I am looking to install a solar system for my house but in a phased approach to limit initial costs. Phase 1 would be to ensure constant power supply (i.e. eliminate loadshedding). Phase 2 would be to reduce monthly electricity costs (currently approx R3000pm).

My average power usage (tracked over last 8 years) is 37.5kWh per day, 33% of which is due to my geyser alone (a single 200l, 4kW Kwikot geyser).
I have CBI timers installed on my geyser and pool pump. I also have a gas stove.
 

• Phase 1: install 8kW Sunsync Inverter with a single 5kW (1C) battery (i.e. essentially operating as a UPS) to ensure constant power supply through loadshedding. Loadshedding in Port Elizabeth is currently no longer than 2 hours at a time which i dont expect will change in the next 6 month when i expect to be able to proceed with phase 2. As part of phase 1 loads will be split into essential and non-essential with essential circuit operating lights and plugs only! Geyser and pool pump will of course operate off non-essential circuit.
• Phase 2: begin adding solar panels and additional batteries (in 5kW increments). The timing of phase 2 would depend on available finances as well as when i could source my prefered black on black panels (aesthetically nicer) which are proving difficult to source. The number of panels and batteries installed is subject to a cost comparison calc based on the note below.

Note: As the NMBM municipailty allows for feeding of power back into the grid a completely off grid system (many panels with many batteries) is not necessarily required.
My understanding of the principle (disregarding baterry storage) is as follows:
In general residential solar systems generate power during off peak periods (sunlight hours) with any surplus power pushed back into the grid at a "low" tarrif. Approx 70% (not sure if this is accurate) of daily power is then drawn during peak and night time periods (peak periods = high tarrif) resulting in a cost differential that is charged by the municipality (ToU tarrif). Should this cost differential over the lifespan of a battery be lower than the cost of a battery itself (required to store excess power), then it makes sense to rather use the grid as a battery (rather than store self generated power in expensive batteries).

Questions:

• I have heard it is not good practice to install a battery with a lower capacity than the inverter size (in this case 5kW battery with 8kW inverter). Although i realise a 5kW (1C) battery will mean the inverter is unable to operate as max capacity, considering this phase is only for 2hr loadshedding periods to feed essential loads, is this anticipated to be a problem?
• Once installed should the 5kW battery ultimately end up regulalry tripping during load shedding (should essential loads exceed +-5kW), i could install a second 5kW battery.
• I am considering using the iGen3 5kW battery which is locally manufactured and therefore locally supported. I understand it is a LiFePO battery, 1C and is compatible with Sunsynk inverters. It appears also to be reasonably priced. Any thoughts and or alternatives?

Any thoughts on the above solar setup would be highly appreciated.

Regards
Richard

Think twice before beginning to export power to the grid. Do your research about the monthly admin fee, the monthly access fee, and only then the difference between the buying and selling rates, not only the difference during peak and off-peak times, but also within the same tariff period (which are not interchangeable), and compare expecially the off-peak time of year to the winter peak... study the tariff booklet long and hard before taking that step. If you have a choice to remain on the current tariff while not exporting, especially before you get panels installed, this should be a strong consideration.

About the 5kWh battery on a 8kW inverter, as long as you know what to expect, and mainly intend for it to carry you through 2hrs of loadshedding at a time, carrying just a few essentials, that's fair enough.

with regards to your battery vs inverter size, i was worried about the same. but it is doable, wev had our system for just over a week (not nearly long enough so treat my points as assumptions not proven fact yet). so far we have had no trips, we have also had no grid power for 4 days due to eishkom, and despite this, still no trips. we can draw 3.5kw (2*3000c pylontechs) at a time on an 8kw inverter, but we do have egoli gas so in the evening our heating needs aren't very hectic and in a our household (4 adults and 2kids) it has been easy to ask everyone to be careful of running either the iron, electric kettle  or microwave at the same time which are our only real big draws. to be safe though i got 3 tuya plugs from takealot, rated for 16a, in the evening if the iron is on the kettle and microwave plugs turn off, if the microwave draws more than 700w the other appliances cant be turned on etc. its not perfect as the tuya plugs still take a few seconds to pass commands via the cloud (local tuya via home assistant would be faster im told). saying all that i think one more battery at least, to take the draw to 5kw and allow for a margin of error is my next priority

Edited May 21, 20233 yr by Woody

7 hours ago, Woody said:

saying all that i think one more battery at least, to take the draw to 5kw and allow for a margin of error is my next priority

Pylontechs are C/2 batteries, so you will need 4 x 3000C to supply 5kW continuously. That gives you about 0.7C.

