Quote:
Originally Posted by NeilBlanchard
Rob, how many of what type of batteries do you have in this system?
Are you 100% off the grid, and how much do you use on a typical day/month/year?
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Hi Neil,
I have 8 Rolls 530S batteries in series. 530/2 x 48 = ~ 12.7KWH.
Here's what I'm trying to say about being off the grid. When I originally started designing my system in 2006 this is the direction I was going. Now we have intertie/off grid inverters (My two Outback GVFX3648 inverters). When the grid is up my inverters send power back to it, only after my batteries are fully charged. The second criteria is how much energy my dedicated circuits* are using. If the sun is out then those circuits are running from my modules. Any extra power above what I'm using gets sold to the grid as intertie.
If the grid goes down then I run off grid on my batteries. So technically I'm not off the grid and that's better. I could shut off the intertie and run off grid but my batteries would come into play when the sun went down and their life would be diminished from use. The way it is now my batteries only get used during a power failure which happens here 3 or 4 times a year and the batts will last much longer.
Let's say the grid is up and it's night or overcast and my critical circuits need power. The grid supplies it, not my batteries but the next day when the sun comes up I sell that power back to the grid so I'm not buying power in the long run.
I don't need dump loads, relays to switch off, etc., the grid is my dump load, I guess you could say.
The figures are just starting to come in as my previously off grid system is only working for a couple of months as intertie/off grid (before the inverters were modified it was off grid only). Last month I generated over 1 MegaWH above what I used which all got sold back to the grid.
Since I have two systems, the intertie at 6.4KW and the intertie/off grid at 4.2KW the strictly intertie has no batteries to back it up so I lose that power when the grid goes down. With the 4.2KW system easily running my house I'm not concerned but I'm adding wind to run here also. We get good wind across my 4 acre front field, especially in the winter (I've been monitoring weather for several years) and that will compliment my PV. I also have a small stream that runs well in the spring and fall that I want to make in micro-hydro for.
*About dedicated circuits:
For those of you who don't know how sub panels work, I use a sub panel with all my important breakers on it, freezers, well pump, fridge, critical lighting, etc. This sub panel runs off my intertie/off grid inverters constantly regardless whether the grid is up or down. When the grid is down the batteries feed the inverters and are charged by PV. When the grid is up PV runs the inverters or if the sun is down, the grid runs them.
The only time I would need a dump load is if the grid went down for a very long time and if that happens I'll add one. Right now All my generated power gets utilized and dumps aren't needed.
What you want to do is conserve you system and batteries as much as possible. So use the grid when
you need it and you'll have the best of both worlds.
Sorry for the long post,
Rob