Environment >   Zero carbon design    |     Waste & business practice    |     Energy & panel performance

Solar fraction - Over a year, homeowners can expect 30-70% of their hot water to be heated by the sun. Better positioned panels in low occupancy homes may approach this 70% “solar fraction”, while the same size panels which are less well positioned, or in homes with 3-4 people may achieve the lower solar fraction. Positioning panels on roofs is, however, far less critical than many people think. Almost every home in UK has a roof which is positioned within 20% of optimum, when it comes to collecting sunlight. Even a west facing roof at 30 degrees pitch collects around 85% of a maximally positioned panel, which is typically due south at 30 degrees pitch. It is worthwhile considering panel performance and how much sun it intercepts seriously: but one should be prepared to compromise and to bear in mind that maximising annual panel gain is different from maximising usable energy gain, given that a panel which may collect the most energy over a year may not necessary deliver 100% usable energy, because you may have an excess of energy arriving in summer. Therefore, where possible, it may sometimes be important for solar suppliers to position panels steeper than “annual optimal” to gives customers more useful energy over the year, particularly in spring and autumn, at the expense of a summer surplus.

Solartwin wins DTI SMART award
Ten of Britain's brightest businesses have benefited from DTI support to achieve real commercial success. Three of the ten awards were to environmental businesses, including ourselves, Solar Twin Ltd of Cheshire.