I'm over my head

[Brush Ape]

Brush Ape, Your only problem is that your battery bank is about half the size it needs to be for an AGM bank. The rest of the system will work fine. If I were you I would contact Vmax Battery and tell them that you bought the wrong size battery. See if you can send them back and get 8 of the 350AH 12 volt AGMs. The 350s are 769 bucks, 6160.00 total and the best price I could find by far. It won't hurt to ask, if they won't you can still sell them as new to someone as another poster said. The 350s would be set up like your 175s, 2 strings of 4 for a 700AH bank that will take up to a 200 amp charge. You just need to check the strings once in a while to make sure the voltage is about the same. By the way, the 350AH batteries weight 185 lbs, so 2 couple of guys and a good 2 wheel hand truck are needed. Anyway, that's what I would do. Good luck on the return if you decide to go that direction.

So from the standpoint of where I am now, staying with AGM batteries makes the most sense? And swapping the ones I have for 350ah will get me there from here? This seems to be the most cost effective at the moment. Also, when I do replace the AGM batteries at the end of their life, do I go with something like the Rolls S 1400-EX? Or because I'm grid tied will it never pay for itself as they'll reach chronological end-of-life before I get that much use from them? Does how gently they are used extend chronological life at all? I'm sure proper maintenance extends the life as it does with all things.

[Logan005]

Be hopeful, If your batteries make it 5 to 6 years, that a new better, cheaper technology is on the market. I am hoping the Salt Stack battery will claim the market by then.

[Raj]

The truth is that grid tied battery systems will never pay for themselves. The cost of the system, battery replacements and component failures over time will make recouping your cost all but impossible. However, the whole reason for having a hybrid system is that for a price you get the best of both worlds. Cheap power while the grid is up and when the grid is down you will not be without the basic electrical needs that you prefer. Now back to the batteries, There are differences between AGM and FLA batteries, AGMs more efficient and can take a wider range of charging amps because they have a much lower internal resistance. They are also easier to maintain and tolerate a greater depth of discharge. However they are very sensitive to overcharging and it's harder to diagnose problems because you can't check the SG of the the electrolyte. Careful monitoring and proper settings can help mitigate that. As far as the next set goes, I agree with Logan005, cross that bridge when you get there. Who knows what will be available. If money were not an issue I would say go for a single string of batteries. String imbalance would be one less thing to be concerned about. However, a little additional monitoring could save you a couple thousand bucks. On a different note. The Radian inverter you have has a mode called grid zero. This will allow you to set your self consumption of the power that you generate to what ever depth of discharge of your battery bank that you want. Meaning, you can daily cycle 20 to 30% of the battery bank, except during very cloudy days, to achieve up to 1500 or more battery cycles, while at the same time leaving 50 to 60% available for emergency needs. The whole time you stay connected to and use grid power. This, in your case, could shave off about 8 to 10 kwhs a day of your power consumption depending on how much battery reserve you want. Of course you can also sell to the grid, this would cut your electric bill even more but will not cycle the batteries regularly. Again it will not likely pay for itself, but as long as you have it you might as well use it to reduce your electric bill a bit. I don't look at this type system so much as an investment, but as insurance.

[Sunking]

Brushape it is way to late now, but you really messed up on the design. If your intent was to have power during outages, there are two ways to go about it.

1. Is a conventional Grid Tied system and use a whole house generator with an ATS. This allows you to run everything like normal during power outages. You get to set back and watch your neighbors suffer while you set inside nice and cool air conditioned house, watching TV, drinking a nice cold beverage and eating a hot home cooked meal. Then take a hot shower.

2. With a hybrid system, you size the batteries to only last a couple of house during a power outage. Your Inverter has a small ATS that only allows Emergency loads to operate like a fridge, some lights. amd a recptacle or two to plug in a TV or Laptop. Bare minimum. You use a very small less expensive battery. When th ebattery discharges is when your smaller generator comes on line, and recharges the battery and shuts off. Repeats cycle until power comes back on.

