The Oxford Ecohouse: The 1990s Solar Dream
The Oxford Ecohouse was designed as a pioneering British Ecohouse in North Oxford. It is best known for having the first solar roof in Britain. The house was designed to provide a healthy and comfortable environment in current and future climates and to require minimal fossil fuel energy to do so. This is achieved in three stages: First of all the basic building is designed to stay warm in winter and cool in summer by careful design of its form, orientation, window openings, structural shading, day lighting throughout the house and the use of high levels of thermal mass internally to store warmth and coolth in the fabric of the building with flexible and effective natural ventilation pathways designed to distribute it to where it is required for comfort. The house is largely heated with a single high stove, or Kakkleoven, with backup gas heated radiators in the north facing rooms.
The Ecohouse, occupied from April 1995 was built with the first UK integrated solar roof including a 4kWp of BP Solar array of Saturn 585 photovoltaic panels; 5m2 of AES Solar solar hot water panels and two Velux roof lights integrated into the single south facing roof. It is owned by Susan Roaf, Professor of Architectural Engineering at Heriot-Watt University. The six bedroom suburban family home also has additional passive solar heating from the sun space and was designed to eliminate cold bridges across the external envelop of the house that has high levels of insulation in walls, floors and the roof (see: Roaf, Fuentes and Thomas (2012). Ecohouse: A Design Guide, Earthscan).
The solar panels are all still generating electricity well and hot water despite having had no maintenance over their lifetime. Over the last 20 years they have generated enough heat and electricity to give this six bedroom home one of the lowest carbon footprints for any UK building using only 13.2 kWhm2a of gas and electricity and producing only around 6 kg CO2m2a each year, a fraction of the impacts of most modern buildings. The SMA PV inverter has similarly worked continuously without maintenance and is almost as efficient as the latest models on the market.
In 1995 the integrated solar roof cost around £28,000 including £18,000 for the at cost PV panels, the cost of manufacturing the novel aluminium support system and the bulk of the related systems in use. The PV system then had a 66 year payback.Today similar PV systems with feed-in tariff support on adjacent homes have a payback of around 10 years. The building of this first UK solar roof would not have been possible without the support of the following solar pioneers and their companies that have all gone on to, or continued in significant roles in leading solar companies in the UK and beyond: George Goudsmit (AES Solar Ltd); Bruce Cross (EETS and GB-Sol Ltd); Steve Wade (Windandsun Ltd); Werner Klein (SMA GmbH); Gordon Grant (Velux); Ray Noble (BP Solar); Alan Dichler (Consultant); Paul Trimby (centre for Alternative Technology) and Manuel Fuentes and Valpy Fitzgerald (Oxford Brookes University). The 1 "“ 1 million solar roof celebration at the Oxford Ecohouse on the 7th of July is being held to pay tribute to, and celebrate, the contribution of every single person or organisation in the UK with a solar system today.
After 2012 the UK installed solar energy capacity has grown exponentially, not least because of the plummeting costs of solar panels in Britain. On Friday afternoon on the 3rd July 2015 15 percent of all electricity consumed in the UK was being generated by solar energy which is a remarkable achievement. The rate and scale of the expansion of the solar markets has been phenomenal, but as with all renewables that harvest clean free energy from the sun and air they are only intermittently available. Therefore the ability to store them and use them when needed represents the next great step towards a 100% renewable energy lifestyle and society.
The Oxford Ecohouse designers always understood the need for storage and provided it in the form of the very heavy mass of the walls and floors of the Ecohouse within the insulated envelope. This built-in thermal storage, along with the design of the form and shading of the house is what keeps the home at a stable warm temperature in summer and cool in summer. The 300 litre hot water storage tank of the solar hot water system also stores the heat collected from the sun in water for use overnight. Until now the big challenge has been to store the solar energy generated during the day by the PV cells, to shift it into being usable at night when there is no light. 
The 2020s solar dream must be to have homes that rely almost 100 percent on the energy they can harvest from their own sites. The Oxford Ecohouse already has highly efficient AEG white goods and these are manually activated, typically when it is sunniest. The next major area to tackle is that of the light fittings. The house now has low energy lights and in order to make sure that the energy required at night is minimal the house will be re-fitted with LEDs, using the Philips brand that was the original choice for the Ecohouse's low energy lights 20 years ago. The ultimate step is to revisit the design and management of the gas boiler backup systems, controls and displays.
But first we will meet the challenge of storing electricity with the exciting new SUNNY BOY 3600 / 5000 SMART ENERGY, combining the PV inverter with battery storage. It will fit easily into the existing electrical system with an effective capacity of 2 kWh that can not only offset fossil fuel generated energy consumption during the day but also makes it possible to use our own solar energy around the clock. Just as the Ecohouse 20 years ago used the first generation SMA inverter for its original system this is the first SMA wall-mountable, series-produced PV inverter to feature an integrated lithium-ion battery and is a world leading product that provides the opportunity for our dream of living in an energy independent house to come true. The integrated Webconnect function will provide worldwide access to our daily consumption and yield data via Sunny Portal so everyone can see how far we have gone in becoming a genuinely zero energy home.
