More ways to use solar energy

The GSHP uses electrical energy just like a fridge. Some of this electrical energy is generated using 12 solar photovoltaic (PV) panels (polysilicon) on the main roof of the house. These panels face south and convert light into electricity even when it is cloudy. They obviously perform best when in direct sunlight and these are capable of producing a maximum of just under 2kilowatts of electrical power. This is enough to run approximately 150 low energy light bulbs or a 2 bar electric fire. Only in full sunlight though!  We also have 10 PV panels (monosilicon) on the Garden Room roof which were installed in November 2010.  These qualify for the full FIT tariff unlike the house array.  The "payback" time on this system is around 8 years.  The gradual reduction in the FIT affects new installations in the retrofit, up to 4kWp group, therefore payback times have increased accordingly.


The graph above is a comparison of the average energy per day generated by the House solar PV panels up to 31 March 2011 and the average monthly "day length".  The graph suggests that the electrical energy generated is mainly dependent on the number of hours of daylight, the weather conditions being averaged out during each month.  Since the sun is lower in the sky during the winter, the angle at which the sun's energy is incident to the panels is not optimal, this is one reason why the blue line is lower than might otherwise be expected for these months.  UK readers won't need telling that the weather in 2012 has broken several records with drought being a problem early in the year in some regions and record amounts of rainfall washing out our British summer.

A summary of the past couple of years follows - feel free to skip it if you're not an anorak like me!  The end of 2010 saw heavy snowfall and a record breaking couple of months in terms of low temperatures.  2011 started with a cold and overcast January with a couple of sunny days at the end of the month and into February as last year.  Gale force winds and rain greeted us in Lincolnshire as February closed with grey, dank days and poor PV generation. This overcast but mainly dry weather continued until  31March 2011 with the occasional sunny day producing over 8kWh of electricity from EACH of the 2 solar arrays and good water heating from the solar thermal panels. Overall, the March 2011 generation from the house array was down on the previous 2 March totals. April, in particular, and May saw good generation from both arrays.  The combined output on some days has been around 23kWh.  The unusual pattern of generation continued throughtout June and July 2011 as can be seen in the chart on the statistics page but August 2011 has been poor.  Into September and a few good sunny days turned into a very windy, autumnal scene and then into an excellent warm/hot finish at 28.4C!  October 2011 broke all records with a temperature locally on 1 October of 28.6C and 30.0C at the Robin Hood Airport near Doncaster.

November and December 2011 contrasted greatly with last winter.  Predominantly dry weather and mild conditions with no snow in mid Lincolnshire.  Very high winds dominated the weather in early January 2012 followed by unseasonally mild temperatures.  The lowest daily generation of the 2 arrays was 0.2kWh and the highest, 8.9kWh in the period December 2011 to 14 January 2012.  The highest January generation of electrical energy since the panels were installed has been obtained this year.

There has been a bizarre Spring of 2012 with warm, sunny weather in March then dull and wet weather throughout April, part of May and most of June.  The drought order declared in eastern England was lifted in mid June owing to the quantity of rain which has fallen during these 3 months.  Very unsettled weather has continued through the summer months but, now the young folk have gone back to school, September has started with beautiful, warm conditions and good solar irradiation.


Solar PV on top roof, solar thermal bottom right and Velux bottom left

In our system, the direct current (DC) of the panels is converted to alternating current (AC) so that it can be connected to the national grid. As an alternative, especially in remote locations, batteries can be charged by the DC for use when needed to run lighting etc.  We saved 1.03 tonne of CO2 in the first year by generating electricity using the solar PV panels!  The total savings from the house PV array are 3.808 tonnes of CO2 and 1.694 tonnes of CO2 from the Garden Room array as of 12 September 2012 and the total emissions from 1 March 2011 to 29 Feb 2012 for the house were 5854.2 kg of CO2.


Greenhouse Gas saved by Solar PV in the year to 29 Feb 12 was 1046.19 kg of CO2 by the House array and 955.62 kg of CO2 by the Garden Room array.

Two solar thermal panels are located on the lower south-facing roof. These absorb the heat energy from the sun and the fluid in them is then pumped through a coil in the domestic hot water cylinder. During the summer months all of the hot water requirements of the house are met using this free energy and the solar thermal panels also make a contribution during bright winter days. The GSHP will also automatically heat the hot water if necessary.  Once a week the GSHP ensures that the hot water is pasteurised to kill legionella bacteria.

Passive solar heating is obtained by opening the external shutters on the Velux Integra windows, at the far end of the lower roof, to allow the sun to heat up the mass of the floor and stone walls in the room beneath like a giant storage radiator.  This heat is then gradually released in the cooler evening and overnight to the rest of the house.  If the room below these Velux windows gets too hot then the shutters can be closed to keep the sun's heat out of the house.  The Velux windows can also be opened to ventilate the area and reduce the temperature in this part of the house if necessary.  If it rains, they close automatically!  There are also South facing windows (see photo at top of page) which provide additional passive solar heating controlled using internal venetian blinds and/or curtains.

The chart below shows the CO2 greenhouse gas emissions in the 3 years from 1 March 2010 to 29 February 2012 compared to the previous emissions from the smaller house before the changes.  The first year result for the CO2 emissions were a saving of 5788.47kg of CO2 compared to the emissions from the house before extensions, the improvements in insulation and the installation of the renewable energy systems.  As you can see, the latest result is even better!

Apparently the 2009/10 winter was one of the coldest in the last 100 years, if fact the coldest for 31 years in England, so the renewable energy systems were put to the test.  The winter of 2010/11 has broken the records again!  We had 18 inches of snow falling at the end of November and the coldest December since records began around a hundred years ago.  Our overnight minimum hit -17.3C and it was still -16.4C at 9am on 6 December 2010.  Once again the GSHP has coped well.  The recent winter 2011/12 has been mainly mild but -13.5C on 11 Feb was the coldest minimum night temperature recorded here at The Grove for this latest winter period.


Final result for Years 1, 2 and 3 CO2 emissions compared to smaller house pre-changes


next page