Adding batteries to solar edge se11400h-us inverter

Welcome to the forum Derrickp,

From what I can see--Yes, you are correct. This inverter is a Grid Tied Inverter that is used to take energy from the solar array and pump it into your local breaker panel--And feed your local appliances and any excess power back through the utility meter (turning it backwards) to reduce your bill.

The GT Inverter is designed to turn off when the AC mains fail for everyone's safety. And typically, the GT inverter is isolated from your backup genset (GT Inverter disconnected from genset by the transfer switch--Most Generators do not like being fed energy from a GT Inverter--It can damage the generator).

The above is a very short answer to a very complex question. There is a long set of answers too--But lets ask about what you want to backup with Off Grid (or Hybrid) AC inverter and battery bank.

What loads do you want to run? A refrigerator, lights, maybe central heat and a well pump? How often do you lose power (few days a year, a month at a time after an ice storm)? Roughly, where is your home located (amount of sun)? Or do you want to run the whole place (fridge+, electric stove, water heater, "everything") and, again, for how long (hours, days, forever--Such as transition from utility power)?

Again, a short answer is that your system is the least costly/most $$$ efficient setup for a typical home. GT Solar is cheap, can have a good return on your money (utility rate plans, state PUC regulations have a big effect here). And the genset basically only costs you money (fuel) when the power is out (days or a week a year usage).

Looking at your loads... A 12 kWatt GT Solar system suggests that you use maybe 24 to 48 kWH per day or ~720 to 1,440 kWH per month. That is around the USA/North America average for a home with substantial utility loads (around 500-1,000 kWH per month is "average").

If your 24 kWH genset is 1/2 loaded--Or 12 kWatt (12,000 Watts) of load--And you look at a 12 kWH battery bank--The battery would last you about 1 hour (or less) for off grid/emergency backup power--Not very much. If you only need a little backup power (fridge, LED lights, small water pump, laptop computer, cell phone charger, etc.), you may get away with 3.3 kWH per day (or 100 kWH per month). And a 12 kWH battery system may last your 2-4 days of storage (excluding solar charging/genset running).

Once you have decided on how much energy (Watt*Hours or kWH per day) you need--If this is short term (days/week) or long term ("going off grid" for 9+ months a year)--Then can look at your existing GT Solar and backup genset and figure out what hardware you need to attain your goals.

Just beware (rough numbers to follow)--A genset may cost $1.00 per kWH to run (and near zero costs when not running). And full off grid solar may cost $1-$2+ per kWH (you may much of the money "up front" and pay more when the battery bank wears out (5-7 years typical--Perhaps longer with LiFePO4 batteries) and the electronics die (around 10+ year life, solar panels 20+ year life). Vs--What you presently pay for electricity (somewhere around $0.10 to $0.40 per kWH for much of the US).

And off grid backup solar is >>$2 per kWH (if only used days or a few weeks a year).

There are lots of details I have skipped over... Sort of need to know what your needs may be prior to diving into more technical (and confusing) answers.Your thoughts?

-Bill

The typical solution is to use a Hybrid AC inverter connected to the battery bank. AC1 input to grid, AC2 optional generator AC input, and AC out to your loads--Either the whole home, or a subset of your home's power for emergency/off grid power (i.e., may avoid powering an electric water heater, baseboard heating, etc... Power lights, washer & natural gas/propane dryer, fridge/freezers, optional induction cook top (or use propane/natural gas stove), etc.. All solar panels connect to MPPT solar charge controllers what are then connected to the battery bank (or an "all in one" hybrid AC inverter black box). The solar panels charge the battery bank, and the hybrid inverter "manages" the battery bank charging--Use AC1 utility power for home to AC out when battey bank needs charging (could use AC1 for charging too--depending on configuration programming). Once battery bank is full, hybrid inverter dumps power out to AC1 for use inside the home, reducing utility usage, or even back feeding power to the grid (more or less like your present GT system does--With battery storage on the side).

There is a possible alternative scheme. Basically the same as above--But no solar charge controller. GT Solar inverter is connected to AC Out... With utilitiy power functioning, works just like your GT solar system with a backup battery bank. If AC mains fail, hybrid inverter switches to Off Grid Mode, and the GT Inverter supplies power to AC out--Between the Hybrid inverter and GT inverter, modulate AC frequency... Hybrid inverter outputs 60 Hz, GT inverter outputs 100% of available solar power (run AC loads, hybrid inverter charges battery bank). When bank is full/AC loads are light, hybrid inverter modulates to 59/61 Hz, GT inverter backs down 0% output (throttling back GT inverter) to keep your AC Out voltage at 120/240 VAC and not over charge the battery bank (there are different feedback methods to control GT inverter output--Just one example). Obviously, whatever Hybrid Inverter you choose, it must be compatible with the GT system you have today (and the hybrid inverter must be larger than the GT inverter system (must be able to sink all GT inverter power--Again, details matter a great deal here in hardware choices and system configuration).

