Battery Backup for a Grid-Tied system

[NetComrade]

Found this guy using Ac Coupled Schneider SW to "fool" his SolarEdge Grid Tie inverter. Says it works, but grid disconnect is manual. Figured i'd share.. haven't looked too much into it, but seems like a fairly cheap solution

https://www.youtube.com/watch?v=F1q5uIzjj_M

[ButchDeal]

Batteries are expensive, and do wear out. Fuel is expensive, and difficult to acquire during emergencies.

To give you some context: I was thinking of prolonged outages and how much fuel I could save by having a good combination of generator and battery (and at this point I am assuming, bimodal does not care too much if it's connected to grid power or generator power).
<SNIP>

P.S. does bimodal also charge the battery from Grid/Generator?

If you are just looking for backup then the batteries can lost a bit longer as they will be cycling much less.

Most bimodal inverters have multiple AC inputs. OutBack Radian is a good example with several AC connections (3 in total).
In a typical grid tie system with generator, you would use AC connection 1 for the gird, AC connection 2 for generator, and AC connection 3 for emergency panel (your loads that you want up all the time).

Yes the bimodal inverter can charge from the grid as well as from the generator.
You would also (in a DC coupled setup) have MPPT charge controller(s) which would allow the batteries to charge from solar as well as to power the inverter. from solar.

[NetComrade]

AFAIK, PotomacEdison doesn't have differential pricing based on time of day. Furthermore, electricity here is fairly cheap compared to the coasts, it was raised recently, but still at around 0.11 kWh

Batteries are expensive, and do wear out. Fuel is expensive, and difficult to acquire during emergencies.

To give you some context: I was thinking of prolonged outages and how much fuel I could save by having a good combination of generator and battery (and at this point I am assuming, bimodal does not care too much if it's connected to grid power or generator power). On fuel consumption, Onan 20ES 70A generator I have consumes 15lb of propane hourly (at peak). On low end Honda 1000W can run 4 hours on half a gallon. Using an artificial price of $2 per lb for either fuel (and ignoring fuel differences), a big generator can cost $30/hour while a little one $0.25/hour. I would not need as much peak power at the house, but even if my fuel cost was half that, at $15/hour the cost and the logistics hauling it become a challenge.

I have not experienced a prolonged outage in 5 years I have lived in the mountains where all of electricity is at mercy of trees/weather/crazy drivers, as it's overhead. While our house has been spared of multi-day outages, plenty of locations in the neighborhood have been without electricity for up to a week. The cost and fuel related logistics do become a challenge in those situations (gas station is 10+ miles away, and can easily run out), hence my desire to try to balance battery size (initial and replacement costs) and fuel consumption.

2 x week long outages at $15/hr in fuel would pretty much buy a battery ($5K), which i think is pretty feasible in my situation over a period of 10 years or so.

P.S. does bimodal also charge the battery from Grid/Generator?

[Mike90250]

.....I will start thinking on how to integrate a bi-modal into existing setup with it being cost-effective.......

The battery is the costly part, it wears out and needs replacing. You can work the snot out of it, and buy/sell with hours that are advantageous to your billing plan and try to get your battery costs down that way, but leaving the battery idle, so you have a giant UPS running your house, is not cost effective either.

[ButchDeal]

Thanks all for either making fun or trying to address my ignorance.

I did see that SolarEdge + Generator is exclusively prohibited in the manual and voids the warranty. The link I shared above (on the forum) showed a member trying that and SolarEdge showing error (and forum errors commenting that he's lucky something didn't break)

I will start thinking on how to integrate a bi-modal into existing setup with it being cost-effective.

Thanks again for steering me in the right direction.

if you are looking for backup, your other option is to upgrade (replace) the solarEdge inverter with a bimodal inverter. The most straight forward method is to use the SolarEdge version as you will still have the optimizers and just have to replace the inverter. Check out the StorEdge and the LG Chem RESU10H battery. Note that the StorEdge will work without batteries so you can add the battery at a latter time.

[NetComrade]

Thanks all for either making fun or trying to address my ignorance.

