#1 June 17, 2013 11:08:00

david.woodward
Registered: 2012-06-15
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Export Meters


There has already been some discussion about export meters in other threads and a few of you have brought this up with us recently. It would be nice to get a discussion going about your experiences and findings with regards to your generation and energy usage.


We're also happy to collect your export data alongside your generation data as we might have use for it in our future research. If you'd like to send it into us please just attach a data file to an email.








Edited david.woodward (June 17, 2013 11:08:00)

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#2 June 17, 2013 13:29:00

rogerhoward
From: Southend
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Export Meters


None of my workmates have seemed able to believe that my little 4kW solar installation is capable of providing any useful daytime electricty to my neighbours.


So after finding myself with a new Smart Meter (see http://www.microgen-database.org.uk/forums/general-discussion/split-rate-import-tariffs?pn=2 thread), I decided to go onto Export Metering to establish the facts. My Smart Meter was remotely reconfigured last Wednesday. So far it seems that we're using about 2kWh/day of solar when we're not at home, and about 4kWh/day when we are at home.


Interestingly, the reconfigured meter seemed to already on Wednesday have a whopping export meter reading - i.e. it had in fact been logging the exported ‘leccy right from the start!


So for the 91 days - 3 months - since smart meter installation, my stats seem to be
-  438kWh Grid usage
-  317kWh PV usage (72.4% of grid usage)
- 1153kWh Generated
-  836kWh PV Exported (72.5% of generated).


I would never have guessed that I’d been exporting such a high proportion!


What other stats do people have to share for comparison?


Roger www.pvoutput.org/list.jsp?userid=21047










Economy 10 tariff provides 6.9p/kWh off-peak import between 12am-5am, 1pm-4pm and 8pm-10pm; http://www.pvoutput.org/aggregate.jsp?id=21047&sid=18934&v=2&t=m on approx. 63% off-peak usage, 22% solar usage, and 15% peak-rate usage.
1,900kWh annually is exported, mostly in summer, on approx. 3,200kWh generation. Approx. 4,500kWh/year is imported, mostly for (a) winter and springtime off-peak Storage Heaters, and (b) off-peak hot water Immersion heating (which is “dumb”, i.e. not linked to the solar PV).
PV array is split East-West. Income is from Phase II 21p/kWh Feed-in-Tariff plus smart metered 3.2p/kWh Export Tariff.

Edited rogerhoward (June 17, 2013 13:29:00)

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#3 June 20, 2013 22:45:00

bhommels
Registered: 2011-10-03
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Export Meters


A bar graph illustrating where our generated PV energy went for April 2013 can be found here:


www.tinyurl.com/nlu9zsv


The height of the bar is the total generation in kWh, for the SSE facing 2.88kWp array (URN93). The green section of the bar indicates general household consumption, yellow means grid export, and red corresponds to the energy consumed by the immersion heater controller for providing domestic hot water.


Total generation for April was 346 kWh, of which the household consumed 85, 116 kWh went into the hot water tank, and 145 kWh was exported to the grid (42%). For March, the figures are 172, 52, 75, and 46 (27%).


The grid import for April was about 120 kWh. Annoyingly, a relatively large proportion of that is used by our electric shower unit. Needless to say the shower is in line of attack for improvement!





Edited bhommels (June 20, 2013 22:45:00)

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#4 July 1, 2013 14:15:00

DaveCBoA
Registered: 2013-06-23
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Export Meters


I have a smart meter which was installed by Scottish Power (before I had my solar system installed.) I have not kept a detailed record of export but keep an eye it and will now start to keep a monthly record. Currently I have generated 4260 kWh (over 20 months) of which 3019 kWh was exported, ie around 70%. Even though Sc Power installed the meter they will not pay me for the units exported, only the assumed 50%. They blame Ofgem for this saying that's all they are allowed to do!!





Edited DaveCBoA (July 1, 2013 14:15:00)

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#5 July 2, 2013 17:42:00

HelenDaisy
Registered: 2012-03-03
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Export Meters


So how would your payment work if you had used 70% instead of exporting 70%?  Would they still pay as if it were  50% or would some miracle happen at their end to enable them to pay you less?





