Inverter for grid tie AND off-grid?

[daserra]

Hi everyone, I'm hoping for a bit of advice.
I'm on grid at the moment and I want to initially add 4k of PV to minimise electricity use (not wanted to be on any sell-back scheme but if the meter turns back on it's own well hey..). Later on I'd like to add 600-1000 Ah 48V battery and go totally off grid. I aim to use the transitionary time to find out how much exactly I need (at the moment I'm heating water and running a pool pump with electricity and use 27kWh/day hopefully dropping down to 15 with solar hot water and some economising).
Is there and inverter that can serve these 2 uses and the ability to double up to give 8kW if needed?
I'm in Portugal so PVsolar is a no-brainer.

[stephendv]

For grid tie, you could use an SMA sunny boy.  Then when you want to switch to off-grid, you could buy an additional SMA sunny island battery inverter and you'll need to do some simple settings change on the sunny boy to put it into off-grid mode, then the two will then be able to work together.

It's well documented under the sunny island pages on the SMA site. 

They recommend an island of at least half capacity of the sunny boy, i.e. 8kW sunny boy, and a 4kW sunny island.
Not all the sunny boys can be used in off-grid mode, here's a doc showing compatibility: http://files.sma.de/dl/7910/SB-OffGrid-TI-en-32.pdf

[jonesy]

Even at 15kwh/day and 1000ah battery, you will, in ideal conditions run for 3 days on battery.  But you have to treat the battery with a great deal of respect to ensure a proper life and it has to be fully charged for a period of time on a regular basis.  What would you do after 3 days of no sun? 
That is an enormous consumption - about 20 times mine.  Are you running a business, or a lot of old fridge/freezers?  My largest consumer is my fridge freezer.
There is plenty on this site about going off grid (and batteries), and the general consensus is use grid if you have it; it's difficult to beat the kwh price on grid, and who will repair your off-grid system if it breaks when you are not there and the mrs is? 
I used to be off grid, but haven't looked back since I went on grid.  If you're worried about power cuts get a small genny.

[daserra]

Even at 15kwh/day and 1000ah battery, you will, in ideal conditions run for 3 days on battery.  But you have to treat the battery with a great deal of respect to ensure a proper life and it has to be fully charged for a period of time on a regular basis.  What would you do after 3 days of no sun? 
That is an enormous consumption - about 20 times mine.  Are you running a business, or a lot of old fridge/freezers?  My largest consumer is my fridge freezer.
There is plenty on this site about going off grid (and batteries), and the general consensus is use grid if you have it; it's difficult to beat the kwh price on grid, and who will repair your off-grid system if it breaks when you are not there and the mrs is? 
I used to be off grid, but haven't looked back since I went on grid.  If you're worried about power cuts get a small genny.

Thanks for your reply Jonesy. We are a busy family of four. We run a pool pump at around 3kwh/day, dishwasher, washing machine (at least 1 load /day) and have a htpc on most of the time recording TV, torrents and also acts as a back up device for all the phones etc. I'm still hunting down all the big consumers.
We lived off grid for 10 years in the 90's and we just economised when power was low and sometimes ran a small generator with battery chargers.
We have our own water supply and sewage system and I would just like to not have monthly bills if I can help it and here in Portugal it is much more viable. The power project is still in the early stages and technology has moved on since the last time I researched it all.

[jonesy]

Good  luck in your power hunt.  Your pc is probably around 3kwh/day, plus other devices such as garage door openers, routers, cordless phones, digital clocks on cookers, microwaves, alarms, TVs that are 'off' etc probably account for another 3kwh.  Sadly the meter misses nothing and all those little devices soon add up. American size/large fridges take tons of power too, as do old ones. 

Your post hasnt attracted the usual off griders, so perhaps you need to re-post with a 'how big a battery will I need for 15kwh/day'

[Justme]

Your post hasnt attracted the usual off griders, so perhaps you need to re-post with a 'how big a battery will I need for 15kwh/day'

I think we have all looked in but have all been brow beaten previously trying to get newby off gridders to reduce excessive consumption down to an affordable level.

For example our total household usage averaged over a year is 3kWh per day. Before we were off grid it was 27kWh.

There are 2 adults and a teenager in the house & we regularly have the older kids back for a few days / weeks too.

We have all the normal stuff everyone else has.

[stephendv]

We've had the mini-split Air conditioner on every now and then during the summer.  Peak solar harvest was about 12kWh/day from a 4.4kW array in Spain.  That was harvest, not use, so use could be another 2kWh on top of that during the evening.  An I'd bet we could pull a lot more during the summer.

EDIT: Just went through the logs for summer, and yes we hit 14kWh _solar harvest_ in July.  And the batteries still went into float, so we could pull even more.

[camillitech]

Your post hasnt attracted the usual off griders, so perhaps you need to re-post with a 'how big a battery will I need for 15kwh/day'

I think we have all looked in but have all been brow beaten previously trying to get newby off gridders to reduce excessive consumption down to an affordable level.

For example our total household usage averaged over a year is 3kWh per day. Before we were off grid it was 27kWh.

There are 2 adults and a teenager in the house & we regularly have the older kids back for a few days / weeks too.

We have all the normal stuff everyone else has.

Ditto only mine is 3.5 average over eight years and that's for two properties, two fridges, two freezers and two TV's what on earth do you do with 27kwh per day  I'm building a house which is totally electric, DHW, CH the lot and it won't use anywhere near that.

Good luck, Paul

[Justme]

The 27kWh was when there was 3 adults & up to 4 teenagers all in a big farm house.
Elec cooker & kettle. Heat lamps for the young stock ect.

I also had a butchers business running on the same meter.

I guess also another reason for so few responses is that there just is no cost effective way of doing on & off grid as they want with one device.

[brackwell]

stephen,

Have i got this right? - you have a 4.4kwp solar pv that gives 14kwh/day in july IN SPAIN.  If so that is ridiculously small.  I must have misunderstood.

 daserra,

Purely out of curiosity why would you want to go off grid when you are on grid as opposed to just minimising your on grid consumption to near zero ?

Ken

[stephendv]

stephen,

Have i got this right? - you have a 4.4kwp solar pv that gives 14kwh/day in july IN SPAIN.  If so that is ridiculously small.  I must have misunderstood.

Bear in mind it's off-grid, it only gives us what we use.  So although it's capable of more, we can't use it all   Not in july anyway.

[nowty]

stephen,

Have i got this right? - you have a 4.4kwp solar pv that gives 14kwh/day in july IN SPAIN.  If so that is ridiculously small.  I must have misunderstood.

Bear in mind it's off-grid, it only gives us what we use.  So although it's capable of more, we can't use it all  Not in july anyway.

As a comparison, my 4kw Grid Tie makes circa 4000 kwh's a year but my 3.5kw Off Grid only makes 2000 kwh's as with Off Grid you only generate what you use as there is nowhere to export to.
In summer the Off Grid could generate 1000 kwh's more if I had the use for it.

[billi]

as with Off Grid you only generate what you use as there is nowhere to export to.

i guess  hot water  is some sort of export  and perhaps el. car one day

[clockmanFR]

Hats off to stephendv, he is saving is PV panels so not to degrade them so quickly.   

[stephendv]

Hats off to stephendv, he is saving is PV panels so not to degrade them so quickly.   

Getting a longer life in the wiring too.  Fewer electrons running up and down causing corrosion of the copper