Can you guys recommend me a system before I do something stupid and spend too much?

[someguyondiysolarforum]

Hi everyone, I have existing solar on my roof with about 14 panels. I believe it is 140w 255w panels. I saw something in the paperwork about enphase micro inverters. I am located in San Francisco and tired of paying PG&E exorbitant rates. I was interested in Tesla Powerwall 3 but I saw a youtube video that said it is not compatible with existing solar panels? I was looking through youtube videos and I was thinking about getting the EG4 18k hybrid inverter along with 30kwh of server rack batteries. I don't know if this is over kill or not. I currently use about 700-800kwh of electricity per month or about 30kwh per day. I charge my tesla model y about 5-6 times a month. Through my research, I don't think my panels will produce enough electricity for my use but I want to be able to do energy arbitrage and store energy in the batteries from the grid. What do you guys think of my plan? Can you guys recommend me a system that fits my needs for less money? Thank you guys in advance.

EDIT: Hi guys, I went on the roof today and took pictures of the equipment pictured below. so it is actually 255W canadian solar panels with enphase M215 micro inverters. so does this mean 255w * 14 panels = 3570. then 3570 * 5 (hours of sunlight) = 17850 kwh per day?

 

[DIYrich]

Eg4 18kpv, eg4 powerwall batteries. Existing pv as ac pv into the 18kpv. About as cheap as you can get. Other options that don't export to the grid might be cheaper, but the enphase ac pv might be an issue to coordinate charging to net zero the grid.

What are your time of use pricing? When will you be charging the EV?

What is your total production? What is your total usage? Not clear if the 30kwh is gross or net of solar.

TOU arbitrage can subsidize the cost of the battery, but rarely pays for it.

 

[Supervstech]

Hi everyone, I have existing solar on my roof with about 14 panels. I believe it is 140w panels. I saw something in the paperwork about enphase micro inverters. I am located in San Francisco and tired of paying PG&E exorbitant rates. I was interested in Tesla Powerwall 3 but I saw a youtube video that said it is not compatible with existing solar panels? I was looking through youtube videos and I was thinking about getting the EG4 18k hybrid inverter along with 30kwh of server rack batteries. I don't know if this is over kill or not. I currently use about 700-800kwh of electricity per month or about 30kwh per day. I charge my tesla model y about 5-6 times a month. Through my research, I don't think my panels will produce enough electricity for my use but I want to be able to do energy arbitrage and store energy in the batteries from the grid. What do you guys think of my plan? Can you guys recommend me a system that fits my needs for less money? Thank you guys in advance.

Your current panels compute out to a max average kWh per day of 9800. At the age of the panels, likely far less. Also likely several of the enphase inverters are broken.
Are you planning on keeping the panels you have, or replacing them? The 18K will require rewiring all the panels.

 

[DIYrich]

The 18K will require rewiring all the panels.

Bring in as ac pv into the 18kpv.

 

[CaliSunHarvester]

to do energy arbitrage and store energy in the batteries from the grid

This sounds like a good plan, charge battery with off peak rates and use it during peak rate time.

However, with PG&E the difference between peak and off peak is something like 15% only, and you may lose 15% in the TWO conversions (AC to DC when charging, DC to AC when discharging). You may even lose 20%, depending on the inverter/ charger.

 

[Supervstech]

Bring in as ac pv into the 18kpv.

So... double conversion losses? Hmmm.

 

[CaliSunHarvester]

double conversion losses

I was thinking the same. I looked up for my SungoldPower/ SRNE charge-inverter the "max inverter efficiency" is 92%, in other words, you are guaranteed a minimum loss of 8% in ONE conversion:

 

[Hedges]

It is all about $$.

Your existing PV system is a sunk cost. How much does it produce, summer and winter?

PG&E rates are high, but the spread between on and off peak isn't so wide. Maybe between $0.15 and $0.35, and varies with season.
Batteries cost money, lifetime cost per kWh has to be compared to utility rate spread.

Battery & battery inverter cost likely isn't worthwhile to arbitrage $0.15/kWh, especially with 10% to 20% round-trip power loss. If someone builds a DIY battery for $0.025/kWh (cost over lifetime cycles, not storage capacity for one cycle) they might come out ahead.

