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Posted

Hi

I have been reading furiously for the last week, from Victron wiring guides, to spec sheets to maps and calculators for solar power not to mention this forum and a couple of other local ones.

The current system is just a UPS for the internet and a battery lantern so starting from a clean slate. The UPS needs new batteries and the second lantern could use one too...

Based on the Eskom postpaid bills that used actual meter readings the average (over two months) daily usage is below 8kWh per day. A few years back it was below 6kWh so that figure is nothing special.

The electrical consumption doesn't change much between Summer and Winter probably due to using a gas heater and not running the wellpoint pump for irrigation in Winter.
Based in Cape Town, the best roof surface is facing mostly north but slightly to the East at 14.5 degrees. The slope of the roof is 33 degrees.

Already have LED lights throughout, an efficient fridge and freezer, solar flat panel rooftop geyser that pre-feeds the electric geyser in the roof space which has a geyser blanket and some pipe lagging. There is no TV, tumble dryer, aircon or pool. Stove / Oven are both electric and are non induction although the oven has a fan. I do have a has hot plate when Eskom is really playing up and meal time can not wait.

The primary goal is to reduce the impact of load shedding as I work from home during the day and sometimes the evenings too. That means having power for telecoms, lights and coffee, run a microwave, washing machine, dishwasher, vacuum cleaner and so on during load shedding. And no the washing machine, vacuum cleaner, microwave won't typically be running at the same time and especially not during load shedding if the battery is being used... 😉

The secondary goal is to save on electricity costs. I get that with my low usage I won't recoup the costs of the battery and inverter but Eskom has forced my hand on that front. The solar panels should hopefully pay themselves off and then make a small dent in the other capital costs.

I am trying not to over capitalise but I do want to allow for future expansion without having to rip and replace too much. I want to be able to blend power from Solar, Battery and Eskom sources. Hence the choice of the Deye inverter.

I am trying to right size the system using tools like:
https://globalsolaratlas.info/detail?c=-33.331676,17.471008,9&s=-33.826505,18.49411&m=site&pv=small,14,34,4.5

https://powercalculator.ibc-solar.com/

https://re.jrc.ec.europa.eu/pvg_tools/en/

I am thinking of the following system:
Inverter: Deye 8K
Battery chemistry: LiFeP *
Batter size: Probably 5kWh but maybe 10kWh if there is a good reason.
Battery brand: Undecided, but Freedom Won eTower, Revo, Dyness, Pylontech are being looked at.*
Solar panel type: Mono
Solar array size: About 4.5kW.#

* I was originally keen on the Hubble but then it seems they do not use LiFePO which I want for longevity and the greater discharge rates. If this is incorrect then please point me to the spec sheet that states which of their batteries use this cell chemistry.

# I get that the solar panels are perhaps oversized but I am trying to cater for the Cape winter when there are overcast days.

I have a sparky lined up to wire into the DB and issue the CoC. I am pretty handy and I can read so a self install of the panels is an option. However that roof is pretty steep... I am not afraid of computers, serial cables or firmware upgrades as I have gone deep down that rabbit hole many times before. 😄


I am open to suggestions and would love to hear your experiences on the options. Suppliers and installer suggestions would also be useful.


Cheers,

Smitty

Posted

As a low user of only 8kwh a day I would start with a 5kw Sunsynk and only add a 2nd one if needed. Also it seems as if a 5kwh battery will be fit for purpose. Only get a 2nd one after using the 5 for a month or 2. ROI is greatly affected by spending a R25 000 that might not be needed.

As you are working from home loads can be adjusted to use during the day. The 4.5kw panels can produce an easy 18kwh during the summer day time with full sun. 2nd battery only needed if you have long Eskom outages.

Just my 2c worth.

 

  • 2 weeks later...
Posted
On 2022/04/29 at 6:45 AM, Scorp007 said:

As a low user of only 8kwh a day I would start with a 5kw Sunsynk and only add a 2nd one if needed. Also it seems as if a 5kwh battery will be fit for purpose. Only get a 2nd one after using the 5 for a month or 2. ROI is greatly affected by spending a R25 000 that might not be needed.

