Electricity: towards 'Distributed Generation'

• The primary source of electrical power to buildings is being shifted from the grid to on-site ('Distributed Generation').

• The grid delivers only around 37% of the primary energy input as electricity to the end user, the rest is wasted.

• The government claims that more carbon savings can be made, more rapidly, from small-scale, site-based, generating technologies than can be made from a national power industry where transformation from fossil fuels to renewables / nuclear generation is more problematic.
 

Grid fuel mix 2008

Emissions compared

Driving change : The Code for Sustainable Homes

 
Code level 5

• Level 5 eliminates all emissions associated with heating and lighting
• Part L loads will be net zero (ie 100% reduction in emissions)
• Part L includes:
- space heating
- domestic hot water
- electricity for building services (pumps and fans)
- fixed lighting
• Part L does not include:
- grid electricity for appliances & cooking

Code level 6

• Level 6 eliminates all emissions associated with all electricity consumption
• Grid electricity is allowed to be imported but:
- Grid electricity must be offset on an annual basis
- Emissions must be net-zero

The big leap taken between Codes 5 and 6 is the introduction of the need for renewable technologies to ensure net-zero emissions connected with all electricity consumption including appliances and cooking.
Though the Code emphasises on-site renewables, it does allow for off-site technologies provided that ‘This additional power must be renewable power produced either within the area of the building and its grounds, elsewhere in the development, or elsewhere as long as the supply is via a private wire arrangement with robust contractual agreements in place to ensure continued supply over time.’
A ‘Private Wire Arrangement’ is defined as an arrangement where ‘… where any electricity generated on or in the vicinity of the site is fed directly to the dwellings being assessed, by dedicated power supplies’.

 

Low and zero carbon technology: on-site suitability

Technology	Scale of development
	Micro	Small	Medium	Large
PV	x	x	x	x
Micro wind	x	x	x	x
Small wind		x	x	x
Large wind				x
Low heat to power ratio micro CHP (fuel cell)	x	x	x	x
High heat to power ratio CHP (eg Stirling)		x	x	x
Medium CHP			x
Large CHP				x
Medium biomass CHP			x
Large biomass CHP				x

(Chart: courtesy of the Renewables Advisory Board)
 
 

Low and zero carbon electricity-generating technologies

   

PV Cells

		Readily applicable to most buildings
		Easy to retrofit
		Expensive
		Requires adequate roof area, may not meet demands in blocks of flats

 

Wind

		Larger turbines are more efficient
		Low capital cost
		Smaller turbines are usually inappropriate in urban areas
		Planning issues

 

Micro CHP: Low heat to power ratio 1.25:1 (fuel cell) 

		Desirable heat to power ratio (the lower, the better)
		Will fill the gap for small scale heat & power where biomass is unfeasible
		Only just becoming commercially available = relatively untested
		Non renewable, emissions require off-setting

 

Gas-fired Micro CHP: High heat to power ratio 6:1 (Stirling) 

		Established infrastructure
		Relatively cheap (2010) fuel supply
		Fuel is sensitive to price and future availability
		Non renewable, emissions require off-setting
		Likelihood of 'heat dumping' in buildings with low heat demand

 

Biomass fired CHP

		Renewable
		Wide variety of fuel sources
		Immature and unpredictable supply infrastructure
		Requires storage

 
   

Possible design strategies

   

Scenario 1: Biomass CHP

   
  • Consider using Biomass CHP where additional electrical demand can be met by PV and where wind power is feasible
 

If biomass is unfeasible...

 

Scenario 2: Gas-fired CHP

   
 • Consider using gas-fired CHP where additional electrical demand / C0₂ off-setting is met by PV and wind where feasible

If CHP is unfeasible...

    

Scenario 3: Renewable electricity

   
  • Consider using renewable electricity to provide zero carbon heating and where additional electrical demand can be met by PV and where wind power is feasible.
 

If the above technologies are unfeasible...

    

Scenario 4: Renewable heating technologies

   
  • Consider using renewable heating technologies (biomass) and where additional electrical demand can be met by PV and where wind power is feasible.
   
 

Downloads

   
• Potential for Microgeneration, Study and Analysis - DTI, 2005

 
Further information

 
• Renewables Advisory Board ( www.renewables-advisory-board.org.uk )
• BERR ( http://bit.ly/bYMgiO )

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