You can compare battery cost to spread during summer, likely in the $0.25 to $0.32 range. Some commercial battery offerings may be competitive, others decidedly aren't.

The Lithium Poly chemistry I'm playing with would last less than 10 years cycled daily (according to warrantied life), so I might get more out of it cycling summer only. If it lasts 15 to 20 years, twice warranty period.

LiFePO4 with claimed 6000 cycle life could last 16 years daily, so cycling only in the summer would push that out to 32 years. May exceed calendar life, and time-value of money impacts payback.

From a purely $$ standpoint, if battery system only saves you 2x its purchase price in reduced bills, over many years, I think some other investment would be better. If you buy a system for backup purposes, maybe it can at least pay for itself by cycling and the backup is free (but then it is empty at 9:00 PM, so power failure at night leaves you without power.)

 

[someguyondiysolarforum]

Your current panels compute out to a max average kWh per day of 9800. At the age of the panels, likely far less. Also likely several of the enphase inverters are broken.
Are you planning on keeping the panels you have, or replacing them? The 18K will require rewiring all the panels.

Hi I went on the roof today and saw that it is actually 255w canadian solar panels. I am not sure if anything is broken. I plan to keep the panels but I also want to add a few more panels but I was wondering if there was some type of mount for flat roofs that is non-penetrating?

 

[someguyondiysolarforum]

It is all about $$.

Your existing PV system is a sunk cost. How much does it produce, summer and winter?

PG&E rates are high, but the spread between on and off peak isn't so wide. Maybe between $0.15 and $0.35, and varies with season.
Batteries cost money, lifetime cost per kWh has to be compared to utility rate spread.

Battery & battery inverter cost likely isn't worthwhile to arbitrage $0.15/kWh, especially with 10% to 20% round-trip power loss. If someone builds a DIY battery for $0.025/kWh (cost over lifetime cycles, not storage capacity for one cycle) they might come out ahead.

You can compare battery cost to spread during summer, likely in the $0.25 to $0.32 range. Some commercial battery offerings may be competitive, others decidedly aren't.

The Lithium Poly chemistry I'm playing with would last less than 10 years cycled daily (according to warrantied life), so I might get more out of it cycling summer only. If it lasts 15 to 20 years, twice warranty period.

LiFePO4 with claimed 6000 cycle life could last 16 years daily, so cycling only in the summer would push that out to 32 years. May exceed calendar life, and time-value of money impacts payback.

From a purely $$ standpoint, if battery system only saves you 2x its purchase price in reduced bills, over many years, I think some other investment would be better. If you buy a system for backup purposes, maybe it can at least pay for itself by cycling and the backup is free (but then it is empty at 9:00 PM, so power failure at night leaves you without power.)

I am currently on the e-tou-d plan .46c off peak but I am thinking about switching to one of the EV plans where its only .34-.36 cents per kwh off peak. I can only switch to this plan if I have batteries because the EV plan hours for peak/part-peak/off-peak is too restrictive. I am still trying to do the math to see if its worth it. But I kind of want to do it for fun and learn too

 

[Hedges]

$0.20 spread 2/3 of the year, $0.32 or $0.36 spread 1/3 of the year.

6000 cycles is 16 years daily cycling, 49 years cycling just the more expensive 4 months.

What price and capacity battery + inverter do you see that could make sense?

Here's an example. If 6000 cycles, I think $0.11/kWh. A second battery should bring that down, but you'd need more PV to fill it.

EG4 PowerPro ESS Kit | 14.3-28.6kWh Capacity | Current Connected

Revolutionize energy management with the EG4 PowerPro ESS Kit: Reliable, safe, and user-friendly. Take control of your energy journey now!

www.currentconnected.com

 

[Quattrohead]

Also likely several of the enphase inverters are broken.

The Enphase M215 is the most reliable micro-inverter available, someone on the interwebs was monitoring various open systems in the SW USA for years and the MTBF of the M215 was 1300 years.
So yes you can AC couple your existing system into say an EG4 18K with two or three power pro batteries and add more panels by the PV connections later. This will give you a very flexible system and can be permitted if you want to go all out.