Anybody up for a challenge? Help me verify savings of a new Grid-Tie system with "Time-of-Use" billing.

[TimC]

I've crunched numbers. I just want to know if someone would be up for looking at my numbers (as detailed as you can stand) and see if I'm calculating accurately.

I know in the end the sun shine makes all the difference, so, I'm just basing it on standard assumptions. My first question will have to do with... What percent of my day use billing is likely to drop with average production during the day? Yes, I need to be more specific, but, I don't want to bore everyone that is not interested in this. (I'll just bore nerds like me that want to look at what effect time of use rates will have on my savings.

We can do this in PM, emails, whatev! Or, keep it live in the forum. Thanks, Tim

 

[FilterGuy]

Lets keep it live in the forum.

Do you know what the rate schedule from the utility company looks like? Here in CA we have Peak, Off-Peak and "in between" hours. The hours change by day of the week and Summer vs Winter. On top of that they have graduated tears. (The fist 'x' KWH cost less than the next 'x' KWH.) What makes it even more complicated is that new solar installs are on a different rate schedule than older installs.

I tried calculating it many years ago, but gave up when I had to start making assumptions about level of production for different parts of the day. After I got my system installed (in 2007), it reduced my bill almost exactly what the installer predicted, so I was happy. Since then I have done a lot to reduce consumption (More efficient lighting and appliances and the kids moved out). Consequently, I only pay the minimum ~$10/month connection fee. (That might change next year when I am no longer grandfathered in to the old rate schedule. I'll probably be looking at batteries for my house when that happens)

 

[TimC]

Hi FG, Our rate structure is much simpler. It sounds like CA has a structure more favorable to customers, but, ours is still a great structure.

There are two rates; On-Peak and Off-Peak. On peak is 12 hours during the day with option to chose 6a-6p or 7a-7p. Off-Peak, obviously is the other nightly 12 hour period. Saturday, Sunday and holidays are 24 hours Off-Peak. My average rate/kWh over 23 months is 13 cents/kWh. Off-Peak charges average 9 cents/kWh and On-Peak average 20 cents/kWh. So, it should be simple, right? An interesting side note; during my first phone call to wholesalesolar.com the guy told me that Off-Peak during the night and On-Peak during the day was very unusual. I didn't argue with him as I know every utility has a different approach. Not sure I understand the concept that demand increases at night in some places, but, what do I know.

My questions have to do with how changing our habits by using self generated power while the sun is shining (cloudy days less so) will reduce our bottom line. WE-Energies, our utility, mentioned that yearly production is considered to determine billing. Not sure how that works yet, but, they have a statement on their web page that reads:

Peak shaving – Allows customer to reduce electric demand charges. Peak shaving may provide a win-win for utility and customer by relieving electrical system stress during peak-demand periods and by allowing customer to avoid on-peak demand charges and higher-priced on-peak energy.

I assume that means they credit high production days toward my bill which would result in reductions in December when production will likely be zero. I do know that they do not buy more power than you use off the grid, so, if I produce 6000 kwh/year and only use 5000 kwh/year I'm donating 1000kwh. So, it's important to size my array to nail down just what I use so I don't over invest dollars.

I'll continue with specifics to my situation in the next post.

Tim

 

[TimC]

BTW, I don't think I mentioned this will be a Grid-Tie system, no storage. And, I can attach a pdf of the data and calculations if someone really wants to dive into this. We are mostly locked indoors so I might get a taker!

Looking at 23 months of billing history I've crunched numbers as follows;

Off-Peak kWh 66.45%, On-Peak kWh 33.55%
Off-Peak $ 47.42% On-Peak $ 52.58%

I'm shooting for production of 82% of current use; 4621kWh/year x .82 = 3790 kWh/year
82% is due to space constraints rather than financial.

So, if I consider 82% production and 82% credit across the board it is easy to figure a payoff and savings. And that calculation is very favorable with a payoff of just under 10 years not considering tax incentive and 7.25 years with the tax incentive.

What I want to know is, will daytime production during On-Peak rates offset all of my day use and part of my off-Peak use? What reduction of each rate should I assume will result? I realize that is the $64,000 question. And it is not critical that I know the answer. I'm just hoping someone with a similar time of use rate structure might have some data that would back up my assumption that my On-Peak billing could drop to close to zero and Off-Peak billing will drop by the production of 82% or thereabouts.

