Upgrades - Battery & Inverter

[solerpowor!]

I have a grid-tied 10k system with 23 Hanwha Q.Cell monos (305W/ea; ~7kW) and some 360W polys rounding out the remaining 3k. I'm using a SolarEdge SE7600H-US. The system runs great. Total installed cost gives us an ROI of something like four years which is acceptable to me!

Anyway, I want to add a battery. There are two reasons for this:
First - I want our refrigerators (qty2) and freezers (qty2) to keep running during a power outage.
Second - I want to be able to use my solar installation during a power outage which you cannot do without a battery.

Numbers -
According to my inverter's history, I have about 9.0hrs of ~2.5kW solar exposure in August (hot/humid combo for us). This means I need to run off of a battery for up to 14h 45m in August (avg Aug temps are 105*f - 80*f with humidity) to keep the appliances running.

According to online resources, a fridge uses about 1.5kW a day. 1.5kW/day * 4 = 6kW/day. 6kW * .62 [14.75hrs of 24.00hrs] = 3.72kW to ride through the night. Does this seem reasonable?

So - the questions are:
1.) What is the most cost-effective inverter+battery combination available to deliver a 7.5-10.0kW output that will also allow a battery connection? I would prefer to have an inverter that is battery agnostic but I know most of the big brands will impose limits on the brands of batteries that I can use.

2.) Are there "silent" batteries that we can mount in a bedroom closet or will they all have an electrical hum/cooling fan that will disturb light sleepers? I want the battery in a climate controlled area instead of exposed to the elements or even in a shed if it can be avoided.

I plan to source the battery and inverter independently and hire out the install unless it's something that can be done DIY.

Alternatively, is there a way to install second a small inverter and dedicate some panels to charging batteries and powering a couple circuits that feed the refrigerators? Will this be able to keep the main inverter online during an outage? This seems like a much more complicated option.

 

[chrisski]

Grid tied batteries are beyond me. What gets me lost is the permitting and inspection process for a grid tied system.

A coworker looked at expanding his system with a Tesla powerwall to his 10k system but installer said this only came with a purchase of 5 kw of panels.

 

[DThames]

Adding batteries to an existing grid tie system has some challenges, which often depend on the existing equipment. I have a grid tie system with micro inverters, so I for sure would have to buy an inverter to run off of the batteries during an outage. Also, I am grid tied with an agreement with the power company. I can't really change my system without going back to the power company with my change plans and go into all of that again with them. So we added a separate system for emergency power. We added a subpanel and moved some circuits to that panel. The panel has a dual input, one way feeds off the grid, the other way feeds off the standby inverters. That second system has batteries, inverter/charger, and solar panels to charge those batteries and also extra power so (in a power out event) we can run some things during the day and be charging batteries at the same time.

Depending on your PV strings that are coming in, you might have the option to buy an inverter/charger that in the event of a power outage, you could switch a PV string over to that charger. When the power was normally up, the batteries could be maintained by a grid powered charger. "All In One" units have grid charger, solar charger, and inverter all in one box. If you could use one of your DC stings in a power out event, you would not need "extra" panels for your emergency system.

 

[pollenface]

Grid tied batteries are beyond me. What gets me lost is the permitting and inspection process for a grid tied system.

A coworker looked at expanding his system with a Tesla powerwall to his 10k system but installer said this only came with a purchase of 5 kw of panels.

A friend of mine was trying to get a Tesla dealer to sell him a battery for months, same thing, they wouldn't talk to him unless he was purchasing a complete system. He did eventually find an installer to do it but shortly after recceived a dirty letter in the mail from the utility company stating that "because he had installed a battery and become semi-self-suffcient, his feed in tariff would fall to zero cents/kwh." They don't tell you that in adverts. This is Western Australia