Help reconcile Solarcity usage to electric bill

For this month, I finally have a 42kWh carry forward on my electric bill, meaning my demand for power was less than what my panels produced over the course of one month.

But I can't quite figure out what my *total* kWh usage was for the month. Here are the numbers:

Solarcity kWh production: 300 kWh
Utility kWh pulled from Grid: 173 kWh (bought)
Utility kWh pushed the Grid: 215 kWh (sold)
leaving a 42 kWh carryforward to next month

So what was my total kWh usage (demand) for the month?

Thanks.

Ah.. I see now. Thanks.

araxara said:

All I can say is "Wow!" You don't use much power in a given month. This is pretty close to my solar energy production for one day (200kWh) - and I have very little cary forward.

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I have a 1100 sq 2-story house. I only use it for my "office" during the day. I spend the rest of my time at my g/f's house.. where I also charge the Model S. For my birthday, she had a NEMA 14-50 socket installed. Who could ask for a better girlfriend!?!?! :love:

So my power consumption is basically: 1 Fridge, 1 Tivo, 1 computer 24x7, 1 gas-fired heater, 1 NEST, and a few lights, routers, switches, webcams, etc. When I'm there, the lights in my office might be on if it's dark outside.

The usage goes up in the summer because I have a 25000btu mini-split A/C system, but I only use 1 of 3 zones to cool my office.

Also, every quarter the water company has a conniption because I use less than 100cf of water per month.. basically a toilet flush here and there and drinking water. So every quarter, they have to do a truck roll to make sure my meter isn't broken or that I'm stealing water. My monthly water bill looks like this: 1 0 1 1 0 0 0 1 0 0 hcf.

I have 15 solar panels -- I think it's a 3.75 kW DC system. Very small... but it's covering a lot of my demand. Before I had it installed, I was using about, on average, 550kWh/month.. I went through my house and shut down many "extras" like a second media server that I really wasn't using.. I replaced it with an SSD hanging off my main computer. I now turn off my dual monitors when I leave the house. So that my usage is now below 300kWh is really surprising. I'll have to wait until summer to see how much more energy they produce and how much the A/C consumes. But so far, I'm very happy with the solar panels. The winter is supposed to be when they produce less than you consume, but the summer will be the real test.

Electric700 said:

All I can say is "Wow!" You are a role model for the entire world! If everyone could have a net surplus of 42 kWh every month from renewable energy, we'd all be set!

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Just an update. I had 100kWh surplus last month.

I decided that instead of racking up a solar surplus every month that I might not ever use, that I would start charging my car at my house instead if my girlfriend's house. I have a 14-50 at her house for 40 amp charging, but only 24amp charging at my house (which I'm only at during the days, I use it mostly as an office).

Anyway, I wanted to monitor my actual usage more closely, so I got a whole house elec monitor (Efergy Elite with Engage Hub) and its awesome. With no car charging and no A/C running, my whole house uses about 400 watts continuous, but when I'm car charging and working there with the A/C on, it shoot up to 6.0kW(this is a one day sample-yesterday). Of course that's net of the solar panel production, which was about 1kw during the 4-5 hours I was there. I've seen it go as high as 2.9kw on really clear sunny days at high noon, and it's not even the peak of the summer yet.

So we'll have to see at the end of the month how much an affect charging there has on my solar net surplus.

It's particularly cool because I can literally tell people that I'm driving on 100% sunlight.

It really is that simple. Although it could vary depending on your own electrical panel. In my case, the two main 100Amp feed lines from the pole were vampire tapped to the solar panel inverter (sorry, I don't have a pic).. that only caused a problem because it was very hard to find enough space to fit the top half of the Efergy current taps to fit around each main feed cable (I can post a pic later or Monday).

Maybe it was not a problem, but it was a little nerve-wracking to be trying to adjust/move around 240v/100amp feed cables around to make space for the two taps to fit. Everything was insulated of course, but it's no fun messing with that kind of live wires. In a normal panel, there should be plenty of room to fit the taps, and in that case, it probably would take 2 minutes to install the two taps and the transmitter.