Edited HelenDaisy (July 2, 2013 17:42:00)

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#6 July 2, 2013 18:26:00

DaveCBoA
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Export Meters


In that case I would receive less but I reckon most houses with a 4kW system will export more than half. As about 80% of power is generated in the summer months and there is much lower domestic demand in summer (unless you use aircon which is very unusual in UK!).





Edited DaveCBoA (July 2, 2013 18:26:00)

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#7 July 3, 2013 09:17:00

default
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Export Meters


Over the last 2 years my actual export percentages are around 40% in the winter and 60% in the summer.





Edited default (July 3, 2013 09:17:00)

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#8 July 3, 2013 18:16:00

default
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Export Meters


David,


I record both my Generation and Consumption data of my 3.84KW PV array at 5 minute intervals to PVOutput, which calculates the export values in real time.


Despite my best efforts at scheduling white goods devices to coincide with sunny periods I was exporting. well over 60% of my 3710Kw annual generation. So in May 2012 I installed a proportional (to generation and house load) controller which is connected to my unvented hot water Cylinder immersion heater. This dumps a large proportion of generation that would be exported, into my hot water tank.


However, I have a large 220ltr hot water Cylinder and this only has a top mounted immersion heater which is 36" in length. Those of you who have this type of setup will know that it takes (depending on the cold water temp and the current Cylinder temp) about 7 to 10Kw of export before the immersion thermostat shuts off and you have half a Cylinder of hot water. At this point export to the grid will recommence. So to get around this issue I have installed a 12V 6watt DC pump and 2 low differential thermostats, one at the top of the tank, and one at the bottom, and run copper 15mm piping from the top of the hot water cylinder and teed into the cold water feed at the base through the pump. A none return valve is used to stop backflow through the pump when hot water is drawn off.


I have the top thermostat set to activate the pump when it is 3 degrees below the immersion thermostat value of 65C. It then pumps the hot water from the top of the tank to the bottom which stratifies the water. When the temperature at the top of the tank drops by 2 degrees to 60C pumping stops, still maintaining at least half a Cylinder of hot water. This is important because if you use thermostats with a wide differential on a day where only 7 to 10Kw is generated, like in spring or autumn, then you can end up pumping all your hot water to the bottom of the tank, and end up with a Luke warm tank all round. Using a low differential thermostat setup constantly allows the immersion heater not to trip out and to keep converting what would be exported into hot water.


If the water temp in the Cylinder is below 32C then I can sink over 20Kw of generation into it without exporting. The bottom thermostat on my tank stops the pump when the temperature at the bottom of the tank reaches 60C, the immersion then continues to run until it reaches 65C where its thermostat trips. This results on a 15 to 20Kw day of 220ltr of hot water at 65C at the top of the tank and 60C at the bottom.


So that I can see the status of the hot water in the tank. I have four cheap LCD temperature sensors attached to the length of the tank so that I can see at a glance how much hot water is in the tank and at what temperature.


I know I am making a rod for own back telling you about this as loads of questions are sure to follow. So here is the data.


This year I have exported just over 6% of my generation to date of 1971Kw that includes two weeks when I was on holiday and the device was not in operation.


I calculate I save about £100 per year in Gas consumption from not using the CH Boiler to heat water from April to October, and helping to heat the water for the rest of the year. (2777Kw at 0.36p per Kw)


The total cost of all the devices, pumps, thermostats etc was about £300 so it has a payback of three years.


What about the ethical point of view that you are using 1800Kw of generation that is deemed to be exported and you are getting paid 0.034p per Kw for? Well there are a number of ways to look at this. Firstly whoever set the 50% export figure knew that 50% export is way too low, so I am being under paid. Secondly even when SMART meters come to every household and they may amend the export to be actual figures. I may lose £60 but I am saving £100 so a £40 profit (at current tariff) can still be made. I would much rather use electricity that I have generated to meet my hot water needs, rather than importing GAS.


