Report 6 (of 6): The Oxford Solar House - England

Until recently, the majority of buildings with conventional energy supplies were planned without considering the energy demand. It was believed that fossil fuel sources would be available as an inexhaustible supply of energy and that there would be sufficient reserves to cover any demand. The depletion of fossil fuel reserves and the threat posed by it to our environment has now lead to alternative sources of energy in buildings being considered.

There is a growing demand in overseas markets for photovoltaics to support rural infrastructure development programmes. The integration of photovoltaic modules into the structure of a building can have a number of benefits besides electricity production, including the use of the solar elements as a roof covering or shading elements. Currently, there is little demand in the United Kingdom, but cost reductions, climate change, cultural changes and developments in technology are beginning to increase the potential of photovoltaics as a viable contributor to power demand.

The Oxford Solar House is the first low energy house in the United Kingdom with a fully integrated photovoltaic roof. It was designed to function as an ordinary standard family home which requires only a minimum amount of energy for heating, cooling and lighting. In order to optimise the value of the electricity generated by the photovoltaic system, the energy demand in the house was reduced by using all available energy saving technologies but without impairing the comfort of the occupants.

The house was built to evaluate the potential for photovoltaics to contribute cost effectively to domestic and industrial energy supply and to demonstrate the potential of solar energy to replace as much as possible the environmentally damaging electricity and gas supplies in a dwelling which result in carbon dioxide emissions that fuel climate change.

Location

The construction of the house took about eighteen months and it was completed in March 1995. The house is orientated roughly east-west with a south facing rear elevation which provides good solar access. The house receives approximately four peak sun hours in summer, but only 0.6 peak sun hours in winter (Dichler, 1994). During the summer months, energy surpluses are predicted to be around 12 Kwh per day which is greater than the house energy deficit in winter. The house therefore has a positive energy balance. Power has to be drawn from the utility during night time and winter days.

Design of the Solar House

The house is laid out with rooms arranged round a central core incorporating a service duct, stairs to the first floor and a hallway to the entry porch. Bathrooms are positioned over the kitchen to reduce the length of pipe needed and hence, material used. The front and back doors are protected by a porch to the north and a two storey double glazed conservatory to the south, with a balcony on the first floor between two bedrooms.

Warm air is taken in from the conservatory air space through ground and ceiling level vent windows and French doors. It circulates through the house by convection to the kitchen and upstairs bathrooms where it is expelled through windows.

Gas fired appliances are used for cooking all year round and in the winter months they are used to preheat water for the washing machine and dishwasher, and for heating three radiators in the north facing rooms for two hours a day. The use of gas appliances removes a potentially large electricity burden that would normally be connected to the utility supply. At ground level, a wood burning Kakkleoven is the main source of heating. The walls, windows, floor and roof are well insulated to ensure low heat loss and there is triple glazing throughout the house except in the sunspaces. Materials were chosen carefully for transport energy, durability and heat storage. Heating and Hot Water Systems

The house is divided into two zones for space heating. The ground floor has only one north facing room and the first floor has two rooms facing south and two facing north. The three north facing rooms have a central heating system installed while the larger south facing rooms rely on solar gain and conservatory preheating. The efficient wood burning Kakkleoven on the ground floor supplements solar gain during winter. Internal temperatures are uniform throughout with the greatest fluctuation on the ground floor resulting from doors being opened.

The house has a flat plate solar collector which is mounted on the roof co-planar with the photovoltaic system. The solar hot water collectors are used to supplement the energy demand for domestic hot water and supply about 77% of the household requirements including the washing machine and dishwasher (Viljoen, 1995).

The heating demand is reduced by maximising passive solar gain, by providing thermal mass to even out temperature swings, and through good insulation. The gas energy demand for hot water is minimised by installing a solar hot water system. The grid electricity demand is reduced by installing energy efficient appliances, and by using a photovoltaic array mounted on the roof.

Ventilation

The house has no mechanical ventilation system but there is no condensation because the air and wall temperatures are typically the same. The house has a wide range of operable tilt and turn windows and vents to the sunspace which prevent it from becoming stuffy.

Photovoltaic System

The photovoltaic system is connected to the electricity supply and is regarded as the main power supply. It was designed to export surpluses to the National Grid utility, importing power only when it is essential and unavoidable, such as night times and overcast conditions. Low consumption appliances and careful timing in use are essential to spread the electric loads.

The photovoltaic modules are mounted between the skylights of the roof. Edge frames were used and the modules were carried on an aluminium substructure mounted to the roof. The frames were designed to fasten, by simple means, to as standard a roof structure as possible.

Economic Performance

One of the most attractive aspects of roof integrated photovoltaic sysems is that the modules can be used in place of a conventional roof. Building integration of photovoltaic leads to reduced costs for infrastructure, installation and ground work; savings in materials; less installation and planning costs; and integrated maintenance and operation.

Currently, the homeowner, Susan Roaf, is paying £0.070 per unit to the utility company, and the utility company is buying the exported electricity at £0.027 per unit. The cost of the imported electricity is £106.60 and the income from the electricity exported is £45.60. Thus, the household is paying £61.00 for consuming 2964Kwh in a year.

It is incredible that not only is there enough energy generated to sell back to the electricity company but there is a sufficient amount to power the electric car. The car takes three hours to charge to travel 30 kilometres.

For more information, please contact:

ITDG would like to thank Oxford Brookes University and Doctor Susan Roaf who provided the original material on the Oxford Solar House.

References

Sue Roaf, Manuel Fuentes, Stephanie Thomas: Eco House: A Design Guide
This book provides an authoritative look at all aspects of Eco-house design, including an introduction to the key issues of form and construction in Eco house design, ecological building materials and methods and how to design for natural ventilation in different climates. It also looks at health issues in housing and has chapters on how to build solar hot water, solar electric and water conservation systems into your home. The book includes 21 case study Eco houses from around the world, looking at design issues for different climates. The book guides the reader through this fascinating area, by providing a good grounding in the nature of energy efficient design and giving tips to the students and practitioners.
£24.99 (Butterworth-Heinemann) 2001, ISBN 0750649046

Roaf, S.: 21AD/PV: Photovoltaics - School of Architecture, Oxford Brookes University.

Dichler, A. (1994): Review of the Technical Merits of a Proposed Photovoltaic House in Oxfordshire. ETSU.

Viljoen, A. (1995): Low Energy Dwellings.

This programme is one in a series of five about what ordinary women, often in very challenging circumstances, are doing to build better lives for themselves and their families.

TVE/ Practical Action gratefully acknowledge support for the HANDS ON programmes from the UK's Department for International Development (DFID), the European Commission (EC), the UN Foundation and UNDP/The Equator Initiative in collaboration with the Government of Canada, IDRC, IUCN, BrasilConnects and the Nature Conservancy.