I have the exact same monitor at my girlfriend's house, but only tapped into the two hot lines that feed the NEMA 14-50 outlet, so I could monitor exactly how much power I was using to charge my car. That was pretty easy to install.

The only downside with this system (you get what you pay for I guess) is that it can't sense power direction.. so when my solar panels are back feeding the grid, it appears as positive usage in their graphs and monitor. Right now, my panels are generating 2.8kW, but Efergy says that I'm using 1.6kW of energy, when in reality, I'm back feeding 1.6kW of energy to the grid. That's a 1.2kW difference. Assuming my house is still only using 500watts, where's the other 700watts going? I'm going to assume that's how much energy the Solarcity inverter is consuming itself in order to operate. I can't find any specs on that.

Here's a screen shot from the Engage hub website -- you can see where the solar panels kicked in:

Zaxxon said:

Hmm, interesting. That limitation would seem to greatly limit its usefulness, as the only time the reading would be accurate is at night. Could still be useful for spot-measuring various loads, I suppose.

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They say they are working on enhancing their system to allow two transmitters (a second one on the solar array) and do net usage reporting, but they don't know when that will be added.

I may add my own second transmitter and taps just on the solar feeds, so I can do my own net metering monitoring. But as-is, it's still useful to me.

BTW, when I ordered the monitor, I just assumed it could detect power flow direction (net metering). But when I installed the taps, there were non-directional, so that was a first clue that it wouldn't work as I originally intended.

I could prob return the entire set up, but like I said, even with that flaw, it's still interesting, as I'm mainly using it to track how much power car charging takes compared to my net metering surplus.

And it's fun to have.

Damn!! I asked them about that yesterday and they said "we're working on it"... The only diff I see is that the U.S. Usually had two feeds for each grid and solar, needing four taps instead of two. I shall ask about this Monday!

Ok, I have a lot of answers and results for people wanting to monitor their solar and usage with these Efergy monitors.

My first pair of senors were set up to monitor the power usage (demand) in my house, and that worked great.

I asked Efergy about their "Engage Solar Kit" available in Australia (mentioned above), and they told me it's already available to me if I get a second set of sensors to measure the solar generation. Since I already had a set of sensors and a transmitter at my g/fs house on the 14-50 I was using there, I just took those two sensors and the transmitter to my house.

So to envision how my power panel is set up, I have two 120V hot lines from the grid entering the box (call this segment #1).... then in the middle of each of those two main leads are big vampire taps where the two hot lines from the solar inverter are tapped into the mains (call the solar leads segment #2). Then after the solar taps, the two hot lines go into the main breaker box and breakers (call this segment #3). So that provides the following monitoring points:

Segment #1: Total Net Metering power either flowing in or out of the grid
Segment #2: Total Solar generation
Segment #3: Total house power demand, regardless of source (grid/solar)

I set the Efergy monitor taps (jackplugs) around Segments #2 and #3, resulting in the following graph on their website -- I can monitor total house demand and solar generation:




But this still doesn't give me real "Net Metering" monitoring, which I think most people would want to see. I could get a third set of sensors and a third transmitter (for an additional ~$75) and tap Segment #1 to track the Net power in addition to the two existing taps, but these jackplug sensors do NOT track power flow direction, so even if solar power was backfeeeding the grid, it would still show up as a positive amount, not negative.

I have filed a enhancement request to Efergy to just add a third line to the graph that is the difference between solar generation and total usage to display actual Net metering, but I have no idea if/when they would add that as an option.

But luckily, Efergy allows the Engage Hub users to download their own data at the Day, Hour, and Minute resolutions in a CSV file. From those downloads, I can create the graphs that I would like to see which is the same as the graph above, but adding the net difference. Here are those results, both at the Minute and Hour resolutions. The spikes you see on 5/26 is where I was charging my Model S at 24amps (NEMA 14-30):




So except for the fact that I can't monitor Net Metering in real time, this is a pretty good secondary option to provide all the data that I want. Hopefully Efergy will add this to their real-time graphs-- that would be perfect.