We still have not really talked about your AC loads for the home... 2.5 MWH per month (your GT harvest--Summer/winter/average?) is:

• 2,500,000 WH per month / 30 days per month = 83,333 WH per day
• 3 * 10 kWH battery bank * 0.70 typical cycling (20% to 90% State of charge range) = 21,000 WH per cycle
• 83,333 WH per day / 21,000 WH stored energy = 4 hours of "off grid power" (based on your GT system)

So we have a pretty big disconnect between what seems to be your daily loads vs the size of storage you are looking at...

Just to give you an idea of a "rule of thumb" system design. Say we start with your battery bank. 2 days of storage and 70% of capacity (20% to 90% SoC for longer battery life). You could back down to 1 day of storage (2x more daily loads) if you don't have longer periods of clouds/have a backup genset.... Choices...

• 21,000 kWH of useful battery storage * 0.85 AC inverter eff * 1/2 days storage = 8,925 WH per day
• 8,925 WH per day * 30 days = 267,750 WH per month = 268 kWH per month

Typical north American home uses around 500 to 1,000 kWH per month... Suggest getting to 300 kWH per month with some conservation. Get to 100 kWH per month for maximum conservation (smaller home, very energy efficient, using propane/wood/natural gas/etc. for heating/cooking/hot water).

Of course, there is energy used during a sunny day (i.e., battery bank is only used if AC power fails, and sun is down to power evening/night time loads)... Typically break AC loads into "base loads" (loads that must run sun shine or not such as lighting, refrigerator/freezers, well pump for home water, work computer, etc.) and "optional loads" such as irrigation pumping, electric cooking, washer/dryer, TV/entertainment system (when sun is shining, OK to use backup genset, based on good weather forecasts, etc.).

I don't "know" if you are using 2,500 kWH per month or not--In California we have to design our GT systems to, on a yearly average, "break about even" on power used vs GT power generated... During summer, we "go negative" on our bill (bank our power). And during winter we use more power than we generate (draw from bank)... At the end of one year, either we pay the for the extra utilty power we used, or if there is a balance in the bank, it is reset to zero and we start again (excess power generated is "lost"--Although, we can get a little money back these days for extra power generated).

Another issue to understand... Li Ion battery banks almost always have/need a BMS (battery management system). Lithium batteries if you go "outside" 0-100% state of charge (over discharge, over charge), you ruin the cells (almost?) immediately. A BMS can be "simple" (cuts off the battery bank is outside allowed per cell voltage range--Lose all DC system power--More or less an "emergency" shutdown). And/or it can communicate with the Hybrid Inverter/Solar charging system to keep the battery bank within the limits and handle things more gracefully (force less charging, start genset, etc.). Also BMS can feed status back to the inverter/charging system for user review (logged data, available via Internet, etc.).

Anyway--I suggest that you better understand your loads--Daily energy budget is more useful than monthly numbers (remember, your battery bank only stores a day, or a few days of energy--You cannot store/use energy from last week for the next two weeks, etc.).

And talking about battery bank, hardware, etc. design/costs/etc.. without knowing your daily loads--Is difficult to size a system for (are you really looking at 83 kWH per day average, or closer to 3.3 to 9 kWH per day for "power fail" emergency usage)?

Energy needs are a highly personal set of choices. The system needs to meet your needs--Not my guesses at your needs or based on what "works for me". Start with your loads and work on "paper designs" first. Once you have sized the system, you can start looking at hardware specifications and costs next. Designing a system without a "loads" target is pretty difficult. You may end up with an over/undersized system that either does not match your true needs, or is overly expensive to run/maintain.

If you have reasonably stable AC mains power (few hours to few days a year power outages)--Your present GT Solar system plus adding a backup generator system is probably the most cost efficient. GT Solar just "works" for decades without much/if any maintenance. And the genset only costs you fuel when it is running. And you have fuel choices--Gasoline or Diesel... Or Propane/Natural Gas... Or even tri fuel gensets (gasoline, natural gas, propane, etc.). Fuel storage, noise, and fumes are always part of the design--How much can you do/accept? Neighbors? City/county Codes, etc...

If you are looking at months of power failure (ice storms, rural area) or what to look at "going off grid" (personal "green" program, don't trust utility, don't trust society), that is different set of questions that off grid solar can help (saving money on power--Not usually--Hybrid systems end usually costing more $$/kWH than utilty power--Plus you pay a lot of money "up front" for the install).

And if you decide to move forward... Will you do the design/install... Will you have an installer? Who will do ongoing maintenance? What if something breaks--Will installer/mfg be there to back you up/do the work? Stuff breaks/wears out. 10+ years down the road electronics fail, battery bank replacement, etc... Money in bank to take care of. Fitting 10 year new hardware into 10-20 year old system, etc... (mix and match old and new solar/off grid/GT equipment/panel/etc. is not always easy).

-Bill