural businesses. Source: SMA

Power supply for essential appliances guaranteed for a few days

The period fo which Sunny Backup can supply a family of four persons when the electricity network lets them down, was calculated by SMA on the basis of a “small” PV system with an output of 5 kW. The typical electricity consumption of 11 kWh per day in a society used to a comfortable lifestyle will have to be restricted, since even without big loads of washing, with limited television viewing and “simple” cooking still 5.5 kWh are required per day for light, heating and the stove. The battery in the smalest Sunny Backup Set has a capacity of 140 Ampere-hours and with a voltage of 48 volt it provides a significant 6.7 kWh of which 80 %, i.e. 5.4 kWh are utilisable. Thus our exemplary family will have a full day’s supply of electrical power for essential appliances from the battery alone. If the performance of the solar power system is added, the calculation looks even more favourable: on an average summer day the 5 kW system will provide 18 kWh solar power so that the entire energy consumption can be covered and unrestricted electricity use is possible. Even on an average winter day the PV system still has an output of 2.5 to 3 kWh - and can bridge a power failure of two to three days together with the said battery.

SMA will be presenting Sunny Backup at the Intersolar 2007 from 21. – 23. Juni in Freiburg in Hall 4 at Stand 4.4.69.

Martin Rothert (left), Senior Product Manager of SMA Technologie AG, and Volker Wachenfeld, Head of Product Management, with award-winning Sunny Backup System.



Photo: Martin Rothert (left), Senior Product Manager of SMA Technologie AG, and Volker Wachenfeld, Head of Product Management, with award-winning Sunny Backup System. Source: SMA

Material and images: SMA Technologie AG. Editor: Solarserver, Rolf Hug

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