12, 24 or 48V solar generator?

12, 24 or 48V solar generator is an important question to answer before setting out.

There are few things to face squarely before starting out on this little venture of building a solar farm.

Firstly, the set up costs are substantial and trying to do it on the cheap is the direct route to heartache. Doing it right the first time means it hurts only once.

Mistake number one, for me was a 12V MPPT and 2kW inverter.




Secondly, forget the ego and glamour of being off the grid and making a contribution to the environment and all that stuff. You really need to be hard nosed about it; otherwise you're going to be ranting.

I know, because I have the T shirt. Do it right the first time.

The folk I come into contact with who are fed up with their solar farms are those who build a Mickey Mouse 12V system with less than a kW of panels. A low voltage means high current, and that means significant heat losses in the cabling.

The other disadvantage is that you can't easily expand the system. You'll be astonished how quickly the greed factor kicks in; once you discover that sunshine is free, you'll start wanting your solar generator to do a lot more than run the computer and supply a few LED lights.

I started with a small system, just for lights and computers. Then South African started experiencing almost daily load shedding, often with no warning and we started to think about running the fridge. So we upgraded at considerable expense to 24V and an extra battery, as in graphic above.

Then the good wife wanted to cook in the electric oven, and I wanted power to run my carpentry tools; another expensive upgrade to 48V.

Do it right the first time. A Mickey Mouse 12V solar generator will not do much for the environment, and it will frustrate you. Bite the bullet and go straight to a forty-eight volt solar generator.


12, 24 or 48V solar generator

12, 24 or 48V solar generator will determine whether you end up being a happy greenie, or not.

This is a 24V system; it's a move in the right direction, but not far enough.

There are two important formulae to grasp.

  • V = IR

Increasing the voltage V by a factor of 4 from 12V to 48V means dropping the current I by a quarter, where R is the resistance.

  • Heat losses = current squared x resistance.

If you drop the current by a quarter, then the heat losses decrease by a fourth squared; by sixteen.

Trust me, I'm a doctor. I'm also a physics major. Don't put in a 12 or 24V solar generator. Go straight to 48V.

If you can't grasp the basic math and physics here, then it's best you don't build your own solar generator.





Building a 12V Mickey Mouse solar generator will not do much for the environment, nor will it satisfy your aspirations.

You'll be told that it's a lot more expensive and, yes, it is; but your cabling could be one sixteenth thick compared to 12V, and you won't need to go through the pain of upgrades like I have.

There is a downside; well, really it's not a disadvantage in the long run. You must have at least four batteries to make up 48V instead of only one.

But that means four times the storage capacity, and you won't drain your battery on the first night, ruining it, like a friend did. 

In short, if you only have a thousand dollars, forget the environment, ignore your supplier and go out and buy a petrol generator. It's not really satisfactory, but you'll be a lot less unhappy than with a 12V solar system.

You see, your regulator, called a MPPT and your inverter are dependent on the voltage. To change from 12V to 24V and then maddeningly to 48V is an expensive and frustrating business. Do it right the first time, even if you think you'll never expand your system. It's guaranteed you will want to; and won't be able to, except at great expense.

It really is frustrating having to return your components and plead with the supplier to trade them in and give you a good price on an upgrade. Plus they are heavy, and the courier charges are exorbitant.

Am I making myself clear? You see, I have the T-shirt. Do it right the first time, and go straight to 48V. Perhaps in the future we'll see 96V systems.




Incidentally, be careful because the direct current produced by your solar panels bites; even worse than AC. Never open the circuit on a summer's day when your PVs are pumping. I cover them with blankets when I am connecting wires, and drop the breaker at the MPPT, if worried about electrocuting myself.

You may be dealing with up to 150V and that gives a very significant jolt with direct current; it doesn't let go like AC does.


More about volts

Recently when servicing one of the panels in a string of three, I temporarily connected only two; late in the afternoon they read 62V and supplied 220W.

When again connecting the third PV panel in series, the voltage rose to 94V, but here's the interesting part, the wattage shot up to 520, more than double. The higher the voltage, the more efficient the whole system becomes, with few losses in the cabling and probably elsewhere too.


Solar charge controller

The solar charge controller, or MPPT as it's known, enables your batteries to draw a lot more energy from the panels; it keeps the voltage in the wiring near to 150V instead of around the 10V of a flat battery; that improves the efficiency enormously. You simply can't do without the maximum power point tracker.

Read more about this subject at solar charge controller MPPT.


Inverter for home

The inverter for home that you choose is an ultra important choice. If you can possibly afford it, go for the biggest that is your range, because you'll be otherwise upgrading shortly at unnecessary extra cost; I've already made it clear whether I'd choose of the 12, 24 or 48V solar generator.

How I wish that I had gone straight to this 10KW beauty; it's been a difficult learning curve and you can learn from my mistakes. Go big from the beginning; it only comes in the 48V system.

Finally, I made the right decision; a 48V system with a lovely powerful inverter. I just wish somebody had advised me to go straight here from the beginning; I would have saved myself a bundle and a lot of frustration.

Now we can use the electric oven, during the day when the sun is shining. The hob is still gas but we barely use it because of that induction cooktop stove that you can see on the left; it uses half the electricity and heats at twice the speed.

A solar electric oven is a treat; it draws 2.0kW which the inverter handles with ease, but only when the sun is shining brightly. In fact, I put up an extra 900 watts of PV's facing west just so Helen could bake and roast in the late afternoon.


All the excess power during the day is mopped up by the solar swimming pool motor and chlorinator.

A pool is a luxury in these days of high electricity prices, using about 8 units per day but your solar generator will handle it with ease.

It looks a bit like the Martians landed on the roof in the night!

And I can mow the grass, use my carpentry tools, bake bread and do anything and everything, but only on a sunny day. To do that in inclement weather you'd need a huge bank of batteries. I'm not in favour of going off the grid; it's a lovely romantic notion, but not cost effective.


» » 12, 24 or 48V generator?





Bernard Preston

Bernard Preston is a physics major who, after seven years of teaching science turned to something quite different; better health with chiropractic.

Yet his love the physical sciences has left him and retirement has provided the time and space to return to his roots.


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