Large-scale PV retrofit

by P Kolbeck, NovaPro, Denmark

During 1996-97, the Municipality of Kolding and the Danish Ministry of Housing and Urban Affairs carried out a large-scale retrofit project on a residential block in the town of Kolding involving almost 1,000 m2 of PV panels.

The project at Kolding aims to reduce energy consumption in housing and, at the same time, to develop further the Danish knowledge base on photovoltaic (PV) technology. Special attention was given to ensuring a successful architectural integration of the PV system into the existing urban area.

The PV installation formed an integrated part of an urban rejuvenation project which included comprehensive building improvements, introduction of energy efficient installations and remodelling of the surrounding area.

Kolding is a mid-size town (population 60,000) located in the southern part of the Jutland peninsula. "Solgaarden" is a five-storey residential building from the late 1930's and is one of the region's best examples of international modernism of the period. The Solgaarden building is well suited for an experiment with PV, due to its size and orientation. In addition, "solgaarden" actually means "sun-court" in Danish.

The objectives for installing the PV system in "Solgaarden" were:

  • to demonstrate the potential for employing PV in a multi-storey  older residential building;
  • to adapt to the architectural and technical challenges of  integrating PV panels into an older building;
  • to clarify the extent to which the annual energy use in a  large residential building can be met by PV energy;
  • to realise ways of halving the amount of fossil energy used in large residential buildings;
  • to collect experience about the operation of a large-scale  PV system with reference to performance, maintenance, durability,  consumer response and accounting principles.

The system
The PV system is divided into two main parts: a larger 757 m2 system on the roof and a smaller
175 m2 system integrated into the building's eight balcony enclosures on the south facade.

The roof mounted system is in the shape of four continuous bands of semi-transparent, mono-crystaline PV panels with a steel gallery. The roof installation is made up of 846 PV modules with a maximum output of 89.5 kWp. The eight glazed tower structures enclosing the balconies have a total of 80 PV modules with a combined maximum output of 16.5 kWp.

The system operates in 16 sections, each with an inverter providing 230 V ac to the local electrical grid. The PV-generated energy supplies around 60% of Solgaarden's electricity consumption. Surplus energy is sold to the local power utility, KOE. Total annual production for the PV system is around 100,000 kWh.

The principle of using of the electricity generated by the PV system on site has an economic advantage over selling the full 100,000 kWh/year to the utility ­the electricity sales would not cover the cost of importing energy for the building's needs. By substituting as much of the purchased electricity as possible by PV-generated electricity before selling the remaining PV electricity to KOE, Solgaarden saves considerable amounts of money on Danish taxes on CO2, SO2and electricity, and on VAT.

In order to optimise the potential for savings, each of Solgaarden's 80 apartments has had a PV meter installed. The meter displays:

  • the apartment's current consumption share of the PV generated  electricity;
  • the apartment's share of electricity sold to KOE;
    the apartment's share of electricity sold to KOE;
  • the apartment's share of electricity purchased from KOE.

The objective is that this information will help the tenants become more conscious of their energy consumption.

Energy and environment
The total yield of the PV system at Solgaarden is around 100,000 kWh/year, corresponding to around 60% of the complex's electricity consumption. The effect of the PV system on emissions levels has not been calculated. Without the system all the electricity consumed would have been drawn from the grid.

It is still too early to asses the electrical savings resulting directly from the installation of the PV system since tenants have, as a part of the urban rejuvenation project, also had new electrical stoves and other appliances installed in their apartments. The energy goal is still to reduce the use of fossil fuel to 50% of present levels.

The cost of the total urban renewal project was DKK 76 million of which the installation of the PV panels amounted to around DKK 22.4 million. Special grants were given to the project from national funds.

The Solgaarden project has proved that the large-scale retrofitting of older residential buildings with PV panels can help reduce energy consumption based on fossil fuels and that, with careful design, PV-based energy generation can be integrated successfully into an existing urban environment.

For more information contact the CADDET Danish National Team in Tølløse. 

The CADDET Renewable Energy Newsletter is a quarterly magazine published by the CADDET Centre for Renewable Energy at ETSU, UK.

The articles published in the Newsletter reflect the opinions of the authors. They do not necessarily reflect the official view of CADDET.

Enquiries concerning the Newsletter should be addressed to Pauline Toole, Editor, CADDET Centre for Renewable Energy, ETSU, Harwell, Oxfordshire OX11 0RA, United Kingdom. Tel: +44 1235 432968, Fax: +44 1235 433595.