diy solar

diy solar

Residential Payback for Off-Grid Solar Q1 2023 (grid connected)

lots of folks say that Texas has no net metering, thats not really correct
there is no mandated rule about it here
Certain areas and providers do offer it.
I have a plan where I am credited monthly for what I send to the grid as far as the electric usage cost. but not for the distribution cost, up to my bill amount. no rollover and no cash back
current cycle is over in 2 days
I used at night 400 kwh
I sent them 800 kwh
since I sent more than I used, I will pay only the delivery charge for the 400 I bought at about 5 cents each
so bill is $20 plus $5 fee = $25

the extra 400 kwh I sent them over the 400 kwh I used at night it wasted and I received nothing for it
 
GregTR said:
I'm going to say that these numbers are also rather optimistic based on my actual data.

First of all, very few homes would have south facing unobstructed roof areas to support that size of solar installation AND also consume so little power. My home is a 4,000 sq ft house and I could only put 16/44 my panels on the south roof and I use over 25,000 kWh/year. Expecting that size system to fit on the south roof of a house is unrealistic.

Second, the system efficiency is far worse than 10% when it's all combined, a Sol-Ark will use 2.4 kW/day as will any battery system just sitting idle, not counting any other losses.

Again, if you find an installer that will put a 17kW PV on my roof with a Sol-Ark 15K for $2/W without battery and before tax incentives you're selling snake oil. I dare you to find ANYONE do this work for this much today.
The $9K for 30kWh battery is also awful generous, it is if you don't pay sales tax and you don't mind 6 LG4 units just laying around without a rackmount.

Bottom line, your numbers are the absolute bare minimum in a theoretical dream house that I highly doubt anyone can get to on their own and anyone trying to get into solar based on these numbers will be very disappointed to learn that they're not attainable.



I'm going to repeat what I said, the number is not reasonable. My energy provider who offers free electricity from 9PM to 7AM and charges $0.29/kWh from 7AM to 9PM estimates that the average user will end up paying $0.17/kWh on average. This would indicate they estimate that the average user uses ~58% of their electricity between 7AM and 9PM. if we assume even distribution within this time period (which we shouldn't as we all know about the peak use being after 6PM) it would mean that a mere 37% of electricity usage would occur during daylight hours (8AM to 5PM). The real percentage is probably even worse given the real use models indicating higher use in the evenings.
Click to expand...
the LP4 units are $9k with a cabinet

The install numbers represent lucrative trade money but to be fair most installers re taking advantage of a shortage market, the trades are catching up on fair pricing for installation IMO, hence why we are on a DIY solar forum. Mom and Pop Electricians will get into this when they realize the money to be had in a local service radius

Have been doing Grid-tied systems since Net metering went away in rural Texas in 2016, you read the export vs the production over a year. these were anywhere between 39% and 58% daytime
If this was a specific case study you can pull the info off your house and adjust accordingly, will not affect the calcs too much
 
2000kwhr/month? That’s your problem right there, that’s crazy consumption!!!

We’ve struggled to hit 1000kwhr/mo during the dog days of summer. Trim the usage and you’re payback will be so much easier!
 
Texican said:
lots of folks say that Texas has no net metering, thats not really correct
there is no mandated rule about it here
Certain areas and providers do offer it.
I have a plan where I am credited monthly for what I send to the grid as far as the electric usage cost. but not for the distribution cost, up to my bill amount. no rollover and no cash back
current cycle is over in 2 days
I used at night 400 kwh
I sent them 800 kwh
since I sent more than I used, I will pay only the delivery charge for the 400 I bought at about 5 cents each
so bill is $20 plus $5 fee = $25

the extra 400 kwh I sent them over the 400 kwh I used at night it wasted and I received nothing for it
Click to expand...
we mean full retail compensation, PURPA requires them to buy it for something.
 
740GLE said:
2000kwhr/month? That’s your problem right there, that’s crazy consumption!!!

We’ve struggled to hit 1000kwhr/mo during the dog days of summer. Trim the usage and you’re payback will be so much easier!
Click to expand...
Wouldn't that be half the revenue return? the setup cost on a smaller system may be higher per watt, but I agree that reduction is the best roi before doing a system
 
Texican said:
lots of folks say that Texas has no net metering, thats not really correct
there is no mandated rule about it here
Certain areas and providers do offer it.
I have a plan where I am credited monthly for what I send to the grid as far as the electric usage cost. but not for the distribution cost, up to my bill amount. no rollover and no cash back
current cycle is over in 2 days
I used at night 400 kwh
I sent them 800 kwh
since I sent more than I used, I will pay only the delivery charge for the 400 I bought at about 5 cents each
so bill is $20 plus $5 fee = $25

the extra 400 kwh I sent them over the 400 kwh I used at night it wasted and I received nothing for it
Click to expand...
It's no net metering when you have to pay delivery charge on anything used. Sure you can get "some" money for your solar export but it's never dollar for dollar, at least not in Texas.

