Residential PV Solar Power

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mattwnz

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Topic # 185176 12-Nov-2015 17:31

A house I am looking at buying currently has some PV solar panels on the roof, as well as an invertor inside the shed. Currently this isn't hooked up to the house, but instead feeds power back into the natural grid, which they get paid very little for. Think it maybe around 5 cents /kW unit, which is terrible.

If I was to buy this house, I was wondering the best way to take advantage of this arrangement, and thoughts from anyone else here who are using PV cells to partly power their home? Ideally the power generated is best used in the house, as it is essentially free power, which the electricity retailer is buying for a pittance. Essentially it appears that all the house owner has achieved so far, is getting is slightly cheaper power. In the UK I believe that that generated power rolls back the meter, so in many cases the power companies actually pay you for over generation. But I can't see that applying in NZ, due to them paying it back at a less that wholesale rate.

Also I was wondering what is the most solar freindly/environmentally friendly power company, eg. which power company pays the best rates for solar generated power.

Currently I am not sure why the invertors aren't powering the house directly, I mean can it be done and what equipment is needed? There is currently no battery storage to store any oversupply, and they were planning on installing that at some stage. I was thinking that these new Tesla Powerbanks could be a solution for it, when they finally make it into NZ, rather than having a shed of lead batteries. Would be interested in peoples feedback. I am guessing this will become a more mainstream thing in coming years with these new Tesla Powerbanks.

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Reply # 1427073 12-Nov-2015 17:41

An import export meter will take the power in one direction, and add it to one register, and if its going the other direction, it adds it to the export register which you get paid stuff all for.

The way to minimize that is to schedule your loads for when the panels are producing, so timer on the hot water cylinder to cut power to it except for daytime and a bit into the evening if its not fully heating, and see if you can start your dryer in the morning before you leave the house etc.

Some systems exist to automate this to a degree, but it seems to be prettymuch in its infancy at the moment. There is no way to have your fridge do its defrost automatically once the hot water is up to temperature etc.

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timmmay

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Reply # 1427075 12-Nov-2015 17:46

The national grid usually sells power for around 5-8c/kwh, so they're just paying market rates really. You are better off using it yourself though. A friend of mine has his powering his two hot water cylinders and spa pool, but I'm not sure that's a good way to go.

Getting even a little bit of storage would really help time shifting your generation. @jeffnz may be able to help with batteries and advice.

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mattwnz

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Reply # 1427076 12-Nov-2015 17:59

timmmay: The national grid usually sells power for around 5-8c/kwh, so they're just paying market rates really. You are better off using it yourself though. A friend of mine has his powering his two hot water cylinders and spa pool, but I'm not sure that's a good way to go.

Getting even a little bit of storage would really help time shifting your generation. @jeffnz may be able to help with batteries and advice.

Thanks. I probably need to get an expert in to look at it, as it will probably be a case by case thing. But adding storage I can see will have many benfits and make it more usable.

My point with the way the UK does it, is from what I have seen, you get paid the retail rate for the power you generate, as it rolls back the meter. So you can make about 4 times the wholesale rate. But I guess that may change when it becomes more mainstream.

richms

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Reply # 1427079 12-Nov-2015 18:06

mattwnz:
Thanks. I probably need to get an expert in to look at it, as it will probably be a case by case thing. But adding storage I can see will have many benfits and make it more usable.

My point with the way the UK does it, is from what I have seen, you get paid the retail rate for the power you generate, as it rolls back the meter. So you can make about 4 times the wholesale rate. But I guess that may change when it becomes more mainstream.

That is a crazy way to do it, as its basically making the power companies act as a reseller for your power for no profit. It will have to change. That is what happens if you put a grid tie inverter onto an old mechanical meter which is why they have prohibited the importation of plug in grid tie inverters as a friend found out when trying to bring one in off aliexpress to stick in their motorhome so that they got some use of its solar panels while it was parked up.

