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New Solar Installation - Technical questions, Optimising ROI and >95% Off Grid


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Afternoon all!

We have just installed a new system, and seems that we got most of it right.  Now busy learning, and tweaking and finding more stuff to spend money on!  Any comments are welcome, my thoughts are to double batteries, add a heat pump, and some automation to optimise when we use the power.

Setup

1 x 8.8kW Inverter  - SunSynk
2 x 4.8 kWh batteries - Pylontech UP5000
14 x 600W Solar Panels - Canadian

We're adding

2 x 4.8 kWh batteries - Pylontech UP5000
1 x 3.6kW Geyser Heat Pump - probably ITS
3 x WiFi smart switches (for pool pump, geyser, and underfloor heating)

Observations

Base load through the night ~ 500W
Increases with morning activity a bit, but not much.
Pool pump at around 09h00 adds .75kW
Base load during the day is just under 1.5kW

Power hogs

Geyser adds 3.6kW usually between 2-2.5 hours, doing it manually while still learning the installation.
Usually start it between 09h00 and 10h00.
We have 1 x 200l that serves the whole family.
The load varies between about 4.8 and 5.2 kW.

Kettle.  Induction Hob.  Dishwasher?  Washing Machine? Microwave?
Occasionally we see an extra 3kW, pushing us to 8kW.
What else could draw that much for 15-20 minutes?

Daily Load

We're averaging about 40kWh per day.
About 65% from Solar
About 35% from Grid
Evening and early morning about 6 hours at 1.5kW
Night about 8 hours at 500W
So 13kWh of storage needed, call it 15kWh to be safe.

Generation

We're averaging around 25-30kWh by lunch time over the last week which has had a fair amount of cloud and rain, then batteries are fully charged, geyser is done, and we're easily serving anything that's drawing.  So we're getting plenty extra that we're just dumping.

Ooops!

Max discharge (and charge) rate was set at 40A by the installer.  So stuff shut down when we used just under 2kW during load shedding at night.  
Fixed this, now at 100A.  50A per battery (cos it's parallel).
Shutdown was set to 20% capacity and Reset to 20%.  Now to 10% and 20%.

Thoughts

We don't need to be 100% off the grid. 
To avoid having to pay Eskom a few R100 a month because of rain or cloud is just not worth the extra investment.  
W're charging the batteries to 50% from the grid at night, for cover 4 hours load shedding.  4.5 kWh (nominal) should be enough if we don't do anything weird.  It's not enough for cooking etc.

As long as we are still using some grid, then the ROI on a battery is about 5 years.  4.8kWh x R2.89 per day is just over 5 years for a R 26,000 battery.  It's clear that two more won't be a waste. 

At the moment our maximum load during night load shedding is just under 4kW.  Sometimes it's a bit tight...  We have an Induction hob and a gas hob for cooking.  The induction is very efficient, but it can draw serious current for short periods.  Like 31A, roughly 7kW!  We rarely use it at those levels, but the 4kW discharge needs to be increased as we usually cook at night.

Putting in a a heat pump reduces that load from 3.6kW (for 2 hours) to about 1.2kW.  Seems like a no brainer, will even allow water heating for emergencies like daughters sleepover parties, wife's mud wrestling, and so forth.

We feel that we're generating enough kWh during the day.  Seems that we need to address:
1. Storage for the night
2. Power hogs at night
2. Load

Questions?

1.  Battery setup will take 200A maximum discharge, but this would go over the maximum 8.8kW of the inverter.  Is 180A cutting it to fine (48V * 180A) and should we rather set to 160A.

2.  Can we just mirror the discharge rate for the charge rate?

3.  How many people adjust their panel angle each month / season?  I saw a calculation that showed 88° in Summer, down to 40° in winter.  Is this significant or not worth the effort?

4.  Is 10% right for the shutdown?  Should it be higher than 5% or is it okay if the specification for Depth of Discharge is 95%.  Do we need some wiggle room here?

5.  Is 20% good for Reset?  I understand the Reset to be when it powers back up again, and that this should higher than shutdown so it doesn't flap when storage hovers around the shutdown limit.  
What is reasonable for this gap?  5%? 10%?  More?