Tim

 

[MisterSandals]

What I want to know is, will daytime production during On-Peak rates offset all of my day use and part of my off-Peak use? What reduction of each rate should I assume will result?

This is the tricky bit here in California. Maybe some is true for your power company.
Here, ALL the power you use comes thru your meter and you buy that from the power company at their rate. ALL the power you generate you "sell" back to the power company at a significantly lower rate.

So, the actual meter reading, is only half of the story, even though it may spin backwards. Our utility connection boxes have an internal meter that is used in conjunction with the external meter. I've spent hours trying to estimate the power i was using vs how much i was generating and keeping track of changes to the visible meter.

This along with what Filter Guy mentioned, fitting generation and usage into the MANY rate schedule slots, is maddening.

So I too gave up and am at least content with getting credit for what I am generating.

Mind you, its a total ripoff paying $.25/kwh and receiving $.13/kwh at any point in time.

 

[FilterGuy]

An interesting side note; during my first phone call to wholesalesolar.com the guy told me that Off-Peak during the night and On-Peak during the day was very unusual. I didn't argue with him as I know every utility has a different approach. Not sure I understand the concept that demand increases at night in some places, but, what do I know.

The peak usage is in fact during the day when factories and stores are running and everyone has their AC going. Before solar generation was a factor, this meant that the most expensive power was mid day. In some states like CA and TX, there is now so much Solar power that during the day, they sometimes have more power being produced than consumed. Consequently, the rates have shifted so the most expensive power is in the evening when solar is no longer producing but people are still up and about, consuming power.

A few interesting side notes to this:

• There have been days where the CA utilities had to pay other states to take the excess power. (If the shutdown continues into the summer, this is going to happen every day)
• This is why there is so much interest in grid scale storage. (It captures the excess, but perhaps more importantly, it stabilizes the grid)
• The CA state government, in there infinite incompetence, has added to the problem by passing a law that requires all new residential construction have solar but has done nothing to help figure out how manage the changing grid generation problem.
• I am grandfathered into a rate structure from before this all became a problem. Consequently, I sell at a high price during the day and purchase at a low cost in the evening. Unfortunately for me, I am going to loose the old rate structure next year and they are going to put me on a new rate structure; probably more like what @MisterSandals has. (I can't complain though, I will have had the old structure for 14 years and my system has paid for itself many times over)

 

[TimC]

Mister Sandals, I would agree that is a rip-off compared to our utility. We pay the same rate as they credit back to us. We can't produce more than we use unless we jump through a few regulatory hoops to become more than self-sufficient. To be clear, we can produce more than we get credit for, we just won't get credit for the extra production.

Basically, the utility (and ultimately the customers) are gaining from our personal investment into infrastructure instead of the utility investing their dollars. WE-Energies, at least since I have been a customer for some 40 years, has encouraged conservation and is now encouraging customer generation. While the state PSC might have rules to push that I think our utility has always supported it. No, I don't have a relationship with WE-Energies other than being a customer : )

Tim

 

[TimC]

... Consequently, the rates have shifted so the most expensive power is in the evening when solar is no longer producing but people are still up and about, consuming power.

That is very interesting! I suppose as renewable energy production gets more common that will happen throughout the country.

• There have been days where the CA utilities had to pay other states to take the excess power. (If the shutdown continues into the summer, this is going to happen every day)
• This is why there is so much interest in grid scale storage. (It captures the excess, but perhaps more importantly, it stabilizes the grid)
• The CA state government, in there infinite incompetence, has added to the problem by passing a law that requires all new residential construction have solar but has done nothing to help figure out how manage the changing grid generation problem.
• I am grandfathered into a rate structure from before this all became a problem. Consequently, I sell at a high price during the day and purchase at a low cost in the evening. Unfortunately for me, I am going to loose the old rate structure next year and they are going to put me on a new rate structure; probably more like what @MisterSandals has. (I can't complain though, I will have had the old structure for 14 years and my system has paid for itself many times over)

FG, do you think that what's happening in CA is good for the consumer in the long run? I mean, taking power generation into the hands of many may be more secure and support small installers, suppliers, etc. to compete in the market better? I think it might hurt small scale "producers for profit" if the market gets tight though.

Tim

 

[FilterGuy]

BTW, I don't think I mentioned this will be a Grid-Tie system, no storage. And, I can attach a pdf of the data and calculations if someone really wants to dive into this. We are mostly locked indoors so I might get a taker!

