The collector considered in this study is a Direct Flow evacuated tube collector [17] which is part of a physical research programme by the authors. The gross area of each collector unit is 4.245 m2 (1.996m*2.127m L/W) and the absorber area per unit is 3.02m2.

Using the maximum number of these units that can be physically accommodated within the boundaries of each roof, the potential collectors’ yield for each house is calculated and shown in Table 5. This yield clearly depends on the geometry of the house i. e. roofs’ size, orientations and overshadowing as mentioned in 2.1. For flats 9 and 12 the total roof area of the building is assumed to be available for use of these flats (top floor flats). For flats 5 and 12 it is unknown what share of the building’s roof or terrace could be used, therefore only vertical collectors are assumed to be mounted on external walls. For the houses all the roof areas (except those facing north) are considered to be used and no vertical external surfaces are used. A significant part of these roof surfaces are not covered by collectors, due to the fact that the specific collector type comes in a standard size.

Figure 3 contains 12 graphs, one for each of the 12 houses modelled, showing the monthly thermal energy requirement in relation to the monthly collectors’ yield. All graphs show predictions using the tmy2 weather data. On two of the houses (with the highest and lowest demands) the predicted demands with the actual weather data of year 2007 are compared to those with the tmy2. Year 2007 was a significantly warmer year than average for Cardiff and therefore the predicted space heating demand is much lower than average and the solar thermal energy availability calculated with this data is much higher. This comparison reveals a much larger potential for solar thermal as average temperatures increase.