Battery back-up system to complement my Solarcity system.

[90cummins]

Earlier I started a thread titled (SolarCity installing a 6.37kw system on my house!!!)
This new thread is to discuss a Battery back-up System to complement my new Solarcity system.
At this point in time any battery back-up system I may install is not compatible with my Solarcity system primarily because of warranty issues. They will not repair the system if they (find or think) my system may have caused the failure.
So this system will be separate from the Solarcity/grid side and connected to the generator side of my auto transfer switch.
I'm currently looking into a 6kw battery backup system to supplement my new Solarcity system with perhaps 12 hours of autonomy so an outage will not disrupt my routine.
I have gasoline & diesel generators (120/240 volt) for back-up and battery charging purposes but I have been thinking about using a brushless Niehoff 24v 300 amp generator to recharge the batteries and support my battery backup system for prolonged periods.
The reasoning for my consideration of DC is this;
AC generation requires 1800 or 3600 rpm, a DC generator on the other hand requires only enough speed & hp to excite the field to start production and meet the demand load.
This allows fuel savings because the engine may be operated much slower speed for fuel savings, extended life and less noise. The generator voltage is self-regulating and eliminates the inefficiency of creating AC power at 3600 rpm to operate an AC powered charge controller to produce DC power for battery charging purposes.
24v DC generators are simple and cheap to acquire and are easily adapted because of the belt drive.
A 300 amp generator will produce 200A at 24v (4800w) at 2000 rpm generator shaft speed.
The sweet spot for fuel efficiency for a 9 or 10hp Yanmar diesel is 2500 to 3000 rpm at which speed a Yanmar L90 and L100 produce 5.5 and 6.2kw respectively.
At 2250 rpm both Yanmar痴 produce close to 5kw. Based on the output curve of both the generator and engine a direct drive or 1 to 1 ratio would work.
Any thoughts on my plans are welcome.


At this point in time I have the following in place to support myself during a power outage.
1) 6.7hp Yanmar diesel 5kw generator 120/240v
1) Rebuilt Yanmar L90 Diesel with tapered crankshaft.
1) Rebuilt Yanmar L100 Diesel with tapered crankshaft
2) Generac XL4000 generators
1) 25kw PTO generator
1) Rebuilt 6kw Silent Chinese diesel generator which is for sale.
1) 3kw Yanmar generator not running.
Planning on purchasing an 24v AIMs 6kw split phase pure sine inverter/charger.

90cummins

 

[roadhunter]

Wow. I'm not even sure what to say after reading about all your electrical generation equipment. Looks like you have spend a small fortune between the PV system and all the generators and batteries involved. Why?

 

[SPIKER]

Wow. I'm not even sure what to say after reading about all your electrical generation equipment. Looks like you have spend a small fortune between the PV system and all the generators and batteries involved. Why?

agreed seems to be going way overkill, and battery systems usually are between the solar panels and inverters so that the sun charges batteries and when sun goes down the power still flows out of the batteries and into the inverters. Power around here flickers a few times a year and drops out once or twice less than an hour usually only 3 or 4 mins. Even on rare major ice storms is it out for more than 6 hours, a simple 5000 or 7500 watt portable generator can run for days, cost 500 bucks and set for months without issue...

M

 

[dave1949]

My grid-tied system installer said to disconnect (open the breaker in circuit panel) the solar system when using the generator. The reasoning was if the sun is shining during a grid outage, the solar system is effectively feeding power to the generator and most generators don't handle that well.

If you had a bank of backup batteries, then keeping them charged via a normal AC powered charger would seem to be the simplest thing to do.

To make use of the batteries, you would disconnect the solar system from the grid, disconnect your service main from the grid, and using a second inverter dedicated to that purpose, connect the battery bank output to your home's service panel via a dedicated breaker. At that point, it looks electrically just like connecting an AC output generator to the panel.

How long the batteries provide power depends on how much amperage you draw and the capacity of the battery bank.

You could use a generator to recharge the batteries during an outage, or you could disconnect the batteries from the service panel and connect a generator instead.

Without some fancy and likely expensive transfer switch(es), plus risking Solar City saying you are adding non-standard stuff, it would be fairly cumbersome to do all that, plus the expense of the batteries. I'm not sure what you really gain with a battery bank that would be worth it.

 

[MossRoad]

I agree. Just a backup generator would suffice, it would seem.

 

[90cummins]

Wow. I'm not even sure what to say after reading about all your electrical generation equipment. Looks like you have spend a small fortune between the PV system and all the generators and batteries involved. (roadhunter)

It started during the approach of Y2K, that’s when I bought my 25kw PTO generator and my 4kw Generac.
Then I found another Generac for $200 so I bought that.
I’ve had a diesel tractor since the 80’s and bought a Dodge CTD in 1990. The efficiency, reliability and the stability of diesel convinced me to move towards a diesel generator.
Diesel engines can sit for years unlike gasoline generators which gum up.
I also have heating oil on hand that can be used if a prolonged event happens.
I purchased my first Yanmar generator for $450 with issues then bought another Yanmar with issues for parts. They then sat apart for 5 years while I slowly acquired parts when I started to be concerned about the attacks on substations (which are not widely reported).
I found a new Mil spec Yanmar on e-bay and bought it to get it going.
The other two Yanmar’s were rebuilt using $400 I received from a Solarcity referral.
I’m looking to sell the Chinese generator and the Generac’s.
Did I spend a small fortune, not really!
I had several serious medical issues such as two liver transplants, one stroke; I’ve also had my colon removed. Now I have fatigue issues and I don’t smoke or drink!
I’ve had too much time to think about what I should be doing and what I can no longer do.
So to keep my home safe & warm I’ve done what few think is necessary.
I can power my entire home with a 4kw generator.
My 40x60 garage can also be supported by 4kw.
I now have Solar and I’m working on a battery backup!
I PREFER TO BE PREPARED
90cummins

 

[SPIKER]

Be aware that Battery Systems require a lot more maintenance than all your other devices, regular water level checks corrosion mitigation and even well kept systems often only last a few years till replacement of the batteries are needed. Partly as they sulphate up from setting, regular sessions of charging & discharging etc...

Mark

 

[texasjohn]

Wow, 90cummins, you've assembled quite an assortment of power preparedness!! My hat's off to you and best wishes with your physical challenges.:thumbsup:

 

[TnAndy]

Be aware that Battery Systems require a lot more maintenance than all your other devices, regular water level checks corrosion mitigation and even well kept systems often only last a few years till replacement of the batteries are needed. Partly as they sulphate up from setting, regular sessions of charging & discharging etc...

Mark

Depends on the battery, Mark. This is a sealed, 20yr rated AGM battery pack I have on my system. Also have a pulse de-suphatnator on it.

Even with 'normal' wet cells, like L-16's, I see 8-10yrs regularly on them if cycled lightly and minimal maintenance done on them.

The number of times batteries are cycled and the depth of discharge is the real issue on battery life. Kept in backup mode, batteries will last a heck of a long time.

 

[TnAndy]

I PREFER TO BE PREPARED

I tee-totally get that ! (Eagle Scout, Class of 1965)

I went the opposite route of your system, building a 6kw grid tied/battery backed system in stages over several years (2.1, then 3.2, then 6 ) first. Then I added another 5kw of grid tie only (Enphase micro inverters) simply to rid us of a power bill forever. Now we produce, on average, what we use.

Also have two generators, a 5kw Coleman 'cheapie', an 8kw Miller Bobcat welder, and picked up a 4kw 1800rpm Onan I'm going to convert to propane.