Evaluating the triple bottom line in the implementation of photovoltaic systems in UK social housing

The Intergovernmental Panel on Climate Change warnings regarding the detrimental effects of carbon dioxide emissions and global warming have gained acceptance amongst many governments (IPCC 2001). The UK government has agreed to reduce emissions, implement a package of enabling measures (UKCCP 2000) and issued an Energy White Paper (HMSO 2003) calling for a diversification of energy supply policies which will include renewable sources.

Housing accounts for approximately 25% of UK CO2 emissions and as providers of social housing, Registered Social Landlords (RSLs) and their tenants are major contributors. RSLs are deliverers of national policy in several areas and contribute to the attainment of governmental environmental, social and economic targets and impact upon the wider demands of housing policy, healthcare, education and law & order (DETR 1999, Cole and Shayer 1998).

Photovoltaic (PV) electricity generation could deliver “free” electricity to the low income households historically housed by RSLs. PV helps address such issues as fuel poverty and could be used as a stimulus for creating interest in areas of low demand for social housing.

RSLs provide housing solutions which cross traditional economic, social and environmental divides and this lends their modus operandi to the concept of the triple bottom line. The triple bottom line enables social and environmental aspects to be considered alongside economic considerations within decision-making frameworks (Elkington 1999, Andreason 1995).

Using a qualitative research methodology, this paper assesses current commercial viability of PV installations on RSL developments and identifies key barriers to implementation. The paper also investigates whether the application of the triple bottom line can liberate RSLs from viewing PV as a non-viable option by enabling a greater emphasis to be placed on the social & environmental aspects of PV. The paper considers whether a framework for RSLs to improve their decision-making processes by embracing social & environmental factors is feasible.

ε-bounded state estimation for time-delay systems with bounded disturbances

A new problem on ε-bounded functional state estimation for time-delay systems with unknown bounded disturbances is studied in this paper. In the presence of unknown bounded disturbances, the common assumption regarding the observers matching condition is no longer required. In this regard, instead of achieving asymptotic convergence for the observer error, the error is now required to converge exponentially within a ball with a small radius ε > 0. This means that the estimate converges exponentially within an ε-bound of the true value. A general observer that utilises multiple-delayed output and input information is proposed. Sufficient conditions for the existence of the proposed observer are first given. We then employ an extended Lyapunov-Krasovskii functional which combines the delay-decomposition technique with a triple-integral term to study the ε-convergence problem of the observer error system. Moreover, the obtained results are shown to be more effective than the existing results for the cases with no disturbances and/or no time delay. Three numerical examples are given to illustrate the obtained results.

Partial state estimation for linear systems with output and input time delays.

This paper deals with the problem of partial state observer design for linear systems that are subject to time delays in the measured output as well as the control input. By choosing a set of appropriate augmented Lyapunov-Krasovskii functionals with a triple-integral term and using the information of both the delayed output and input, a novel approach to design a minimal-order observer is proposed to guarantee that the observer error is ε-convergent with an exponential rate. Existence conditions of such an observer are derived in terms of matrix inequalities for the cases with time delays in both the output and input and with output delay only. Constructive design algorithms are introduced. Numerical examples are provided to illustrate the design procedure, practicality and effectiveness of the proposed observer.