Author Topic: Solar power and timing electricity consumption  (Read 2568 times)

mustachianteacher

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Solar power and timing electricity consumption
« on: November 09, 2013, 02:05:20 PM »
Hello all! I am a daily reader but infrequent poster simply because I can usually learn all I need to know simply by reading along. Until now. ;-)

We are just a few weeks away from having our solar panels fully activated and tied to the grid. We are using Solar City (the panels are leased to us for a fixed $56/month for 20 years), and they estimate that, on an average day, the panels should generate 75% of our average daily usage. When these averages were calculated, though, they were averaging a year's worth of numbers, and because we live in an inland valley of Southern CA, we use a crazy amount of electricity to run the A/C from July-October. (Temperatures regularly top 100 during those months.) Our furnace is gas, so winter heating doesn't affect our electric usage much, if at all. Anyway, I'm thinking that on many days like today, when it's clear and sunny and we need neither heat nor A/C, we may be able to generate 100% of our usage. Just guessing, of course, since I don't know anyone IRL who has panels and/or understands how it all works.

Now my question: I don't think your solar system has any way to store generated electricity. There is no battery or anything like that. Because of that, is it the case that it would be wise to try and use our major appliances while the sun is out and producing electricity for us? Say I ran the washer and the dishwasher after sunset. Would I then be drawing power from the city utility, rather than from the power our panels have produced?

I apologize for the naiivete this question shows. I just figured someone here might know before I dial up the Solar City folks. Thanks!

geekette

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Re: Solar power and timing electricity consumption
« Reply #1 on: November 09, 2013, 04:39:29 PM »
You should definitely talk to Solar City, but it seems that since this system is "tied to the grid", you would just be paying for whatever you used beyond your system's output.  So when the sun's out, your solar cells are feeding into the grid, and the meter runs backward, subtracting off what you've used from the from the power company.  Unless you're on a time of use system, I don't think it should matter.

monarda

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Re: Solar power and timing electricity consumption
« Reply #2 on: November 09, 2013, 05:42:03 PM »
Geekette is totally correct. We have solar panels.

As geekette says, the panels collect sunlight and run your meter backward, first subtracting off what you've used during the daytime. The net-metering system keeps track of what you don't use and contribute to the grid. The meter runs forward for the electricity you use at night and on cloudy days.

Our monthly bill looks like this:

xxx kWh used this month,                                              $YY.zz
Credt for aaa kWh returned to the grid this month.         ($BB.cc)
Amount due:                                                         =$YY.zz - $BB.cc

The gross amount generated by the panels = xxx + aaa + amount used by the house during the daytime.
You won't know what this gross amount is, unless you have a monitoring system (we have Enphase Enlighten) directly connected to the panels.

I assume your $56 per month is independent of usage.

Time of use metering could be worth it if you use electricity mostly at night. If your AC is running during most days, then it is very likely NOT worth changing to TOU metering.

mustachianteacher

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Re: Solar power and timing electricity consumption
« Reply #3 on: November 09, 2013, 09:26:00 PM »
Thank you, monarda. Now that I'm reading that, I realize that this was explained to me at some point, but I had totally forgotten.

Yes, the $56/mo is fixed, independent of usage. Considering that it is the only expense associated with "going solar," and the fact that our average electric usage (factoring in those A/C-heavy months) is $90/mo, we should start seeing savings right away. It still seems a little too good to be true sometimes, and we're not even all hooked up yet!

monarda

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Re: Solar power and timing electricity consumption
« Reply #4 on: November 09, 2013, 09:55:37 PM »
Glad to have helped.

Just curious, what's the size of your system? 
We paid cash for our ~2KW system in 2011, and got two different incentives, bringing the price per KW down from over $6000 to around $3000.  At $56 per month for 20 years, I'm wondering what's the interest rate factored into these leasing options.  I haven't gotten a quote for leased systems around here. But I've seen articles that the installed rate before incentives has come down to about $5000 per kW.

mustachianteacher

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Re: Solar power and timing electricity consumption
« Reply #5 on: November 10, 2013, 10:33:37 AM »
If I'm reading the papers correctly, we have a 3.5 KW system, which is 14 panels. We had the option to pay the full cost of the lease upfront at a discount; that would have been around $8,800. With this plan, we end up paying $13, 440, so $3,840/KW. There were also a bunch of other options (a payment that rises with inflation, or putting down a certain amount and paying off the rest in monthly increments), but I like the predictability of a fixed payment. We also did not have the $8,800 lying around to just pay up front, although that definitely would have been the best deal. At the end of the 20 years, we can either keep the panels (although I was told that by then, they would be producing less), upgrade and start over with a new 20-year lease, or renew our lease in 5-year chunks.

monarda

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Re: Solar power and timing electricity consumption
« Reply #6 on: November 10, 2013, 11:12:32 AM »
Thanks!
We'll be expanding our system sometime in the next ~5 years and I'm interested in all the new leasing and financing options that have been developed lately. The price sure keeps coming down to go solar!