Solar PV Queries

Forums › Home Workshop DIY › Solar PV Queries

tdgeek

29746 posts

Uber Geek

Trusted

Lifetime subscriber

#217823 13-Jul-2017 16:50

Ive got Solar HW, and Im keen on Solar PV with no batteries. Being an electrical noob, I have some very basic questions for the knowledgable ones here. (You can comment, then laugh! )

1. Say Ive got a 3kW Solar PV, and its generating 2kW at the moment. If I turn on something that uses 1.2kW Im using solar to run that. If I turn on something using 1.5kW, and solar only has 800W free generation happening, does the solar 800W plus grid 700W power the device? Or does solar say, sorry cant manage that, the grid will have to power it all?

2. Or does the PV connect to the house input where the grid does, so effectively the house is getting one feed? And if so, does PV get first dibs so it can be used up before the grid tops it up?

3. Does an install include the gadget that allows sending spare PV power back to the grid for the small credit?

4. I dont know what kW is small, medium and large. Any guide will help. I guess if I can locate the Wattage of the key appliances thats a guide?

I do realise that Solar PV, as I have solar HW and gas hob is a lower use case, and on days like this its a lost cause. But we get good sun here in ChCh, and an ability to expand the panels economically, and consider a battery later, or even now, is on the table. If its that flexible to expand, thats great

In case it gives a clue to house wiring capability, home is 6yo, 5 bedrooms, 2 storey. I guess 2 story doesnt help but the solar tubes are up there. There is access to the back of the property via a double gate

Cheers.

(now awaiting @aredwood )

Aredwood

3885 posts

Uber Geek

#1822041 13-Jul-2017 16:57

Short answer. The solar inverter connects to your switchboard. And depending on solar output vs house load your meter either records exported power or imported power. The meter records imported and exported power separately. And it is up your power company what they will pay you for exported power compared to what they will bill you for imported power.

Jase2985

13462 posts

Uber Geek

ID Verified

Lifetime subscriber

#1822045 13-Jul-2017 17:03

1. it will take from the grid what it cant generate, it will give back to the grid any extra that it generates

2. solar first grid second

3. if its grid connected then yes if its not then you can only use power from the panels

4. wattage in guides is next to useless unless something is running full bore then it never uses the wattage on the label. you need to use you power bill to give you an estimate, or failing that get something that can monitor your power right down to every 10 seconds or so so you can see when you are using it and get an indication of how much each appliance uses.

here is todays power usage: (click to make bigger)

ive only just started monitoring power (1st of july) but ive spent $140 on the device to monitor it so i can better spec solar panels when we build.

Jase2985

13462 posts

Uber Geek

ID Verified

Lifetime subscriber

#1822048 13-Jul-2017 17:06

ps i can tell you what everything is on the graph :)

blakamin

4431 posts

Uber Geek
Inactive user

#1822049 13-Jul-2017 17:11

As for size... How much power do you use in a day on average? How much sun do you get?

If it was me, I'd get the biggest system you can afford (but I live in a very sunny place that has an average payoff time of 7.6 years), but this all depends of efficiency, hours of sunlight, orientation, roof space, etc.

tdgeek

29746 posts

Uber Geek

Trusted

Lifetime subscriber

#1822056 13-Jul-2017 17:19

Jase2985:

ps i can tell you what everything is on the graph :)

Very cool. Does this device plug in somewhere friendly or a sparky is required?

By matching the graph to what you know is on? I imagine with the detail (real time?) you can get a good handle on everything even if the device cant ID each power using device in the house. Perfect for deciding what panels to get, and batteries if you are going to use those as well. Also for measuring an individual device such as HW, watch graph, turn HW off, watch graph.

tdgeek

29746 posts

Uber Geek

Trusted

Lifetime subscriber

#1822062 13-Jul-2017 17:26

blakamin:

As for size... How much power do you use in a day on average? How much sun do you get?

If it was me, I'd get the biggest system you can afford (but I live in a very sunny place that has an average payoff time of 7.6 years), but this all depends of efficiency, hours of sunlight, orientation, roof space, etc.

I will have to look at usage. Genesis app shows hourly and daily in $ or kW, so before EK takes over I need to review all that. Its not consistent here, as we can be 2 adults, or daughter is home, or homestay(s) may be 0, 1 or 2.

I work from home, so easy to manage solar HW, and PV when ideal to maximise what its generating.

While I should be, Im not overly bothered with payoff time. Its a sunk cost, adds some value, and subject to maintenance or a need to replace panels, it can keep on giving. If battery cost wasn't too bad, thats an option, but that may be where Id look at payback time more

MichaelNZ

1390 posts

Uber Geek

Trusted

Integrity Tech Solutions

#1822072 13-Jul-2017 17:52

First off, I have solar and am off the grid (Where I live in New Zealand). Personally, I'd give grid feed a miss unless your usage corresponds with your solar system's peak power production - ie: you use the power yourself.

tdgeek:

2. Or does the PV connect to the house input where the grid does, so effectively the house is getting one feed? And if so, does PV get first dibs so it can be used up before the grid tops it up?

The source which supplies the highest Voltage is where the energy comes from.

WFH Linux Systems and Networks Engineer in the Internet industry | Specialising in Mikrotik | APNIC member | Open to job offers

Sharesies

Trade NZ and US shares and funds with Sharesies (affiliate link).