I have been thinking about what you wrote but I do have a limit on the space for the inverters so I will probably only be able to fit one. Otherwise I would agree that a 5KW inverter and a 5kWh battery combination would be optimal from an ROI point of view.

With the recent load shedding, and I expect a lot more as Eskom in the future, the ability to continue working and living while the power is out is a must. At this point I do not worry about ROI because I expect the future price of electricity to be vastly higher due to the compounding effect of yearly price increases and the cost of downtime is too high. I'll still spend money on solar panels to claw back some of that and to gain a degree of grid independence.

In sort I think I am going to need to go with an 8KW inverter and batteries to match. Not much point having an 8KW inverter that can draw more than a single 5kWh battery can supply.
 

On 2022/04/29 at 6:45 AM, Scorp007 said:

As you are working from home loads can be adjusted to use during the day. The 4.5kw panels can produce an easy 18kwh during the summer day time with full sun. 2nd battery only needed if you have long Eskom outages.

Eskom load shedding windows are generally two hours but occasionally (maybe once a year) the power fails to come on after load shedding and leads to an extended outage of around 12 hours.

Ja the panels are going to over produce a lot of the time and no grid feed in available as far as I know for Eskom direct residential supply. However, panels are comparatively cheap and can feed the batteries so over sizing the array for days with poor sun, e.g,. Cape winters, seems like prudent decision.

Thanks for weighing in, I do appreciate it.

 

I am looking at 2x 48kWh Dyness wall mount batteries at this point.
 

Posted

I took the dive last year in August and then added Solar Assistant end of October.
My usage was and is pretty similar to yours. Between 250 and 300kW per month.
My full system is in the signature.
I manage with one 5,5kW battery and I have many a time considered the extra R25k for a second battery just to give me complete peace of mind.
My system is in island mode, i.e. I use either my solar or if I need to I switch over to Grid via a change over switch before my main DB.
We had some really cloudy days where I switched to grid to ensure my battery is charged fully before sunset. 
My usage from the Grid since December has been around 20kW per month average. Even at R3 per kW that is about R60. That would be R720 per year or R7200 over ten years ignoring electricity price increases. And that is what has stopped me from adding another battery. It makes no economic sense to have bragging rights of zero grid usage when the additional battery cost is 3 times the amount of using Grid for that little bit. 
Only once in the beginning did my battery end up at 20% SOC. Normally it is between 30 and 40% at sunrise and fully charged just after 9 now in the wintertime.
At 10 my Geyserwise switches on the 3kW element to heat the water to the max the Geyserwise allows. The rest of the day the flat panel Geyser conversion continues to heat it further.
I obviously manage the high load appliances manually to stay within the 5kW limit. 
My Solar system stats for the last 6 months or so are in the table below.
Lots of spare capacity during the day. I probably only use about 20- 30% of the potential energy of the panels per day. 
image.png.7ccbddca322541844995ba6886111d8e.png

Posted
On 2022/05/13 at 5:55 AM, Scorp007 said:

2 x 48kwh? Or 4.8kwh 😄

2 x 4.8kWh otherwise Eskom would be facing some serious competition from solar if batteries were that cheap. 😅

Posted
On 2022/05/13 at 8:01 AM, zsde said:

I took the dive last year in August and then added Solar Assistant end of October.
My usage was and is pretty similar to yours. Between 250 and 300kW per month.
My full system is in the signature.
I manage with one 5,5kW battery and I have many a time considered the extra R25k for a second battery just to give me complete peace of mind.
My system is in island mode, i.e. I use either my solar or if I need to I switch over to Grid via a change over switch before my main DB.
We had some really cloudy days where I switched to grid to ensure my battery is charged fully before sunset. 
My usage from the Grid since December has been around 20kW per month average. Even at R3 per kW that is about R60. That would be R720 per year or R7200 over ten years ignoring electricity price increases. And that is what has stopped me from adding another battery. It makes no economic sense to have bragging rights of zero grid usage when the additional battery cost is 3 times the amount of using Grid for that little bit. 
Only once in the beginning did my battery end up at 20% SOC. Normally it is between 30 and 40% at sunrise and fully charged just after 9 now in the wintertime.
At 10 my Geyserwise switches on the 3kW element to heat the water to the max the Geyserwise allows. The rest of the day the flat panel Geyser conversion continues to heat it further.
I obviously manage the high load appliances manually to stay within the 5kW limit. 
My Solar system stats for the last 6 months or so are in the table below.
Lots of spare capacity during the day. I probably only use about 20- 30% of the potential energy of the panels per day. 
image.png.7ccbddca322541844995ba6886111d8e.png

Thank you, this is very useful information!

