Hybrid energy systems

Outlook Standard energy systems for individual dwellings nowadays are still mostly conventional in Europe and most other places. For electricity generation most dwellings are connected to the national grid, and the grid electricity is also mostly generated by non-renewable sources such as fossil fuels or nuclear power. For heat generation the use of fossil fuel (gas in particular) represents the larger part as well. The use of renewable energies to replace fossil fuels is starting to become more widespread, with a few examples of technologies which have now become the dominant option (for instance solar water heating in Israel) The problems with renewable energies are known, they are dispersed, not easy to harvest and often not predictable. They are also expensive. These are the main reasons why they have not developed quicker in the past, it is relatively well established that individual renewable systems are usually not suitable for most cases as is the case for a majority of conventional energy systems. It makes sense therefore to look at whether combining these technologies into hybrid energy systems can improve the system overall. The potential benefits of hybrid systems could include: Optimise performance of overall scheme as compared with individual technologies Minimise mismatch between energy generation and usage Reduce overall demand or wastage Reduce carbon emissions Optimise cost of the installation Hybrid energy systems include 2 major parts:  ◊ Electricity generation  ◊ Heat generation We will assess the feasibility of hybrid energy systems according to the following priorities: The building should be 'low carbon' Physical integration of the technologies within the building must be possible If possible, the system cost should be viable ♦  Electricity Generation In electricity generation we will assess what contribution individual technologies can provide (wind, PV and CHP) and how a hybrid combination could improve the scheme. Electricity storage on site is not considered since we have assumed grid connection in the scope of the project. The inter-connection of different sources using inverters and other devices is well established and therefore will not be addressed. ♦  Heat Generation Heat generating options are assessed according to the demand in the various case-studies. The inter-connection between different sources of heat will be analysed, more particularly the problem to combine various inputs and outputs of heat which have different temperatures. The hybrid systems should also include heat storage options (short term and long term). The potential benefits are to manage the surplus energy generated but also to deal with the different output temperature of various heat systems. Furthermore, heat recovery systems are also applied since air to air heat exchangers are devices designed to recover heat from exhaust to inlet ducts in order to preheat or pre cool fresh air introduced to a building. Natural ventilation options are also considered within the hybrid system, in order to reduce accordingly either the heating or the cooling loads. Finally we believe the first step of studying hybrid energy systems for low carbon buildings is really to look carefully at the demand (electrical, space heating and cooling) as renewable are a complicated subject when it comes to make things work and reducing adequately the demand is a key part of the solution.