Electricity:
towards 'Distributed Generation'

Introduction

• 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 (see also ‘Photo Voltaic Cells’) readily applicable to most buildings easy to retrofit expensive requires adequate roof area, may not meet demands in blocks of flats
	Wind (see also ‘Small Scale Wind Turbines’) 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) (see ‘Micro CHP’) Established infrastructure Relatively cheap (2008) 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 (see also ‘Biomass’) Renewable Wide variety of fuel sources Immature and unpredictable supply infrastructure Requires storage

 

Possible design strategies

A likely strategy in adopting renewable technologies to meet with heating and power requirements. In order of preference:

Scenario 1: Biomass CHP

Where biomass CHP is feasible
• select biomass CHP
• Additional electrical demand is met by PV and wind where feasible

if biomass is unfeasible

Scenario 2: Gas-fired CHP

Where gas-fired CHP is feasible
• select gas-fired CHP
• Additional electrical demand / C02 off-setting is met by PV and wind where feasible

if CHP is unfeasible

Scenario 3: Renewable electricity

Where renewable electricity is feasible
• select renewable electricity to provide zero carbon heating
• Additional electrical demand is met by PV and wind where feasible

where above technologies are unfeasible

Scenario 4: Renewable heating technologies

• Use renewable heating technologies (biomass)
• Additional electrical demand is met by PV and wind where feasible

 

Downloads

• Potential for Microgeneration, Study and Analysis - DTI, 2005
• Code for Sustainable Homes - (Department for Communities and Local Government: February 2008 )
• Code for Sustainable Homes - Technical Guide - (Dept for Communities and Local Government: Oct 2008 )

Further information

• Renewables Advisory Board
• BERR