RENEWABLE ENERGY SUPPLY SYSTEM.
Having worked hard to create a low energy design, reducing the potential energy demand for the building, we worked with Steve Wade from Wind and Sun, to design and install a novel renewable wind and solar grid connected energy supply system.
This system is designed to meet the anticipated annual electrical requirements of the building. In order to give a balanced supply throughout the year a combined wind turbine and photovoltaic (PV) solar system was used. Initially the possibility of obtaining true autonomy by means of battery energy storage was considered. However, due to the multi-user nature of building, precise electrical requirements and patterns of use were difficult to ascertain. These factors would mean any battery store would need to be large and hence unduly expensive. Since a reliable mains electricity supply was readily available (100m away) it was decided to opt for a grid connected system, resulting in more renewable generating capacity for the available budget. In this type of system no on-site energy storage is used. Power generated is first used by electrical loads in the building and any surplus exported to the grid, when power being generated is less than that being consumed, top-up is available from the grid and imported as normal. All power flows are ‘seamless’ from the point of view of the user. The aim is to achieve a numerical energy autonomy for the building with a net export to the grid over a whole year. In this situation the grid effectively acts as an ‘energy store’ instead of a site battery system, avoiding the problems of managing and disposing of toxic batteries from the site at 5 to 8 yearly intervals. Eastern Electric’s recent move to implement net metering (i.e. the same cost for import and export of energy ) makes grid connected schemes like the York building much more attractive and viable for the decentralised local production of on site renewable energy.
In order to optimise the use of on-site generation and to make energy flows transparent various displays are incorporated in the main area of the building. These show: wind turbine generation; PV array generation; building electricity consumption; and a bar graph display showing whether, and how much, power is being imported from or exported to the grid. By observing these displays, electrical loads can be managed to match available power generation and care taken so that no energy is wasted. The Eco Centre power system is made up of the following:
1.7kWp Photovoltaic Solar Array This consists of two sub arrays of 850Wp, each using 10 BP Solar 585L Saturn Cell frameless laminates wired in series to give ~ 180 VDC output. The Saturn cells used are the most efficient commercially available, and the most cost effective, giving a maximum kWh energy produced for a given roof area. The laminates are mounted on a framework above the roof, sited, in groups of five, on four sections of the conservatory roof. The framework is integrated into the roof by means of special Klober PV mounting slates, ensuring that there is no penetration of the waterproofing layer of the roof. Because of the public nature of the building, UV stabilised polycarbonate sheets are fitted above the PV’s to provide protection against vandalism. It is envisaged that these might reduce output of the PV array by approx 5%. The output of each PV sub-array feeds two SMA Sunny Boy SWR-700 inverters.
2.5kW Wind Turbine. Made by Proven Engineering this is mounted on an 11m self-supporting tower and produces power at ~ 120VDC which is fed to an ASP 2.5kW TopClass inverter. The wind turbine controller is included to divert power to a heater in the event of power outages or for maintenance. The wind turbine has good low wind characteristics whilst being protected against strong winds and should give reasonable yield despite the urban nature of the York site. The inverters convert DC power generated directly into 230 VAC. These AC outputs are then paralleled together, synchronised with the grid supply, and can either supply power to the centre’s load circuits or export power to the grid as appropriate. Each of the inverters contain protective circuitry to shut down the systems in the event of power cuts or variation of grid power quality outside statutory limits. The system design and installation was carried out by Wind and Sun.
The conservatory pre heat buffer zone and super insulation levels with minimal heat losses, combined with thermal mass, create considerable thermal inertia eliminating the need for a full central heating system. A 4/6kW efficient Clearview Vision wood burning stove fuelled from timbers locally harvested, provides a social focus to the main space. The 10,000 Bthu back boiler and mini max control system provides hot water to a few small radiators, which compliment the heat gains from the occupants and appliances.
LOW ENERGY APPLIANCES
All appliances have been carefully selected to eliminate unnecessary electrical demand and to optimise the efficiency of the required essential items, including low energy lighting and lap top computers etc.
LOCAL RAIN WATER SUPPLY
All the building’s drinking and washing water requirements are met by collected rainwater from the main conservatory roof via zinc gutters, down pipes and a Wisy filter to be stored in a buried 1500 litre ex orange juice container. Water is then plumbed through a Klieber 5 micron cartridge filter and a K15S stainless steel UV steriliser to a 60 litre holding storage tank in the roof loft for gravity feed to the outlets.
One disabled and two unisex Sun- Mar Excel (non electric) dry composting toilets were fitted by Eastwood Services, with a non mechanical stack effect soil vent pipe system to allow evaporation to air of excess urine. Dried human solids, along with kitchen wastes and garden debris material, will be composted and then returned to the land as an invaluable non toxic fertiliser. The above simple system demonstrates that human wastes do not need to become toxic pollutants of our rivers and seas, but can be recycled and reused within an integrated eco-system to become an invaluable resource furthering new life within the boundaries of the site.
HEALTHY INTERNAL ENVIRONMENT
The naturally absorbent and breathing masonry construction creates a vapour hydroscopic envelope without the risk of condensation. Scatter rugs over timber floors, non volatile solvent, water based Ecos paints and natural OS colour stains to exposed timber along with the avoidance of formaldehyde based toxic materials, have lead to a healthy internal air quality.
The York Zero Co2, Environmental Education Centre makes a valuable contribution to the ongoing sustainable â€œBuilding For a Futureâ€ debate. It points to a future possibility where whole community based projects could be positive energy producers rather than negative energy consumers.