Thank you for making it this far, any other obvious tips, please!
 

Edited by BluePeter
Fomatting, grammar
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1) The inverter determines how much it wants to pull from a possible max 200A. So no problem here. Cable sizes should be your determining factor not the supplier(battery) or the consumer(inverter).

2) yes

3) No, most pylontech batteries will shutdown at around 10%. Even if it advertises 95%. Cell imbalances will trip the BMS and it will shutdown. Set to 15% and forget.

4) 20% is fine

With regards to your projected generation figures. Be careful. Winter is coming and there is lower solar irradiance and this simply can't match the yields you get in summer.

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25 minutes ago, root said:

1) The inverter determines how much it wants to pull from a possible max 200A. So no problem here. Cable sizes should be your determining factor not the supplier(battery) or the consumer(inverter).

2) yes

3) No, most pylontech batteries will shutdown at around 10%. Even if it advertises 95%. Cell imbalances will trip the BMS and it will shutdown. Set to 15% and forget.

4) 20% is fine

With regards to your projected generation figures. Be careful. Winter is coming and there is lower solar irradiance and this simply can't match the yields you get in summer.


Awesome

1.  Good point, I'll double check the cable sizes.  I don't think it's a problem though, I saw them, they're huge!  
3.  Any thoughts about Panel angle?
4.  Good advice, will set to 15%.  Where did you get this data / information that they shutdown around 10%?  

Generation.  Yes, agreed.  This is what I'm getting, I'm too new at this to project anything yet!  I did see some data that showed big differences in generation in the Cape through the season, but little variance in Johannesburg as the shorter days are offset with absolutely clear days.  I'm not making any assumptions yet, but here's the graphs:
https://mybroadband.co.za/news/energy/451432-why-south-african-solar-power-systems-can-underperform-in-winter.html

And thanks for your input!

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2 hours ago, BluePeter said:

Kettle.  Induction Hob.  Dishwasher?  Washing Machine? Microwave?
Occasionally we see an extra 3kW, pushing us to 8kW.
What else could draw that much for 15-20 minutes?

Could be that your dishwasher and/or or washing machine are going through the water-heating portion of the cycle, as opposed to just washing/spraying/tumbling.

2 hours ago, BluePeter said:

We're averaging around 25-30kWh by lunch time over the last week which has had a fair amount of cloud and rain, then batteries are fully charged, geyser is done, and we're easily serving anything that's drawing.  So we're getting plenty extra that we're just dumping.

I would suggest holding off on the heat pump until you've first put in the extra batteries, monitored, and then decided if you still need the heat pump. Wasn't sure if you're saying it's already decided.

I just don't see much point in installing an energy-saving heat pump at a time when you've already got a surplus of power that you're dumping. Your 8.4kW of mostly idle panels from lunchtime until evening should go a long way regardless towards charging your extra 9.6kWh of storage.

Unless you don't mind just spending the money on the heat pump for the hell of it.

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14 minutes ago, GreenFields said:

I just don't see much point in installing an energy-saving heat pump at a time when you've already got a surplus of power that you're dumping. Your 8.4kW of mostly idle panels from lunchtime until evening should go a long way regardless towards charging your extra 9.6kWh of storage.

Unless you don't mind just spending the money on the heat pump for the hell of it.

Damnit!

Already made the emotional decision to buy the heat pump, it's like R16k.  Feeling all self righteous that I made the proper decision and now you come along and make a perfectly valid point.

Hmmmm.   Definitely need to give this heat pump thing more thought... Thanks.

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11 minutes ago, BluePeter said:

Damnit!

Already made the emotional decision to buy the heat pump, it's like R16k.  Feeling all self righteous that I made the proper decision and now you come along and make a perfectly valid point.

Hmmmm.   Definitely need to give this heat pump thing more thought... Thanks.

