SRP calculator for determining solar savings and comparing basic, TOU, and EZ-3 rates

[WhittakerJ]

All,

In trying to figure out how much money I was actually saving with my PV array I created this program. All you have to do is fill in your production numbers from the SRP statement and the solar calculator crunches everything for you based off of today's rates. It took me a few hours to create this and I feel like it's a great tool for anyone who has an SRP grid-tie system.

Calculates actual numbers:
1. Your return on investment or ROI.
2. The number of years the system will take to pay for itself.
3. The amount of money you would save on EZ-3 VS. Basic or TOU VS. Basic
4. The monthly savings in your electric bill from solar.
5. The total amount of electricity that you’re paying for.
6. The monthly percent of energy that comes from solar.



Mod note - before placing links to your site get the OK from user name Jason

[Volusiano]

I'm using a spreadsheet as well to track my production vs usage to calculate ROI based on my being on the TOU plan. I'm only about 3 months into having my solar system up and running so I don't have a whole year worth of data to enter yet.

It's pretty straightforward to calculate things after having a year's worth of solar production and usage data under your belt to figure everything out. What I find it harder to do is to make prediction for ROI and payback BEFORE you have solar in place (to help you decide on properly sizing your system and how much you're willing to spend based on ROI). Well, it's straightforward if you're on the basic plan, but it's a challenge if you're on the TOU plan, because your usage pattern will change after the solar is in place for sure, so you can't use past data to predict future data.

For example, before solar, you probably try to conserve and minimize using AC during on-peak in the summer time (set thermostat higher than normal), and schedule off as many high load demands to off-peak times as possible. But once you have solar, and especially if you design your system like I did such that most of your solar production in the summer time will fall within the 1-8pm on-peak period, you're going to change your use pattern for sure. You're going to want to set the thermostat during on-peak to a more comfortable level than before solar, and even start scheduling more high load usage (like laundry, EV car charging) to on-peak time now as needed, because you can "afford" to do it now with solar and not have to worry about minimize paying the high on-peak price from the utility company.

[WhittakerJ]

I'm using a spreadsheet as well to track my production vs usage to calculate ROI based on my being on the TOU plan. I'm only about 3 months into having my solar system up and running so I don't have a whole year worth of data to enter yet.

It's pretty straightforward to calculate things after having a year's worth of solar production and usage data under your belt to figure everything out. What I find it harder to do is to make prediction for ROI and payback BEFORE you have solar in place (to help you decide on properly sizing your system and how much you're willing to spend based on ROI). Well, it's straightforward if you're on the basic plan, but it's a challenge if you're on the TOU plan, because your usage pattern will change after the solar is in place for sure, so you can't use past data to predict future data.

For example, before solar, you probably try to conserve and minimize using AC during on-peak in the summer time (set thermostat higher than normal), and schedule off as many high load demands to off-peak times as possible. But once you have solar, and especially if you design your system like I did such that most of your solar production in the summer time will fall within the 1-8pm on-peak period, you're going to change your use pattern for sure. You're going to want to set the thermostat during on-peak to a more comfortable level than before solar, and even start scheduling more high load usage (like laundry, EV car charging) to on-peak time now as needed, because you can "afford" to do it now with solar and not have to worry about minimize paying the high on-peak price from the utility company.

Volusiano,

You could actually plug all your variables into the PVWatts calculator http://gisatnrel.nrel.gov/PVWatts_Viewer/index.html

Once you generate an hourly excel chart you could plot all of that into the Excel calculator I created to see exactly how much off-peak or on-peak electricity you would be using and the cost of the leftover uncovered electricity. It might be tedious getting it all entered but it could be easily done.

[Volusiano]

Volusiano,

You could actually plug all your variables into the PVWatts calculator http://gisatnrel.nrel.gov/PVWatts_Viewer/index.html

Once you generate an hourly excel chart you could plot all of that into the Excel calculator I created to see exactly how much off-peak or on-peak electricity you would be using and the cost of the leftover uncovered electricity. It might be tedious getting it all entered but it could be easily done.

I'm already using PVWatts to get annual production estimate for my solar production. That's only half the equation. The other half of the equation is to estimate your future consumption (the part I highlight in bold in your statement).

