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Meter reading & solar pv

 
Solar Photovoltaic (PV)
Last Post by atommyk 3 years ago
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Si Fillo
 Si Fillo
(@si-fillo)
Trusted Member Member
Joined: 3 years ago
Posts: 36
Topic starter 05/02/2023 10:11 am   [#808]

Good morning,

Having recently moved into a property with solar pv & heat pump, I'm wanting to try and better understand my home energy setup which leads, I fear, to a rather basic question...

I have a 12 panel, 3kw solar pv array and would like confirmation on how my smart meter (I believe SMETS1) interprets the electricity I generate.

Let's say I use 50kwh in a day and solar generates 5kw.Does my smart meter know what is pulled from the grid and what is solar generated?

Does the smart meter stop 'going around' when I am consuming what is being generated? So in effect I am charged for 45kwh I have pulled from grid? (I will then also get the relevant import/export fit payments)

or

Can my smart meter not decipher what is grid/solar and I am just charged for 50kwh of use, thus relying on fit payments to get reimbursed for the 5kwh solar generation (at a much lower rate).



   
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 ronin92
(@ronin92)
Estimable Member Member
Joined: 4 years ago
Posts: 64
05/02/2023 10:43 am  

The smart meter samples the instantaneous power flow at frequent intervals over a period.  All inflows are added together to constitute import.  All outflows are added together to constitute export.  Both are separately charged/rewarded.

So say you have a electric oven with a 3kW element that is thermostatically controlled and currently averaging 2 kW to maintain oven temp.  To simplify things, there are also no other loads in the home.  When the element kicks in it draws 3kW.  The panel is instantaneously generating 2 kW.  The 1 kW difference is registered as an import at that instant.  A minute later, the thermostat turns off the element.  The 2 kW from the panels are then registered a 2 kW export.  So even though your 2 kW average oven load is the same as your panel output, the panel generation regularly "misses" the oven consumption resulting in electricity charges for you.

Because you pay so much more for import than export, instantaneously matching local consumption to your panel generation as much as possible is key to getting value out of your panels.  It is remarkably difficult to do because so many electric loads are on on/off control! Doing it well involves batteries but that involves a fair bit of outlay.  You can also install a cheaper hot water diverter to consume all excess generation as DHW heating - that only credits your excess generation at gas price in most cases.

The FiT meter is separate and for FiT scheme purposes only.



   
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 atommyk
(@atommyk)
Active Member Member
Joined: 4 years ago
Posts: 12
05/02/2023 10:48 am  

Conventionally, your inverter would supply the electricity to your house when the solar PV generates it, and only top-up with a draw from the grid when required. Of course, if your solar array generates eg 1.5kW and your house draws 2.5kW, then the remainder of 1kw will come from the grid.

If your PV is generating but there's no draw from the house, then the electricity will usually be exported and you get reimbursed (provided you have signed up to an export tariff). The export tariff is separate to the import and can be with a different company. We have signed up with octopus agile because it gives us the best reimbursement - referral link attached. 



   
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