How to calculate energy used

I have a home solar installation which provides around 34 kWhrs per day. I am not sure how to calculate what percentage of that I am using to do, say, a complete recharge of my Leaf.

Thanks for any advise.

Larry

Same here, except ours averages around 24-25Kwh/day. I was wondering the same thing. When our A/C isn't running and it's charging during the day, most of it is being charged with the PVs.

Hi folks. I track this stuff obsessively.

My solar PV system in Southern Calif has been generating about 31 kWh per day this week. I have a TED energy monitoring system installed in my power panel to track my energy usage.

I ran my LEAF down to "turtle mode", basically empty once, and then I measured 26.1 kWh to recharge it to 100% that night, so that's my best estimate of what it takes to fully charge a LEAF at Level 2. Level 2 uses about 3.7 kW, measured at the power panel. If you time your charging, you can calculate how much power is being used. Just multiply your hours of charging by 3.7 and that will give you the approximate kWh that you used for that charge.

By the way, if you are in Southern Cal Edison's region, or the region of another utility that offers Time of Use rates for EV charging and also offers net energy metering for solar PV systems, you should definitely consider going onto one of those rate plans. It really magnifies the benefits of solar, because you get a large credit for the solar power that you generate during Peak hours and you get charged much less for the power that you use during Off Peak hours. Heavy air conditioning or other uses during Peak hours can reduce this benefit, of course.

You can see my monthly mileage and power consumption figures at the end of each month's post on my blog, linked below in my signature. Page back through my 2010 postings to see my TED system installation, etc.

Cheers

I don't think that's what the OP meant. For me, there is no way to know the true cost per Kwh using our PVs. For example, charging for one hour (L2) without using the PVs costs about $ .30, but with the PVs, it's obviously less, but how much less?

LEAFfan said:

I don't think that's what the OP meant. For me, there is no way to know the true cost per Kwh using our PVs. For example, charging for one hour (L2) without using the PVs costs about $ .30, but with the PVs, it's obviously less, but how much less?

Click to expand...

You could take the capital cost in $/KW and divide by the expected KWHr production for the number of years you intend to maintain the PV system. According to the California Solar Initiative, the current $/W is $8.50 ($8500/KW) and for San Jose area the capacity factor is around 20%. Getting the $/KWHr is $8500/KW divided by production (number years times 1752 KWHr per year) I get $0.485/KWHr for 10 years, $0.194/KWHr for 25 years and $0.121/KWHr for 40 years. This simple assumption makes no adjustments for maintenance or the cost of money or future cost of electricity but it puts a value on the PV installation. The cost of night time lighting from PG&E is $0.12/KWHr which I use to compare the base load cost of electricity from PG&E.

LEAFfan said:

I don't think that's what the OP meant. For me, there is no way to know the true cost per Kwh using our PVs. For example, charging for one hour (L2) without using the PVs costs about $ .30, but with the PVs, it's obviously less, but how much less?

Click to expand...

For the cost part of the question, you'd need to learn more about your utility bill and the rate structure that you're on with your utility. Such questions as: do you have special lower rates for charging during Off Peak times, like in the middle of the night, when are the Peak and Off Peak hours of the day, etc.

As I learned to understand our utility, SCE's, billing system, I also asked myself whether it would be better to charge during peak solar production hours, rather than wait for the off peak times. I did the math and found that it is far better for us to charge late at night. The reason is that we get a large credit per kWh generated by PV at peak hours, and we are charged much less per kWh for our night time charging. This is on a special time of use rate plan for EV charging and with net energy metering for solar PV customers. Your mileage may vary, of course.