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.
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.
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.
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.