Impact of Distributed Solar Generation in Low Energy Housing on the Electrical Grid
Passive solar design combined with energy efficient appliances and active solar systems have been implemented in many new house designs and housing developments. However their aggregated impact on the electrical grid has not been sufficiently monitored and documented. A new housing development at Lochiel Park, Adelaide, Australia, is a leading example low carbon development; being constructed using a number of passive solar design and demand side management features, and roof mounted photovoltaic systems on all homes. To evaluate the impact of these features on the electrical grid, the performance of all dwellings is being monitored in detail. The paper summarises the overall household energy consumption patterns. It describes the aggregated seasonal energy and power interaction with the local electrical grid. In particular it focuses on the net power imported from the grid and exported to it during peak summer and winter demand periods. The results demonstrate the reduced energy consumption and power demand during peak events in comparison with typical Australian homes. It also shows the seasonal and maximum impacts of aggregation of rooftop solar generation on the energy and power exported to the grid. Introduction and Background The energy consumption of Australian commercial and residential buildings has been increasing throughout the last 2 decades. The energy used by Australian buildings accounts for approximately 20 per cent of Australia's greenhouse gas emissions. On average, space heating and cooling represents 41% and domestic water heating about 30% of the energy demand of the 8.5 million Australian homes with heating and cooling of buildings directly responsible for 11% of Australia's national greenhouse gas emissions despite the temperate climate of major Australian cities [1, 2] The number of residential dwellings will be around 10 million in 2020 compared to 6 million in 1990. The energy consumption of the residential sector was about 402 PJ in 2008 and is projected to increase to 467 PJ by 2020, showing a 56% increase in residential sector energy consumption over the period 1990 to 2020 [3] Due to the abundance of cheap energy in the past, housing designs and constructions have not considered energy efficiency as a high priority. Aesthetics, larger built area at minimum construction costs have been the key elements in marketing both new and existing dwellings. A typical traditional Australian home is detached, single or double storey, around 200m in area and has 3 4 bedrooms. It is constructed of brick veneer walls with single glazed, mostly unshaded windows. Roof and wall insulation is becoming the normal practice to comply with building regulations. In 2008, 77% of Australian dwellings had one or more space heaters and two thirds had space coolers [1] This number has witnessed a rapid increase in the last 10 years and has resulted in a substantial impact on the summer peak demand during heat waves which take place for a few days in the year in many of Australia's largest cities. The necessary augmentation to generation and particularly distribution infrastructure has been mainly responsible for large increases in electricity tariffs. Lochiel Park Green Village Upon completion in 2012, the Lochiel Park Green Village will have 106 houses including 23 social housing units. The homes being built in the Green Village have a comprehensive list of sustainable features which include optimised allotment design for maximum benefits from environmental elements, passive solar design with high envelope energy rating [4] (a minimum energy rating of 7.5 stars using the Australian Nationwide House Energy Rating Scheme which currently mandates 5 6 stars for new housing) mandatory use of best available energy efficient appliances in each home, use of solar electricity (1kWp per 100m of floor area) installation of energy management systems, electrical load limiting devices, and gas boosted solar hot water systems [5] There is also an arrangement with the utility for special bundled tariff. The Green Village performance targets include 66% and 74% reductions in energy and greenhouse gas emissions respectively in comparison with the Adelaide average for 2004. Each of the 106 houses incorporates a touch screen computer and an in home display, a programmable logic controller, and an array of intelligent meters and sensors, which comprehensively measure and display general electricity, water and gas usage, in real time. Furthermore, each property has a fully customisable load management system installed, which allows devices to be deactivated during periods of peak electricity demand. In addition, 9 houses are being monitored in detail. Indoor air temperature/relative humidity and individual appliance electricity usage are also being recorded. Impact of Solar Systems on Net Electrical Supply and Demand The impact of the solar energy generation is demonstrated in Figure 1 below, which shows the aggregated monthly average consumed electrical, solar and net energy per household. Note that the numbers adjacent to the months along the x axis in this figure are the number of houses monitored during that month which increased over time. The average Lochiel Park home consumes 5520kWh of electricity per annum (15.1kWh per day) of which 57% is locally generated and only 2340 kWh per year (6.4kWh/day) is supplied by the grid. Figure 1 Measured average electrical energy consumed, generated and provided by the grid (Net) per household per month. Operating under the Adelaide climate, the study [5] has shown that on average, the solar electrical systems installed at Lochiel Park (average size 2.2kWp) generated 2.4kWh/kWp in June and 5.5kWh/kWp in January with an annual average of around 4.0kWh/kWp. As more distributed photovoltaic systems are being installed in Australian dwellings, this result provides direct evidence for estimating the impact of rooftop solar electrical systems on the grid and anticipated emissions reduction. The gathered data [5] demonstrates the impact of the number of occupants in a household and their behaviour on the electrical grid. In winter (June August) the range per household varied from feeding the grid 100kWh/month to drawing 1 200kWh/month from it with the average winter demand on the grid being 400kWh/month. The summer period (January February) shows a maximum input to the grid above 400kWh/month and a maximum demand on the grid of 950kWh/month with the summer demand of all houses averaging around 150kWh/month. While only one house consistently produced more energy than it consumed and negative emissions, 50% of the monitored dwellings produced more electricity than they consumed and 40% of them produced negative net emissions during the period October to April due to the high performance of the photovoltaic systems during that period [5] Figure 2 aggregates 15 minute data for the instantaneous solar and net electrical power per house (average of 21 houses) during the coldest period of 2010. The minimum temperature recorded during this period was 3.7degC and the maximum 13.4degC. The figure shows that the average solar power generated is low, as expected for the winter months, and when combined with a high electrical demand for heating, this increases the net electrical 0 100 200 300 400 500 600 700