Usage monitoring with solar - Doh!

Temrael

Hi all,

We got our solar system commissioned last Friday and we're slowly learning about its performance and how to shift our energy usage to the daytime etc. One thing made me laugh on Sunday...

I was using our simple clip-on usage monitor (one that goes on the mains feed and then connects wirelessly to a display unit) to try and gauge our grid usage. I figured it would be good to know what I was drawing from the grid so I could see when I was using more than I was producing.

I was horrified to find that even after the dishwasher cycle finished I was still taking more than 2kw from the grid! I tried to think what could possibly be using that much electric then it dawned on me...

My energy monitor can't tell the difference between electric being drawn from the grid and electric being sent to it. And what I was effectively monitoring therefore was the net of my solar production and my usage (i.e. the balance that I was sending to the grid)! :rotfl:

Am I right in thinking that there's nowhere I can clip my current monitor (like around the meter or something) to measure my grid-supplied usage in real-time? I don't yet have a smart meter btw.

What do you guys do? Is there a different/cleverer sort of monitor I would need to measure just my grid usage?

Thanks,

ajbell

I have a Geo monitor which just shows generation then I have a dumb monitor which is like yours and can't tell the difference between import and export and then I have an iboost buddy which is smart and gives you a net figure based on import and export.
I am afraid to say that I know the wattage of everything I use and when I see a few hundred watts to spare I will try to match my usage with my generation.
I don't like to export anything.

Temrael

Ahh ok thanks for that, I can't have an iBoost, sadly as I've not got a hot water tank (just a combi boiler).

I've done a bit of Googling and there do some to be some monitors specifically designed to measure one's grid usage vs production but they look to be quite a bit more money. I guess now I understand that it's not measuring direction I can just take that into account for now while I'm still learning.

We'll obviously move dishwasher, washing machine and EV charging to daylight hours whenever possible but that will still leave us producing an excess most of the rest of the time I'd think (if the current early results are anything to go by). It's not ideal from pure economics, but I guess it's not the worst problem in the world.

EricMears

I have a Wattson meter that tries to work out what is being generated, what used and the difference between them. Can't say I'm wildly impressed with its accuracy though.

Depending on how your system is wired, it may be possible to measure the input to the consumer unit. Obviously that falls down a bit if the inverter is connected directly to the CU but sometimes they can have a separate 'mini-CU' of their own so that 'real' CU input can be measured.

My CU is a split-load type. Very few circuits (but one of them includes the inverter) are connected to the non-RCD side but virtually all the heavy users are on the RCD-protected side. I can therefore measure (most) usage with a clamp around the wire connecting the two parts of the CU.


HTH

Martyn1981

Temrael wrote: »

Ahh ok thanks for that, I can't have an iBoost, sadly as I've not got a hot water tank (just a combi boiler).

I've done a bit of Googling and there do some to be some monitors specifically designed to measure one's grid usage vs production but they look to be quite a bit more money. I guess now I understand that it's not measuring direction I can just take that into account for now while I'm still learning.

We'll obviously move dishwasher, washing machine and EV charging to daylight hours whenever possible but that will still leave us producing an excess most of the rest of the time I'd think (if the current early results are anything to go by). It's not ideal from pure economics, but I guess it's not the worst problem in the world.

My Solaredge kit now shows export, and has a clamp on device. I don't know exactly how it does it, but it's definitely monitoring export as it's often greater than generation (the ESE clever SE inverter, doesn't know there is a separate WNW system).

ajbell

Am I the only one that takes offence at the idea of exporting my precious kwhs? .

Dave_Fowler

I've built a circuit which can differentiate between imported and exported power. It uses a single clip on current clamp as used by the simple Owl power monitor. The circuit is built on a piece of Vero board.

The circuit checks the phase of the mains supply and compares it with the current measured by the current clamp. If it is in-phase then it is import, if its out of phase it is export. The output from the current clamp is switched between two outputs, one for import and the other for export.

I've used one current clamp and two Owl monitor receivers - one displays import and the other one export.

If you're handy with a soldering iron and understand a bit of electronics, it is not too difficult to build. Drop me a PM if you're interested.

Dave F

mre15

Does your electric meter have a red led that flashes. If so then a geo minim led version can be used.

Zarch

emonPi and https://openenergymonitor.org/ is what you're after.

I had exactly the same issues with older/useless monitoring not knowing the difference between ins and outs once solar was added to the mix.

emonPi and their other offerings use an onboard circuit board to determine the differences and is really spot on and accurate.

It works independent of your inverter etc (which aren't always wholly accurate either)

Granted, a full two clamp emonPi set up is close to £200, but it just works!! I love mine!!

Temrael

Thanks all, lots of options there! What a knowledgeable bunch you are.

The Geo Minim LED monitor that MRE mentioned looks like good value (my grid supply meter has a flashing LED).

I've not really got any soldering experience sadly, that sounds very clever though, Dave.

I take the point that exporting is admitting defeat to a certain extent, but I guess if I've moved what usage I can to daylight hours, and am using all I need but still producing a surplus then (short of battery storage) there's no alternative but to export it?

1961Nick

mre15 wrote: »

Does your electric meter have a red led that flashes. If so then a geo minim led version can be used.

I'd just like to add that the Geo range of pulse counting monitors are virtually 100% accurate.