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  # 1427799 14-Nov-2015 00:12

A Rheem 300L Mains pressure cylinder can be bought for $1439 Retail inc GST. It will take 18.75Kw/hr to heat it fully from cold. (50 deg temp rise cold to hot). Therefore each kW/hr of storage costs $76.75 And you can make the cost per kW/hr even cheaper just by turning up the thermostat. Storage losses can be reduced by adding more insulation.

Tesla powerwall - US$3000 = NZ$4592. So each kW/Hr of Tesla powerwall storage costs $656 And you will probably need to add GST, retail markups ect onto that as well. And any battery will loose capacity as it ages. Yet a 300L hot water cylinder will still hold 300L of water after 10 years. And the cylinder has a 10 year warranty as well.

So battery costs will have to come down alot Before they will even be close to the same as hot water cylinder storage.





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  # 1427802 14-Nov-2015 00:23

@JimmyH depending on what model continuous flow gas heater you have. You might be able to add a cylinder that is heated only by solar with the gas providing any necessary boosting. Although if you are using Natural gas, You will be better off just sticking with your current setup as Natural gas only costs approx 6c per kW/hr.

But if you are on LPG, that costs approx 16c per kW/hr. So adding a cylinder could be worthwhile. You could even use electricity to heat the cylinder when wholesale power spot prices are cheap. And then switch back to gas when spot prices rise.





 
 
 
 


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  # 1427867 14-Nov-2015 08:23
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JimmyH: Looks interesting, but every time I run the numbers on solar generation (after including cost of capital and depreciation etc) I can't make them work. Solar water heating, however, (heating the water directly, not using PV) does seem to add up. If only I had a cylinder instead of continuous flow gas.

@Reg1952 - I'm not going to open up a debate about state asset sales, about which you clearly feel strongly. However, based on my calculations of solar PV, which I admit I haven't updated for 12 months or so, I suspect you would have been better off putting the $18,000 into Genesis shares rather than putting it into PV and trying to save and sell them power.



It was impossible for normal kiwi investors to buy genesis shares in those sums via the standard Govt offer.

Some american guy was in the news for getting 1 million dollars of them. 

I applied for 20k of shares, but was allocated 4k. 

Just saying. 

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  # 1427877 14-Nov-2015 09:18
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Aredwood: A Rheem 300L Mains pressure cylinder can be bought for $1439 Retail inc GST. It will take 18.75Kw/hr to heat it fully from cold. (50 deg temp rise cold to hot). Therefore each kW/hr of storage costs $76.75 And you can make the cost per kW/hr even cheaper just by turning up the thermostat. Storage losses can be reduced by adding more insulation.

Tesla powerwall - US$3000 = NZ$4592. So each kW/Hr of Tesla powerwall storage costs $656 And you will probably need to add GST, retail markups ect onto that as well. And any battery will loose capacity as it ages. Yet a 300L hot water cylinder will still hold 300L of water after 10 years. And the cylinder has a 10 year warranty as well.

So battery costs will have to come down alot Before they will even be close to the same as hot water cylinder storage.



Yes for a large family more hot water storage is a very good form of storage, but with just my wife and I we find 180 litres is more than enough. I had thought of buying a spa pool as we don't even have a bath just a shower. But if we want a spa I can just go around visit my son for free LOL. At this time of year we are not using a lot of power. But where battery storage would be of value will be in winter when we have the heat pump running after the sun goes down until it comes up.

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  # 1427953 14-Nov-2015 13:00
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Aredwood: A Rheem 300L Mains pressure cylinder can be bought for $1439 Retail inc GST. It will take 18.75Kw/hr to heat it fully from cold. (50 deg temp rise cold to hot). Therefore each kW/hr of storage costs $76.75 And you can make the cost per kW/hr even cheaper just by turning up the thermostat. Storage losses can be reduced by adding more insulation.

Tesla powerwall - US$3000 = NZ$4592. So each kW/Hr of Tesla powerwall storage costs $656 And you will probably need to add GST, retail markups ect onto that as well. And any battery will loose capacity as it ages. Yet a 300L hot water cylinder will still hold 300L of water after 10 years. And the cylinder has a 10 year warranty as well.

So battery costs will have to come down alot Before they will even be close to the same as hot water cylinder storage.


That is a good comparison. It probably shows that more people should install hydronic underfloor heating, to heat their house as people only need so much hot water for normal household usage. Would people get more efficiency if they used solar to power a heat pump to heat the water?
Also saw on tv, someone connecting solar directly to electric heating coils installed in the floor for underfloor heating, so the power generated was essentially being stored in the thermal mass of the slab.

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  # 1427955 14-Nov-2015 13:11
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It appears if you have mains gas, you are better off selling your solar power back to the grid at 8 cents, and buying gas to heat your water at about 6 cents. This problem I have found with getting info on solar from companies , is that they won't tell you the most economical solution out their, unless the system they are selling is the most economical. They will only tell you about the particular system they sell. So independent advice is needed from an expert who doesn't necessarily sell a particular system.

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  # 1428066 14-Nov-2015 17:43
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surfisup1000:
JimmyH: Looks interesting, but every time I run the numbers on solar generation (after including cost of capital and depreciation etc) I can't make them work. Solar water heating, however, (heating the water directly, not using PV) does seem to add up. If only I had a cylinder instead of continuous flow gas.

@Reg1952 - I'm not going to open up a debate about state asset sales, about which you clearly feel strongly. However, based on my calculations of solar PV, which I admit I haven't updated for 12 months or so, I suspect you would have been better off putting the $18,000 into Genesis shares rather than putting it into PV and trying to save and sell them power.



It was impossible for normal kiwi investors to buy genesis shares in those sums via the standard Govt offer.

Some american guy was in the news for getting 1 million dollars of them. 

I applied for 20k of shares, but was allocated 4k. 

Just saying. 


Ring a sharebroker. Place an order that size and you will have it the next day.



 
 
 
 


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  # 1428551 16-Nov-2015 00:32
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JimmyH:
surfisup1000:
JimmyH: Looks interesting, but every time I run the numbers on solar generation (after including cost of capital and depreciation etc) I can't make them work. Solar water heating, however, (heating the water directly, not using PV) does seem to add up. If only I had a cylinder instead of continuous flow gas.

@Reg1952 - I'm not going to open up a debate about state asset sales, about which you clearly feel strongly. However, based on my calculations of solar PV, which I admit I haven't updated for 12 months or so, I suspect you would have been better off putting the $18,000 into Genesis shares rather than putting it into PV and trying to save and sell them power.



It was impossible for normal kiwi investors to buy genesis shares in those sums via the standard Govt offer.

Some american guy was in the news for getting 1 million dollars of them. 

I applied for 20k of shares, but was allocated 4k. 

Just saying. 


Ring a sharebroker. Place an order that size and you will have it the next day.




You have to pay brokerage fees, unlike when the offer came out. Also not sure about Genesis, but other ones there were perks with buying some of the power companies, which you wouldn't get if you buy off the normal market. 

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