The Details

The Photovoltaic Arrays

The east facing Roof array consists of 10 Romag Powerglaz SMT 185Wp Modules connected via a SMA SB1700 Inverter to the UK grid. Rated at 1.85 Kwp.

The south facing Roof array consists of 6 Romag Powerglaz SMT 185Wp Modules connected via a SMA SB1200 Inverter to the UK grid . Rated at 1.1Kwp.

The provision and installation of the cells, inverters and connection the to the grid was performed by Ion Energy Ltd. Work started on the 7th June 2010, the east array was up and working is 3 days the south was delayed by 6 days as we discovered a fault in the ridge tiles on the roof that I had to get fixed before the panels were installed.

The measurements System

This is a DIY system put together by my self using ready available devices, software from the net and programs I have produced myself.

To measure the power generated I am using two of the OWL home monitoring devices (CM119) and one USB connect system available from

I had difficulty interfacing  with the USB device but after searching online I found the Electric Owl Project this project consists of two parts the owl server a console application that interfaces to the USB connect and transmits the data messages on a TCPIP port. The second is a Java application that graphs the power on you PC. The owl server is the component I used.

I then wrote four C# programs that read the data messages from the TCPIP port produce the table and chart data that are uploaded to this web site.

The charts are produced using RGRAPH charting software from

Using my surplus power to heat my hot water.

Over the past 2 years I have noticed that I am exporting about 75% of what my solar cells generate but am only being paid for 50% so I have been thinking of ways to improve this. It should be noted that I get paid the 3.3 pence per unit (the export rate) on 50% of the generated power however much is used or exported; this is because I do not have an export meter. This will change when smart meters are rolled out.

So the solution I am adopting is to fit a low wattage (1Kw) immersion heater to my hot water tank and an intelligent switch that monitors when I’m exporting and switches the immersion on. If say the sun goes in or the wife makes a cup of tea and I start importing power the switch turns off the immersion

The switch that I first choose proved the concept and when the sun was out and nobody at home used the surplus power generated to meet my hot water needs. The old switch operated with 3 states OFF, half Power and full power so that when I’m not exporting more than 1 Kw, the switch will try half power (500 Watts). This worked fine but when other household devices were being used that have short high peaks of power usage like the kettle, dishwasher or washing machine not so well. The new switch the immersun Solar PV immersion heater controller operates with 100 steps and responds much quicker to changes in demand. This new switch was installed by Ion Energy Ltd a local immersun installer.