I'm of a different opinion, you made the right choice by getting the heat pump. He did mention that your production is going to be low in winter and that is where you will need the heat pump the most. Not sure if you stay with family members like my wife and daughter, the shower with boiling water and that means you will have to switch on your geyser in the early hours and that will drain your 4 x 4.8Kwh batteries so fast that you will wish you had gone with the heat pump. Heat pump or gas water heater are the best solution for water heating when you have solar, IMHO

Edited by hoohloc
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22 minutes ago, hoohloc said:

I'm of a different opinion, you made the right choice by getting the heat pump. He did mention that your production is going to be low in winter and that is where you will need the heat pump the most. Not sure if you stay with family members like my wife and daughter, the shower with boiling water and that means you will have to switch on your geyser in the early hours and that will drain your 4 x 4.8Kwh batteries so fast that you will wish you had gone with the heat pump. Heat pump or gas water heater are the best solution for water heating when you have solar, IMHO

It's definitely worth extra thought. 

At the moment we turn the geyser off (manually, will fix that) around 16h00.  Kids shower in the evenings, I'm early morning, the wife a bit later (she goes running at 04h30, not entirely sane).

We haven't had an issue with hot water so far.  Lot's to think about, that emotional decision to buy still prejudicing my choice...

Thanks!

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21 minutes ago, hoohloc said:

I'm of a different opinion, you made the right choice by getting the heat pump. He did mention that your production is going to be low in winter and that is where you will need the heat pump the most. Not sure if you stay with family members like my wife and daughter, the shower with boiling water and that means you will have to switch on your geyser in the early hours and that will drain your 4 x 4.8Kwh batteries so fast that you will wish you had gone with the heat pump. Heat pump or gas water heater are the best solution for water heating when you have solar, IMHO

Fair counter-arguments to consider, but I'll stick to the opinion to monitor first, and then decide. Since this is still on-grid, I think that this leeway exists. Ultimately it's for the buyer to do as he pleases.

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30 minutes ago, BluePeter said:

Hmmmm.   Definitely need to give this heat pump thing more thought... Thanks.

Think about it by all means. Then do it. 

My main geyser is on a heat pump. As you've noted, load is less and run time shorter, so I get away with having the heat pump on the backed up side of the DB.

I control the heat pump with its built in timer. Because it's on the backed up side of the DB we always have hot water irrespective of when load shedding happens. It first switches on at 6:00, and I might push that forward to 5:00 if I have to go to the office. 

I had the heat pump before I had solar. After I'd watched it for a while and seen how the system reacted I had it moved over to the backed up side of the DB. 

The other thing you could try is to downgrade the element in your geyser. I've done this for my guest geyser (not backed up). I can usually heat that in about two hours in the afternoon, never drawing more than the available PV. 

I wouldn't run the two geysers at the same time. This is where timers come in. 

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Although I have a ITS heat pump for 9yrs I can agree with GreenFields on holding back. 

I would at least look at the 4.7kW ITS heat pump for the 200L geyser. If not you are are going to have a much longer run time to heat the geyser than with an element. Not sure if the current 4.7kW ITS is made with an inverter start unit like mine. This saves short term current spikes when starting. 

Remember in winter a heat pump can take double the time it takes in summer to heat water due to lower COP and colder water entering the geyser. 

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2 hours ago, Bobster. said:

Think about it by all means. Then do it. 

 

Thanks, good to understand your setup.

Unfortunately, I'm fairly similar to you, except I generally think less, and just do...
To use an apt metaphor, in life I don't test the temperature before getting into the bath.  I jump in with both feet, and then deal with whatever I find.

But I think there's enough maths in all this to be able to make informed decisions, which is why all this input from others is so valuable.

Appreciate the response.

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1 hour ago, Scorp007 said:

I would at least look at the 4.7kW ITS heat pump for the 200L geyser. If not you are are going to have a much longer run time to heat the geyser than with an element. Not sure if the current 4.7kW ITS is made with an inverter start unit like mine. This saves short term current spikes when starting. 

Remember in winter a heat pump can take double the time it takes in summer to heat water due to lower COP and colder water entering the geyser. 

Price on the 3.6kW equivalent heat pump is R2k less than the 4.5 and 5.4 models.

It's not material.  So the question is to heat faster, but with higher load, or slow and steady.  Is bigger / faster always better?  A load of 1.8kW compared to 1.2kW is worth it for faster hot water, I guess.

