Our PV system is running - but a question about metering?

Our system was installed in late September/early October and finally turned on last Wednesday. It's a 6K system. The power company installed a bi-directional meter and there is also a dedicated PV meter to show total output.

Last year we used about 600kWh during the month of October. So I was thinking right around 20kWh per day. Our system is making approximately 25kWh per day, so we should have a bank of 25kWh between Wednesday and Sunday.

I read the power company's guide to reading a bi-directional meter. I know that between Wednesday and Sunday the kWh delivered BY them went from 380 to 405 - so we used 25kWh or their power, right?

Our PV meter shows 119kWh produced during that time period. The bi-directional meter says that 99kWh have been received by the power company, 60kWh during peak hours.

Since we have only used 25kWh of their power but given to them 99kWh, wouldn't the meter be "spinning backwards" rather than going from 380 to 405?

Also, if we produced 119 and sold them 99, we only used 20kWh of our power. Plus we used 25kWh of their power - 45kWh total over 5 days. That doesn't seem possible, since the average usage for October is right around 20kWh/day. Maybe it is right, but I doubt it. We aren't running the a/c, but the kids are still watching TV and I'm still using the computer and we're still running a fridge, ceiling fans and lights.

I figure there must be something I'm missing here. I must not be reading it right, because nothing makes sense as far as the numbers go.

Yeah, I know it's Priuschat - but I know there are some PV users out there, so I thought I'd give it a shot.

 

I'm not sure how you're figuring we're using more than we think - my point is that it is showing that we are using much LESS than I think.

I expect it to show that we are using 20kWh per day. We are producing 25kWh per day, so at most APS should be getting 5kWh per day from us. Instead, their meter shows that they have received 99kWh from us - out of 119kWh we have produced, they have received all but 20kWh of it. So we're only using 4kWh that we produce each day, the rest is going to APS.

Their meter also shows that we have received from them 25kWh between Wednesday and Sunday - so 5kWh per day from them. 5kWh per day FROM the grid plus the 4kWh per day that we are producing - so we are only using 9kWh per day? That's less than half of what I expect that we would use.

So it's definitely NOT #3. I believe we should be using 20kWh per day and the numbers are showing that we are using 9kWh per day. It doesn't sound right, and if there is an error it is in our favor.

 

Hmmm...I could probably get the company to invoice me for something in 2009. We would have waited to turn it on but the solar people are carrying the $18,000 rebate for us and they needed it sooner rather than later.

We have a kill-a-watt and have used it to find the energy vampires. We reduced our usage during the summer quite a bit by adding solar shades to our windows, getting a more efficient refrigerator and installing programmable thermostats. We brought our August bill from 1900 in 2007 to 1450 in 2008. I just didn't think the changes we made would be enough to bring winter usage from 600/month to 300/month. I guess it's possible, though.

From the numbers I have seen, we are getting what we expected to get - I was thinking on average 30kWh/day. Less now, around 25kWh and more in the summer, around 35kWh. That all seems to line up with what we're seeing.

The one thing that confuses me is that meter not running backwards. I am not sure why it would go to 380 to 405 if we have indeed sold 99 to the grid. I would expect it to start moving backwards.

 

It's a digital meter. Here are the instructions for reading it: http://www.aps.com/main/green/choice/choice_11.html
The meter tells us these things:

how much APS has given us (was 380, now 405)
how much APS has given us peak hours (was 60, still 60)
how much APS has received (was 0, now 99)
how much APS has received peak hours (was 0, now 69)

The second meter tells us one number: how much power produced by the PV system. That number has gone up consistently each day and was at 119 yesterday afternoon.

I checked the meter on Wednesday when I got home from work and it told us APS has given us 380, of which 60 were peak hours. Since Wednesday, it has gone to 405, so APS has given us 25. None of them were peak hours, since the second number is still at 60. The number they have received was 99, of which 69 were peak hours. So my thought is that you would take 380 and subtract 99, but that isn't what happened. If they gave us 25 but we gave them 99, that should have pushed the number down from 380 to 281, shouldn't it?

I e-mailed our solar people and they are going to look into it. It would seem that everything is working except the meter spinning backwards part. I thought that is what happened, but I suppose it's possible that they don't set it to go backwards and just do the credit on the accounting end. In which case there really isn't a reason for a bidrectional meter.

We are getting credit for the voltage we are backfeeding into the grid - when the meter reader comes out, he'll see the kWh given back and how many at peak. That is being measured and credited, but it isn't being applied against the hours used.

 

I suppose it does, it's just odd to me. We probably were running the a/c last year at the beginning of October. We haven't run it at all this October, except for about 3 hours in my photo studio. I guess taking away the a/c, plus a small change due to the more efficient refrigerator and light bulbs would be enough to push it down to 10kWh/day.

The one thing I'm absolutely certain of is that we are producing a LOT more than we are using! That's good since we can bank it for those summer months when I'm sure we're going to fall short.

 

I think I've figured out the problem.

When they said "bi-directional" I assumed that the meter would spin in two directions. In actuality, bi-directional just means that it measure the power going in two directions. So long as it tells us how much is going their way and how much is coming our way, we have the necessary information to measure usage. We really have MORE information than a meter that just spins backwards - we can see how much we are using and how much is on peak as well as how much we are giving them and how much is on peak.

The numbers do work out, compared with the dedicated PV meter it looks like they are buying a LOT of the energy generated by our system. This afternoon we're up to 147kWh generated total, and they've bought 125kWh.

The kWh APS give us goes up during the times when the solar is not working. The kWh we give them goes up during the times when it is working. At the end of the month they'll take the hours they give us minus the hours we give them, and credit us for the excess.