3kW Grid Tied Solar PV: Watts and Warts.

Forums › Home Workshop DIY › 3kW Grid Tied Solar PV: Watts and Warts.

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269 posts

Ultimate Geek

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#936680 18-Nov-2013 15:01

Parewanui: Pertinent post at /.

Arizona Approves Grid-Connection Fees For Solar Rooftops...
http://hardware.slashdot.org/story/13/11/16/1422227/arizona-approves-grid-connection-fees-for-solar-rooftops

Not that the fee is a good thing.
But then The article has some interest gems like...
'Arizona Public has about 18,000 solar customers'
(pop. 6.5million, sunny climate)

Hmm - interesting.
There are a few questions here such as are there any "line charge" fees and if so how much. If that cost is still built into per unit cost then it is understandable?
They also say that the state power company "is required to buy solar power from customers with rooftop panels". Is the buyback rate designated also? I guess in an environment like NZ the power companies simply pay less for exported power or refuse to take it.

timmmay

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#936795 18-Nov-2013 17:34

In consumer mag, free, I haven't read it yet. Article here.

Porboynz

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#937456 19-Nov-2013 17:59

timmmay: In consumer mag, free, I haven't read it yet. Article here.

I just read the consumer article which represents the facts in a logical sequence unlike my meanderings. I am forced to agree with most all of it as my latest calculations indicate a longer payback than initially calculated. But what about the Geek value? Priceless.

Porboynz

110 posts

Master Geek

#937462 19-Nov-2013 18:17

Energy Monitoring
It’s important to Measure so you can Manage. I bought an original Cent-a-Meter maybe 5 years ago at an Auckland home show. There is an easy to read indoor display that connects by wireless to a current clamp inside the fuse box. I stationed the indoor readout by the front door and it’s been great. Many is the time I have given it a glance on the way out the door and seen an unusually high kW reading which sends me off to find out what’s been left on by accident. On the flip side you get grumpy when you realise the power consumption of MySky, Tivo, NAS boxes and WiFi AP’s. I was able to identify a number of seriously high standby power hogs, but like most of us I pay up and shut up for the convenience of time shifted movies and sports and not having to reset a digital clock on the stove, microwave, stereo, etc etc. Who knew we needed so many clocks?

The Cent-a-Meter does not have a PC connection or web interface, I obviously needed a technology update so I would be well informed about my PV installation wherever I was. The Enasolar Inverter has a web interface and records useful stats on its performance, but it does not measure the household consumption to give you a view of what was generated, what was consumed and what was exported. There are a few web connected monitors to choose from but my installer did a puppy dog sale on me and installed an Owl Intuition monitor as part of the install. He said if I didn’t like it he would remove it and credit me. Like that was ever going to happen. The Owl uploads data to a cloud based portal via a hub that connects to your router with a RJ45 ethernet cable and wirelessly connects to a fuse board transmitter that has 2 current clamps. One clamp measures current output by the PV, the other measures the household current consumption. It can therefore calculate what’s generated, what’s used by the house and what’s exported to the grid. All this and I can reach it via a PC, Android or iPhone app. Clever stuff and I’m very happy with it. After 30 days it reports the following, with the Meter and Inverter readings for comparison. You can see there is some variance, but it’s not a major. You can enter your tariffs and get actual costs in $$, graphs of usage, CO2 estimates, the lot.

30 Days Data

After 1 month here are the results: (14th October to 14th Nov)

Inverter Generated 459kWh
Meter Imported 459kWh (15.3kWh per day)
Meter Exported 229kWh (7.6kWh per day)

Assumptions
Solar used by house is 459-229=230kWh (7.6kWh per day)
Total House consumption is 230+459=689kWh (23kWh per day)

Summary
The house is using 50% of what is generated and exporting 50% averaged over 30 days.
Exporting 229kWh to Meridian returns 150kW @ $0.25 and the remaining 79kW @ $0.10 = $45.40 credit
Importing 459kWh @ $0.294 = $134.95
Power bill estimate is therefore $134.95 less $45.40 = $89.55 plus 30 days at $0.3852 = $11.56 Total $101.11 ($99.99 would have been nicer)
Last year’s Oct/Nov bill was $193

Meridian or Contact?
229kWh exported with Meridian results in a $45.40 credit and with Contact its $45.53 so not a significant factor for me. It looks like Contact is the company to be with during the summer months when the exported power is greater or if you had a larger capacity installation, and Meridian the best for winter or a smaller installation. This is ignoring what you pay for imported power for simplicity.

The challenge remains to use as much of your generated power as possible by time shifting dish washing and clothes washing. A solar installation coupled with a heat pump water heater that heats up your HWC during the day would be a good scheme. Having solar HW panels negates this option to some degree.

benmurphy66

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Ultimate Geek

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#937546 19-Nov-2013 20:44

Do you mind me asking what you paid for the Owl? I am about to buy one (like tonight) from the UK. I am getting the Intuition-LC as I have 3-phase power. I want to get a nice baseline of what my usage is to help me spec my PV installation

Aredwood

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#937569 19-Nov-2013 21:43

Do you know if the owl energy meter compensates for varying power factors? I would like to get a whole house power monitoring system but whatever I get must be power factor aware. And would also like to be able to measure and record power factor Vs time and KVAR Vs time. Since almost all loads in my house are either electric motors, electronic devices or lights (mixture fluro and LED).

richms

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#937570 19-Nov-2013 21:50

All the clamp on ones I have looked at either ignore power factor and in all but one case ignore line voltage, so you get at best a reading in kVA, but usually just kA*230 with no regard for waveform even.

The plugin meters are vastly more accurate than the whole house ones.

