Gridtied AC coupled batt inverter/charger, and contingency operations

[Hedges]

24 seraphim 425's.

That's 10kW (STC), probably 8.5kW (PTC), barely over the continuous wattage figure we've heard. Should produce about 40 to 45 kWh/day in the summer.
If you can orient some toward AM sun and some toward PM, could give more hours of good production without exceeding that undocumented 7.2kW AC limit.

nice bank of 16 of the 310AH lifepo4's

17kWh, nice amount of backup. PV can recharge at up to 0.5C
That battery gets you through the night, and daytime 40% of PV recharges it while 60% runs AC loads.

 

[opticalcarrier]

ill be all afternoon sun - the garage faces SSW and is the only feasible location for panels to collect light.
still, i think ill be *very* pleased here.

also, i have considered the fact that 40-45 kWH/day generation will probably be about half my needs. given that ill only be generating that during a 6 or so hour period (correct me if im wrong here), it comes to mind that in many cases i wouldnt even be using all the power I generate.
its flat out unfeasable to sell power to the POCO (I sell to them at half the rate they sell to me (8c vs 3.5c) plus the deal requires me to pay an even EXTRA $25/month fee. so instead of selling any extra to them maybe i should just bank what I dont use, then empty the bank after the sun goes down?

 

[Hedges]

Sounds like zero-export is the way to go then. System should be able to power A/C plus charge your battery during the afternoon.
I'm not familiar with what Sol-Ark can be programmed to do, but if you had time of use rates then shaving peaks into the evening, otherwise draining battery at a lower rate such that if a power failure occurs your power stays up on battery until PV begins producing again.

My deal is better (for now). I get credit at same rate I pay, but the rate varies with time of day. I pay $10/month fee (maybe that's a minimum charge and not a fee on top of $10 worth of electricity if I am a net consumer.) For now I say, because my 20 year anniversary of permission to connect comes around soon. I think I'm moved to NEM 2.0 at that point, maybe not too much different.

One degree of freedom you have with the panels is flat vs. sloped on the roof. The south most area could have panels parallel to the roof (just a few inches up for cooling.) The North end you could consider sloping the panels toward the south. In my area we're allowed up to 18" high without mechanical permit, so a pair of rails running down the fall line of the roof could be on short and tall standoffs, tilting the panels. If more than one row you have to decide how far apart to avoid shading the next row.

6 hours is 90 degrees rotation of the earth, so from 45 degrees off-angle one way to the other way. Within that sweep of the sun, area of panel presented to the sun ranges from 0.7x to 1.0x back down to 0.7x panel area. There is some power produced outside those times.

 

[Ampster]

That is a DC to AC ratio of a little above one to one and should work well. Later if you find you need more solar generation you can incrementally add micros/panels a few at a time. Keep us informed.
What is the tradeoff of 48v DC pump vs 240v AC? There are some discusions about well pumps on other threads, but I have not seen that isdue discussed.

 

[fafrd]

Sounds like zero-export is the way to go then. System should be able to power A/C plus charge your battery during the afternoon.
I'm not familiar with what Sol-Ark can be programmed to do, but if you had time of use rates then shaving peaks into the evening, otherwise draining battery at a lower rate such that if a power failure occurs your power stays up on battery until PV begins producing again.

My deal is better (for now). I get credit at same rate I pay, but the rate varies with time of day. I pay $10/month fee (maybe that's a minimum charge and not a fee on top of $10 worth of electricity if I am a net consumer.) For now I say, because my 20 year anniversary of permission to connect comes around soon.

When did you enter into your agreement???

I think I'm moved to NEM 2.0 at that point, maybe not too much different.

The biggest material change from NEM1 to NEM2 is that you will pay ~10% tax on the value of each and every electron you take in from the grid (regardless of how many electrons you may have supplied to the grid). Without use of a battery to self-consume off of stored energy rather than take your nighttime power from the grid, it’ll amount to close to 10% of your old electrical bill (though PG&E has been raising rates every year, so your non-solar electrical bill would quite a bit higher now than it was almost 20 years ago!).

