Hybrid v AC-Coupled Solar/Battery Inverters ACvDC

Hi All,

I appreciate there are other threads on this topic, but my question is slightly different.

I get the differences between Hybrid and AC-Coupled Inverters and Batteries. But the installer I chose to go with has imposed their own view on what should be done, against the advice and designs from everyone else I got quotes from, and advice from my own family-electricians. This installer wants to install a separate Solar inverter and battery inverter. The reason they state is that because the array is 150 metres from the house (ground mount), the AC inverter must be located outside at the array itself and only AC taken into the house, because of DC voltage drop.

All my family electricians and the other installers say nonsense. Better to have a hybrid inverter in the house as it's one integrated and simple system and take DC direct from the array, but using thicker 8AWG wires in order to minimise voltage drop (2% only, according to the tables).

I will have 20kws of Pylontech batteries in my house.

Please help me with any of your valuable inputs...I don't care so much about the cost, but I want to make sure I have the best, smartest and most efficient installation.
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Comments

  • Spies
    Spies Posts: 2,028 Forumite
    First Post Photogenic First Anniversary Name Dropper
    The benefit of AC connected is that you will technically have the benefit of the battery output PLUS the solar, versus the hybrid inverter being limited to whatever its spec is (3.6 or 4kw for example).
    4.29kWp Solar system, 45/55 South/West split in cloudy rainy Cumbria. 
  • Spies said:
    The benefit of AC connected is that you will technically have the benefit of the battery output PLUS the solar, versus the hybrid inverter being limited to whatever its spec is (3.6 or 4kw for example).
    Forgive my ignorance on how electricity works, but if for example I have my Heat Pump that can draw 20amps and my battery inverter only supply 13 amps, does the system import 7 amps to make up the difference or does the system take all 20 amps from the grid?
  • Spies
    Spies Posts: 2,028 Forumite
    First Post Photogenic First Anniversary Name Dropper
    Spies said:
    The benefit of AC connected is that you will technically have the benefit of the battery output PLUS the solar, versus the hybrid inverter being limited to whatever its spec is (3.6 or 4kw for example).
    Forgive my ignorance on how electricity works, but if for example I have my Heat Pump that can draw 20amps and my battery inverter only supply 13 amps, does the system import 7 amps to make up the difference or does the system take all 20 amps from the grid?
    It will draw what's 'missing' from the grid, if you had separate inverters for solar and battery, it would take the maximum it can from battery, then top it up with the solar, then finally use the grid.
    4.29kWp Solar system, 45/55 South/West split in cloudy rainy Cumbria. 
  • QrizB
    QrizB Posts: 13,822 Forumite
    First Anniversary First Post Photogenic Name Dropper
    The reason they state is that because the array is 150 metres from the house (ground mount), the AC inverter must be located outside at the array itself and only AC taken into the house, because of DC voltage drop.
    This seems a bit odd but it depends on the configuration of your array.
    If your array is a single string, the operating voltage of your array could easily be 400VDC or more. That will have a lower loss over a 150-metre cable run than 240VAC will.
    N. Hampshire, he/him. Octopus Go elec & Tracker gas / Shell BB / Lyca mobi. Ripple Kirk Hill member.
    2.72kWp PV facing SSW installed Jan 2012. 11 x 247w panels, 3.6kw inverter. 30MWh generated, long-term average 2.6 Os.
    Taking a break, hope to be back eventually.
    Ofgem cap table, Ofgem cap explainer. Economy 7 cap explainer. Gas vs E7 vs peak elec heating costs.
  • Spies said:
    Spies said:
    The benefit of AC connected is that you will technically have the benefit of the battery output PLUS the solar, versus the hybrid inverter being limited to whatever its spec is (3.6 or 4kw for example).
    Forgive my ignorance on how electricity works, but if for example I have my Heat Pump that can draw 20amps and my battery inverter only supply 13 amps, does the system import 7 amps to make up the difference or does the system take all 20 amps from the grid?
    It will draw what's 'missing' from the grid, if you had separate inverters for solar and battery, it would take the maximum it can from battery, then top it up with the solar, then finally use the grid.
    This is what my hybrid system does?
    Ie. Solar first, then battery, then grid if i need that much extra? 

  • QrizB said:
    The reason they state is that because the array is 150 metres from the house (ground mount), the AC inverter must be located outside at the array itself and only AC taken into the house, because of DC voltage drop.
    This seems a bit odd but it depends on the configuration of your array.
    If your array is a single string, the operating voltage of your array could easily be 400VDC or more. That will have a lower loss over a 150-metre cable run than 240VAC will.
    Thanks so much for the reply.
    There will be two strings of 8 panels, each string with Open Circuit of 420 volts at 11 amps.

    I did read from another message board that "you MUST use your highest voltage across your longest run with the thickest wire you can afford".

    So I'm still ost as to why this solar company is advocating an inverter underneath the array, bringing back AC which will lose more voltage % compared to the whole. 

    Should I insist on DC and a hybrid inverter? I don;t want to get another supplier as the wait now is over 9 months.
  • Spies
    Spies Posts: 2,028 Forumite
    First Post Photogenic First Anniversary Name Dropper
    Spies said:
    Spies said:
    The benefit of AC connected is that you will technically have the benefit of the battery output PLUS the solar, versus the hybrid inverter being limited to whatever its spec is (3.6 or 4kw for example).
    Forgive my ignorance on how electricity works, but if for example I have my Heat Pump that can draw 20amps and my battery inverter only supply 13 amps, does the system import 7 amps to make up the difference or does the system take all 20 amps from the grid?
    It will draw what's 'missing' from the grid, if you had separate inverters for solar and battery, it would take the maximum it can from battery, then top it up with the solar, then finally use the grid.
    This is what my hybrid system does?
    Ie. Solar first, then battery, then grid if i need that much extra? 

    I wasn't suggesting it works differently with a hybrid inverter vs ac connected, the main take away is that with 2 inverters you get twice the output potentially.
    4.29kWp Solar system, 45/55 South/West split in cloudy rainy Cumbria. 
  • 70sbudgie
    70sbudgie Posts: 749 Forumite
    First Anniversary First Post Name Dropper
    You could find that with 2 invertors, you'll get the same push back from the DNO as if you had an inverter >3.68kW. That may or may not be an issue depending on where you live. 
    4.3kW PV, 3.6kW inverter. Octopus Tracker. Zoe. Ripple x 2. Cheshire
  • 70sbudgie said:
    You could find that with 2 invertors, you'll get the same push back from the DNO as if you had an inverter >3.68kW. That may or may not be an issue depending on where you live. 
    Excellent point. But I THINK I'll be OK with the DNO as my neighbour has a 26 panel system on his roof exporting to the grid. I'm only installing 18 panels max so will limit the export from the inverter to 3.68 via software settings so can then rely on the G99 or is it G100 certificate.
  • 70sbudgie
    70sbudgie Posts: 749 Forumite
    First Anniversary First Post Name Dropper
    G100 is export limitation. G98 covers the standard domestic install, but I'm not sure what capacity G99 starts. I thought it was about 7kW, but that doesn't match the 3.68kW that I know is the hassle free limit.
    4.3kW PV, 3.6kW inverter. Octopus Tracker. Zoe. Ripple x 2. Cheshire
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