My point is that if you don't already have ACTUAL usage data yet with solar yet because you haven't installed your solar system yet, then you can't know exactly how much off-peak or on-peak electricity you would be using like you said above. The best you can do is take the previous 12 months' actual usage WITHOUT solar as your next 12 months' estimate after the solar system gets installed. And what I'm trying to say is that last 12 months' actual usage without solar is not going to be a good reflection of the next 12 months' estimate with solar if you're on the SRP TOU plan. This is because you'll most likely shift a lot more of your usage into the on-peak summer period once you're on solar compared to when you didn't have solar yet.

So your spreadsheet (or mine) is only good and gives accurate calculation AFTER we've had a solid and real 1 year worth of TOU or EZ3 usage data under our belt (with the solar system already in place) to populate the spreadsheet.

[SunEagle]

I'm already using PVWatts to get annual production estimate for my solar production. That's only half the equation. The other half of the equation is to estimate your future consumption (the part I highlight in bold in your statement).

My point is that if you don't already have ACTUAL usage data yet with solar yet because you haven't installed your solar system yet, then you can't know exactly how much off-peak or on-peak electricity you would be using like you said above. The best you can do is take the previous 12 months' actual usage WITHOUT solar as your next 12 months' estimate after the solar system gets installed. And what I'm trying to say is that last 12 months' actual usage without solar is not going to be a good reflection of the next 12 months' estimate with solar if you're on the SRP TOU plan. This is because you'll most likely shift a lot more of your usage into the on-peak summer period once you're on solar compared to when you didn't have solar yet.

So your spreadsheet (or mine) is only good and gives accurate calculation AFTER we've had a solid and real 1 year worth of TOU or EZ3 usage data under our belt (with the solar system already in place) to populate the spreadsheet.

Having some way of estimating your payback is better than nothing.

Sure your usage will change based on having a PV system but there are other variables that will come into play over the lifetime of the system. Your electric rates can change, the weather patterns can (and have) change, your family size may change and the electrical equipment you use will change as you add or replace older less efficient appliances.

If you think about all of these variables that can change you will never be able to come up with an accurate ROI. But using your spreadsheet and past history you can at least come up with something close and then make changes once you get more history.

As I said what you have is better than nothing.

[WhittakerJ]

I'm already using PVWatts to get annual production estimate for my solar production. That's only half the equation. The other half of the equation is to estimate your future consumption (the part I highlight in bold in your statement).

My point is that if you don't already have ACTUAL usage data yet with solar yet because you haven't installed your solar system yet, then you can't know exactly how much off-peak or on-peak electricity you would be using like you said above. The best you can do is take the previous 12 months' actual usage WITHOUT solar as your next 12 months' estimate after the solar system gets installed. And what I'm trying to say is that last 12 months' actual usage without solar is not going to be a good reflection of the next 12 months' estimate with solar if you're on the SRP TOU plan. This is because you'll most likely shift a lot more of your usage into the on-peak summer period once you're on solar compared to when you didn't have solar yet.

So your spreadsheet (or mine) is only good and gives accurate calculation AFTER we've had a solid and real 1 year worth of TOU or EZ3 usage data under our belt (with the solar system already in place) to populate the spreadsheet.

This is my second PV system that I've had in a completely different house. I'm not so sure I personally shifted my usage once I got solar to be honest with you. Even if I did the variance was less than 10% so the estimates were still pretty accurate.

The main reason for me creating this spreadsheet was to get exact cost savings numbers after you're installed. Everyone will tell you approximately this much or approximately that much. But it's nice to have solid figures in hand for peace of mind, especially to compare how much it would be if you were on basic, TOU, or EZ3.

[Volusiano]

Yes, I agree with Sun Eagle that having an estimate is better than nothing. That's what I did in my spreadsheet, too -> to forecast/estimate the ROI. I never said estimates are no good.

I only wanted to clarify and point out the difference between estimate and exact calculation because I sensed that the OP's goal for the spreadsheet he set up is to calculate the exact ROI, not just estimate. And it looks like he just confirmed this goal in the post above.