The only one I know of that still offers real kWh for kWh NET metering with annual rollover with no delivery charge is Green Mountain Energy but the caveat is that the system has to be installed by them which is an instant no go for most.
 
SignatureSolarJames said:
the LP4 units are $9k with a cabinet

The install numbers represent lucrative trade money but to be fair most installers re taking advantage of a shortage market, the trades are catching up on fair pricing for installation IMO, hence why we are on a DIY solar forum. Mom and Pop Electricians will get into this when they realize the money to be had in a local service radius

Have been doing Grid-tied systems since Net metering went away in rural Texas in 2016, you read the export vs the production over a year. these were anywhere between 39% and 58% daytime
If this was a specific case study you can pull the info off your house and adjust accordingly, will not affect the calcs too much
Click to expand...
Again, I'm still waiting for a source that is willing to install a 17kW system for $2/W. I requested several quotes when I had my system installed last year and the offers ranged from $2.50-$3.70/W, not a single one came eve remotely close to the $2/W mark. Saying that "mom and pop will get into it soon" is not the same as "this is what's on the market today".

You claim that the daytime usage going from 38% to 58% "will not affect the calcs too much" is definitely wrong.

Here are some numbers:
17 kW system, daytime production is ~60 kWh. If we assume that this is for a place that uses ~60 kWh/day then with 38% daytime use you'd need 37 kWh of storage while with a 58% daytime usage you'd need 25 kWh of storage. That is a 12 kWh storage difference which, at $300/kWh is $3,600! On a $24k system that's 15%. Obviously the numbers you presented are "ideal" for the LG4 6-stack which is incidentally what Signature Solar happens to sell and is probably the sweet spot from a pricing perspective. Having to add two or more 5kWh units would make the numbers far less optimal having to buy an additional rack, more wiring etc.

I also challenge the $700 for wiring in your estimate. You would need a disconnect box by the meter and depending on where you want to mount your inverter in relation to your meter and breaker box conduit and wire prices can far exceed your $700. As I said, your numbers are "bare minimum" numbers that I challenge anyone to come close to.
 
740GLE said:
2000kwhr/month? That’s your problem right there, that’s crazy consumption!!!

We’ve struggled to hit 1000kwhr/mo during the dog days of summer. Trim the usage and you’re payback will be so much easier!
Click to expand...
I know, right! My base load on my house is 24 kWh/day that comes out to 720 kWh/month without running the A/C, heat, washer, dryer, oven, cooktop.

In the heat of the summer I had daily loads of ~120kWh, I guess this is what I get for living in a McMansion and driving and EV.

As for the usage vs. payback, the numbers are the same or actually a bit better with higher usage. If you want to use the same energy then a larger system will probably have a better ROI than a smaller system due to fixed costs being the same on a small or large setup. Smaller usage and smaller system just means less expenditure but the ROI doesn't change.
 
So I don't have equations for you but I do have a chart that shows daily consumption distribution at my house from October - January.

DailyConsumption.png

You can clearly see that my daytime consumption is dwarfed by my nighttime consumption.

My daytime consumption (consumption that can be offset by solar) averages 15.8 kWh while my consumption that cannot be covered by solar averages 31.2 kWh. That is a 34%-66% split which is EXACTLY what my utility company estimates most consumers will experience.

Caveat/Disclaimer: This consumption does not take into account EV charging and space heater consumptions that happen strictly at night at my house due to getting free electricity at night. If I didn't get free electricity I'd use my gas furnace and charge my EV during the day.

Since my average night time consumption is around 31 kWh, the 38 kWh battery I have is pretty optimally sized especially when you consider that my solar surplus (grid export) for this same period averaged 34.5 kWh.

So my numbers show that my PV and battery are fairly optimally chosen for my winter consumption, can't wait to see how the numbers will look in the summer. I suspect I won't be able to meet my nighttime demand with solar and was it not for the free night time electricity I would have to switch to daytime EV charging to bank the summer PV surplus during the day.
 
GregTR said:
Again, I'm still waiting for a source that is willing to install a 17kW system for $2/W. I requested several quotes when I had my system installed last year and the offers ranged from $2.50-$3.70/W, not a single one came eve remotely close to the $2/W mark. Saying that "mom and pop will get into it soon" is not the same as "this is what's on the market today".

