Posted by: @wesleyp1874

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Hello can anybody advise please..this may be a silly question as I'm not familiar with the workings of the inverter.  We have 11 panels installed avout 4.84kw)  S Solax X1-Boost-G4 invertor.  No Battery.  No contract to sell back into the grid.  I use the Solax Cloud app to monitor performance.  On a good day I might get about 18kw solar output.  The app also tells me that the domestic consumption is exactly the same.  Does this simply mean that every bit of solar power produced has been used in our house?  On a bad day the Solar Output is way down but according to the app so is domestic consumption.  Does the inverter juggle between power sources and prioritise solar power use over electricity from the grid?  

All inverters will use solar power in preference to drawing power from the grid.  If the available power is insufficient, power will be drawn from the grid.  This is 'real time' so if the sun goes behind a cloud and you are boiling the kettle, the power comes from the grid if you dont have a battery.

When there is excess solar power the behaviour depends on the inverter.  The most common set up is that they will export to the grid up to a maximum of 3.68kW, this will occur whether or not you get paid for the export.  However they can be set up to export none, or a greater amount (which requires permission from your DNO).

Not sure what solax cloud does but you need to distinguish between kWh (energy) and kW (instantaneous power - ie rate of use of energy).  Your panels may well generate 18kWh over the day, but only a proportion of this will get used locally because, if the instantaneous demand from the house (kW) does not exactly match the instantaneous production from the panels (kW) then either grid import or export will occur,  How Solax reports this I do not know.

Without a battery (and even with one) you will usually generate in summer a lot more than you can consume, you can get paid for this and its madness not to.  Typically self-consumption is about 40-60% averaged over the year.  With a 4.84kW peak array you should be generating about 4000kWh annually, so you will be exporting 2000kWh.   Octopus for example will pay 12p/kWh so thats roughly £240 per year you are missing out on.     

Hope that helps. 

Posted by: @wesleyp1874

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Hello can anybody advise please..this may be a silly question as I'm not familiar with the workings of the inverter.  We have 11 panels installed avout 4.84kw)  S Solax X1-Boost-G4 invertor.  No Battery.  No contract to sell back into the grid.  I use the Solax Cloud app to monitor performance.  On a good day I might get about 18kw solar output.  The app also tells me that the domestic consumption is exactly the same.  Does this simply mean that every bit of solar power produced has been used in our house?  On a bad day the Solar Output is way down but according to the app so is domestic consumption.  Does the inverter juggle between power sources and prioritise solar power use over electricity from the grid?  

As @jamespa stated, all inverters will try to serve any needs from the house by converting the output of your PV before importing. Your inverter being a PV inverter with an optional CT, it could be limiting or preventing export.   

What happens when your consumption is below what PV could deliver may depend on your installation, so a diagram or more details would help us. Even confirming the kw rating of your Solax inverter. Theoretically if an inverter is not consuming all the DC power the PV panels are producing, that can just get lost at the panels (this happens if say your Solax inverter can only take 3kw and the sun is shinning strong and your panels could deliver 4.84kw). In some cases, the inverter will convert as much as it can and that is exported via your grid connection. There is also a small loss of 2-3% in any DC to AC conversion.  

It's worth adding that if you have a hot water tank and immersion (and don't have a heat pump or battery) a solar diverter is a  worthwhile investment.  A 150l hot water tank is about 5kWh so for the price of a solar diverter-about £400, you get something almost as useful as a 5kWh battery.  You can't play ToU tarrif games, but there again you aren't paying £5k for the hardware.

Thanks again for the answers.  I didn't realise I could be exporting excess energy back into the grid.  We were sat outside in the gareden the other day in bright sun.  Nothing on in the house apart from fridge/freezer, tvs on standbye etc, wondering what might be happening to all that solar power we could be generating!  Nor had I heard of solar diverters.. we do have an immersion heater in our tank..so could be useful..

Posted by: @wesleyp1874

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I didn't realise I could be exporting excess energy back into the grid.

We can discuss this further with you.

Before you could receive money for such export (known as the Smart Export Guarantee or SEG), you need to register with your Energy Supplier.
You will be asked for the MCS certificate which should have been supplied by the installer of your solar panels and inverter.

So if you chose to use an installer who wasn't MCS-Approved, then you won't have a certificate. He could still be a good installer of course!

There are other ways forward, and the absence of an MCS certificate wouldn't prevent you have a solar-diverter. But I'm starting with the basics.

Whatever you say, the amount you will be charged for power from the grid will normally be much greater than the amount that you will get paid for exporting to the grid.

Ideally you want to use all the power generated by your solar installation to offset any grid import, but to do that you really need a battery installation as well.

Attached is a screenshot showing my solar generation, grid import & battery use from last week.

You can see that by using the battery I utilised over 99% of the power generated by my solar panels and, as a result, my power cost for the week was half of what it could have been.