But while the calculation with real world data already collected after the system has been installed will give you exact year-to-year ROI numbers, payback time will never be exact, but will get more accurate as you collect more actual data over the years.

[WhittakerJ]

Yes, I agree with Sun Eagle that having an estimate is better than nothing. That's what I did in my spreadsheet, too -> to forecast/estimate the ROI. I never said estimates are no good.

I only wanted to clarify and point out the difference between estimate and exact calculation because I sensed that the OP's goal for the spreadsheet he set up is to calculate the exact ROI, not just estimate. And it looks like he just confirmed this goal in the post above.

But while the calculation with real world data already collected after the system has been installed will give you exact year-to-year ROI numbers, payback time will never be exact, but will get more accurate as you collect more actual data over the years.

This spreadsheet does give you an exact calculation of how much money you saved if you put in 1 years worth of data. It also computes if you would be better off on the basic plan. It is the closest thing to an ROI that you could possibly achieve based on real numbers.

Of course there are always going to be variances in solar where your production one year will not exactly match the previous. But in my system I have never seen that variance to be greater than a couple of percent which would barely change the ROI. I also realize systems become less efficient over the years but there is no way to calculate for that, that I'm aware of.

[Volusiano]

This is my second PV system that I've had in a completely different house. I'm not so sure I personally shifted my usage once I got solar to be honest with you. Even if I did the variance was less than 10% so the estimates were still pretty accurate.

For my case, I'm sure I will shift my usage around a lot once I got solar, especially in the summer time. Being on TOU with SRP, your summer on-peak rate is at least 3x the off-peak rate. So I used to run the AC down to 75F just before (not well before, but only just before) the 1PM on-peak start time so that the house stays nice and cool for the next 2 or 3 hours before it gets uncomfortably warm and start triggering on the AC again. I also moved the thermostat setting up a few more degrees during the on-peak time to minimize AC starts. So the house gets a little warmer, but not too uncomfortably warm during on-peak time. I utilize the ceiling fans more and at the next higher speed to keep cool during on-peak.

Now that I have solar, and my panels are all west facing, most of my solar production will be during the summer on-peak time, I hope that I wouldn't have to do those things anymore. In fact, I hope to get excess on-peak credits that I can bank and use for the winter, when the on-peak times changes to 5-9am and 5-9pm when there's no solar production at all.

Other high energy usage like laundry, car charging, pool pump may also have to be shifted around because you now have to manage 2 buckets of credit, so you need to balance the buckets more evenly.

[Datacruncher]

Great looking xls, but is there one for pre-solar non_TOU both Purchase and Lease

All,

In trying to figure out how much money I was actually saving with my PV array I created this program. All you have to do is fill in your production numbers from the SRP statement and the calculator crunches everything for you based off of today's rates. It took me a few hours to create this and I feel like it's a great tool for anyone who has an SRP grid-tie system.

Calculates actual numbers:
1. Your return on investment or ROI.
2. The number of years the system will take to pay for itself.
3. The amount of money you would save on EZ-3 VS. Basic or TOU VS. Basic
4. The monthly savings in your electric bill from solar.
5. The total amount of electricity that you’re paying for.
6. The monthly percent of energy that comes from solar.


Download link -
Mod note - before placing links to your site get the OK from user name Jason

I am looking for something similar, but one that would calculate/approx savings by going solar, both for Purchase and lease, and with purchase I'd like to consider both 1) "FULL system covering 95-100% usage vs Partial system covering only upper Tier 3&4 in Calif. I have put together a spreadsheet but it is soo convoluted, as it is the only xls I've every done, that it doesn't look so nice at all and I don't have any review on it by anyone else. and requires knowing whats what. Have one or Know of one???? And the SAVINGS CALCULATOR i am looking for should have some way to do scenarios of rising costs. From the looks of you xls I think it would be fantastic. Though it should already exist somewhere I would think.

[ds018]

PV array calculator

Is the link still available for download, I didnt see it any of the posts.

Thanks

[aravinthr]

Hi WhittakerJ,
Could you send me the spreadsheet, I went solar recently, I would like to keep track of solar production and savings. Mine is a bit more complicated, because, I need to account for additional service charge and the demand charges, I can start making changes if I had a starting point. Thanks.