Looking at 23 months of billing history I've crunched numbers as follows;

Off-Peak kWh 66.45%, On-Peak kWh 33.55%
Off-Peak $ 47.42% On-Peak $ 52.58%

I'm shooting for production of 82% of current use; 4621kWh/year x .82 = 3790 kWh/year
82% is due to space constraints rather than financial.

So, if I consider 82% production and 82% credit across the board it is easy to figure a payoff and savings. And that calculation is very favorable with a payoff of just under 10 years not considering tax incentive and 7.25 years with the tax incentive.

What I want to know is, will daytime production during On-Peak rates offset all of my day use and part of my off-Peak use? What reduction of each rate should I assume will result? I realize that is the $64,000 question. And it is not critical that I know the answer. I'm just hoping someone with a similar time of use rate structure might have some data that would back up my assumption that my On-Peak billing could drop to close to zero and Off-Peak billing will drop by the production of 82% or thereabouts.

Tim

Looking at your numbers.

* Your solar production will happen during on-peak hours so it will all be purchased for On-peak prices.
* Your On-peak usage is 4621K*33.55%=1550KWh/year
* Your Off-peak Usage is 3071KWh/year.

At the end of they year, your on-peak purchase should be ~0KWH and your off-peak purchase should be 3071 - (3790-1550) = 831KWh
I think this means your net power bill should be ~ 13% of your current bill.

Not Bad!

 

[TimC]

Looking at your numbers.

* Your solar production will happen during on-peak hours so it will all be purchased for On-peak prices.
* Your On-peak usage is 4621K*33.55%=1550KWh/year
* Your Off-peak Usage is 3071KWh/year.

At the end of they year, your on-peak purchase should be ~0KWH and your off-peak purchase should be 3071 - (3790-1550) = 831KWh
I think this means your net power bill should be ~ 13% of your current bill.

Not Bad!

FG, I like what your thinking!

 

[MisterSandals]

• There have been days where the CA utilities had to pay other states to take the excess power. (If the shutdown continues into the summer, this is going to happen every day)
• This is why there is so much interest in grid scale storage. (It captures the excess, but perhaps more importantly, it stabilizes the grid)

I have a friend that works at the Moss Landing power plant. Around the beginning of the year, he said they were unloading semi-trailers, many semi-trailers of battery banks with fork lifts for "battery storage". I looked online then but found nothing.

I just found this online. This news article seems to address these two points you made:

Tesla battery power plant approved in Moss Landing

Monterey County Planning Commission unanimously approved a joint project between Tesla and PG&E to build the facility.

www.ksbw.com

 

[KBWaldron]

Mind you, its a total ripoff paying $.25/kwh and receiving $.13/kwh at any point in time.

Don‘t know if I agree. Are those numbers total kwh rates or just the generation? I hope for your sake it is total, as in Ontario where I live we are about half that. My all-in cost for an off peak kWh is ten cents, Canadian. On peak is about fourteen cents.
So, based on the assumption that is total cost, consider your provider isn’t paying other producers twenty five cents a kWh. You are also paying in that buy rate for transmission, distribution, system maintenance, and possibly regulatory charges. When you sell back, you are a producer and get to sell your power through their distribution system. If you want to get more for that excess power invest in batteries, don’t sell back, instead saving even more by not paying for the time you would have had to buy more by instead drawing from the batteries.
I live in Ontario, and here my actual generated electricity cost less all those other costs is about 55% of my bill. If twenty five cents is the generation cost in your area, then all the more reason to invest in batteries.

 

[FilterGuy]

FG, do you think that what's happening in CA is good for the consumer in the long run? I mean, taking power generation into the hands of many may be more secure and support small installers, suppliers, etc. to compete in the market better? I think it might hurt small scale "producers for profit" if the market gets tight though.

This gets into a huge debate around the very complicated economics of solar generation.

Since the solar power is not reliable, the utility has to maintain the ability to generate enough power to satisfy the needs on cloudy days and at night, even though they are not using it. They also have to maintain the grid to deliver that power. This is all expensive. Meanwhile the people that put in solar are buying less electricity. Therefore, the utilities have to amortize the cost of the system over fewer KWh sold.... meaning the cost of electricity from the utility must go up. As grid scale storage comes on line, some of this will change. The utility will still have to maintain distribution, but their generation costs should start going down.

Note: The above is a gross simplification of the situation. It is actually a lot more complicated.

