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Solar advise


Gerrie
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Never ever buy smaller than 5kw inverter. 5kw is the minimum. make sure the power factor is 1. do not buy a 5kva 4000w inverter.

Some people does have smaller inverters but I have found that with my 2,4kw inverter I am always trying to reduce the load in order for it to stop complaining.

we never use more than 3kw but we are often at 105% and then the thing goes mad. 

I am running 2 deep freezers, 1 refrigerator, 2x desktop pc 2 x tv, 1x laptop 2 x koi pond pumps all these run around 500w.

What I do during the day is run the tumble dryer and Iron (not together) when the kids are at school and we don't use a lot of power.

When i bought my inverter I did not understand power factor and wanted a 3kw inverter and got a 2,4 it said 3KVA but because of the power factor it is actually a 2,4kw inverter. 

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1 hour ago, Krokkedil said:

Some people does have smaller inverters but I have found that with my 2,4kw inverter I am always trying to reduce the load in order for it to stop complaining.

this is the problem with an island system. It has to cater for the maximum power consumption of your house. My advice is to rather go grid tied. You can size the inverter for the average consumption and the grid will absorb the peaks.

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5 minutes ago, excitedphoton said:

Also stay very far away from lead acid batteries, they really are terrible.

Amen to this. For a start they won't last very long. You'll have to replace every couple of years and so you will probably break even in the long run by buying lithiums. Plus the lithiums will take up less space and you won't have any danger of spilling the electrolyte. 

And another amen for the rating of the inverter. Don't take a short cut there.  I have a 4.6 kw Goodwe. We have learned the hard way to be careful what we turn on at a time. In particular if the dishwasher and the microwave are both running, then wait until one of those finishes before turning on the kettel - or use the gas stove. The 20a limit on the backed up circuits applies all the time, no matter how much solar power is available. 

We have learned to live with the limitation on the backed up loads, but the smaller the rating of the inverter the less you can back up and the more compromises you will have to make.

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I don’t know about burning my fingers, but I definitely have paid more than I needed to for some solar panels. Once you have bought a certain wattage of panels, you are pretty much tied to that wattage, unless you buy another MPPT. My advice is to buy as many of that particular panel as you can at one time before they become obsolete. 
I have 6 x 305w 73 cell panels. These are now quite scarce. If I want to add more, I have to pay about 20% more for that 305w panel than what I pay for a 330w panel.

It is better to know how many panels you need from day one and buy them all at once. Also go the biggest and most common size you can find. 

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8 hours ago, excitedphoton said:

Also stay very far away from lead acid batteries, they really are terrible.

I would like to see the unbiased pros and cons of lead acid vs Li-Ion.

I accept that Li-Ion will take over but are we past that point already? 

I don't accept that lead acid batteries only last a 'couple of years' 

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@Richard Mackay,

The answer depends on your usage and assumptions.  For daily cycle (off-grid) use LiFePo4 batteries are much cheaper per kWh over the life of the battery.

Example: US3000: 6000 cycles x 80% DOD x 3.5kWh = 16800kWh in life.  At R20k per battery, this works out to about R1.20 per kWh.

Any reasonable lead acid battery will cost at least R2000 for [email protected]  Assuming you get 1000 cycles at 50% DOD total production is 1000 cycles x 50% DOD * 1.2kWh = 600kWh.  At R2000 per battery, this works out to R3.30/kWh

Of course it ALL depends on you assumptions.  Can you really get 6000 cycles from your Pylon? On the other hand, can you really get 1000 cycles at 50% DOD from lead-acid?  Perhaps you can half Li-ion cost by getting local "second-life" batteries?

Other factors: Li-ion takes up less space, need less maintenance, has BMS and balancers built in, has higher round-trip efficiency and hence generates less heat, is cooler😎

On the other hand, for UPS/standby (anti-load shedding) use lead-acid is a good option.  Certainly you will never get near using 6000 cycles in that scenario, so Li-ion's biggest advantage is negated.

I bought Pylons - if I was doing it again I would look very hard at the "second-life" option.  My batteries only go through about 120 full cycle equivalents per year, so I will never get near using 6000 cycles.  It may be a bit of overkill.

Edited by Calvin
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