Trying to understand the goal total energy cost offset vs a percentage

[BudT]

Sorry if the title was not real clear, but I have seen some conflicting reports. My original goal was 100% offset of our energy bill w/ exception of required monthly charges to stay grid tied. Some information for reference is listed below:

*Current Annual Usage is 32,500Kwh averaged over 2 most recent years. Hoping to work this down through upgrades in appliances as needed and a more conscious use of the resource.
*No major increases in consumption expected, w/ exception of possibly 1 or 2 EVs in the future.
*Using a bifacial 460w panel on a ground mount and 5.33hrs of sun, it looks like it would require 36 panels ....... 460x36x5.33x365=32,216,652/1000=32,216Kwh
*Our monthy bill has averaged $325 for the same time period.
*Net metering buyback is about 0.5:1.0 w/ Entergy Texas.
*Plan originally was to install a battery system as well, but as another member pointed out, being grid tied with net metering has similar benefits without the battery expense. The thought here was for surplus generation usage at night (1:1 vs 0.5:1) and outages. For outages we have a fairly large portable generator, 12.5kw surge, and could eventually install a standby.

My thoughts are, with energy cost only going up, and the benefit of the tax credit, it would seem logical to target a 100% offset, or as close as possible. However, I have seen some make statements that based on the ROI, 50% offset was the right target for them. I guess I just want to be sure that there is not something that I'm not thinking about. If there is, then going with a smaller array, ground mount system, and one Sol Ark 15 instead of 2 (I have 2 - 200 amp panels) would make a substantial difference in the initial cost of the system. Kinda starting to struggle a bit from information overload on this topic, so if I forgot to include some info, please let me know.

 

[BentleyJ]

You mentioned Sol-Ark. Unless you are sure you will be adding batteries to the system at some point, you don't need that type of inverter. It would be worthwhile to consider going with a larger grid-tie only system. Enphase microinverters for example would simplify the process a great deal. The new IQ8 series can even produce power when the grid is down without batteries. Although this has limited utility since it doesn't help at night or during rain storms.

Some quick napkin math as I like to call it.

If NET metering is 0.5 :1.0 then the proposed 32,216kWh system will not yield NET 0 utility usage because all of the generation is done during a 6 to 10hr period, 8hrs avg. During that 33% of the 24hr day the credits are building up but only at 50% value. Off hour electrical usage accounts for 67% of the 24 hr period at 50% value = 33%. Overall the system should yield a minimum of 67% annual savings. Its probably true that a larger part of your consumption would be during the day so the savings will actually be greater than 67%. Lets be generous and say 75%.

Average monthly bill is $325 x 0.75 = $244
$244 x 12mo. = $2,900 in annual savings. In 10 years that is $29,000. (probably more since you'll be off setting higher rates in the future)

If the proposed Sol-Ark system (no batteries) costs $30,000 after tax credits you have a 10 yr payback.

The question is this: How much more are you willing/able to spend on a larger PV system or batteries to capture the remaining 25% of the $325 monthly charge? Of course, there is the added benefit of having backup for grid outages.

The remaining balance of the monthly avg utility bill is $81 which is $972/yr. In 10 years that's another $10,000 in savings.
Battery sizing:
32,500kWh x 0.25 = 8,125kWh which is 22kWh per day on avg.
A 25kWh rack of batteries would cost approx $8,000.

Maybe its worth considering batteries.

 

[BudT]

You mentioned Sol-Ark. Unless you are sure you will be adding batteries to the system at some point, you don't need that type of inverter. It would be worthwhile to consider going with a larger grid-tie only system. Enphase microinverters for example would simplify the process a great deal. The new IQ8 series can even produce power when the grid is down without batteries. Although this has limited utility since it doesn't help at night or during rain storms.

Some quick napkin math as I like to call it.

If NET metering is 0.5 :1.0 then the proposed 32,216kWh system will not yield NET 0 utility usage because all of the generation is done during a 6 to 10hr period, 8hrs avg. During that 33% of the 24hr day the credits are building up but only at 50% value. Off hour electrical usage accounts for 67% of the 24 hr period at 50% value = 33%. Overall the system should yield a minimum of 67% annual savings. Its probably true that a larger part of your consumption would be during the day so the savings will actually be greater than 67%. Lets be generous and say 75%.

Average monthly bill is $325 x 0.75 = $244
$244 x 12mo. = $2,900 in annual savings. In 10 years that is $29,000. (probably more since you'll be off setting higher rates in the future)

If the proposed Sol-Ark system (no batteries) costs $30,000 after tax credits you have a 10 yr payback.

The question is this: How much more are you willing/able to spend on a larger PV system or batteries to capture the remaining 25% of the $325 monthly charge? Of course, there is the added benefit of having backup for grid outages.

The remaining balance of the monthly avg utility bill is $81 which is $972/yr. In 10 years that's another $10,000 in savings.
Battery sizing:
32,500kWh x 0.25 = 8,125kWh which is 22kWh per day on avg.
A 25kWh rack of batteries would cost approx $8,000.

Maybe its worth considering batteries.

Well, it is said that experience is the best teacher. Unfortunately, right now I am so inexperienced on this subject, that it is difficult to phrase a question well enough for y'all to understand what I am trying to ask, lol! You understood me perfectly and thank you for the generous answer. It is really good information backed up by figures I'm still struggling to know how to look for. What I do know is this is going to be a substantial investment in a purpose that I believe in. I want and need to get it right the first time. The more I dig in to it, the more I need to come up for air to digest it. From your answer I believe we are on the same page as to the value of the batteries and the role they would play in the capturing 100% of the value as opposed to a 50% value at buyback. Also, the batteries would take the place of the whole house standby generator which will be another $10k +/-. Also, I appreciate your suggestion of the Enphase microinverters, good food for thought that I will look into.

The other member who I mentioned, that pointed out using the grid as my "backup battery" also made a really good point that is worth exploring. As I learn more through reading post from y'all, I realize that there is only one correct answer. The answer requires understanding what you really want and what your goals are, and clearly with all the equipment and knowledge available, that can be very custom and individualized.

 

[BentleyJ]

Also, the batteries would take the place of the whole house standby generator which will be another $10k +/-.

Exactly, you could get something like a 5000W Champion Inverter generator and a stand alone charger just for emergencies. That would be $1,500 or less leaving $8,500 for batteries.

Also, I appreciate your suggestion of the Enphase microinverters.

If you decided to go with a large grid-tie only system and live with the 50% hair cut on NET metering, Enphase makes for a clean install with no inverters hanging on the wall. There would be a combiner box which includes the communication module.
The down side to Enphase is that if you later decide to add batteries their proprietary system is way over priced and undersized in my opinion.