Jaxson

8042 posts

Uber Geek

Trusted

#1822092 13-Jul-2017 19:02

You'd want to give some thought to how you can force your usage to align with your generation, such as start delay timers on dishwasher/dryer etc, and a timer that allows electric hot water cylinder to run during daylight hours only for example.

If you have an old school meter, the disk will run backwards. Power companies don't like that, as you're saving the consumer rate when this happens.

Typically they'd want you to move to an import/export meter, which charges you the full consumer price for power you take, but pays back the much much lower industry rate when you contribute back into the grid.

PV makes a huge amount of sense to me, especially if you are at home during the day, like elderly running heat pumps for cooling during summer for example. If you are out at work most of the day, and your base load is low during the day, then there's not a lot to be gained, unless you can do some load shifting to align your use with the sunny parts of the day. No batteries to worry about, it's all good.

You will have to have your switch board labelled up the ying yang, to convey that even when the mains are isolated, it could still be live. And there's options around DC cabling to one converter, or little micro converters attached at the panels feeding AC out directly. It's quite involved in practise, but the concept is sound.

MichaelNZ

1390 posts

Uber Geek

Trusted

Integrity Tech Solutions

#1822093 13-Jul-2017 19:10

Jaxson:

You will have to have your switch board labelled up the ying yang, to convey that even when the mains are isolated, it could still be live.

Actually, only 2 decals:

1. A green circular sign with "PV" in white lettering

2. A red sign with the location, maximum Voc (Volts open circuit) and Isc (Amps short circuit) in white lettering.

There is a bunch of other signage requirements but that's all for the switchboard.

Source: AS/NZS 5033:2014

Note: Although solar systems are covered by other additional standards, only the above mentioned includes solar-specific signage requirements for the switchboard.

WFH Linux Systems and Networks Engineer in the Internet industry | Specialising in Mikrotik | APNIC member | Open to job offers

Jase2985

13462 posts

Uber Geek

ID Verified

Lifetime subscriber

#1822108 13-Jul-2017 20:14

tdgeek:

Jase2985:

ps i can tell you what everything is on the graph :)

Very cool. Does this device plug in somewhere friendly or a sparky is required?

By matching the graph to what you know is on? I imagine with the detail (real time?) you can get a good handle on everything even if the device cant ID each power using device in the house. Perfect for deciding what panels to get, and batteries if you are going to use those as well. Also for measuring an individual device such as HW, watch graph, turn HW off, watch graph.

has a base station which need power and Ethernet, mine is next to the PC, and the current clamp/transmitter, the clamp needs to be on one of the main feed cables either at meter or the input to the power board. i have an older school meter box so just opened that and the cables were there. clamped it on and put the transmitter outside the box and the box is metal and did interfere with the signal a little.

it measures power every 6/12/18 seconds (user selectable).

those peaks during the day are the HWC topping its self up, turns its element on for 4-5 minutes. the ones prior to about 6am are the heater in the kids room. the first peak was the HWC doing a top-up and me switching on the heat pump when i got up. next peak was my shower, then the big peak was the wifes shower, she had to deal with grumpy 4 year old so it was on longer than normal.

base load during the day is between .5 and .8kwh, and because we both work remote from home we dont use a lot during the day, as you can see, we could put timers on a few things to move their usage to peak hours but due to deciding to build we are going to forgo that.

tdgeek

29746 posts

Uber Geek

Trusted

Lifetime subscriber

#1822117 13-Jul-2017 21:22

Jase2985:

tdgeek:

Jase2985:

ps i can tell you what everything is on the graph :)

Very cool. Does this device plug in somewhere friendly or a sparky is required?

By matching the graph to what you know is on? I imagine with the detail (real time?) you can get a good handle on everything even if the device cant ID each power using device in the house. Perfect for deciding what panels to get, and batteries if you are going to use those as well. Also for measuring an individual device such as HW, watch graph, turn HW off, watch graph.

has a base station which need power and Ethernet, mine is next to the PC, and the current clamp/transmitter, the clamp needs to be on one of the main feed cables either at meter or the input to the power board. i have an older school meter box so just opened that and the cables were there. clamped it on and put the transmitter outside the box and the box is metal and did interfere with the signal a little.

it measures power every 6/12/18 seconds (user selectable).

those peaks during the day are the HWC topping its self up, turns its element on for 4-5 minutes. the ones prior to about 6am are the heater in the kids room. the first peak was the HWC doing a top-up and me switching on the heat pump when i got up. next peak was my shower, then the big peak was the wifes shower, she had to deal with grumpy 4 year old so it was on longer than normal.

base load during the day is between .5 and .8kwh, and because we both work remote from home we dont use a lot during the day, as you can see, we could put timers on a few things to move their usage to peak hours but due to deciding to build we are going to forgo that.

Thanks for all that, very cool. I guess a new meter box will have a way to connect the clamp? Our home is 6yo. I'd like one of these, as we also want to measure what panel capability we would need, and also might give a guideline to potential battery storage. Can you advise the device name and model?

Tks again, great info

Jase2985

13462 posts

Uber Geek

ID Verified

Lifetime subscriber

#1822198 14-Jul-2017 05:36

http://efergy.com/nz/products/energy-gateways/

i got the engage hub kit. it can take extra sensors so if you did get solar and battery storage tou could connect up a couple of extra sensors to monitor that too.

not sure about new meter boxes, you just need easy access to the main power cable, be it before the meter or after. but it needs to be before anything else gets power. have a look and see, you might be in luck and it might be easy to get to.