Under normal operation, the panels do not even charge the batteries. Your Inverter built-in charger does that .via commercial AC power or generator. Only during power outagge do any of the panels charge the battery during the day. Otherwise that is what the generator is for. Normally you would not even use all the panels to charge the battery on a large system like yours of 8000 watts. You would only use a small portion of panel wattage to do that if you elected too. Say somethin glike 1600 watts using only 1 charge controller, not 4. That is insanity.

Her eis what you are doing. You store up power in the batteries and sell it to the POCO. Here is the part you will realy find funny, at least I do. Ic cost you $1 in battery cost to make 1 Kwh. You then sell it to the POCO for 12-cents. You are loosing 88-cents for every Kwh you sell to the POCO from your batteries. Your are giving free power away. Pretty funny stuff don't you think? I do.So do most of th eothers once they figure it out. I know you rPOCO is laughing all the way to the bank. You should be laughing too.

I sure would hate to have your friends who set you up like this. You would not need any enemies.

Sorry I cannot help you anymore. .

[sensij]

So from the standpoint of where I am now, staying with AGM batteries makes the most sense? And swapping the ones I have for 350ah will get me there from here? This seems to be the most cost effective at the moment. Also, when I do replace the AGM batteries at the end of their life, do I go with something like the Rolls S 1400-EX? Or because I'm grid tied will it never pay for itself as they'll reach chronological end-of-life before I get that much use from them? Does how gently they are used extend chronological life at all? I'm sure proper maintenance extends the life as it does with all things.

I've been thinking more about this, and from the standpoint of where you are now, I'm not sure any changes need to be made. Your inverter is smart, and that makes a big difference. The excess power that your array can generate won't actually hurt the batteries if your inverter/charger is in float stage of the grid tie function, passing any excess current back into the grid. Your charge controllers are wired into your inverter, as shown in this diagram, not directly to your batteries, right?

The only time the excess power will hurt you is in the following conditions:
1) You've discharged the batteries.
2) You don't have grid power available to recharge them.
3) Your chargers are in the bulk stage during a time of day in which the the maximum charge current in excess of whatever current is being consumed by the active loads is higher than the safe operating limits.

I don't think these three things will stack up very often. Once your utility swaps your meter, and if you've configured your inverter for grid-tie correctly, it should be safe to turn the system on. I would flip the switch at night, so the grid can get your batteries recharged without exposing them to the PV system yet. Even in daytime operation, if you are watching the current going to the batteries and it starts to exceed the levels mentioned earlier in the thread, you could just add some load... run the laundry, dishwasher, whatever it takes to consume the excess current and keep the battery charging at a safe level.

In the meantime, I would suggest spending some more time figuring out exactly what a grid-down scenario means for you. It is not good enough to have a vague idea of what you want to power... you really need to make a detailed list of what will be running, for how long, and estimate the power and energy requirements for each item. One step in the process might be to do a dry run.... One night, flip your main breaker off and run around your house unplugging things, as you suggested. Leave the power off for a couple hours, and with a current meter, watch the amperage coming out from the battery. It isn't perfect, but should give you an idea of how your loads stack up against your battery capacity. It is possible that with the MATE3, the inverter will report this value for you, I'm not sure. Turn your power back and recharge your battery from the grid.

Re-reading the thread, I see you mentioned that you have a Radian load center. Have you set that up to have only your critical loads in it? If so, if might save you some steps, if during grid-down you can just disconnect your inverter from your main service panel and instead have it only power the load center.

One thing you do not want to do is intentionally discharge the battery to offset your loads or feed power back into the grid. As sunking suggests, the penalty to your battery life will far exceed the financial benefit of the energy cost your are offsetting. However, in pure-grid tie operation, which is how your system should operate more of the time, the benefits of net metering will help offset some of the costs of your system. It might not ever pay for itself, but if the value of this system is as insurance, I believe it is still consistent with your goals.