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Garage Wiring, Coffee Roasting, Voltage Drop and Solar

Fultonius
Hi Folks,


I do a little coffee roasting. It's a 1300w machine, with a 230v heater element (40 Ohm - upgraded from a 240 / 44 ohm version). When running, it's drawing 5 amps and the voltage is dropping to 221v (around 229v before connecting).


Annoyingly, this means long roasting times in summer, and very long in winter! (not ideal)


So, here's my dilemma. I'm trying to consider the effects of voltage rise if I have batteries and an inverter. Obviously, I could get a variable output 1.5kw pure sine inverter and run it islanded. I have 7 x 16 ah 12v batteries redirected from going to the scrappies, which would have plenty juice to run this. I've been thinking for a while about putting a few solar panels on the roof and that's where it gets complicated.


Obviously the wiring from the house to the garage (at the bottom of the garden, so maybe 30m of wire) is a bit underspecced for what I need. Upgrading this would give me more chance of getting the correct voltage, and would probably make sense if I plan to put any "unused" power back to the grid. If the panels/inverter were grid-tied, what voltage would I end up with in the garage while running the roaster? My assumption is the amps will flow from the inverter to the roaster, and the grid will not have any effect? However, that's where my concern is - if my local voltage is higher, will that then default to pushing back to the grid and pull my voltage down?
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    What I really want is to use fill the batteries during the day when our loads are low, and use them in the evening (induction hob, washing machine etc.) when the loads are higher - peak shaving.

    There are systems about that'll do that sort of thing - one of the IET publications talks about them at some length. It's not a trivial problem to solve - generally you'd want to regulate inverter output (and battery charge) according to overall household demand, available local generation, and possibly time of day and/or market electricity price (if you're on one of the smart meter tariffs that offers lower prices at times of low national demand). At the very least you'd need some current sensors a long way from your garage!


    Then there's the issue of grid-connected inverters - as soon as you start exporting back into a grid connected system there's a whole stack of legislation and technical standards to comply with - not least so DNO workers can't be endangered by a cable that's disconnected from their supply, but possibly back-fed from yours. Commercially produced inverters will be type-tested to show compliance - that wouldn't be economic for an experimental setup.


       - Andy.
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    What I really want is to use fill the batteries during the day when our loads are low, and use them in the evening (induction hob, washing machine etc.) when the loads are higher - peak shaving.

    There are systems about that'll do that sort of thing - one of the IET publications talks about them at some length. It's not a trivial problem to solve - generally you'd want to regulate inverter output (and battery charge) according to overall household demand, available local generation, and possibly time of day and/or market electricity price (if you're on one of the smart meter tariffs that offers lower prices at times of low national demand). At the very least you'd need some current sensors a long way from your garage!


    Then there's the issue of grid-connected inverters - as soon as you start exporting back into a grid connected system there's a whole stack of legislation and technical standards to comply with - not least so DNO workers can't be endangered by a cable that's disconnected from their supply, but possibly back-fed from yours. Commercially produced inverters will be type-tested to show compliance - that wouldn't be economic for an experimental setup.


       - Andy.
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