People like myself that use the grid as a battery should be paying some part of the cost to develop and maintain the generation capacity and the grid. That is why the utilities are starting to implement rate structures that purchase from consumers at a lower rate than they sell to the consumers. The big debate is what the difference should be.

None of the above gets into the incompetence and greed of our politicians and utilities. Unfortunately, the waste and greed is probably driving prices more than anything else. I am going to leave it at that...... My blood preassure goes up when I get to talking about how terrible the CA government and Utilities are.

 

[MisterSandals]

Are those numbers total kwh rates or just the generation?

They were actually "angry estimates" :*)

Here are real numbers.
2nd half December:
Part peak: 24.43 kWh @ $.218
Off peak: 118.92 kWh @ $.2016

1st half January:
Part peak: 18.46 kWh @ $.224
Off peak: 70.19 kWh @ $.207

There are "distribution fees" and MANY taxes, and regulatory and environmental fees on top of this. And $.07 / kWh to Silicon Valley Clean Energy Electric Generation Charges.

I will see if i can figure out a number for generation. Most of the numbers they provide are Net numbers and obfuscated elsewhere as monthly totals.

(tried and could not get my generation credit per kwh)

 

[TimC]

Looking at your numbers.

* Your solar production will happen during on-peak hours so it will all be purchased for On-peak prices.
* Your On-peak usage is 4621K*33.55%=1550KWh/year
* Your Off-peak Usage is 3071KWh/year.

At the end of they year, your on-peak purchase should be ~0KWH and your off-peak purchase should be 3071 - (3790-1550) = 831KWh
I think this means your net power bill should be ~ 13% of your current bill.

Not Bad!

And, and, and... We now go out of our way to use power at night, Off-Peak. Clothes washer, dish washer, woodworking tools, furnace actually runs much less during the day, etc. So, I suspect those numbers will get even better because I'm thinking we would almost totally flip our routine and use our appliances more during On-Peak and even less Off-Peak. My wife will be baking up a storm if we can use the range during the day (not that we don't, but...). At least we'll flip our routine on sunny days for sure!
Can ya tell I'm excited about this solar thing!
Tim

 

[TimC]

Sorry, duplicate post!

 

[FilterGuy]

One more point: As utilities try to grab back the cost of the grid from the folks with solar, more and more of the folks are deciding to put in batteries. These behind-the-meter storage solutions means the utilities are loosing even more sales....and that makes the situation even more complicated. As solar and storage prices continue to drop, this is going to get to be a larger problem... and since the politicians and utilities are never proactive... they are going to find themselves in a huge mess.

 

[FilterGuy]

And, and, and... We now go out of our way to use power at night, Off-Peak. Clothes washer, dish washer, woodworking tools, furnace actually runs much less during the day, etc. So, I suspect those numbers will get even better because I'm thinking we would almost totally flip our routine and use our appliances more during On-Peak and even less Off-Peak. My wife will be baking up a storm if we can use the range during the day (not that we don't, but...). At least we'll flip our routine on sunny days for sure!
Can ya tell I'm excited about this solar thing!
Tim

I know how you feel. When I first put in solar I was crazy excited. Seeing the meter actually run backwards was amazing! I did the same thing... how could I shift usage so I maximized the benifit? Over time I made the house more efficient and our usage dropped to the point that I only pay a required minimum ~$10 connection fee so now I don't even think about it.

 

[MisterSandals]

Over time I made the house more efficient and our usage dropped to the point that I only pay a required minimum ~$10 connection fee so now I don't even think about it.

How big is your array?
How many kWh do you use? (consumption number on page 5)

 

[FilterGuy]

FG, I like what your thinking!

Keep in mind that I was making a lot of gross approximations. Cloudy days, winter sun, position of the panels, inverter efficiency and many other factors of the real world will change things. However, I think you will still be happy with the result.

 

[FilterGuy]

How big is your array?
How many kWh do you use? (consumption number on page 5)

My array is only 4.7KW.... That is less than my consumption but since I am grandfathered into the old rate schedule, I sell power for more than I buy power. The net result is my bill is essentially zero even though I get more power from the grid than I supply to the grid. Next year that is all going to change when I loose the old rate structure. I will be looking at it very closely when that happens. I am already planning to install batteries to do peak shaving in the evening.

To be honest, the rate structure I am currently on is not fair to everyone else.... but I will enjoy it while I can. I am pleasantly surprised I have been able to keep the old rate structure for as long as I have.