• 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.
•‘Distributed generation’ or ‘onsite generation’ is the generation of electricity from many small energy sources. Distributed generation is the antithesis of centralized generation such as fossil fuel or nuclear power stations. The main advantage of distributed onsite generation over centralized generation is that electricity supply does not suffer the inefficiencies of transmission over long distances. There is also a modicum of improved security of supply.
The 1997 – 2010 Labour government failed, largely due to its aversion towards nuclear power, to develop a future energy strategy that committed to and successfully combine a mix of supply technologies whilst meeting with the relatively novel vagaries of supply of fuel post North Sea gas as well as the newly adopted carbon reduction targets of 2020, 2030 and then 2050.
Time moves on. Potential fuel suppliers have firmed-up and new supply technologies such as ‘fracking’ have been developed. The current Coalition government appears a degree more catholic in its identification and commitment towards technologies and fuels that will fill the upcoming ‘energy gap’. On the other hand, though it has maintained aspects of Labour low-carbon policy as well as introducing its own, it lacks a commitment towards achieving the carbon reduction targets (characterised by David Cameron as ‘green crap’) identified by the EU and former Labour administration.
The July 2013 report ‘UK Future Energy Scenarios’ published by the National Grid looks in detail at the fuel mixes of two fundamentally different energy generation scenarios:
Slow Progression
Developments of renewable and low carbon energy is slow. The carbon reduction target of 2020 is met but not the renewable energies target.
Illustration courtesy of the National Grid
Gone Green
Meets the targets. 15% of all energy from renewable sources by 2020 and an 80% reduction in greenhouse gas emissions by 2050.
Illustration courtesy of the National Grid
Apart from notably a now significant contribution from nuclear, both scenarios include a growth of some sorts in distributed generation.
Emissions compared
Low and zero carbon technology: domestic 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.
Further information
• Renewables Advisory Board ( www.renewables-advisory-board.org.uk )
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