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mattwnz

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Reply # 1427081 12-Nov-2015 18:09

richms:
mattwnz:
Thanks. I probably need to get an expert in to look at it, as it will probably be a case by case thing. But adding storage I can see will have many benfits and make it more usable.

My point with the way the UK does it, is from what I have seen, you get paid the retail rate for the power you generate, as it rolls back the meter. So you can make about 4 times the wholesale rate. But I guess that may change when it becomes more mainstream.

That is a crazy way to do it, as its basically making the power companies act as a reseller for your power for no profit. It will have to change. That is what happens if you put a grid tie inverter onto an old mechanical meter which is why they have prohibited the importation of plug in grid tie inverters as a friend found out when trying to bring one in off aliexpress to stick in their motorhome so that they got some use of its solar panels while it was parked up.

I suspect they will still be making a small margin, and then there will be the fixed daily fees, I can't see power companies losing. If it is a problem, I suspect it will or already has changed.

Dynamic

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Reply # 1427101 12-Nov-2015 18:39

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timmmay: The national grid usually sells power for around 5-8c/kwh, so they're just paying market rates really. You are better off using it yourself though. A friend of mine has his powering his two hot water cylinders and spa pool, but I'm not sure that's a good way to go.

Getting even a little bit of storage would really help time shifting your generation. @jeffnz may be able to help with batteries and advice.

Batteries for storage are expensive. Storing the energy as hot water is relatively cheap. The energy is locked in to the hot water, but the power savings should be very worthwhile I would think.

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timmmay

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Reply # 1427122 12-Nov-2015 19:24

Dynamic:
timmmay: The national grid usually sells power for around 5-8c/kwh, so they're just paying market rates really. You are better off using it yourself though. A friend of mine has his powering his two hot water cylinders and spa pool, but I'm not sure that's a good way to go.

Getting even a little bit of storage would really help time shifting your generation. @jeffnz may be able to help with batteries and advice.

Batteries for storage are expensive. Storing the energy as hot water is relatively cheap. The energy is locked in to the hot water, but the power savings should be very worthwhile I would think.

It is for my friend, who has two hot water cylinders and a spa pool, but wouldn't help me much. Storage is expensive, but you can get good deals on storage sometimes. You don't need to store a days power, even time shifting enough to cook dinner or run heating for a little while would be a benefit.

Though I have to say I'm saving more on power by moving to Flick Electric than my friend who spent $12K on solar.

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JWR

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Reply # 1427125 12-Nov-2015 19:28

Dynamic:
timmmay: The national grid usually sells power for around 5-8c/kwh, so they're just paying market rates really. You are better off using it yourself though. A friend of mine has his powering his two hot water cylinders and spa pool, but I'm not sure that's a good way to go.

Getting even a little bit of storage would really help time shifting your generation. @jeffnz may be able to help with batteries and advice.

Batteries for storage are expensive. Storing the energy as hot water is relatively cheap. The energy is locked in to the hot water, but the power savings should be very worthwhile I would think.

There is that! Water is a very strange liquid and one of it's abilities is to store a lot of heat.

Also, just use as much of your own electricity generation as you can and sell as little back as possible.

Use smart controllers etc. to do washing etc.. when your generation is high.

Dynamic

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Reply # 1427126 12-Nov-2015 19:28

timmmay: I'm saving more on power by moving to Flick Electric than my friend who spent $12K on solar.

I would love to move to Solar or Wind generated power, but the payback period would have to be 5 years (or ideally 3 years) for me to be interested. That's quite a way off. Hopefully the aluminium-based battery technology matures quickly as it has the potential to reduce costs significantly.

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richms

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Reply # 1427128 12-Nov-2015 19:33

Im going to be putting 4.something kw of panels on the NE facing garage as soon as I can get someone to re-do the roof (building contractors hate small jobs) which should cover my water heating and some of the other load. $9k for the panels installed. As that loses the sun at about 3:30pm totally, I can if needed stick some on the NW facing shed to get more power later in the afternoon and hopefully not have too much overlap between them in the middle of the day since they will both be off axis.