Unfortunately I paid for the inverter and batteries on Wednesday. Oh well, should be able to carry on more or less as normal once it is installed. The two batteries should hopefully prevent them from being a bottleneck in term of current draw by the inverter. Also those grey months of winter with short days are more of a problem in Cape Town than Johannesburg so hopefully a larger battery bank will help tide me over. Might also have an added benefit being able to work the batteries less hard.

I do agree on your analysis of the cost versus benefit of remaining on the grid versus adding another battery.

My original goal was to become grid independent rather than to be completely off of it. The kWh unit cost is now R2.11 so the price is not the problem but the reliability sure is.
On the other hand Eskom is now charging almost than R2015 per year just for being connected to the grid. That fee goes up each year by the same percentage as fee for the power consumption goes up. Forecasting or predicting is never easy but the way the past increases have compounded year on year is scary. Assuming an 8% increase per year an additional battery would be paid for in 8 years just by the network connection charge. Factoring in decreased power purchases of 20kWh per month would drop that to seven years. In short Eskom is actually incentivizing me (and others) to go off grid with that connection charge.

Hmn did a search and found this 2016 paper for South Africa's Eskom.
https://www.wits.ac.za/media/wits-university/conferences/misgsa/documents/MISG 2016 Utility Pricing Death Spiral.pdf

As I recall we are in low growth pattern since 2016. The future is looking dark if you'll pardon the pun...

Yes, I can imagine that a lot of the generation potential of your panels does not get used and you can't store that much of it either in the battery. At least you are using your water heater as a thermal battery to make the most of those panels. I have been measuring the water heater and the consumption (water heating and standing losses) is currently about 2kWh per day per person, although this is with a flat plate solar geyser as the source of the replacement water. As mentioned earlier the HWC does have a gesyer blanket and the pipes have some heavy duty lagging fitted on anything that felt warm to the touch, including overflow, and other pipes. The water saving shower-heads also help a lot.

For most countries having a bunch of power pushed into the gird when it is not needed in the middle of the day is not useful, but here we have such a generation shortfall, as evidenced by the large amounts of emergency generation being used (ZAR billions of diesel) and still having to load shed to prevent the grid from collapsing, it would actually help. We could use any excess solar for our pumped storage and to keep those OCGT off while we fill up or at least don't drain the diesel tanks. I.e., desperate times calls for desperate measures and we are deep in it at this point. Who knows we (think of all those shops and offices with solar) may get the option to feed in to Eskom at some point. I can't even find the Eskom paperwork for that and have no panels yet so it is currently a moot point but at least the capability will be there if it becomes viable. Failing that it will operate in a zero feed in mode.


 

Posted (edited)

Imagine what LS would be like if it wasn't for the estimated 7000 MW of PV installs in the country. Quite a bit of this is also used from batteries during the no sun/peak periods.

Edited by Scorp007
Posted
On 2022/05/15 at 9:14 AM, Scorp007 said:

Imagine what LS would be like if it wasn't for the estimated 7000 MW of PV installs in the country. Quite a bit of this is also used from batteries during the no sun/peak periods.

I am sure load that shedding would be worse without the solar installs. My point is that when we reached the stage of 24 hour a day load shedding then it means that Eskom is desperately short of generating capacity and  then every bit of solar feed in helps because Eskom can dial back on draining the pumped storage or diesel tanks for the open cycle gas turbines. In fact as long as there is pumped storage that can be pumping back up hill then solar is useful to the grid provided there isn't already existing generation capacity that is sitting idle. Most electrical grids around the world have surplus generating capacity during the day between the morning and evening peak demand while ours is regularly running short.

With our backlog of maintenance on our generation units, our electrical grid is in dire straights and has been for years. Taking demand off the grid helps it one way because it allows more units to be fixed whether planned or unplanned. On the flip side, losing paying customers or at least large chunks of their power purchases when they have started using alternative energy, is not going to help, especially if there was cross-subsidisation was going on, i.e., those lost customers were the ones paying a premium price.

