Hello everyone.

 

I am seriously starting to consider going completely off the grid and terminating our Eskom Supply point on the farm, just the monthly connection fee i.e. R5000 can make a good dent in financing a solar system. Current consumption is around 70Kwh a day, peak loads around 12kw, but would like a bit of an oversized system.

This is where I need the opinion of you guys. We are currently on a three-phase system but there is no three-phase equipment running anymore, would it be worthwhile switching to single-phase?

 I have a lot of trees around the house, but there is clear and secure area where I would get full unobstructed sun every day. But it’s around 70m away from the farm’s DB board, could that potentially be an issue?

 

Would a system like the following be adequate? 

2x12kw Inverters (if going single phase) and for redundancy

40kwh of battery storage (maybe a generator for rainy days)

25-30kWp PV array

 

Thank you. 

I have gone through much the same journey: 3 phase rural ESKOM feed to single phase off grid.  About the same usage as yours - your sizing sounds about right.

2 points to consider:

1. Invest in newer, energy efficient appliances. (fridge/freezers and especially inverter aircons of you use them - I replaced my 5 most-used a/cs with inverter units and it made a huge difference).  There is a lot of energy to be saved in the typical house.  (You may already have done this.)

2. Try to get a conversion to pre-paid (so-called LandLight 60A) supply.  In my case ESKOM simply left my old 3-phase transformer on the pole and now uses only one phase from it, so the conversion was cheap (but VERY slow...). The rates are comparable to the fuel costs of a diesel generator, but without the capital and maintenance and noise and hassle.  I had bought a generator before I knew about this option, but have only used it once in 5 years...

Good luck.

Single or 3-phase is a tricky one.

What equipment and appliances are you running? There's some things that are better 3-phase like motors/pumps/compressors, the single phase versions have much higher and prolonged start currents which can cause inverters to trip. Inverter air conditioning is a good way to reduce start currents.

I'd suggest a full load audit where you list every single electrical appliance along with its kwh consumption, start/run currents etc. Then as Calvin suggests look at the low hanging fruit such as air con, hot water geysers, cooking stoves, halogen lighting, fridges/freezers sitting in a hot outhouse etc and see which appliances are worth replacing with gas for example or maybe even worth buying a newer version that's more efficient. Then plan your solar requirements after that.

Good evening @Chris Freestate and welcome to the forum.

1 hour ago, Chris Freestate said:

Current consumption is around 70Kwh a day, peak loads around 12kw, but would like a bit of an oversized system.

A] Is the 70 kWh a day measured over a 12 hour period or a 24 hour period?

B] To oversize the system would be wise and if there is enough space to install the inverters, install an extra inverter to share the load.

1 hour ago, Chris Freestate said:

We are currently on a three-phase system but there is no three-phase equipment running anymore, would it be worthwhile switching to single-phase?

If there is currently no 3 phase equipment in use and you are sure that you will not in future use any 3 phase equipment then I would definitely consider to move over to a single phase system, 3 phase inverters are really expensive in comparison to single phase inverters, e.g. 3 phase 15kW hybrid inverter is about R50k where 3 7.2kW Kodak's would be about R30k and the 15kW works out to 5kW per phase so with the Kodak you would get 2.2kW more per phase.

 

1 hour ago, Chris Freestate said:

 I have a lot of trees around the house, but there is clear and secure area where I would get full unobstructed sun every day. But it’s around 70m away from the farm’s DB board, could that potentially be an issue?

If the inverter has a high voltage MPPT then the voltage drop would be about 1.5% if the temperature is kept below 50oC.

Kind Regards

GerhardK83

On 2024/10/30 at 10:28 PM, GerhardK83 said:

Good evening @Chris Freestate and welcome to the forum.

A] Is the 70 kWh a day measured over a 12 hour period or a 24 hour period?

B] To oversize the system would be wise and if there is enough space to install the inverters, install an extra inverter to share the load.

If there is currently no 3 phase equipment in use and you are sure that you will not in future use any 3 phase equipment then I would definitely consider to move over to a single phase system, 3 phase inverters are really expensive in comparison to single phase inverters, e.g. 3 phase 15kW hybrid inverter is about R50k where 3 7.2kW Kodak's would be about R30k and the 15kW works out to 5kW per phase so with the Kodak you would get 2.2kW more per phase.

 

If the inverter has a high voltage MPPT then the voltage drop would be about 1.5% if the temperature is kept below 50oC.

Kind Regards

GerhardK83

Where will the least V drop be? If you mount the inverter close to house or close to the panels? 

The higher the V the lower the V drop but what about DC vs AC?

On 2024/11/05 at 10:58 AM, Vaal said:

Where will the least V drop be? If you mount the inverter close to house or close to the panels? 

The higher the V the lower the V drop but what about DC vs AC?

Voltage drop over a cable are affected by the following factors

A] The resistance of the cable which is calculated with the following formula

R = (ρ * l) / A

ρ - Rho which is the specific resistance for the material the cable is made of

l - length of the cable in meter

A - cross sectional area of the cable in mm2

B] Temperature of the cable

In SANS 10142 they use mV/A/m and there are a couple of formulas which is used to calculate the voltage drop over the cable.

DC, single phase AC and balanced three phase AC has the same losses over the cable, unbalanced three phase AC is calculated as for single phase AC and a neutral current is also calculated.

It is much cheaper to mount the inverter closer to the house than closer to the solar panels because if you have a couple of inverters in parallel the current increases and as the current increases the cable size also increase which can be quite costly especially if you are looking at a armoured cable of 16mm2 or 25mm2 cable of 50+ meters in length in comparison to 6mm2 cables from the solar panels to the inverter or inverters.