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  Reply # 1861086 8-Sep-2017 20:58
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If you are including batteries in your calculations you need to take into account battery life (may require replacing after 8 years). You certainly wont get 25 years.

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  Reply # 1861091 8-Sep-2017 21:20
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larknz: If you are including batteries in your calculations you need to take into account battery life (may require replacing after 8 years). You certainly wont get 25 years.

 

No batteries were harmed in the making of this thread.

 

They are a hard sell for many I think. Very expensive, and once you get one and start counting the evening savings, you also need to be saving for the eventual replacement. Certainly there will be use cases where a lower kW battery can make a difference. 

 

 


 
 
 
 


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  Reply # 1861095 8-Sep-2017 21:32
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larknz: If you are including batteries in your calculations you need to take into account battery life (may require replacing after 8 years). You certainly wont get 25 years.

 

you havent seen some of the newer Lithium Ferro Phosphate (LFP) batteries, they can offer 10,000+ cycles with a DOD of 80-90%, so would last the life of the panels. so thats over 25 years


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  Reply # 1861117 9-Sep-2017 01:09
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Im considering going with a solar system with way more panels than what would otherwise be used. Enough panel capacity to meet baseload even when overcast. And only a small battery system (for now). With lots of dump and diversion loads of course.

 

My line of thinking being is that the prices of solar panels and MPPT controllers are unlikely to drop by much. But battery tech has far larger scope for future improvements and price drops. Im considering around 3KW of panels, but pared to just 120AH of storage at 48V. Giving me 2KW/Hr  at 35% depth of discharge, or 1KW/Hr at 18% depth of discharge.

 

As for dump loads, I already have a 300L hot water cylinder. If I buy a second one, retail price is $1660 and it stores 18.75KW/Hr heated to 60deg. If I heat both of them to 70 or 80 deg, I then have well over 40KW/Hr of storage. To get the same with batteries, for example AA Solar list a 5.28KW/Hr LFP battery for $4569. And I would need at least 7 of them. $32000 for batteries Vs $3320 for hot water cylinders. The cylinders can also be cycled as much as you like, and have a 20 year warranty.

 

My house also has a double internal access garage that takes up 1/2 of the bottom floor. That garage is mostly concrete, and the upstairs bedrooms are directly above it. So I just need to insulate the garage, give it's floor a clean, and install a cheap underfloor heating element kit to the floor on each side. Even heating all that concrete to 20deg using free solar heat is a massive thermal mass that will help to keep winter temps in the rest of the house far more stable. And there is always the spa pool if I need another heat dump. I also could buy a cheap non inverter aircon for summer heat dump (literally). Especially as my house gets really hot during summer.






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  Reply # 1861122 9-Sep-2017 06:28
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@aredwood do you have use for 600L of hot water though?


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  Reply # 1861141 9-Sep-2017 07:54
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Jase2985:

 

@aredwood do you have use for 600L of hot water though?

 

 

I assume that the HW never sees any grid power, so when his solar HW cannot keep the one cylinder fully heated in winter or in an overcast week, the hot water stored is there. OTOH it seems wasteful, but HW costs to heat, its been heated, its there when solar HW or PV cant help. My solar HW is going well, but often at this time of year, the HW is only at the top, I can run out (300l ) unless I boost it. If I had 2 cylinders, pre heated, that takes care of that. 


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  Reply # 1861386 9-Sep-2017 17:23
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Jase2985:

 

@aredwood do you have use for 600L of hot water though?

 

 

 

 

It would be great if you used hot water to heat your house!


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  Reply # 1861455 9-Sep-2017 18:19
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The 600L of hot water storage capacity will be for multi day storage. With the cylinders plumbed in series (I definitely won't use 600L a day of hot water). The current cylinder and new cylinder is/will be installed downstairs. So their heat losses will also be continuous background heating to the house in winter. (I will still add some extra insulation to them though). Also water heating is typically 1/3 to 1/2 of the average powerbill. So if you can eliminate electric water heating, That is a big reduction to the powerbill. Having solar electric boosting with multiple boost elements also improves the usefulness of the solar heat from my hot water panels. As the excess solar PV will initially get dumped via the top boost element until the top half of the first cylinder gets heated to 60deg. Then the bottom element of that cylinder runs until the whole cylinder is heated to 70deg. Only then will the second cylinder get supplied with dumped solar PV power in the same heating process. This is so I get both 60+deg hot water even in not so good sun. And I get the best efficiency out of my solar hot water panels, as they will be mostly heating really cold water up to 30deg or so. And it means that I can get legionella bacteria control with only rarely needing to use grid power to do so.

