Bill Dunster: 'On-site renewables can deliver zero carbon homes'

The UK Green Buildings Council statement that on-site renewables cannot deliver the government definition of zero carbon on up to 80% of new homes needs questioning carefully.

It seems that some of the people partially responsible for causing the problems in the first place are now trying to reduce the effectiveness of the proposed government legislation, possibly in an attempt to maintain the value of extensive landbanks purchased before the recession. The real issue is cost, not the technical challenge of delivering zero carbon.

Any environmental innovation increases construction cost in the short term, until sufficient production economies of scale are reached. The code increases its environmental specification at two to three year planned intervals, allowing developers to build out their landbanks before the next code level becomes mandatory, so really there isn’t too much to complain about.

Any environmental innovation increases construction cost in the short term, until sufficient production economies of scale are reached.

70% of the UK is built at a density of 50 homes per ha or under. This particularly applies to new housing developments. At this density it is easily possible to build state of the art energy efficient zero heating specification homes, with passive heat recovery ventilation and thermally massive interiors which require almost no space heating or cooling to provide comfort conditions.

Two simple evacuated tube solar thermal collectors will provide domestic hot water for 50% of the year, through late spring, summer and early autumn. This leaves only 50% of the annual domestic hot water load to meet using reliable programmeable woodpellet biomass boilers serving a typical terrace of six homes.

Only 250 kg of biomass is used per inhabitant per annum. This meets each citizen’s fair share of the limited stocks of biomass available from within the UK without losing agricultural land or wildlife habitat. Such a small amount of biomass is used each year that bills will be around £180 per year for each household. Our own prefabricated boiler house even orders its own pellets over the internet if stocks run down, and deliveries coincide with boiler de-ashing cycles, eliminating the need for expensive energy service companies, utilities and associated middlemen.

Two simple evacuated tube solar thermal collectors will provide domestic hot water for 50% of the year

With the space heating and hot water demand met from a mixture of energy efficiency, passive design and on-site renewables, it is now possible to meet the annual total electric demand from reliable 'fit and forget' solar electric panels mounted on the south facing surface of a conventional pitched roof as long as the best energy and water efficient lights and household appliances are specified.

It is possible to have almost no annual electric bill by choosing the best tariffs offering the same price for exported as imported electricity, and no standing charges. This strategy requires no expensive infrastructure investment, and is equally applicable to both small and large sites – again disproving the UKGBC statement that code level six is more economic on larger sites.

The cost of the Rural ZED microgeneration package is identical to the cost of a site wide combined heat and power system with its expensive heat main distribution and ongoing maintenance staff costs. With a 15% annual fuel price escalator, the payback is under 10 years. By adopting the chancellor’s definition of zero carbon and obtaining stamp duty relief, it is possible to reduce the monthly mortgage payments on the extra premium payable for a zero carbon specification to match the cash that the same household would have spent on a building regulations home purchasing conventional fossil fuel electric and gas services.

On smaller sites at densities above 50 homes per ha it is possible to use the new generation of pellet powered combined heat and power plant units now being introduced onto the European market by continental suppliers.

The Rural ZED housekit was built at EcoBuild in February this year in three and a half days, and is now in production, with a code six kit costing £1,250.00 per square metre to supply and £1,500.00 per square metre erected on typical sites including microgeneration equipment. A worked example showing how a typical urban block achieves this density with a mixture of east/west and north/south homes of various sizes and typologies is available as part of a downloadable pdf on the ruralzed.com website. The reconciliation of the social sustainability, placemaking, and the microgeneration agendas is totally possible using this product with its carefully integrated supply chain and urban design principles.

On larger sites of 100 homes and above – at densities above 50 homes per ha an energy service company-run biomass powered combined heat and power plant or a wire connected large scale community wind turbine will be necessary to meet code level 6. The combined heat and power plant is best achieved by pyrolysis or gasification technologies – which break waste down into synthetic gases – feeding hydrogen rich gas into fuel cell units. This achieves the all-important 60% electric and 40% heat ratios, avoiding heat dumping.

On smaller sites at densities above 50 homes per ha it is possible to use the new generation of pellet powered combined heat and power plant units now being introduced onto the European market by continental suppliers. Within three to five years, both combined heat and power plant technologies will be commonplace with economies of scale starting to cut in fast achieving market viability well before the code becomes mandatory in 2016. If the UK does not stand by these targets – and create a supply chain to meet them – a major European market will be lost to British industry. It is worth noting that exactly the same microgeneration supply chain can be used to reduce the carbon footprint of existing buildings.

The UKGBC recommendation to allow offsite generation puts even greater pressure on scarce communal green grid renewable energy reserves.

The UKGBC recommendation to allow offsite generation puts even greater pressure on scarce communal green grid renewable energy reserves. These are required by our stock of existing homes and public services. About 15% of current national electric supply could be achieved realistically by 2050 even if the entire practical area of UK offshore continental shelf was covered in 2 mega watt turbines at the minimum 500 m spacing. Contributions from tidal energy could perhaps contribute another few percent.

It doesn’t look as though there is any spare offsite renewable energy harvesting opportunity for the UKGBC to adopt, unless they propose stealing our existing homes’ renewable energy futures.