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Dynamic

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Reply # 1427137 12-Nov-2015 19:44

richms: Im going to be putting 4.something kw of panels on the NE facing garage as soon as I can get someone to re-do the roof (building contractors hate small jobs) which should cover my water heating and some of the other load. $9k for the panels installed.

Nice project! What's your expected return on the investment, as in how long before the project pays for itself?

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mattwnz

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Reply # 1427140 12-Nov-2015 19:57

Dynamic:
timmmay: The national grid usually sells power for around 5-8c/kwh, so they're just paying market rates really. You are better off using it yourself though. A friend of mine has his powering his two hot water cylinders and spa pool, but I'm not sure that's a good way to go.

Getting even a little bit of storage would really help time shifting your generation. @jeffnz may be able to help with batteries and advice.

Batteries for storage are expensive. Storing the energy as hot water is relatively cheap. The energy is locked in to the hot water, but the power savings should be very worthwhile I would think.

That is an interesting point about batteries. Currently the house also has hydronic underfloor heating, and a HWC for that which circulates the hotwater around the slab. From what I can gather, this is heated by a large HW heatpump. The underfloor heating heats a slab of about 160 sqm. It also has a conventional electric domestic HWC for normal hot water. So I would have thought it would have been better for them to feed the power directly into either of those, than feed it back to the grid, or for them to wait for the Tesla Powerbanks to come out. I am not sure they have done it in the best way possible, or what the best possible way is going to be for this situation. There are a lot of solar panels, and I think they said they were generating 15kW a day from it.

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Reply # 1427214 12-Nov-2015 21:32

Tesla Powerbanks are actually pretty low capacity. What you want is a bunch of those 150AH batteries in a shed or something, and using as much power as you can while the sun shines - under floor heating, water heating, etc.

Then if you can work out a way to get onto Flick Electric you can use your stored solar during evening peak and run a bunch of stuff during the night off peak rates.

Actually what some could do is skip solar entirely, just charge up a big battery bank at night when power is (for me) around 8c/kwh, heat your hot water cylinder and such, and use the stored power during the day. I suspect the payback time could be lower than solar.

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richms

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Reply # 1427248 12-Nov-2015 21:46

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Efficiancys on charge and discharge on some battery types is already pretty horrific, if you are then also adding on inverter losses etc as well I dont think that 8c in to save use at 22c later on would really make sense. For sure put it all into hot water storage and buy a bigger tank so you have enough for all day at the 8c heating rate, but paying for the batteries and the losses in it would have to have the numbers on real world lifespans and efficiancy of the gear done to see if it was worth it or not. Im thinking it will fall on the not worth it side of the scale.

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mattwnz

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Reply # 1427297 12-Nov-2015 23:35

richms: Efficiancys on charge and discharge on some battery types is already pretty horrific, if you are then also adding on inverter losses etc as well I dont think that 8c in to save use at 22c later on would really make sense. For sure put it all into hot water storage and buy a bigger tank so you have enough for all day at the 8c heating rate, but paying for the batteries and the losses in it would have to have the numbers on real world lifespans and efficiancy of the gear done to see if it was worth it or not. Im thinking it will fall on the not worth it side of the scale.

Apparently the inverter is a new gen one,and has a 'maximum' efficiency of 96.3% .
I am not sure why they had the solar cells installing to be honest, as it has full access to a good reliable electricity supply.It may have been a business thing. But it is a bonus for me, because it is already installed and it doesn't really add to the worth of the house so it is not something I am paying extra for, so I may as well take advantage of it as it is there. So it is really working out the best way to take best advantage. If I can hook it up to the HWC, either via powering the heat pump HWC (split unit) which is more efficient, or directly to a HWC heating coil, rather than buying batteries, and then sell the surplus back to the grid, that sounds like a possible model to follow.

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