Mike and Jenny Dennis are supporters of Green Christians. They have been promoting recycling for over 20 years. Their previous property in Brighton was not suitable for PV panels. On moving to Tavistock this is one of the first things they considered, convinced that they needed to “put their money where their mouth is”.
Both are members of the Transition Tavistock Energy Group. They had their solar panels installed in July 2010. In order to calculate the overall benefits gained with the installation, they have maintained records of the amount of energy generated, how much has been exported to the grid and savings in other fuel use.
Energy reduction and conservation:
Life style changes:
After the installation of the panels, there have been lifestyle changes for Mike and Jenny, based on their review of how they use the electricity.
• Except in exceptional circumstances they only use the washing machine when there is adequate kWh being generated.
• They now tend to cook their main meal at midday rather than in the evening.
• Generally they operate any electrical device when generating energy (e.g. top up laptop and recharge batteries during the day and run these in the evenings using battery power).
• Additional insulation has been added to the loft.
• Thermostats are installed on all radiators to control the amount of energy used.
• A TV powerdown device has been installed and they purchased A rated appliances.
• A range of energy saving devices are used, such as solar powered external light, door number light , radio battery recharger and a wind-up torch.
In July 2010 the Dennis’ had an array of 18 x 215w photovoltaic panels installed on their roof, with capacity to generate 3.87kW/h. The installer of the device was New Generation Energy. . In January 2013, they had an immersun fitted which diverted surplus generation to the immersion heater for hot water. Therefore on good days the Dennis’ have no need to use gas for heating the water for showers etc.
Costs and benefits:
The capital cost was £15000 and approximates to just over £4000 per KW.
In the first year, 3338 kilowatt hours (kWh) was generated, of which 2712 kWh were exported to the grid.
Based upon the national averages, the projected annual income was suggested as £1450 per annum. This would give a payback period of approximately 10.8 years. However, taking into account reduced usage imported from the grid, (electricity usage was reduced by 30% on the first year), Mike estimated that the payback period would be 9 years and 3 months. This was achieved.
The Feed-in tariff commenced on 1st April 2010 and pays 41.3 for every unit generated. This is fixed for 25 years but for installations in later years the rate will be lower. There is an additional small sum for each unit exported to the grid and Mike and Jenny also benefit from a reduction in their electricity bill as they use the renewable energy generated.
In January 2021, through a group tendering process operated by West Devon Borough Council, the Dennis’ acquired a 5.2 kw battery solar storage system to store surplus generated power for use in the evenings and even on occasions to top up the immersion heater if the hot water needs a boost in the morning. They use their battery to power their immersion heater instead of gas or the grid.
It would have been useful to have greater advance knowledge of what power is required by each individual piece of domestic electrical equipment. Start early and do not put off actions that you can do today. You can’t save tomorrow what you spent today.
The best months for light seem to be April, May, June and July and not August as Mike expected.
The average annual amount generated per day ranges from 8.0 to 9.2 kWh with an overall average of 8.6 kWh to October 2021.
There have been 3 days when generation exceeded 24 kWh. They were in May 2020 and two occasions in April 2021.
To the end of October 2021, they had generated 36,881 kWh of which they exported to the grid 24763 kWh. Hence, they exported about 2/3 of the generation.
After the installation of the photovoltaic panels, gas consumption dropped by about 1/3 and subsequently following the installation of the battery, gas consumption has reduced by a further 1/7 compared with previous years. The Dennis’ hope an air source heat pump will eliminate gas consumption completely.
The PV installation has gone well and the Dennis’ would be happy to undertake similar projects in the future. They are looking at alternative options for space heating such as an air source heat pump.
”Transition Tavistock , Food and Energy: Our growing book of community stories” booklet.
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