Solar/LEAF ROI Spreadsheet

Hello,

Last week my LEAF (as I) was very happy to see 30 shiny new 327 watt solar panels installed on my roof.

Today I've been searching here on the forum for a good ROI (return on investment) spreadsheet that takes both the LEAF and the solar panels into consideration. I was unsuccessful in my search. Can someone point me to one or share one here on the forum?

If not, no problem I'll create my own and will share. I was just thinking it would be easier to not reinvent the wheel or at least get a good head start.

Thanks!

eddiebo924 said:

Hello,

Last week my LEAF (as I) was very happy to see 30 shiny new 327 watt solar panels installed on my roof.

Today I've been searching here on the forum for a good ROI (return on investment) spreadsheet that takes both the LEAF and the solar panels into consideration. I was unsuccessful in my search. Can someone point me to one or share one here on the forum?

If not, no problem I'll create my own and will share. I was just thinking it would be easier to not reinvent the wheel or at least get a good head start.

Thanks!

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Congrats! It's a good feeling to be driving around using the electricity you generated on your roof!

I'm curious exactly what you plan on calculating.

The reason you aren't finding anything is that generally speaking the two ROIs are unrelated to each other so you just calculate each of them by themselves.

I'm not familiar with Colorado electricity rates but there are only a few scenarios where owning both an EV and PV create more savings than each of them by themselves. Essentially when you have TOU billing or tiered pricing. As well as if your PV is covering 100% of your usage including the EV usage.

I've never seen someone put together a calculation which figures out what the combined ROI is compared to the individual ROI when the above scenarios apply so if they apply to you I'd love to see what you come up with.

If the scenarios above don't apply to you but you still think that there is an increase in financial benefits by owning both than each one individually let's do some quick napkin math which will show that not to be the case.

QueenBee said:

The reason you aren't finding anything is that generally speaking the two ROIs are unrelated to each other so you just calculate each of them by themselves.

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I've read this statement many times on this forum, but I have to disagree. In fact, each purchase impacts the ROI of the other purchase:

- The installation of PV changes the cost of the fuel for the BEV. For instance, where I live, electricity costs $0.12/kWh if I purchase it from the power company. However, if I install a PV system myself, I can reduce my per/kWh cost of my electricity to about $0.05. In other words, as a result of the purchase of the PV system, I can increase the per-mile fuel savings achieved by the BEV and thereby reduce the time required to return the additional investment required to purchase the electric-drive system.

- On the other hand, the addition of a BEV to the home electrical load increases the amount of electricity consumed each year, often by a large fraction. As a result, the time required to pay back the initial investment of a PV system is reduced due to this increase electrical load.

RegGuheert said:

QueenBee said:

The reason you aren't finding anything is that generally speaking the two ROIs are unrelated to each other so you just calculate each of them by themselves.

Click to expand...

I've read this statement many times on this forum, but I have to disagree. In fact, each purchase impacts the ROI of the other purchase:

- The installation of PV changes the cost of the fuel for the BEV. For instance, where I live, electricity costs $0.12/kWh if I purchase it from the power company. However, if I install a PV system myself, I can reduce my per/kWh cost of my electricity to about $0.05. In other words, as a result of the purchase of the PV system, I can increase the per-mile fuel savings achieved by the BEV and thereby reduce the time required to return the additional investment required to purchase the electric-drive system.

- On the other hand, the addition of a BEV to the home electrical load increases the amount of electricity consumed each year, often by a large fraction. As a result, the time required to pay back the initial investment of a PV system is reduced due to this increase electrical load.

Click to expand...

Having both only changes the cost of fuel for the BEV if you are covering 100% of your usage by PV, have tiered rates, or have TOU rates. Through the below scenarios you'll see that the cost to power the BEV is the exact same in every scenario.

