48V off-grid with AC blend?

Steve_FractalsSteve_Fractals Registered Users Posts: 3
Hi all,

Newbie here, done quite a bit of research already but struggling to find the right all-in-one off-grid inverter for me. 

I'm looking for 48v 3-5Kwh off-grid inverter but with a proper PV & AC blend option. I want a unit that can use a mix of supply from solar PV/Batt and AC when needed so if PV/Batt can only supply say 50% of load requirement then it can supply the other 50% from the AC-in. Most units I've looked at so far either just don't mention this or when I've contacted suppliers, they've said its all AC or all Solar/Batt with no blending.

Does anyone have a list or at least some models that have the blend feature please esp. if these are available in the UK but would be prepared to import if that's my only option?

Comments

  • BB.BB. Super Moderators, Administrators Posts: 32,921 admin
    edited September 30 #2
    Welcome to the forum Steve,

    A quick question... Are you allowed to feed power back into the grid--Or does your utility prohibit power back feed (zero export to grid)?

    Many hybrid inverters (Grid Tied/Off Grid capable with solar and battery bank) will feed excess solar charging power back to the utility--This ensures that all energy that you generate is used--Whether by the home or back to the utility for credit.

    The zero back feed is a little bit more difficult to find.

    Are you looking for solar/battery backup power in the case of utility power failure? Or just trying to save money on electric power?

    Pure Grid Tied (GT inverter(s), no battery bank) is the cheapest/most efficient method of solar to grid.

    Hybrid (GT+Off Grid+Solar+Battery) is much more expensive... But given where energy prices are heading in Europe for the present time--I could see the attraction...

    In the US, GT Solar can generate power at $0.15 or less per kWH. Off grid/battery/hybrid is usually closer to $1.00 to $2.00 per kWH--Although it can be possible to get down towards $0.50 per kWH or less (find good prices for hardware and battery bank, manage your energy usage so you use most of the available solar harvest every day (i.e,. conserve on cloudy days, use washer/dryer/etc. on sunny days).

    I am guessing you are somewhere around London UK? Just to give you an idea of what the sun looks like:

    http://www.solarelectricityhandbook.com/solar-irradiance.html

    London
    Average Solar Insolation figures

    Measured in kWh/m2/day onto a solar panel set at a 38° angle from vertical:
    (For best year-round performance)

    JanFebMarAprMayJun
    1.27
     
    2.04
     
    2.76
     
    3.67
     
    4.17
     
    4.20
     
    JulAugSepOctNovDec
    4.25
     
    4.16
     
    3.26
     
    2.41
     
    1.53
     
    1.05
     

    Not that sunny during "summer", and winter is just horrible. Suggest around 3 hours a day+ is where solar can become cost effective and "useful".

    Do you have an idea about how many kWatt*Hours per day you need... Just to give you some quick math--Say a relatively energy efficient home at 300 kWH per month (typical is usually around 500-1,000 kWH per month depending on lots of variables):
    • 300 kWH per month / 30 days per month = 10 kWH per day = 10,000 WH per day
    Pure Grid Tie:
    • 10,000 WH per day * 1/0.77 GT inverter system eff * 1/3.0 hours per day sun (April thru Sept) = 4,329 Watt array (GT "summer")
    • 10,000 WH per day * 1/0.52 Pure off grid + battery inverter system eff * 1/3.0 hours per day sun (April thru Sept) = 6,410 Watt array (OG "summer")
    And to give you an idea of battery sizing--This is for Flooded Cell Lead Acid for 2 says of stored energy, 50% max planned discharge for longer battery life (we can talk Lithium Ion and such if you wish):
    • 10,000 WH per day * 1/0.52 off grid system eff * 2 days storage * 1/0.50 max discharge * 1/48 volts = 1,603 AH @ 48 volt bank
    300 kWH per month is not a lot of power for a utility connected home... For a very energy efficient off grid home/cabin usually suggest looking at 100 kwH per month (3,300 WH per day) for the basics (LED lights, refrigerator, laptop computer, etc.). And that usually assumes that heating (cooking, hot water, space heating) is managed with wood/fossil fuels and such...