Recently we have started having load shedding only in the evenings so here the batteries come into play and help with peak shifting. Although if anyone shifts their usage / load around during the day to benefit from the hours when the sun shines best, they would have already flattened their usage / load curve.

On that note Eskom really needs variable pricing to encourage everyone to shift their usage as much as possible out of peak load times because this is the most expensive electricity to generate. I would have happily put my fridge, freezer, geyser, and anything else I could on a timer years ago if power was cheaper late at night. Before anyone grabs their pitchfork this would also mean cheap electricity to recharge batteries during off-peak times. 😉

Posted (edited)
On 2022/04/28 at 5:18 PM, SmittySmit said:

Inverter: Deye 8K
Battery chemistry: LiFeP *
Batter size: Probably 5kWh but maybe 10kWh if there is a good reason.
Battery brand: Undecided, but Freedom Won eTower, Revo, Dyness, Pylontech are being looked at.*

Look at batteries and inverter as a combination. In particular, you want comms between the BMS and the inverter. That means that instead of the inverter using whatever best guess method it has to figure out what state the batteries are in and what they need, the BMS will send data to the inverter to indicate what is required.

I have a Goodwe inverter and Revov batteries.

The Goodwe comes preconfigured for (some examples, not a complete list) Pylontech, LG, BYD, Dyness but not the other brands you mention. To run those other brands (Revov in my case) I have to use Goodwe's "self define" mode and forgo comms. This sort of works most of the time, but sometimes it doesn't. Because the BMS and the inverter don't always agree on SOC, I can't use some of the more advanced features on the inverter.

If I had Pylontech batteries I could just connect them, plug the comms cable in and set my Goodwe to know it's talking to Pylontechs. Much better. (and maybe not as simple as I described, but the Goodwe can accept comms from the Plyontechs and so doesn't need to "best guess" the state of the batteries).

So check out the spec sheet for the Deye and for the different batteries. You don't just want to see settings to use brand X inverter with brand Y batteries (Revov provide settings for Goodwe inverters, for example), you want comms between them. This is first prize. 

I have had a fair few battery related problems, and one observation I will offer is that Pylontech seems to be the brand that most inverters know how to talk to.

Edited by Bobster
Posted
11 hours ago, Bobster said:

Look at batteries and inverter as a combination. In particular, you want comms between the BMS and the inverter. That means that instead of the inverter using whatever best guess method it has to figure out what state the batteries are in and what they need, the BMS will send data to the inverter to indicate what is required.

I have a Goodwe inverter and Revov batteries.

The Goodwe comes preconfigured for (some examples, not a complete list) Pylontech, LG, BYD, Dyness but not the other brands you mention. To run those other brands (Revov in my case) I have to use Goodwe's "self define" mode and forgo comms. This sort of works most of the time, but sometimes it doesn't. Because the BMS and the inverter don't always agree on SOC, I can't use some of the more advanced features on the inverter.

If I had Pylontech batteries I could just connect them, plug the comms cable in and set my Goodwe to know it's talking to Pylontechs. Much better. (and maybe not as simple as I described, but the Goodwe can accept comms from the Plyontechs and so doesn't need to "best guess" the state of the batteries).

So check out the spec sheet for the Deye and for the different batteries. You don't just want to see settings to use brand X inverter with brand Y batteries (Revov provide settings for Goodwe inverters, for example), you want comms between them. This is first prize. 

I have had a fair few battery related problems, and one observation I will offer is that Pylontech seems to be the brand that most inverters know how to talk to.

I skipped on Revov because I contacted them and they referred me to an installer. I was looking for prices and specs, not a middleman who has a vested interest in selling me something. This is even more the case when their website is a bit light on details of what their various batteries can do.

In the end I did as you suggested and bought Dyness batteries as they support Deye inverters. I agree that having batteries and inverters that can communicate with each other are important.

The electrician is busy until the end of May so currently I have some large boxes taking up space. Today I started reading the manuals and checking the contents against the packing lists. I am hoping everything is happy when it gets hooked up.

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