This overview of renewable energy for buildings is the first of four weekly articles to be published in the AJ. The other three will be on biomass and combined heat and power (CHP), ground-source heat-pump systems, and solar thermal. These articles will also appear in an extended form on the AJ website ( www. ajplus. co. uk) with further information on each technology.
The website will also cover small-scale wind generation, photovoltaics, and labyrinths and buried tubes (supplying ventilation air).
With renewables, step one is 'don't bother' - unless, that is, you have already done everything possible to cut energy demand.
This can be done through choice of location, form and orientation; making best use of daylight, controlled natural ventilation, insulation and airtightness; use of efficient services; making the building's use legible and manageable; and more. It makes no sense to create unnecessary energy demand then attempt to meet it with renewables; in pretty well every case it will be cheaper to cut emissions by designing-out energy demand. Also, all renewables technologies (especially photovoltaics) currently have higher initial costs than conventional building servicing.
Another reason to get the building's passive design right is to invest in aspects of the building that will be hardest to upgrade in future. Typically these include airtightness, insulation, thermal mass, distribution of daylight, flexibility and longevity of materials.
Renewables have to be part of an integrated design from early on.
Forward planning for renewables is another strategic design consideration. While most buildings built or converted today do not use renewables, this will change. In future, renewable energy will be supplied in significant amounts: nationally, from major wind farms; locally, from combined district heating and power systems; and at the individual building level.
On projects that do not implement renewables today, it could pay to plan ahead, where possible, perhaps by picking a site in the best wind microclimate or ensuring good solar access for future harvesting of energy.
RENEWABLES TODAY The relatively small carbon footprints of renewables (measured as CO 2 emissions per unit of useable energy) are their key attraction in trying to cut carbon emissions. (See figure 3, opposite). The Energy Saving Trust, a non-profit organisation funded by the government and private sector, has produced a summary of the maintenance, running costs, CO 2 emissions and payback periods for renewable energy technologies, as applied to homes. Having spoken to a few designers who have tried to put the case for renewables to clients, the shorter payback periods calculated by the Energy Saving Trust look optimistic and are perhaps better read comparatively, as a payback ranking (see figure 4, overleaf).
With the government focus both on sustainability and security of energy supplies, renewables tend to be talked about interchangeably with microgeneration, ie. energy generation at the building project/community scale. Most microgeneration is based on renewables, though fossil fuels can also be used, such as gas-fired combined heat and power (CHP). But even here, gas might be substituted by biomass in future. As part of preparing its Microgeneration Strategy: Power From The People, the DTI estimated the current number of microgeneration (and thus renewables) installations. (See figure 5, overleaf).
The renewables scene is changing, helped by growing concern for sustainability. Reasons for change include:
rising fuel prices - improving the viability of renewables (while also increasing concern about fuel poverty);
the Renewables Obligation - legislation requiring generators to provide a growing percentage of their output from renewables;
security of future energy supplies - a motive for focusing on microgeneration as well as power supply on a national scale, for example from wind farms;
a maturing market - there are few trained installers and limited production capacity, but signs that this is changing include Wolseley, the UK's biggest building materials supplier, opening its Sustainable Building Centre, including a variety of renewables technologies;
the culture of the industry - this is changing, albeit unevenly and with little willingness to take a lifecycle view and invest more upfront on sustainability. Even so, major commercial developer British Land now produces a detailed sustainability brief, including 'must dos', given to every design team as part of its corporate social responsibility policy - something unheard of two years ago;
sustainability measurement - notably BREEAM, which includes energy and emissions targets; and - legislation - any that sets energy targets is an encouragement to renewables and sustainable design. Local authorities have been highly infleuntial in this area by including a required percentage of renewables in their Unitary Development Plans - often referred to as 'the Merton 10 per cent'.
However, in terms of cutting carbon emissions, it can be counterproductive to insist on renewables; it will often be more effective to spend the same amount of money on the fabric of buildings and improving their insulation or airtightness - investments that usually have lower running costs.
CIRCUMSTANCES ALTER CASES Listed below are the issues you might consider when deciding to choose one technology over another:
? planning - apart from Merton's 10 per cent, the big planning issue is direct impacts. Wind turbines, while disliked by some, are less unpopular outside rural areas - but that could simply be because there are relatively few non-rural proposals yet. Both the solar-thermal panel and photovoltaics industries are working to make their technologies less obtrusive, from refining panel designs to integrating panels into surfaces such as cladding and tiling.
Biomass power plants, meanwhile, can be unpopular because the fuel is bulky, requiring frequent deliveries by lorries.
? density - high building density can reduce solar access, create less favourable wind climates or make it dif-cult to -nd space to tap ground-source heating and cooling. On the other hand, building density creates high load densities, which can make communal/district heating and CHP plants, more viable;
intermittence - biomass is a readily available fuel so can be used as required; the ground is also quite a consistent source of fuel.
But wind and solar are intermittent sources, so if we look to these to provide an average 10 per cent of our energy annually we will need a much bigger contribution at favourable times. While you can store solar-heated water, solar electricity (photovoltaics) and wind-generated electricity are expensive to store, so generally this is not attempted. Rather they are grid-connected, so that if your building is a microgenerator, its meter will run backwards or forwards depending on whether it is a net exporter or importer of electricity at that moment. Research is being conducted into the impact on the national grid of having millions of often intermittent microgenerators (us) connected to it;
load-matching - where generation is intermittent, generation ef-ciency should be improved by matching a building's energy demands to renewable energy output; for example, solar heating a pool in summer or matching photovoltaics to a cooling load.
A similar issue arises when trying to match CHP's heat-dominated output (electricity generation is secondary) to building needs.
Load-matching may also be improved by incorporating more than one renewable source in a project. Project size is another factor in load matching. Solar thermal, photovoltaics and even biomass can work well down to individual dwelling size, while small-scale wind, CHP, district heating and bore-hole ground source systems work more ef-ciently and cost-effectively on a larger scale. Individuals trying to go it alone with renewables sometimes experience a signi-cant loss in ef-ciency. David Cameron's rooftop wind turbine is a good example: it is in the wrong wind climate (too low down, not windy enough) but also too small;
centralised plant - some energy technologies are novel or developing fast, so can be unfamiliar and dif-cult to run.
Centralising the plant, with consumption metered locally, can simplify their use. Also, one central plant is easier to upgrade than individual boilers as the technologies evolve;
codes and standards - clients and designers gain con-dence in renewables systems if they conform to established standards and codes. Heat pumps are well established but whole ground systems incorporating them are more experimental. Photovoltaics have a wide range of standards, wind and solar thermal less so.
At one time in our history, renewables were dominant, with thousands of wind and water mills powering largely rural industries. Nimbyism was hardly an option. While we are not going back to that, nor can we all move to a future of following the few to their rural retreats. Overall, we lack broad visions of what our renewables-based futures could become.