Richard rich.ms

pom532

149 posts

Master Geek

#937594 19-Nov-2013 22:06

Interesting read so far.

Since no one's mentioned it yet I thought I should mention Genesis Energy's Schoolgen program http://www.schoolgen.co.nz/. If you find a school near you it should provide a good example of PV output

Porboynz

110 posts

Master Geek

#937597 19-Nov-2013 22:15

A clamp on meter can not measure power factor to my knowledge. They provide indicative averages only for reactive loads, but OK for my purpose. I did look at getting a device from Aliexpress that has individual phase voltage connections as well as the clamps so likely to be voltage/current phase angle aware. Its a Mieo HA108 but at US$313 I was shy of spending that much $$$ on something I could find no reviews on from China. I did download the user guide and the software, it looked promising but the Owl was under NZ$300 so decision made.

Aredwood

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#937612 19-Nov-2013 22:56

richms: All the clamp on ones I have looked at either ignore power factor and in all but one case ignore line voltage, so you get at best a reading in kVA, but usually just kA*230 with no regard for waveform even.

The plugin meters are vastly more accurate than the whole house ones.

So it seems like I will just have to buy lots of the plug in meters and hack apart the switchboard - disconect the feeds to the lights and other loads that are hard wired and connect to some plugs. So I can plug them into one of the power meters.

Don't use electricity for cooking or hot water. So the only load that would be too big to run off a normal power socket is my TIG welder.

Other possibilities - see if detailed data can be accessed through the IR LEDs on the (not so) smart meter. Or hoping that someone has already made an Arduino based power meter. Can see this turning into another project to add to the list of projects in progress.

Parewanui

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#937825 20-Nov-2013 12:04

Good timing....
A /. poll...

Monthly net electricity use in my household:
http://slashdot.org/poll/2679/monthly-net-electricity-use-in-my-household

The comments are already interesting, but give it a few days and more good ones will appear.

dolsen

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#937863 20-Nov-2013 12:46

Aredwood:

So it seems like I will just have to buy lots of the plug in meters and hack apart the switchboard - disconect the feeds to the lights and other loads that are hard wired and connect to some plugs. So I can plug them into one of the power meters.

Don't forget to investergate the legality / insurability of such mods. Given your next comment, I'm sure you are technically capable of it.

Aredwood:

Other possibilities - see if detailed data can be accessed through the IR LEDs on the (not so) smart meter. Or hoping that someone has already made an Arduino based power meter. Can see this turning into another project to add to the list of projects in progress.

From their 1000 pulse / kw/h led I'm sure you could take the time taken between pulses to work out the power used over that timeframe which would be enough, or, are you looking at using the control leds to set up a communication session with the meter?

mclean

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#938041 20-Nov-2013 17:25

Aredwood: Do you know if the owl energy meter compensates for varying power factors? I would like to get a whole house power monitoring system but whatever I get must be power factor aware. And would also like to be able to measure and record power factor Vs time and KVAR Vs time. Since almost all loads in my house are either electric motors, electronic devices or lights (mixture fluro and LED).

It's an interesting question. I'm guessing that most of the big demands in a domestic situation are resistive (eg cooking, hot water). Also a lot of electronic devices, including electronic lighting ballasts, are pretty close to unity power factor. Heat pumps going for any length of time might alter that.

On a different tack, has anyone found an energy monitor that works for dual-tariff metering, like for controlled hot water? I assume it needs a separate CT for each meter and the ability to program a different tariff for each one. Otherwise the dollar values in the output are going to be meaningless.

Porboynz

110 posts

Master Geek

#938174 20-Nov-2013 21:07

mclean:
Aredwood: Do you know if the owl energy meter compensates for varying power factors? I would like to get a whole house power monitoring system but whatever I get must be power factor aware. And would also like to be able to measure and record power factor Vs time and KVAR Vs time. Since almost all loads in my house are either electric motors, electronic devices or lights (mixture fluro and LED).

It's an interesting question. I'm guessing that most of the big demands in a domestic situation are resistive (eg cooking, hot water). Also a lot of electronic devices, including electronic lighting ballasts, are pretty close to unity power factor. Heat pumps going for any length of time might alter that.

On a different tack, has anyone found an energy monitor that works for dual-tariff metering, like for controlled hot water? I assume it needs a separate CT for each meter and the ability to program a different tariff for each one. Otherwise the dollar values in the output are going to be meaningless.

I think this is a reasonably standard feature for any energy monitor that can have multiple current clamps. The Owl I have has sockets for up to 3 clamps, I suggest this is for 3 phase situations. The PV version I have has 2 clamps for Import and Export but the tariffs can be set for each, plus you can set a time based tariff for cheaper after hours rates. Re the reactive versus resistive load question, I notice that the meter and the Owl software disagree by about 10%, power factor inaccuracy is probably part of this difference.

SQLGeek

135 posts

Master Geek

#938339 21-Nov-2013 09:22

Watching this topic with interest, many thanks for all the interesting data.

I am going through a rebuild in Chch and will be installing PV panels thanks to a 15K sustainability payment from the insurance company. My old house had 3-phase power so is being replaced with 3-phase power. My electrician has told me that having just 1 phase might not be enough as the house is 310sqm and we are a high user of power with a spa, 3 heat-pumps, induction hob, lots of gadgets and wife & kids at home during the day. We have gas hot water.

I would like to get as much capacity as I can for the 15K and don’t want to waste money extra inverters, so do I really need 3 inverters? Could I get away with 1 inverter and have all the day-time stuff on that phase? Or could I just connect 2 phases and have 2 inverters?

Have been getting conflicting answers from the various retailers here in Chch.

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