14 minutes ago, FixAMess said:

Pylontechs are C/2 batteries, so you will need 4 x 3000C to supply 5kW continuously. That gives you about 0.7C.

What is a C/2 battery ? never heard of it ? Pylontech is 0.5C , 3xUS3000C is capable of 111A discharge(5kw+) 

2 hours ago, Nexuss said:

What is a C/2 battery ? never heard of it ? Pylontech is 0.5C

Not sure if you're taking the piss or being serious?

C/2 = 0.5C same as 1/2 = 0.5.

2 hours ago, Nexuss said:

3xUS3000C is capable of 111A discharge(5kw+) 

Yes, they are 37A,    74Ah (C rating) so 37X3 74*3 in parallel = 222 111A. (This would be at 1C), but as you have already stated Pylontechs are C/2, so not recommended to discharge at 111A 222A

Recommended discharge is 37A/battery.

C/2, (0.50C) = 111/2 = 55.2A  = 2640W (55.2Ax48A) @ C/2.

Using the above calc you would require 4XUS3000C. 4XUS3000 = 148A, @c/2 you would pull 74A = 3,5kW...

I have 4 US3000 and regularly pull 100A with no warning or issues from the BMS.

Edited May 22, 20233 yr by FixAMess
Fixed calc values

I am being serious . You are not grasping how c ratings work . 

29 minutes ago, FixAMess said:

C/2 = 0.5C same as 1/2 = 0.5.

Not sure why you are trying to complicate it like that . In the battery world we talk about 0.5C  or 1C or 2C ect. 

 

31 minutes ago, FixAMess said:

Yes, they are 37A, so 37X3 in parallel = 111A. (This would be at 1C), but as you have already stated Pylontechs are C/2, so not recommended to discharge at 111A

This is wrong . The capacity of 3 xUS3000 is 222Ah. 222A divided by 2 is 111A. So you can do 111A continuously. 

 

35 minutes ago, FixAMess said:

I have 4 US3000 and regularly pull 100A with no warning or issues from the BMS.

Yes you wont as you are only pulling 25A per battery and they are capable of 37A each ...

25 minutes ago, Nexuss said:

This is wrong . The capacity of 3 xUS3000 is 222Ah. 222A divided by 2 is 111A. So you can do 111A continuously. 

Yes, you are correct, they're 74Ah, not 37, which is the C/2 rating...I was using the c/2 number already, my mistake.

The recommended discharge rate is 37A per battery so 3 batteries will do..

Thanks everyone for the valuable replies.

It appears that there is no major concern with pairing a 5kW battery with an 8kW inverter for the short term as long as it is understoond that the inverter will not operate at full performance. Consequently loads will need to be carefully managed during load shedding. Should this prove difficult (i.e. regular tripping) then an additional 5kW can be added.

In terms of batteries, i understand an extended warranty on the Sunsynk inverter (5 years to 10 years) is available should Sunsynk batteries be used. It is clear that Sunsynk batteries however are more expensive than equivalent non-Sunsynk batteries. I have also hears that Sunsynk batteries appear to come as both 0.5C and 1C rated.

Question: is the additional cost of installing a Sunsynk battery (=-R3k to R8k depending on the battery) worth paying considering the 5 year extended warranty?

Any thoughts would be appreciated.

19 minutes ago, RichardvdS said:

I have also hears that Sunsynk batteries appear to come as both 0.5C and 1C rated.

My understanding is that the original SunSynk branded batteries we got in SA are just that: Branded. They were bought in and had SunSynk branding applied. And they were 0.5C. And AIUI the new ones are the real 1C deal.