PV newbie

[unicorn]

Sorry if this all sounds stupid, or maybe covered before.
I have a PV system, which has turned me into a miser.
At night when the PV system does not supply power to the house (obviously), can I use a simple setup to keep us going through the night !.
I use around 200 - 400watts per hour during night hours till dawn.
Can I use a 12v car battery with a simple 700watt inverter to power us through the night ?
Can the inverter output be wired across the PV output lines to the board ? (with the PV inverters switched off, I guess)
Is there a lot of switching needed to do this ?
Is the four units used from the grid during the dark not worth saving in the first place ?
I'll start off here with the basic idea before I waffle with a load of rubbish to see what you say.

[dhaslam]

It depends on what your  aim is.     If you want the best return for investment or save expense it is better to  increase PV,   if you don't use the power someone else will use it,  you get paid for it and that  pays  for  your night time  electricity.    If you want  complete grid independence that is a  different matter. Part of the  exercise  involves reducing consumption.  You also need to  use suitable batteries that  will last  and not cost more to replace than the  value of the power stored.   

[unicorn]

Hello,
No I don't want to go completely off grid. The aim was just to use as little of it as possible, and was just wondering if it was a simple matter to offset the nightime usage. But I see what you say about increasing the PV system, although its as big as our electric supplier will allow for a home installation. (6.25KW)
So you are saying just to forget about the small usage at night, that's ok. I wanted some thoughts. Thanks.

[dan_b]

There was a thread on here a few months ago about a company who is launching solar PV grid tie inverter which also has a small battery bank built in for this type of application - to reduce overnight grid consumption. I think it is SMA SunnyBoy?

[dan_b]

Here you go:

http://www.sma.de/en/solutions/medium-power-solutions/sma-smart-home/turn-key-storage-solution.html

Don't think it's launched yet. Not sure what the overall view of the forum is but this would seem to achieve what you're looking to do, although not until next year?!

[M]

Here's another thread about storage (subject close to my heart), with loads of comments about the problems and costs of covering nighttime and other down times. Complex, expensive but certainly on the cards, just not soon enough for an impatient mart.

http://www.navitron.org.uk/forum/index.php/topic,20837.105.html

Mart.

[dan_b]

Conceptually I'd love to be able to add in some sort of plug-and-play, small scale "overnight use" battery storage pack - would be great. Once the ImmerSUN has topped up the hot water tank and offsets the gas cost of my children's many hot baths, then it diverts to topping up a small battery pack that offsets my evening's tv watching.  I don't want to be "off-grid" but would like to be "low-grid".

[todthedog]

Question of size as well, Dan, CM and Biffs storage are not exactly small, although allowing for much greater off grid activity in both time and usage.

[clockmanFR]

Mart what about my little 10.4kwh system designed for her indoors!  . 24v dc at 400ah cost of batts was £360.

http://www.navitron.org.uk/forum/index.php/topic,21161.0.html

Just need to divert, somehow, some of that PV to charge your batts.

Okay I am not using an inverter with this system, as its direct 24v. But you could use a small £150 suitable UPSm needs 24v, like my Pic 1.

And put some change over switches in at the fuse box. 2 pole 3 position, centre Off, Pic 2.

Come on Mart 'you know it makes sense'

[biff]

Dont worry Unicorn,
                        We would not be expecting you to install a system like C/M,s in one evening.
                                                                                                  Biff

[todthedog]

On the seventh day CM rested.
Maybe!

[unicorn]

Very interesting links etc. I see its not as simple as I thought then ! But i'll keep looking at developments. Cheers all.
Victor

[M]

Come on Mart 'you know it makes sense'

You do know that it's ok to take a day off (every year or so) don't you?

I think your 'little' system is sort of what I'd need. But like Dan, I'd really like a plug-n-play setup. Perhaps linked to an inverter replacement as and when they start to fail. I'm hoping that in 5 to 10 years, there will be something simple. Mentioned elsewhere a long time ago, that my ESE is 2.4kWp (13 panels) + 1.2kWp (5 panels) and on 2 inverters, as tricky to find a solution at the time, but now found a Samil3600TL that has the right mix of voltages, and GavinA has suggested a SB3600TL, that would probably be even better, as some shading. So partly looking forward to ditching the 92% efficient (inefficient?) SB1200.

In an ideal world, I'll revisit my idea of adding some SW steep panels (perhaps just 1kWp ground mount) to the ESE system. My DNO approval is on the inverter limits (5.9kW) the panel sizing is irrelevant. So just need a 3MPPT inverter, or go full SolarEdge but that won't be cheap retrospectively. Doubt the tracker idea will 'fly', Wifey's face did not look like it was going to mellow over that one, and I expect it would lose a lot to capping, hence the fixed, steep SW idea.

Keeping an eye on developments, makes me think that there will be a flood of 'reduced grid' kit arriving soon, as the current trickle seems to be growing fast. So fingers crossed for price down / quality up developments. If all the oranges line up, then a suitable inverter with integrated battery could work out well for me.

My problem is that with E/W panels, generation is very low during bottom 4 months, and I'm starting to wonder if battery system losses would outweigh benefits Nov to Feb. I'd be ok, but overall might be better just to export, looking at bigger picture, rather than personal savings. The 'shoulder months' (Mch/Apr & Sep/Oct) could work really well with some storage, and the top months (May to Aug) should be easy, as PV leccy coming out of my ears.

So many ideas, but hopefully not dreams. I reckon by the end of the decade I'll be playing 'reduced grid' too. 

Mart.

[HalcyonRichard]

Hi,
    That 200-400W consumption during the night seems high to me. I tracked down all my consumption with an energy meter. My night time consumption is now 40W - this is the fridge freezer - the only thing left on overnight. Might be very cost effective if you could find out if anything is taking power that you could turn off at night.

Richard

[unicorn]

Sorry Richard, I've just realised your post was to me. Yes the overnight usage. I go to bed with usage at about 60watts. That's with the fridge and freezer off. They do come on occasionally with the peak at about 250watts while they are both on. My mention of 200-400watts was really giving plenty of leeway ! hi. I must get a plug for the sockets and see what the big users are.