hill said:
We built big enough to cover not only the Leaf, but a future plug in. And, in the mean time - the utility pays us a couple hundred for our surplus juice, per year. Nothing wrong with over building if you're planning for the future.
Actually there is a lot of wrong with overbuilding depending on your utility rate schedule. You must really have oversized your system for the utility to pay you a couple hundred extra for surplus juice.
PG&E will only pay 3 cents/kWh for surplus electricity.
Even if you are only getting $200/year, that means you have over 6500 kWh extra per year . That's huge.
How big of a system do you have ?
With PG&E's crazy TOU tiered rates you don't even need to meet 100% of your electricity demand to zero your bill.
With my time usage patterns, I can zero the bill even producing as little as 85% of my energy consumption.
Any additional panels to cover usage between 85% and 100% of my usage would purely be a gift of electricity to PG&E - I would have a surplus of energy charges at the end of the year that would be zero'ed on december 31st. They don't start paying one cent until you have net juice above 100%.
FYI, here my spreadsheet with actual usage the past few years, calculations and estimates
https://docs.google.com/open?id=0B1eSSO_7gwqeQl94bEpGeHhvTnM" onclick="window.open(this.href);return false;
These are good for PG&E territory X which is most of the SF bay area.
It's very comprehensive and a little hard to explain given all the sheets and all the columns. It's best viewed on multiple 2560x1600 30" monitors which is what I used to create it. Anyway, I will try to explain it below...
How-to use :
- if you aren't in territory X, edit the baselines in the sheets named with the rate schedule and dates. Eg. "E1 07-01-2012" and "E6 07-01-2012" for the current rates. Only the baselines change between territories, not the rates, so this is a quick edit.
- Go to the sheet called "estimates".
- Put your current monthly usage on lines 3 - 14 , in columns E through J . If you aren't already on TOU rate, erase the values in columns E through I on those lines, and only put the current total kWh in column J .
- zero column K on lines 2-16 . These solar production numbers only relate to my 2-year old solar system are most likely irrelevant to others, unless you live in San Jose and have a 6.5 kW DC / 5.9 kW PTC system
- you should now have an annual total for the E1 rate in cell L17 . This should match your current bills.
- if you have input data for TOU periods in columns E-I, you will also get an E6 TOU bill estimate in cell N17
- now go to the second part of this sheet that starts on line 26
- edit cell I26 . If your EV charging was already included in the usage data in the top part, zero this cell. Otherwise, put your average daily kWh home charging for the EV. The reason for this section of the sheet is I didn't have the Leaf before and had to estimate the impact of the additional charging on my bill.
- now go to the third section of the sheet that starts on line 51
- on lines 56 - 67, column K, input the projected kWh for each month for the solar system you are considering purchasing. You can get those from PVWatts for example.
- in cell N73, put the total cost of the solar system you are looking to purchase
- cell M70 will have your total estimated annual bill for E1, cell N70 for E6 if you entered TOU period data earlier.
- cell N72 will have the annual dollar savings from adding solar. this is based on TOU though. If you don't have TOU estimates, change the formula to use column M instead of N ...
- you will get a payback period in N74 and payback date in N76
Hope that helps somebody who is considered solar and/or a Leaf ..