My scenarios for calculating the cost of electricity to power a BEV are as follows:
-One has no PV and no BEV and buys electricity from the utility for $0.12/kWh.
-One has no PV and an BEV and every kWh going into the BEV costs $0.12/kWh.
-One has PV covering 50% of their usage and no BEV. The electricity they buy from the grid costs $.12/kWh.
-Adding onto the previous scenario one still has PV covering 50% of their pre BEV usage but now adds an BEV. The extra usage caused by the BEV costs $.12/kWh.



Having both only changes the return of PV if you are covering 100% of your usage by PV, have tiered rates, or have TOU rates. Through the below scenarios you'll see that the savings from PV generation is the same regardless of if there is a BEV.

My scenarios for calculating the savings from installing PV are as follows:
-One has no PV and no BEV and buys electricity from the utility for $0.12/kWh.
-One has no PV and an BEV and buys electricity from the utility for $0.12/kWh.
-One has PV covering 50% of their usage and no BEV. Every kWh they generate saves them $0.12 as they do not have to buy it from the grid.
-Adding onto the previous scenario one still has PV covering 50% of their pre BEV usage but now adds a BEV. The extra usage caused by the BEV costs $.12/kWh and generation is the same thus they still save $0.12/kWh for every kWh they generate.

RegGuheert said:

- On the other hand, the addition of a BEV to the home electrical load increases the amount of electricity consumed each year, often by a large fraction. As a result, the time required to pay back the initial investment of a PV system is reduced due to this increase electrical load.

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Adding additional load does not at all impact the time required to pay back the initial investment. The system is still going to generate the same amount of power regardless of the load. Though to be clear not being grid tied, having a system that generates 100%+ of your usage, tiered rates, or TOU rates will/may provide an increase in the financial benefits from having both vs each one individually.

QueenBee said:

Having both only changes the return of PV if you are covering 100% of your usage by PV, have tiered rates, or have TOU rates.

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Agreed, and I suspect that these conditions apply to many (most?) who have purchased both PV and an EV.

In my case, we both tiered rates and produce approximately 100% of our overall usage, including the EV. So the addition of PV reduces the fuel cost for the EV from being entirely at the higher tier ($0.12/kWh) to the cost of PV-generated electricity($0.05/kWh). Or if I have any months where there is a slight consumption, the fuel may be charged at the lower tier($0.075/kWh).

QueenBee said:

Though to be clear not being grid tied, having a system that generates 100%+ of your usage, tiered rates, or TOU rates will/may provide an increase in the financial benefits from having both vs each one individually.

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Also agreed. And this case likely applies to far fewer cases than the one above. Still, I have read from several posters here that their TOU rates resulted in them producing quite a bit of electricity for the utility for free (sometimes due to a miscalculation of how much the value of the electricity is worth). So adding an EV allowed them to get some return from their PV purchase which would have otherwise been lost without the extra load.

All of these factors can be codified into OP's spreadsheet to allow it to correctly determine the ROIs for the two purchases without neglecting the impacts they may have on each other.

The calculations will be relatively complicated and very personalized to ones particular circumstances. Tiered rates will need to be calculated monthly for th various scenarios to determine how having both change the cost of electricity.

TOU, being that I don't have this I don't really think about it so not sure what one would need to do to calculate the combined benefits.

100% production is interesting. I'm not sure how you figure this one out. Obviously there is an additional benefit if the extra power that is being generated would just be lost so the EV is needed to consume it. Though if your utility would pay you for it then that could be the value assigned for the over generation.

Anyway, I've never tried to come up calculations for these so I would be very interested to see what someone comes up with.

QueenBee said:

The calculations will be relatively complicated and very personalized to ones particular circumstances.

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Absolutely! Since it is not overly easy to make these calculations even with data in hand, I'm not sure it would be possible to figure it out ahead of time. Two major complications that come to mind:

1) Monthly and annual PV production vary (sometimes significantly) due to the weather.
2) Monthly and annual electricity consumption vary (sometimes significantly) due to the weather.