question on power usage following a new PV installation

[solar-forum]

Hi. New subscriber and new solar PV user here.

I am trying to understand my power usage subsequent to our recent Solar PV
installation.

We have 12 x QCell Q Peak G9 380w modules (giving a nominal 4.56kW), a Solis
3.6kW RHI inverter and a 5.12kW Fox LV5200 battery installed. The system also
gives us an EPS to power our oil fired boiler, pumps and shower unit in case
of grid power outage.

Prior to installation, our base power usage (as indicated on our smart meter
IHD) was around 200-250 watts. This covers fridges, freezers, various bits of
computer equipment and devices on standby around the home and in the garage. Our
total annual electricity usage has been running at around 4000-4600 kWh per
annum. Daily usage varied from 10-11 kWh in summer to about 15 kWh in the winter
months.

Now according to the solis monitoring system our daily yield is a very healthy
27kWh (well it /is/ sunny) and as a result we are exporting over 1kW for most of
the day, and as much as 3 - 3.5 kW for a sustained 5-6 hour period during peak
sunshine.

Now to my question. According to our meter IHD, we are still consuming between
£0.50 and £0.80 worth of power per day. Assumimg that this figure includes the
daily standing charge (of £0.22 plus vat) that means we are still pulling between
1 and 2 kWh of power from the grid each day. I don't understand this. Given that
we are producing 27 kWh per day, our battery stores 5.2kW and our nightly usage
will be around the baseline (200 watts per hour) why should we be pulling any
power at all at the moment? (I know we will later in the year).

Is it simply the case that the system will always pull some power as it polls
the grid to check whether it is connected? Or is there something else going
on here?

I would be very grateful for any and all advice. Am I missing something obvious?

 

[Murdoch]

Isn’t your standing charge around 45 p per day ?

is it possible that there are times of the day when you are consuming more than you are producing / have stored?

 

[solar-forum]

Isn’t your standing charge around 45 p per day ?

is it possible that there are times of the day when you are consuming more than you are producing / have stored?

No, I don't think so. Our standing charge is £0.22 per day (and our unit rate is £0.19 - I took a long fix some time ago which does not expire until August next year. Lucky I guess).

I can't see any time where we are using much. The IHD starts the day at around £0.50 - £0.60 (i.e. that is what I see when I get up and all we have been using is 200-250 watts per hour overnight).

 

[up_north]

Are there times when you have high demand appliances on at the same time - kettle, iron etc?

 

[solar-forum]

Are there times when you have high demand appliances on at the same time - kettle, iron etc?

Occasionally yes, but I watch that and only do it when we are exporting. My problem is in understanding why we seem to /start/ the day with a charge of over £0.50 when all we should have used over night is a max of 8 hours x 250 watts = 2 kWh = £0.40 and we have a 5.2 kW battery which should cover the nighttime usage.

For info. now, at 19.45, my IHD shows a grid draw of 20 watts whilst my solis cloud on-line monitor shows a generation of 27 watts.

 

[michael8554]

Is there an app for the Solis that will show a 24 hour graph of house load, PV output, battery input/output, and grid input/output ?

 

[Chewbacca]

there's a similar experience with a Growatt inverter on another recent thread. Have a read through the PV threads, it may answer your question.

 

[solar-forum]

Is there an app for the Solis that will show a 24 hour graph of house load, PV output, battery input/output, and grid input/output ?

There is an android app, but it is next to useless (too slow, buggy and does not show any more than the web application). The web app does not give any information about the battery state, just the PV output. See screenshot attached (edited to obscure personal details).

 

[solar-forum]

there's a similar experience with a Growatt inverter on another recent thread. Have a read through the PV threads, it may answer your question.

Thanks, I'll do that.

 

[Andy1733]

I would check your usage as with hot weather my baseline has gone from 0.50 to 0.68 as I presume the appliance are working harder due to the weather.

So in the 8 hour period your asleep you are using 250w per hour that's 2000w
At 19 p per kW is 38p plus your 22p STD =50p. Am I missing something?

 

[solar-forum]

I would check your usage as with hot weather my baseline has gone from 0.50 to 0.68 as I presume the appliance are working harder due to the weather.

So in the 8 hour period your asleep you are using 250w per hour that's 2000w
At 19 p per kW is 38p plus your 22p STD =50p. Am I missing something?

No, you are not missing anything. But my original question was why that 2 kW had to come from the grid when we have a 5.2kW battery installed.

But having now read loads of other threads here I now think that the grid draw is caused by the inverter checking the grid and also doing a "self-test" routine when the PV powers down in the evening and back on again in the morning. I can understand that monitoring and testing using some grid power, but 1-1.5 kwH pulled each day seems a lot. That tells me that there is an irreducible minimum grid usage and I will always face that. What I have also learned though is that it may be worth my while installing a solic (or similar) PV diverter to send surplus power to the immersion heater. We are currently exporting way more power than we use (and getting nothing for it because we are still waiting for the OK note from the DNO so I can't register for the odd 5.5p per unit we might get).

My thanks to all who have replied to me here and in similar threads on the forum. I'm learning a lot. I do wish though that the solis "cloud" app would show more detail about the state of the battery.

 

[solar-forum]

Thanks, I'll do that.

I have now done that (and my apologies I should have explored further before posting a similar question). The answers by "johnb2713" and "binky" in particular to questions about background usage point to a grid draw of around 1 kWh per day as the inverter goes through monitoring and test loops. That still seems high to me, but in the grand scheme of total savings achieved from the PVA I think that is probably acceptable. I look forward to seeing what happens when the days get shorter.

 

[binky]

it seems rather high to me as well, but then how many kWh are you not buying in? Thoroughly recommend the immersion gadgets, my customers have reported really good things about them.

