Battery Backup for a Grid-Tied system

[NetComrade]

I feel embarassed. The outbacks were part of the original proposal 3 years ago, I didn't get them because I didn't have that much $$$ at the time. This also has the explanation you were looking for

[QUOTEThe Inverters that best match the panel configuration and also allow for one of the inverters to be connected to the Outback inverter charger are a 5000 and 3000. The 5000w will have 21 panels connected (steep roof) and the 3000w will have the 14 panels on the flat roof. The reason for choosing these inverters is to properly DC load the inverters to as close to max DC input as possible (refer to the same web page you sent a link to). The 3000 allows for 4050W/ DC, we will be inputting 3920W. The 5000 allows for 6750W and we will be inputting 5880W. [/QUOTE]

Found AC Coupling Outback/SolarEdge doc.. I think it's what I am looking for. Thank you for your kind pointers.

http://www.outbackpower.com/downloads/documents/technotes/ac_coupling_tech_note.pdf

[NetComrade]

Link below for the diagram by folks that installed my system including 2 solaredge and one outback. In followups they recommended to replace one of the solaredge with a scneider w6848 for the following reason

This past year we installed 20 or so fairly complex systems and, one thing we have learned is that battery back up systems work better if some of the PV is DC connected.

http://www.mtvsolar.com/Resources/Di...ckACCouple.pdf

[ButchDeal]

Well I guess that is why you are so confused. Dealing with mtv solar in WV.

[NetComrade]

ok, upon reading a few more threads on the radian, i think i will stick with the "ROI" advice and just get a generator and wait for something that plugs into solaredge... especially since I am already wired for one, and have one (just need to fix it)

maybe I'll get solar heated water instead this year.. was looking for a quick an easy write off

thank you all and I appreciate the educated and "common sense" responses.

[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.

[ButchDeal]

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

[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

[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]

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]

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

[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

[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.

[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....

[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]

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.

[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.

[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?