How many months do you not have to heat the water with the GAS central heating? It depends on the weather, though in general since the first week in April to the middle of October. So far since April we have had to use the CH Boiler on only four occasions for 20 minutes or so to top up the tank when two or three consecutive dull days with poor generation have appeared.  In the other months of the year it still meets the hot water needs on some days, and other days it helps raise the temp so that the CH boiler has less work to do.


Is it true that even though you are using a proportional controller you can still export. Yes this is true the proportional controller exports roughly 40watt as a buffer to stop you importing. Also, if you have a 4Kw PV system and a 300Watt house load with a 3Kw immersion it is possible to generate upto 4Kw for short periods of time when the sun pops out from behind a cloud. Therefore, you could export a few hundred watts for short periods. Though a lot less than you would do without a proportional controller.


Where did you get your proportional controller from? http://www.intelligent-immersion.co.uk/  highly recommended very good customer service and device performance.


Which thermostats, pump, temperature sensors and none return valve did you use?


Pump - eBay search for “P-38I“
Thermostats  - eBay search “K1BO DC 12V Digital Temperature Controller Electronic Thermostat Aquarium”
Temperature Sensors - eBay search “Mini Digital LCD Display Thermometer Temperature Temp Sensor”
None Return Valve – eBay search “Brass swing check valve 3/4" BSP”

I hope this helps some of you to save some money on your energy bills.


Regards.


 








Edited default (July 3, 2013 18:16:00)

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#9 July 5, 2013 07:45:00

default
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Export Meters


Excellent post Keith! I've got an export meter fitted by SSE when I registered with them for the FIT.  I use it to calculate the amount of kWh I've used from the panels each quarter.  I've got Solar Thermal as well so there's not much point in using an immersion heater.  The savings would be modest anyway.  If I used a kWh of gas to heat the water it would  cost 4.36p inc vat compared with a kWh of exported electricity worth 3.3p. This is assuming efficiency is similar. As it happens I've just had fitted a 13.7 kW log burner for the winter. I use over 20000kWh of gas each year. I'm hoping to use a lot less from now on.





Edited default (July 5, 2013 07:45:00)

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#10 July 5, 2013 09:40:00

default
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Export Meters


It sounds as if you should save some GAS with your setup.


I did forget to mention a few other points in my original post.


If you have a hot water cylinder with a bottom mounted immersion heater or one at the top and bottom of the cylinder then you probably will not require a pumping solution. However, some of the bottom mounted immersion heaters are of a lower wattage so you may not to be able to use all of your potential PV export.


Using am immersion heater to heat your hot water is more or less 100% efficient where as using the GAS central heating is not, as there are losses in the pipe work to and from the boiler etc. Cost of each type of fuel comes into play of course but it does make sense to use your excess PV generation to heat your hot water via an immersion heater.


Before I installed a proportional load controller I used to have my GAS CH come on in summer twice a day for two hours in a morning and from 5pm to 10:30pm to heat water. Now I realise in retrospect this was probably wasteful. My annual GAS consumption was 21,800 Kwh (we also have a GAS hob). During the summer months when no heating was being used my GAS consumption per day with the above scenario was 21Kwh per day.


I had the proportional controller installed in May 2012 and at this point I switched off the GAS water heating altogether during the summer. By the end of the year I had reduced my GAS consumption from 21,800Kwh to 16,800Kwh. This is a significant saving which was mainly due to heating water with excess generation, but also due to wasting energy with the duration I had the GAS central heating active for water heating purposes each day.


I have just read the GAS meter for June which in my location has been the best PV generation month of the year. The total GAS usage for June was 5 units (56Kw) or 1.86Kwh per day used for cooking. This is a significant reduction from my historic 21Kh per day I used in the past. This year the GAS consumption I have used so far is well below what I used in 2012 when I only had the proportional controller from May onwards.


So it pays to not only look at how you can best use you excess PV generation but also how you are using your energy currently


regards


 








Edited default (July 5, 2013 09:40:00)

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