 

[johnb2713]

No, you are not missing anything. But my original question was why that 2 kW had to come from the grid when we have a 5.2kW battery installed.

I think the inverter is of greater importance with your issue. I'm fairly new to solar but I cant see and reason to undersize the inverter by such and amount. If you have a kettle on for example, that will be taking 2 to 3kW, you only need the fridge or freezer to start up then there would be a momentary import of power for the startup. 3.65 kW isnt a great deal of power and you will have very little headroom with this.

But having now read loads of other threads here I now think that the grid draw is caused by the inverter checking the grid and also doing a "self-test" routine when the PV powers down in the evening and back on again in the morning. I can understand that monitoring and testing using some grid power, but 1-1.5 kwH pulled each day seems a lot. That tells me that there is an irreducible minimum grid usage and I will always face that.

What I have also learned though is that it may be worth my while installing a solic (or similar) PV diverter to send surplus power to the immersion heater.

100% agree, I have MyEnergi EDDI, it works very efficiently and is a good help to keep your exports to zero. The nice thing about them is theyre not ON / OFF they will adjust their output 0 to 100% modulates the heating element in the same way, this makes them really useful to minimize export.

I'm only aware of the Growatt inverters behaving in the manner suggested.
All of the grid tied inverters work by way of measuring the voltage and import / export. If it see's youre importing it will increase it's output voltage until the import is zero or there's a small amount of export being measured, I often see minimal exports but usually 15w to 150w being on all of the time.

My thanks to all who have replied to me here and in similar threads on the forum. I'm learning a lot. I do wish though that the solis "cloud" app would show more detail about the state of the battery.

The APP would certainly give you some idea of what/where/when etc.

Heres a graph of today so far. You can see the regular low level of import pulse with do go all day. These little pulses can easily add up to a 1 to 2kWh import.

One other thought, they do have a CT wrapped around the meter tails with nothing omitted?

 

[Andy1733]

No, you are not missing anything. But my original question was why that 2 kW had to come from the grid when we have a 5.2kW battery installed.

But having now read loads of other threads here I now think that the grid draw is caused by the inverter checking the grid and also doing a "self-test" routine when the PV powers down in the evening and back on again in the morning. I can understand that monitoring and testing using some grid power, but 1-1.5 kwH pulled each day seems a lot. That tells me that there is an irreducible minimum grid usage and I will always face that. What I have also learned though is that it may be worth my while installing a solic (or similar) PV diverter to send surplus power to the immersion heater. We are currently exporting way more power than we use (and getting nothing for it because we are still waiting for the OK note from the DNO so I can't register for the odd 5.5p per unit we might get).

My thanks to all who have replied to me here and in similar threads on the forum. I'm learning a lot. I do wish though that the solis "cloud" app would show more detail about the state of the battery.

I run 4.8kw of battery's and they are exhausted after 4 hours so maybe your usage, it's a combo of drawing from grid,. Standing charge and monitoring/test loop.

 

[solar-forum]

it seems rather high to me as well, but then how many kWh are you not buying in? Thoroughly recommend the immersion gadgets, my customers have reported really good things about them.

We seem to be saving a "buy in" of around 9kWh (so down from 10-11 units a day to 1-2) I find that perfectly acceptable. But of course this is all since installation at the beginning of this month which has been pretty exceptional weather wise. The temperature in our loft is completely unreasonable too so of course this may affect the functioning of the inverter/battery. I'm too new at this to know what to expect as yet.

I'm coming to the conclusion that a PVA diverter to the immersion would be a good investment too.

 

[solar-forum]

I think the inverter is of greater importance with your issue. I'm fairly new to solar but I cant see and reason to undersize the inverter by such and amount. If you have a kettle on for example, that will be taking 2 to 3kW, you only need the fridge or freezer to start up then there would be a momentary import of power for the startup. 3.65 kW isnt a great deal of power and you will have very little headroom with this.


I'm only aware of the Growatt inverters behaving in the manner suggested.
All of the grid tied inverters work by way of measuring the voltage and import / export. If it see's youre importing it will increase it's output voltage until the import is zero or there's a small amount of export being measured, I often see minimal exports but usually 15w to 150w being on all of the time.


The APP would certainly give you some idea of what/where/when etc.

Heres a graph of today so far. You can see the regular low level of import pulse with do go all day. These little pulses can easily add up to a 1 to 2kWh import.View attachment 13917

One other thought, they do have a CT wrapped around the meter tails with nothing omitted?

I questioned the capacity of the inverter with the installer prior to installation. Specifically I asked why the inverter was shown as a lower capacity than the PVA output. They replied "If you look closely at the PDF of the Solis hybrid inverter you will see it
has a maximum capacity of 7kw input on the DC side." I assumed that they knew what they were doing in sizing the system.

As for the usage graphs, I can't see anywhere near that level of detail from the solis cloud app. According to my meter IHD now (at 19.45 ) I have used £0.41 today - so if that includes the standing chage, as I now assume it does, I have pulled in about 1 unit from the grid.

 

[solar-forum]

I run 4.8kw of battery's and they are exhausted after 4 hours so maybe your usage, it's a combo of drawing from grid,. Standing charge and monitoring/test loop.

I can't see the state of my battery from the solis info so can't comment. But i assume that the usage I am seeing is as you say, a combination of testing/monitoring plus the standing charge.

 

[Andy1733]

I can't see the state of my battery from the solis info so can't comment. But i assume that the usage I am seeing is as you say, a combination of testing/monitoring plus the standing charge.

Have you considered the Solis dongle?

 

[binky]

the solis portal is pretty decent