Good point about heating water in Winter...  didn't think about that.  

Thanks!

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14 minutes ago, BluePeter said:

Price on the 3.6kW equivalent heat pump is R2k less than the 4.5 and 5.4 models.

It's not material.  So the question is to heat faster, but with higher load, or slow and steady.  Is bigger / faster always better?  A load of 1.8kW compared to 1.2kW is worth it for faster hot water, I guess.

Good point about heating water in Winter...  didn't think about that.  

Thanks!

Obviously requirements differ. On the few winter nights of 0-3 degrees the heat pump can take 3 times the element time. Now in summer my heat pump is quicker than a 3kw element on a 150L geyser. At the quoted temps the COP can drop from 3 to 1.

The thing is with visitors we find some like to relax in a bath. If this is on a winter night then you will appreciate the price for convenience is worth it. 

I can add that I have never used the element since I got the heat pump. I know some people would use the element on these cold night. This is included as standard. 9 yrs ago if one wanted to use the element there was an adaptor needed as the heat pump used the thermostat pocket so no 2nd pocket for the element thermostat. With all the current controllers like Geyser wise it would be a lot easier. 

Edited by Scorp007
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2 minutes ago, Scorp007 said:

The thing is with visitors we find some like to relax in a bath. If this is on a winter night then you will appreciate the price for convenience is worth it. 

We could always insist that visitors bring a fully charged battery!

Thanks again.

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9 hours ago, BluePeter said:

But I think there's enough maths in all this to be able to make informed decisions, which is why all this input from others is so valuable.

For me, early on there was a large element of watching how the system reacted to my moving loads around. At first this was trial & error, but I got better at it. 

We're fortunate with the heat pump and with all gas cooking. That's really two important but big loads that are now Eskom proof. 

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15 hours ago, BluePeter said:

3.  Any thoughts about Panel angle?
4.  Good advice, will set to 15%.  Where did you get this data / information that they shutdown around 10%?  
 

3) Try and optimise as much as possible. The gains are small, but over the life of the system (20y+) those gains add up to a significant amount.

4) Anecdotal evidence watching and accidently shutting down my system and my fathers system. Both Victron systems. I have 5x us3000c batteries, he has 8x us2000c. Both shutdown at around 10% SOC. 

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A battery should be viewed as a way to keep loadshedding at bay, it kills any ROI of your system. Storing solar energy is not cost effective.

A 5kWh battery stores 4kWh of power (20% reserve) so effectively 4 * R2.50 = R10 of electricity per cycle (or per day)

Which means that if you purely stored solar power it would have paid for itself and cycled the full usable capacity every day you would break even in 7 years and 2 months, but we all know this is not realistic since you seldom use all the capacity and there are several days where my batteries only see 60-70% when weather is poor. Assuming that your battery also degrade 20% in 10 years then you will be lucky if you reach ROI in 10-11 years.

Your optimal way of using the battery would be to keep just enough reserve in the battery and run off the grid when you dip below the required percentage. This is exactly what the time of use schedules on the sunsynk/deye allows you to do. There is no shame in switching to grid when it is available. Charging from the grid will cause a 20%  round trip loss and should be avoided (unless the grid will be off most of the night and you need the power to make it to morning).

If you need to heat water for 5am showers then a heatpump is a solid choice (also assuming you need more than 100l of hot water per day), I run mine off my battery and it uses about 1-1.9kWh depending on the season. I heat my water just in time for usage, but on days with excess solar I dump as much energy into the water (that would have been wasted)

Initially I sized my battery to be self sufficient but this proved to be a poor choice pushing the ROI of my whole system to roughly 9years (with current prices and assuming full production every day which is not reality). I have since crunched some numbers and adjusted my understanding. 

1. Solar panels best investment

2. Inverter to automatically manage the use of cheapest power

3. Battery - Grudge purchase due to Eskom's failure to keep the lights on. 

 

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5 minutes ago, iiznh said:

A battery should be viewed as a way to keep loadshedding at bay, it kills any ROI of your system. Storing solar energy is not cost effective.
...
...