    Before spending money on solar--Highly suggest conservation first (turning unused appliances "off" when not in use, most efficient lighting, fridge, insulation, perhaps induction cooker, solar hot water, etc.)...

    Things are getting pretty tight over in Europe right now... I guess that space heating is going to be a critical need for most of northern Europe--And Solar is really expensive for any form of heating (and A/C or cooling).

    Solar water/space heating can be effective... But between plumbing issues (pumps, water leaks, freezing weather, etc.) and such--May not be practical for many people.

    Another option for heating is to look for mini-split "heat pump" systems... The new units are getting 2-3x as efficient for heating vs electric resistance strip heaters (1/2 to 1/3 the amount of electricity) used. And these newer units can still be more efficient than resistance heaters below freezing. There are also heat pump water heaters too... (Note that heat pump systems are not "cheap", and being more complex can be more difficult to repair).

    Of course, trying to find heat pump heating/hot water systems is going to be difficult too (China's lock downs, supply chain issues, etc.).

    Getting more data on your energy usage (if you don't have that yet) is important for solar and conservation (figure out where to spend your time and money).... Things like Kill-a-Watt type energy meters (for plug-in AC loads) and whole house monitors (the whole home usage, and some have options to measure major circuits like heating, A/C, dryer, electric stove) will be a great help:

    https://www.amazon.co.uk/s?k=kill+a+watt+meter+uk&sprefix=kill+a+watt,aps,362 (plug-in energy meters)
    https://www.amazon.co.uk/s?k=whole+house+energy+monitors+for+home+uk&sprefix=whole+house+energy+m,aps,319 (a couple whole home monitors--I am sure there are many others)

    If you have a larger property--Solar Heating can be done even in very cold climates--And can be a DIY (do it yourself) type project:

    https://www.builditsolar.com/Projects/SpaceHeating/SolarShed/solarshed.htm

    However, for many folks, solar electric+conservation+heat pump+etc. is a more practical answer.

    Note that solar hot water can work pretty well with some partial shading. Solar electric panels need exposure to full sun. Even a minor bit of shading (overhead power lines, neighbor's trees, chimneys, etc.) can easily cut solar harvest by 1/2 to even zero harvest.

    I wish I had "better" answers for you and your family & friends. This could be ugly for the next few years.

    -Bill

    PS: Obviously, I know nothing about your energy usage--The 300 kWH per month number was used to show the math for a "moderately" sized system.

    Energy usage is a highly personal set of choices and what works for me may not work for you. Knowing your energy usage (and lots of conservation) will help you design a system that meets your needs.

    -BB
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Steve_FractalsSteve_Fractals Registered Users Posts: 3
    BB. said:
    Welcome to the forum Steve,

    A quick question... Are you allowed to feed power back into the grid--Or does your utility prohibit power back feed (zero export to grid)?

    Many hybrid inverters (Grid Tied/Off Grid capable with solar and battery bank) will feed excess solar charging power back to the utility--This ensures that all energy that you generate is used--Whether by the home or back to the utility for credit.

    The zero back feed is a little bit more difficult to find.

    Are you looking for solar/battery backup power in the case of utility power failure? Or just trying to save money on electric power?

    Pure Grid Tied (GT inverter(s), no battery bank) is the cheapest/most efficient method of solar to grid.

    Hybrid (GT+Off Grid+Solar+Battery) is much more expensive... But given where energy prices are heading in Europe for the present time--I could see the attraction...

