Interface with batteries

[augie47]

Elementary question for you solar guys but I'm way behind when it comes to Solar.
I have a small (7600 watt) solar install with a "Generac" Utility Interface Converter + a battery pack.
Other solar installs I have seen with batteries have been stand-alone or interactive systems but this one has only the connection to the line side service. Since it has to auto disconnect on utility failure, what purpose do the batteries serve ?

 

[Carultch]

Possible purpose #1: zero export and self-consumption. Suppose you had a utility policy that either doesn't allow or penalizes exporting. You could either curtail the solar production, or you could store the surplus in the battery. The batteries are there to keep the power produced on site, to avoid the penalties of export.

Possible purpose #2: taking advantage of a time-of-use value of electricity, to charge during low cost periods, and discharge during high cost periods. This helps mitigate peak demand on the grid, and helps smooth out the power demand vs time curve, as seen by the conventional generation sources. It is rare that you would get a time-of-use meter on a residence anyway, but in a general sense, this is one application of grid-tied battery energy storage. Similarly, grid-tied battery storage can be used to offset peak demand, another issue that rarely applies to a residence.

Possible purpose #3: high DC-to-AC ratios. Suppose you were AC-constrained, but wanted a greater DC rating. When inverters receive more DC power than they can convert to AC, the inverter "leaves sun on the roof" in the form of slightly hotter panels, due to the surplus of DC power that the inverter cannot use. As an alternative to "leaving sun on the roof", you could store in the battery, what you cannot produce as AC. Some inverters allow much higher DC-to-AC ratios when working with their storage system. The batteries allow peak shifting on the production curve, so that the power that would otherwise remain on the roof at the middle of the day, will charge the batteries, and discharge during the evening.

 

[Hv&Lv]

Possible purpose #1: zero export and self-consumption. Suppose you had a utility policy that either doesn't allow or penalizes exporting. You could either curtail the solar production, or you could store the surplus in the battery. The batteries are there to keep the power produced on site, to avoid the penalties of export.

Possible purpose #2: taking advantage of a time-of-use value of electricity, to charge during low cost periods, and discharge during high cost periods. This helps mitigate peak demand on the grid, and helps smooth out the power demand vs time curve, as seen by the conventional generation sources. It is rare that you would get a time-of-use meter on a residence anyway, but in a general sense, this is one application of grid-tied battery energy storage. Similarly, grid-tied battery storage can be used to offset peak demand, another issue that rarely applies to a residence.

Possible purpose #3: high DC-to-AC ratios. Suppose you were AC-constrained, but wanted a greater DC rating. When inverters receive more DC power than they can convert to AC, the inverter "leaves sun on the roof" in the form of slightly hotter panels, due to the surplus of DC power that the inverter cannot use. As an alternative to "leaving sun on the roof", you could store in the battery, what you cannot produce as AC. Some inverters allow much higher DC-to-AC ratios when working with their storage system. The batteries allow peak shifting on the production curve, so that the power that would otherwise remain on the roof at the middle of the day, will charge the batteries, and discharge during the evening.

I want to throw in another newer possibility..
Some invertors can be set to discharge at certain times.
there will be a day when utilities pay MORE than retail for exported power during peak times.
For example, you pay .10 per kWh now for import energy, but during peaking hours the utility will pay you another price for your export other than avoided wholesale rate or higher than retail.
An example would be to pay you .19 per kWh for all exported power to offset having to buy the much higher priced peaking power.
Batteries will help to export should the peaking time be when the sun isn’t at its highest.

 

[RumRunner]

Elementary question for you solar guys but I'm way behind when it comes to Solar.
I have a small (7600 watt) solar install with a "Generac" Utility Interface Converter + a battery pack.
Other solar installs I have seen with batteries have been stand-alone or interactive systems but this one has only the connection to the line side service. Since it has to auto disconnect on utility failure, what purpose do the batteries serve ?

As you stated you have a solar kit that is designed to be connected to the grid or stand alone--not connected to grid. Hence the battery pack.
Some INVERTERS (not converters) are designed for grid tie-in or standalone. For most residential purposes, you need to make the decision whether you want grid tie-in or standalone. This is the first step on deciding to take advantage of solar system.
On STAND ALONE system you intend to become independent and make your own electricity. . . freedom from POCO . You would need storage batteries for this.

On GRID-TIED system you don’t need the battery. . . you will be using the grid to act as your battery. This would be your backup in case your solar system goes south.
In essence, your grid connection is acting like a battery.
Now, the confusion arises when it becomes evident --when you noticed that there is only a connection to the grid : “has only the connection to the line side service” (your word)

In- a – nutshell:

You can only either have one or the other. Grid Tie or Battery Pack solar systems.

Now, the misconception that homeowners have is: why did I lose power yesterday and today (POCO disconnected power because of high winds two days ago) when I have this $30,000 worth of solar panels on my roof?

A 7000 watt solar array and the homeowner’s expectation to run his furnace, microwave and induction stove all at the same time through his 7000-watt solar panels. (duh)
We know it’s not going to happen.

I believe, educating the homeowner through honest pitches by the utility providers and not just focus on business money-making scheme to corral [naive] investors.

This greed also develops as we trudge along the world of finance by enabling solar installers and suppliers while watching homeowners without power shivering in the cold.
We did get our power back last night after that whole day being wrapped up in a triple layer of blankets.

We made it through the day by browsing the web with power from my generator in my Motor Home.

My off-grid solar system (2000 watt) was good for running LED lights upstairs. Could not even run the TV for more than a full length movie.

 

[tortuga]

Possible purpose #3: high DC-to-AC ratios. Suppose you were AC-constrained, but wanted a greater DC rating. When inverters receive more DC power than they can convert to AC, the inverter "leaves sun on the roof" in the form of slightly hotter panels, due to the surplus of DC power that the inverter cannot use. As an alternative to "leaving sun on the roof", you could store in the battery, what you cannot produce as AC. Some inverters allow much higher DC-to-AC ratios when working with their storage system. The batteries allow peak shifting on the production curve, so that the power that would otherwise remain on the roof at the middle of the day, will charge the batteries, and discharge during the evening.

Possible purpose #3 is really interesting.
What DC voltage do the batteries typically operate at in such a system?

 

[Carultch]

Possible purpose #3 is really interesting.
What DC voltage do the batteries typically operate at in such a system?

I found out that "possible purpose #3" is called clipping recapture.

SolarEdge/StorEdge has this option available with a 7.6 kW single phase inverter. It works with the LG Chem batteries at 400V, which coincides with the inverter's fixed DC voltage for the optimizer strings.

Dynapower has solutions that run at 550V-1500V on the battery side, with DC-to-DC converters to interface the batteries to match the solar.