I did see that SolarEdge + Generator is exclusively prohibited in the manual and voids the warranty. The link I shared above (on the forum) showed a member trying that and SolarEdge showing error (and forum errors commenting that he's lucky something didn't break)

I will start thinking on how to integrate a bi-modal into existing setup with it being cost-effective.

Thanks again for steering me in the right direction.

[ButchDeal]

I know this thread is 2+ years old.

I wanted to revisit the topic of "fooling" the SolarEdge inverters into thinking they're grid tied when power goes out.

How is power from grid different from power I would generate either via another source.. I thought characteristics of power were fairly basic and consistent between AC and DC.

After recently installing a generator with automatic transfer switch (with some help) at another location and getting more familiar with it, I wanted to revisit this idea

E.g. power cuts off, generator and solar are on same subpanel, generator kicks in..

Read the installation manual. The inverter should be isolated from the generator so should NOT be on the same subpanel unless you have a bimodal inverter.

The problem with your assumption that all power sources are the same is that your generator is NOT a two way device. You can do what you want by AC coupling a bimodal inverter with your grid tie inverter. The grid tie inverter is not two way but it inverts the power it gets from the sun and the bimodal inverter IS two way. It can inverter from battery to rectify AC back to DC and send it to the battery, when there is more power generated by the grid tie than being used.

The generator on the other hand can NOT magically create fuel when electricity is shoved down its throat....

[Ampster]

.......

I wanted to revisit the topic of "fooling" the SolarEdge inverters.....
How is power from grid different from power I would generate either via another source.. I thought characteristics of power were fairly basic and consistent between AC

The grid presents an infinite load to a grid tie inverter. In other words the grid can take all the energy that the grid tie inverter sends it.
Hybrid (bi modal) inverters fool the grid tie inverter into thinking the grid is present. The hybrid inverter also distributes the output from the gridtie inverter to the house loads and charging the batteries. They also perform another important function and that is they can modulate the output of the grid tie inverter as the.batteries get full or the house loads change. They do this by changing the frequency and the grid tie inverter shuts down some or all the panels. It is not the AC that is different it is the management of the output of the grid tie inverter that makes this scheme work.

Generators cannot do this, and, as others have said, the grid tie inverter will backfeed the generator and the smoke will escape.

[Mike90250]

What do batteries have to do, with AC inverters and generators? Bruce Roe

They can be used as ubiquitous diodes and rectify any problems

[bcroe]

Wouldn't the battery bank act as the capacitor?

I did find a thread of somebody actually trying what I describe (w/o the battery acting as buffer).

https://www.solarpaneltalk.com/forum...-battery/page2

What do batteries have to do, with AC inverters and generators? Bruce Roe

[NetComrade]

Wouldn't the battery bank act as the capacitor?

I did find a thread of somebody actually trying what I describe (w/o the battery acting as buffer).

https://www.solarpaneltalk.com/forum/solar-panels-for-home/solar-panels-for-homes-with-solar-batteries/319183-help-me-with-my-system-design-solar-with-generator-backup-without-battery/page2

[bcroe]

This has been explained many times. One problem is the inverter will try and shove its output into the
poor generator if there is not enough load. Another is the inverter will not work with a small generator.
Try not to let the smoke out of your equipment. Bruce Roe

[NetComrade]

I know this thread is 2+ years old.

I wanted to revisit the topic of "fooling" the SolarEdge inverters into thinking they're grid tied when power goes out.

How is power from grid different from power I would generate either via another source.. I thought characteristics of power were fairly basic and consistent between AC and DC.

After recently installing a generator with automatic transfer switch (with some help) at another location and getting more familiar with it, I wanted to revisit this idea

E.g. power cuts off, generator and solar are on same subpanel, generator kicks in..

In case you wonder what I continue to be smoking, the desired goal
Capex:
* try to save some $$ and minimize investment into bigger inverter
* smaller generator
* smaller battery bank, and subsequent replacements
Opex
* less fuel consumption

[ButchDeal]

That is still an AC coupled solution like the outback and Schneider solutions.

[solarix]

You could put in a SMA Sunny Island inverter that creates an "island" during outages to keep your grid-tied system running. Including the batteries and their 120/240 transformer, it is an expensive but elegant way to go.