    In the US, GT Solar can generate power at $0.15 or less per kWH. Off grid/battery/hybrid is usually closer to $1.00 to $2.00 per kWH--Although it can be possible to get down towards $0.50 per kWH or less (find good prices for hardware and battery bank, manage your energy usage so you use most of the available solar harvest every day (i.e,. conserve on cloudy days, use washer/dryer/etc. on sunny days).

    I am guessing you are somewhere around London UK? Just to give you an idea of what the sun looks like:

    http://www.solarelectricityhandbook.com/solar-irradiance.html

    London
    Average Solar Insolation figures

    Measured in kWh/m2/day onto a solar panel set at a 38° angle from vertical:
    (For best year-round performance)

    JanFebMarAprMayJun
    1.27
     
    2.04
     
    2.76
     
    3.67
     
    4.17
     
    4.20
     
    JulAugSepOctNovDec
    4.25
     
    4.16
     
    3.26
     
    2.41
     
    1.53
     
    1.05
     

    Not that sunny during "summer", and winter is just horrible. Suggest around 3 hours a day+ is where solar can become cost effective and "useful".

    Do you have an idea about how many kWatt*Hours per day you need... Just to give you some quick math--Say a relatively energy efficient home at 300 kWH per month (typical is usually around 500-1,000 kWH per month depending on lots of variables):
    • 300 kWH per month / 30 days per month = 10 kWH per day = 10,000 WH per day
    Pure Grid Tie:
    • 10,000 WH per day * 1/0.77 GT inverter system eff * 1/3.0 hours per day sun (April thru Sept) = 4,329 Watt array (GT "summer")
    • 10,000 WH per day * 1/0.52 Pure off grid + battery inverter system eff * 1/3.0 hours per day sun (April thru Sept) = 6,410 Watt array (OG "summer")
    And to give you an idea of battery sizing--This is for Flooded Cell Lead Acid for 2 says of stored energy, 50% max planned discharge for longer battery life (we can talk Lithium Ion and such if you wish):
    • 10,000 WH per day * 1/0.52 off grid system eff * 2 days storage * 1/0.50 max discharge * 1/48 volts = 1,603 AH @ 48 volt bank
    300 kWH per month is not a lot of power for a utility connected home... For a very energy efficient off grid home/cabin usually suggest looking at 100 kwH per month (3,300 WH per day) for the basics (LED lights, refrigerator, laptop computer, etc.). And that usually assumes that heating (cooking, hot water, space heating) is managed with wood/fossil fuels and such...

    Before spending money on solar--Highly suggest conservation first (turning unused appliances "off" when not in use, most efficient lighting, fridge, insulation, perhaps induction cooker, solar hot water, etc.)...

    Things are getting pretty tight over in Europe right now... I guess that space heating is going to be a critical need for most of northern Europe--And Solar is really expensive for any form of heating (and A/C or cooling).

    Solar water/space heating can be effective... But between plumbing issues (pumps, water leaks, freezing weather, etc.) and such--May not be practical for many people.

    Another option for heating is to look for mini-split "heat pump" systems... The new units are getting 2-3x as efficient for heating vs electric resistance strip heaters (1/2 to 1/3 the amount of electricity) used. And these newer units can still be more efficient than resistance heaters below freezing. There are also heat pump water heaters too... (Note that heat pump systems are not "cheap", and being more complex can be more difficult to repair).

    Of course, trying to find heat pump heating/hot water systems is going to be difficult too (China's lock downs, supply chain issues, etc.).

    Getting more data on your energy usage (if you don't have that yet) is important for solar and conservation (figure out where to spend your time and money).... Things like Kill-a-Watt type energy meters (for plug-in AC loads) and whole house monitors (the whole home usage, and some have options to measure major circuits like heating, A/C, dryer, electric stove) will be a great help:

    https://www.amazon.co.uk/s?k=kill+a+watt+meter+uk&sprefix=kill+a+watt,aps,362 (plug-in energy meters)
    https://www.amazon.co.uk/s?k=whole+house+energy+monitors+for+home+uk&sprefix=whole+house+energy+m,aps,319 (a couple whole home monitors--I am sure there are many others)

    If you have a larger property--Solar Heating can be done even in very cold climates--And can be a DIY (do it yourself) type project:

    https://www.builditsolar.com/Projects/SpaceHeating/SolarShed/solarshed.htm

    However, for many folks, solar electric+conservation+heat pump+etc. is a more practical answer.