 

The large panel size also makes it far easier to self consume more of the solar power. Since my power company doesn't support solar, I will be getting a UPS style solar inverter. Whole house operating from the solar / battery supply. When batteries get too low or load is more than what the inverter can supply - The inverter switches to bypass mode. Whole house supplied by grid power. This means I can self consume alot more solar generated power. As it means that appliances which have a really variable current draw (dishwashers and washing machines are a good example). The battery capacity is still able to smooth out the spikes in current draw. Without needing grid power.

 

Another problem is all of the grid connect solar inverters I have seen so far, can only provide a low output capacity when running in off grid mode. Often as little as 1KW. So having say 5KVA continuous /10KVA peak is far more useful to keep everything running during a blackout.






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  Reply # 1861461 9-Sep-2017 18:28
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Aredwood:

 

 

 

My house also has a double internal access garage that takes up 1/2 of the bottom floor. That garage is mostly concrete, and the upstairs bedrooms are directly above it. So I just need to insulate the garage, give it's floor a clean, and install a cheap underfloor heating element kit to the floor on each side. Even heating all that concrete to 20deg using free solar heat is a massive thermal mass that will help to keep winter temps in the rest of the house far more stable. And there is always the spa pool if I need another heat dump. I also could buy a cheap non inverter aircon for summer heat dump (literally). Especially as my house gets really hot during summer.

 

 

 

 

The thing about heating water from PV panels is - is there a more efficient collector and transfer system?

 

Good PV panels give about 18% efficiency. Considering insolation delivers about 1kW per sq meter (max, roughly) , you are talking about getting 180W from that.

 

If you want to heat water, there must be a better/cheaper way than PV.

 

 

 

 

 

I've taken a look at the ROI for solar and it doesn't look promising to me (YMMV). It might be better for a new build where you can optimise site and roof layout - every per cent from optimised orientation helps.

 

If I was going to do it I wouldn't bother with batteries. Power cuts are short and infrequent where I live and the investment in batteries would not be worthwhile.


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  Reply # 1861469 9-Sep-2017 18:39
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Aredwood:

 

 

 

Another problem is all of the grid connect solar inverters I have seen so far, can only provide a low output capacity when running in off grid mode. Often as little as 1KW. So having say 5KVA continuous /10KVA peak is far more useful to keep everything running during a blackout.

 

 

most of the hybrid ones i have looked at for battery systems give the same output as the input from the solar panels, so anywhere from about 4.8-6kw. most will allow about up to 7.5kw for a short period (10-60 seconds)


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  Reply # 1861472 9-Sep-2017 18:40
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elpenguino:

 

 

 

If I was going to do it I wouldn't bother with batteries. Power cuts are short and infrequent where I live and the investment in batteries would not be worthwhile.

 

 

to me batteries are more about not exporting power back to the grid during the day and having to ability to use it in the evening instead of having to import it.


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  Reply # 1861477 9-Sep-2017 18:52
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I understand. Once the cost of batteries is factored in, how much does that evening power cost you?

 

 

 

Or look at it this way. With the money you invest in batteries, what else could you invest in and would it make you more money?


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  Reply # 1861499 9-Sep-2017 19:13
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Not exactly relevant to this thread but as thermal mass concrete has been mentioned, I recently came accross a home (online ) designed around a concrete thermal mass centrally located wood burning fireplace. Great if you have good supply of cheap firewood.

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  Reply # 1861519 9-Sep-2017 19:38
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elpenguino:

 

I understand. Once the cost of batteries is factored in, how much does that evening power cost you?

 

 

 

Or look at it this way. With the money you invest in batteries, what else could you invest in and would it make you more money?

 

 

depends 5.28KW/Hr LFP battery for $4569 which gives you 4.2kwh with 80%DOD and will last about 10,000 cycles, is ~42,000kwh of power and at .22c/kwh if importing it is $9,200. thats best case, even if you were to store half of that you have paid the system off in ~25 years. i dunno, maybe my calculations are wrong.

 

you could say the same about buying a house and paying a mortgage, what else could you invest in and make you more money and to be honest thats really a moot point.


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  Reply # 1861534 9-Sep-2017 20:12
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Jase2985:

 

 

 

most of the hybrid ones i have looked at for battery systems give the same output as the input from the solar panels, so anywhere from about 4.8-6kw. most will allow about up to 7.5kw for a short period (10-60 seconds)

 

 

Have you checked if that is for offgrid (blackout mode), or only for on grid? As alot of the battery systems can only output at max capacity while the grid is connected. With offgrid power only being available from a separate connection that is often restricted to a low max output current. And there are even some systems that can't output anything if there is no grid power present. Sure for some use cases this is perfectly fine, but for me on grid output capacity is of no use to me.

 

Since my power company doesn't support solar PV, I need to get a system that can't physically export power. Both to maintain safety of people working on the power lines network, and to comply with my power companies terms. And my power company (flick electric) is the only one in Auckland AFAIK that offers a peak/offpeak power plan. So if I switch, I loose the cheap offpeak power. Which is especially good at night.






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