Powering a grid tie inverter from batteries

[Heath]

Does anyone know whether grid tie inverters can be powered from batteries instead of directly from the solar panels?

In case you are wondering, I'm not really interested in getting all kitted up for "In Feed" & getting paid for excess generation.

I was thinking that I just need to generate enough power to offset my fridge & other essential stuff which is on all the time. The problem is that I'm not home most of the time so the background useage is higher in the evening than during the day due to lights & TV etc.

If I could use batteries to store any excess generation of power during the day, I could then feed this back in during the evening using the batteries to power the inverter instead of the solar panel.

Any of this sound feasible?

[Baz]

The inverter would drain the battery into the grid. It is rather tricky but options might be complete isolation from mains at night, secondary circuits for just lights/tv, using the fridge thermostat to cut in the battery only on demand etc.

[rogeriko]

Grid tie inverters run on 300 volts plus of direct current this is the sort of thing that high speed trains run on, certainly nothing I would go near. Also how much would 150 2 volt batteries cost??

[Heath]

I had something much smaller scale in mind!

I've seen 300/600/1200 grid tie inverters that work from as little as 14VDC. I probably only need to generate about 300W (start with anyway).

I currently use a single 12V battery, 80W panel & charge controller with a 500W MSW inverter to power lighting and the TV in the evenings (via lots of trailing extension cables, much to my wife's annoyance!).

I am hoping that a small scale grid tie solution could get rid of the cables while still dipping my toe into renewable energy.

What I don't know is how to control the power output if I were to use a battery as a source, unless the inverter limit's it's own output, in which case no problem.

I don't think draining the battery would be a problem, it's pretty much what I do now on a daily basis.

[dhaslam]

The best batteries cost something like  8p  per kWh stored over the life of the battery, not allowing for losses  in charging and discharging.   If you don't have the  option to grid tie then it is the only way   but  it is better to spend extra money on more panels than miscellaneous other bits.         

[Baz]

I was assuming you had a couple of kw. Your little battery will not see out the year. Not deriding your efforts but you have a lot to learn, and it's all here on the forum, somewhere.

[Ivan]

SMA Island and SMA Backup are designed for similar purposes. Not cheap, though.

[guydewdney]

just go on grid - and the amount of leccy made > leccy used = lower leccy bills. The fact that you pull IN during the evening makes no difference to the fact that you make more 'units' over the day than you use - IF you can get your supplier to accept an export meter or meter that runs backwards.

or go off grid like you have already done with a separate circuit (maybe with a changeover switch?) for your telly ring main?