    Note that solar hot water can work pretty well with some partial shading. Solar electric panels need exposure to full sun. Even a minor bit of shading (overhead power lines, neighbor's trees, chimneys, etc.) can easily cut solar harvest by 1/2 to even zero harvest.

    I wish I had "better" answers for you and your family & friends. This could be ugly for the next few years.

    -Bill

    PS: Obviously, I know nothing about your energy usage--The 300 kWH per month number was used to show the math for a "moderately" sized system.

    Energy usage is a highly personal set of choices and what works for me may not work for you. Knowing your energy usage (and lots of conservation) will help you design a system that meets your needs.

    -BB
    Thanks for all that info. We are allowed to export to grid but only if all installed by approved installer with all kit being in the approved list as well and not allowed battery unless a Tesla £7k type.

    I don't want any export due to the above making it way to restrictive and expensive.

    After lots of reading it seems my best bet is an all in one off-grid inverter unit with grid/utility backup.

    I plan to have a separate panel that feeds certain low powered devices from the inverter. The inverter will also have a feed from grid as backup on the AC-in

    What I have been struggling to find is one of these that can blend Generator/Grid on AC-in with PV solar/batt so if my solar is only producing 60% of my loads then it will blend by topping up the remaining 40% from the AC-in. Lots of units will switch to totally AC-In if load is to much for PV but are an all or nothing scenario rather than a blend.

    I've since read that the off-grid units from MPP have this facility of blending and again from research it seems that these are rebadged Voltronics as are the Axpert king units but still trying to confirm that as the MPP are not available except by import in UK. Unfortunately neither the Voltronics nor the Axpert specifically mention this facility so will try to contact them for confirmation.

    Any other models that can do this blending would be appreciated.




  • BB.BB. Super Moderators, Administrators Posts: 32,921 admin
    Hmmm... Since you are looking for more of a DIY (do it yourself) installation, I wonder if you could take a AC Inverter/Charger and use the generator auto-start function to control a mechanical (or solid state) relay between the grid and the AC Genset input...

    Just program the auto-start based on your needs (say start at 50% state of charge and shut down at 80% SoC) and use to cycle the relay as needed. No back-feed to grid and you are in control of the battery state of charge/health. And it could work with almost any AC inverter with AC Genset and auto-start.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Steve_FractalsSteve_Fractals Registered Users Posts: 3
    Seems that all the all-in-ones made by MPP Solar have the feature of AC blend but lots of the clone/rebadge ones don't. I had this confirmed from MPP themselves now and so have purchased one of their models which does also have generator autostart and also be used without any batteries etc.
  • JRHillJRHill Registered Users Posts: 147 ✭✭
    I upgraded my inverter a few years ago to an Outback VFXR which had a few additional features. One of which is called Support Mode and its function is to bypass the inverter for power but still charge/maintain the batteries. But if you have a surge or high AC demand the inverter will contribute (blend) to the incoming AC be it generator or Grid. I haven't used it as there is no need in my case so I can't offer any additional detail. You could download the VFXR manuals for set up and programming for more information. I think there are other of the newer Outback inverters that have this function as well.
    Off Grid. Two systems: 1) 2925w panels, OB VFXR3648, FM80, FNDC, Victron BMV-712, Mate3s, 240 xformer, four SimpliPHI 3.8; 2) 780w, Morningstar 30a, Grundfos switch, controller and AC/DC pump, 8 T105. Honda EU7000is w/AGS. Champion 3100. HF 4550, Miller Bobcat.
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