One degree of freedom you have with the panels is flat vs. sloped on the roof. The south most area could have panels parallel to the roof (just a few inches up for cooling.) The North end you could consider sloping the panels toward the south. In my area we're allowed up to 18" high without mechanical permit, so a pair of rails running down the fall line of the roof could be on short and tall standoffs, tilting the panels. If more than one row you have to decide how far apart to avoid shading the next row.

6 hours is 90 degrees rotation of the earth, so from 45 degrees off-angle one way to the other way. Within that sweep of the sun, area of panel presented to the sun ranges from 0.7x to 1.0x back down to 0.7x panel area. There is some power produced outside those times.

 

[opticalcarrier]

my rates are static (local co-op, not the big "AL Power" poco) and dont vary at all, not even winter/summer differenting rates.
ok that panel tilting thing is probably waaay too advanced for me right now though (also b/c Ive already ordered all the racking), but I do like the concept.

Re: pumps - Since an AC pump has a high-wattage starting surge, they were saying to just remove that from the equation (from the critical loads panel and the inverter) altogether and going with a DC well pump.

 

[Hedges]

When did you enter into your agreement???



The biggest material change from NEM1 to NEM2 is that you will pay ~10% tax on the value of each and every electron you take in from the grid (regardless of how many electrons you may have supplied to the grid). Without use of a battery to self-consume off of stored energy rather than take your nighttime power from the grid, it’ll amount to close to 10% of your old electrical bill (though PG&E has been raising rates every year, so your non-solar electrical bill would quite a bit higher now than it was almost 20 years ago!).

I think it was around March 1st, 2003.

Is that a cash tax of 10% on what I draw? In other words, generating 110% of consumption won't pay for it?
If so I should implement load control - cut off power to refrigerators/freezers after dark. Maybe store heat in a water tank while the sun shines.

 

[Hedges]

my rates are static (local co-op, not the big "AL Power" poco) and dont vary at all, not even winter/summer differenting rates.
ok that panel tilting thing is probably waaay too advanced for me right now though (also b/c Ive already ordered all the racking), but I do like the concept.

Re: pumps - Since an AC pump has a high-wattage starting surge, they were saying to just remove that from the equation (from the critical loads panel and the inverter) altogether and going with a DC well pump.

Tilting would be a leg between stand-off and rail, maybe 6" to 10" long. I would also do some triangle braces.
If you have the rooftop area, you could space some of your rails further apart to allow tilt in the future.
I think it is vertical rails rather than horizontal which would allow this.

Consider a Grundfos well pump, inverter drive with zero surge.
(I don't know if those are power-factor corrected; see if people have any issues driving them from inverters, especially transformerless inverters.)

 

[fafrd]

I think it was around March 1st, 2003.

Wow, a real old timer / early-adopter!

Is that a cash tax of 10% on what I draw? In other words, generating 110% of consumption won't pay for it?

Yes, exactly. You cannot pay for this tax through over generation credit.

If so I should implement load control - cut off power to refrigerators/freezers after dark. Maybe store heat in a water tank while the sun shines.

Yes, you’ll need to self-consume as much of your solar-generated electrons as you can (and minimize what you draw from the grid).

My goal is to cover 100% of consumption during peak summer season.

That’ll reduce my overall grid consumption to <50% what it has been

The generation credits I use to charge my EV will cost me ~10% of what it would have cost with no generation credits at all, but $6 to $7.50 per 100 miles will still be much cheaper than paying for gasoline at $20-25 per 100 miles...

 

[Ampster]

MI or the tigo rapid shutdown modules have any automatic ability to disconnect everything

The rapid shut down is intended to be manual shut down by firefighters. What process would you want to automatically shut them down? The arc fault circuitry is automatic but it is not panel level like RSD needs to be for firefighter protection.

 

[Hedges]

Yeah, I paid to pave the way for you (and the rate payers who funded my 50% CEC rebate paid as much as I did.)
Wasn't a savings for me, more like break even. Not like now when PV panels are $0.35/W rather than $5/W.

If rate is $0.30 and I have to pay $0.03 cash for a kWh banked and used later, that is still cost effective vs. buying batteries for storage.

Thermal storage may be competitive, especially if I already own it (freezer), just need to add a shutoff mechanism. Could have a second thermostat to re-enable it it crosses a higher temperature threshold. Water tank for domestic heat? Maybe a wading pool in the basement, with heating ducts diverted through a heat exchanger.