1. Solar panels best investment

2. Inverter to automatically manage the use of cheapest power

3. Battery - Grudge purchase due to Eskom's failure to keep the lights on. 

 

That's interesting...
Agree with points 1 and 2.  

But not sure how batteries lower the ROI compared to not having a battery.
I get the round trip cost, storing grid energy in the battery to deliver later isn't really effective.
But surely storing free Solar energy and using this instead of the grid is a saving?

Am I missing something here?

Regarding dumping excess Solar into heating water, are you using Smart Switches for this?

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42 minutes ago, BluePeter said:

But surely storing free Solar energy and using this instead of the grid is a saving?

The free energy that you are storing has a well defined price (the cost of a battery & usable cycles ) vs the cost of the same power from the grid

 

42 minutes ago, BluePeter said:

Regarding dumping excess Solar into heating water, are you using Smart Switches for this?

Yes, smart switches to turn on heatpump. Another smart switch to turn on element once the heatpump switches off. No thermostat other than my own sensor. Smart switch has a failsafe to auto switch off when wifi is lost for more than 5 minutes. All driven from my home automation

Edited by iiznh
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31 minutes ago, BluePeter said:

But not sure how batteries lower the ROI compared to not having a battery.
I get the round trip cost, storing grid energy in the battery to deliver later isn't really effective.
But surely storing free Solar energy and using this instead of the grid is a saving?

I think so too. Or I will at least think about it a bit.

On a good day, right now, I get enough solar to power the house and, for enough of the day, out buildings AND to charge my batteries. Then at night I run off of batteries.

Pre solar I used 13 to 14 kWh a day. Now I produce nearly all of that.

With just panels on my roof, and no load shedding, I would have to run off the grid at night, but I also wouldn't have had to fork out for batteries - the single most expensive component of my system, and by some way.

So the R in "ROI" goes up a bit, but the I goes up quite substantially. So payback gets further away.

Two notes
1) My electricity bill was not great before I went solar. Less than 500 units per month, nearly every month, and I have a prepaid meter.
2) There are what I call "soft returns" as well. These can't be measured on a meter, but they are worth something. Different folks might assign that something different values. It's things like always having the lights on, always having hot water, having continuity of something other than loadshedding. 
 

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40 minutes ago, iiznh said:

The free energy that you are storing has a well defined price (the cost of a battery & usable cycles ) vs the cost of the same power from the grid

Yes, so 4500 cycles * 4.5 kWh = 20.25MWh.
At R 2.89 (now) / kWh that's R 58,500 in saving. 
Battery is R26,000.

Even, 4000 cycles * 4 kWh = 16MWh.
At R 2.89 (now) / kWh that's R 46,200 in saving. 

This is not taking Eskom price increases into account, R3.41 from June...

Edited by BluePeter
Bad maths
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Thanks to Eskom I believe this is the best money I ever spent.
By my calculations and my home usage pattern and system setup I get the following with a break even halfway through year 7
This is one only calculated to 10 years with a MODEST  yearly increase of 5%
This all may change if/when eskom introduce their proposed fixed monthly fees.

solar-system-breakeven-10-years.thumb.jpg.38a4a3104c17624bd20d7f4d97830e86.jpg

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In my case, system 1 1/2 years old. 2 X 5 KW growatt inverters 12 X 450 W panels, 1 X 5.1 KWH LBSA battery, 

  1. No more load shedding.
  2. Reduced my municipality bill by +_ R900/month.
  3. So far used 1.4 MW out of my battery. @ R 1.8 per unit = R 7,200 according with my calculations I've saved +_ R 16,000.00, best investment ever.

See my battery dashboard use in the last 6 months, I must add only use the battery for load shedding. 

image.thumb.png.5fc4de264109ced9870ef02259901263.png

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I purchased an Emporia Vue 2 which tracks power usage of 16 circuits on my DB board. 

Very handy for tracking down rogue users of power 🙂 

https://www.amazon.com/Emporia-Monitor-Circuit-Electricity-Metering/dp/B08CJGPHL9/ 

Reflashed with ESPhome so it speaks directly to Home Assistant and gives me daily as well as real time power usage 

image.thumb.png.a1e0ce9f2e663b5c54543c9b1db8e33b.png

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