You claim that the daytime usage going from 38% to 58% "will not affect the calcs too much" is definitely wrong.

Here are some numbers:
17 kW system, daytime production is ~60 kWh. If we assume that this is for a place that uses ~60 kWh/day then with 38% daytime use you'd need 37 kWh of storage while with a 58% daytime usage you'd need 25 kWh of storage. That is a 12 kWh storage difference which, at $300/kWh is $3,600! On a $24k system that's 15%. Obviously the numbers you presented are "ideal" for the LG4 6-stack which is incidentally what Signature Solar happens to sell and is probably the sweet spot from a pricing perspective. Having to add two or more 5kWh units would make the numbers far less optimal having to buy an additional rack, more wiring etc.

I also challenge the $700 for wiring in your estimate. You would need a disconnect box by the meter and depending on where you want to mount your inverter in relation to your meter and breaker box conduit and wire prices can far exceed your $700. As I said, your numbers are "bare minimum" numbers that I challenge anyone to come close to.
Click to expand...

As far as labor is concerned this is a DIY forum, Electricians would be happy to make the numbers shown, the market is just behind and currently in the business of gouging because of short supply, hence why people do things themselves here. the delta of labor supply wont last forever in my opinion.

Winter numbers are far worse than summer numbers because your cooling load is heavily skewed to the day vs winter being different.


Even if you add 15% (which the year average will not bear out typically) the numbers here are very good.
 
OK, I did check my summer consumption and while I can't really get a solar vs. non-solar metric (I haven't had solar yet) if we assume solar could cover 8AM-6PM and you'd need batteries for the 6PM-8AM period then you are correct ,the data is much more even between these two periods in summer months, it is indeed an almost 50-50 split.

DailyConsumption_Summer.png

Again, this does not include EV charging which is easily time-shifted to either period as needed.
 
GregTR said:
OK, I did check my summer consumption and while I can't really get a solar vs. non-solar metric (I haven't had solar yet) if we assume solar could cover 8AM-6PM and you'd need batteries for the 6PM-8AM period then you are correct ,the data is much more even between these two periods in summer months, it is indeed an almost 50-50 split.

View attachment 132235

Again, this does not include EV charging which is easily time-shifted to either period as needed.
Click to expand...
yep, my mom changed dryer loads to daylight on our system 10 years back as another example
 
Last edited:
Sadly I have no control over my wife's dryer usage habit so I gave up on even trying :) The EV is my job to plug in and manage so I can actually be cognizant of the weather/power consumption.
 
GregTR said:
OK, I did check my summer consumption and while I can't really get a solar vs. non-solar metric (I haven't had solar yet) if we assume solar could cover 8AM-6PM and you'd need batteries for the 6PM-8AM period then you are correct ,the data is much more even between these two periods in summer months, it is indeed an almost 50-50 split.

View attachment 132235

Again, this does not include EV charging which is easily time-shifted to either period as needed.
Click to expand...

What are your big loads during summer nights?
I figure lighting is needed, and cooking. But other than that, can you shift when you consume?

For winter, is it electric heat? Think electric water heater in the day, circulator pump to baseboard radiators at night could work?

GregTR said:
Sadly I have no control over my wife's dryer usage habit so I gave up on even trying :) The EV is my job to plug in and manage so I can actually be cognizant of the weather/power consumption.
Click to expand...

Timer?

Dishwashers often have a delayed start function.
 
My main consumer in the summer is A/C. We have a large home and hot temps in Texas, there is nothing to time-shift here. Based on my daytime load and PV size I will have to rely on grid for the night short of adding more PV and more batteries. But said PV and battery would go unused in the winter months therefore it would not have the optimal ROI of the current setup which gets almost 100% used during the winter months.

Once my current A/C units die I will invest in a heat pump solution that would allow me to use electricity for heating as well as cooling which would make a larger PV and battery more used year around.

We have central air, gas furnace for heat and tankless gas for hot water. I did look at a heat pump hot water heater but once you add up the cost of the unit, the permitting and installation cost, the ROI was not there when compared to the tankless gas heater so until this unit dies I won't be looking at an alternatives just yet.
 
Oh, right. You previously said night time A/C, correct?
I wonder if building ice during the day, using it to cool at night, would be cost effective. Could be a water loop, or water source for heat pump.
 
Hedges said:
Oh, right. You previously said night time A/C, correct?
I wonder if building ice during the day, using it to cool at night, would be cost effective. Could be a water loop, or water source for heat pump.
Click to expand...
One way to do it while not worrying about ice making is to overheat/overcool your house during daytime hours:
 
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