Hello everybody. I am trying to identify the right piece of kit to tell me how much electricity (KWs) are being exported by my PV system at any particular moment so that I optimise my useage. Thanks. It would also help to know how it should be wired in although I'll get an electrician to do it.
Measuring Kilowatts being exported from Solar PV system
Submitted by Guest on Sun, 18/11/2012 - 11:21»
Re: Measuring Kilowatts being exported from Solar PV system
Hello Stephen,
This site is all about people who build the monitoring and, in some cases, controlling/optimising equipment themselves. Parts can come from a variety of sources. If you have some experience of building electronics from kits, then there are plenty of people around here who can offer advice and there are proven kits available from the shop (but you need to supply your own boxes).
If you are only interested in monitoring, then you can install the equipment yourself, all you need is a mains socket close by your inverter for voltage and a cable to clip a current transformer over. If you are interested in using spare energy that would otherwise be exported to heat water, then you do need professional help with the installation (I'm thinking of calypso_rae's Mk2 design)..
If you're not happy to assemble a kit yourself (and it does need some quite fine soldering), then an appeal on these forums for someone to build the kit for you will likely be fruitful.
Re: Measuring Kilowatts being exported from Solar PV system
It's an interesting point about getting a qualified electrician to install the final product. That's fine if the item is a fully-tested and commercially manufactured design. For a start, the electrician would presumably have some clear instructions to go on.
Many of us are both DIY constructors and DIY installers. As Graucho Marx might have said "I wouldn't want to use any electrician who would agree to connect up anything that I had built!"
Re: Measuring Kilowatts being exported from Solar PV system
Robert, Thanks for your reply. I didn't really understand your site. I think I do better now. I am quite handy and I have a soldering kit. I understand volts, amps, watts and KWh but I couldn't design a circuit, although I believe I can follow one.. Can you suggest a set of components from the shop that would enable me to construct a gadget that would measure KWH being exported at any particular moment during daylight hours?
Re: Measuring Kilowatts being exported from Solar PV system
As I said to Robert I didn't really understand this site. I am a fan of Groucho Marx's witticisms too. Once i have identified or built a gadget for my purposes I consider how I am going to fit it.
Re: Measuring Kilowatts being exported from Solar PV system
Can you suggest a set of components from the shop that would enable me to construct a gadget that would measure KWH being exported at any particular moment during daylight hours?
If you just want to show this information on a display panel, I'm sure there are items in the shop to do this. Each measurement cycle would probably take around a second or two with the result being sent to a separate unit for processing and display. Hope I've got this about right.
If you're interested in diverting your surplus power (rather than just monitoring the situation while it slips away), then you may be interested in the Mk2 PV Router thread which I started during the summer. Many constructors have posted information about their builds so you'll find no shortage of good ideas there. For optimal performance, the underlying Mk2 code operates in a continuous manner without pausing for anything. The algorithms for measuring and diverting surplus power are fully interleaved and it all seems to mesh together very nicely.
A number of builders have chosen to integrate some display aspects into my original Mk2 code. Personally, I'm only interested in ensuring that my surplus power is being diverted as efficiently as possible.
If you are fortunate enough to have a disc-style meter which can run backwards, then diverting any surplus power would probably not be a priority for you!
Re: Measuring Kilowatts being exported from Solar PV system
Simples,
Just follow the instructions here: http://openenergymonitor.org/emon/applications/solarpv
Re: Measuring Kilowatts being exported from Solar PV system
Take a look at the shop site. I recommend as the very minimum, if you want a true measure of power:
(You could buy some of this list as a system bundle, adding on the remainder).
You can have either the 433 MHz or the 868 MHz versions of EmonTx and emonGLCD (but obviously both need to be the same frequency), but if you have other radio-controlled kit, you should check its operating frequency first to avoid interference.
You might want a box for the GLCD - or if you're good at cabinet-making, make one - as the 'case' comprises front and back panels and is open at the sides, top and bottom; and various bits do stick out beyond the profile of the front panel.
You'll want a double mains socket near your inverter, and a single one near where you want the display.
Before you buy the kits, take a careful look at the size of the soldering. You should be OK (I'm the same age as you!) but a big magnifying glass on a stand is a big help.
This setup would give you a snapshot reading updated every 5 s or thereabouts. It will not control any appliances. If your inverter is connected into your house wiring near to the consumer unit, you might like to site the emonTx there and add another current sensor which you could use to measure either the house consumption or the nett power flow to/from the grid. The emonGLCD can go anywhere in the house to suit your wishes (unless you have thick stone walls, when you might have a problem getting the signal through. In that case, the 433 MHz version might have a slight advantage).
If you want to cheapen the installation, and you only want to measure current (which will give but an approximate measure of power because you won't know the system voltage you're working with at any instant) then you can leave out the voltage sensor, and you could run the emonTx off 2 AA cells, saving one 5 V power supply.
Re: Measuring Kilowatts being exported from Solar PV system
Thank you all for your input. I will follow up. I forgot to say that my PV system has three arrays of panels and three inverters. I noticed that I should be placing some of the kit suggested near an inverter. How would my three inverters affect installation? The South-facing array produces 47% of the power in a year and the East and West ones about 26% each.
Re: Measuring Kilowatts being exported from Solar PV system
I assume you have a single phase supply. If all 3 inverters feed in at the same point, then you can measure the total power there (assuming the cables come together at one place, you can clip the c.t. around the 3 cables and read the total that way). If they are widely separated, and feed into different circuits of your house wiring at different places, then that might introduce some problems. In that case, you might need 3 c.t's and 3 emonTx's. I'd need to know how everything is wired and the physical arrangement to give you specific guidance.
Unless you want to log all your data to emonCMS (that's a web-based application to record and display your usage), you don't need the emonBase etc that is included in the Solar PV write-up. You can always add that later if you wish.
Re: Measuring Kilowatts being exported from Solar PV system
Robert
Yes, it's only a single phase supply and I think I can find one place where all the feeds come together. I need to clear a cupboard and investigate!
Stephen