Energy Matters Forums

[Smurf1976]

One thing I've learnt in many years of general tinkering and doing "unusual" electrical things is that yes you can get better efficiency, performance etc but the downsides are always the same. The biggest problem is that you'll always have major hassles obtaining spare parts etc for uncommon equipment. The other one is that the cost of equipment normally cancells out any savings from a financial perspective. Mass market may not be the most efficient, but it's cheap...

If it were me then I'd have a preference for a 240V system with 240V appliances and a good quality inverter and battery bank. I would be thinking along the lines of:

1. Install a grid connect system. This will get you a nice set of PV panels that can be used year round and will reduce your electricity bills.

2. Get a separate stand alone inverter and a battery bank.

3. Arrange the charging regulator and wiring such that you can send the output of the PV panels either (1) into the grid-connect inverter or (2) into the battery bank. It would be quite practical to automate the change-over, although a manual system would be cheaper and would probably suffice.

Alternative to the above would be a grid-connect inverter that incorporates a back-up system. These aren't cheap however, and I suspect that two separate systems would end up being cheaper. I'm not certain on that point about cost however.

If going for separate systems, you need to make sure the equipment chosen is appropriate for the task in terms of matching voltages. Don't buy anything without having worked out everything.

4. Small generator for supplemental battery charging if required. Doesn't need to be anything fancy, just something that does the job. Choice of fuel - pick whichever fuel is most easily obtainable when you'd want to use it (petrol, diesel, LPG). There's no point having an efficient generator if you can't buy any fuel to run it.

[bpratt]

4. Small generator for supplemental battery charging if required. Doesn't need to be anything fancy, just something that does the job. Choice of fuel - pick whichever fuel is most easily obtainable when you'd want to use it (petrol, diesel, LPG). There's no point having an efficient generator if you can't buy any fuel to run it.

I'd like to suggest it be either diesel or LPG, as petrol goes off after a while, and chances are is that you won't have any fresh petrol to run it at the time you need it the most.

You might have a long drive to find a servo that has power on to run their pumps to get some fresh petrol too.

[Smurf1976]

I'd like to suggest it be either diesel or LPG, as petrol goes off after a while, and chances are is that you won't have any fresh petrol to run it at the time you need it the most.

You might have a long drive to find a servo that has power on to run their pumps to get some fresh petrol too.

I'd certainly agree 100% in principle.

Diesel - easy to store and fairly safe.

LPG - easy to store and safe as long as the cylinder is in good condition.

Petrol - real nuisance to store and a significant safety hazard. At best, you can add some stabilising stuff and it keeps for a year or two but it's still a safety hazard to have sitting around.

Another one - there are actually kerosene powered generators. They are basically a petrol engine modified to run on kero. They are used in some third world countries because of the safety and storage hassles with petrol that I've referred to. That plus kero is pretty widely used in some parts of the world for other things so it's readily available.

All that said, we're talking about an island and there's no point buying something that needs any fuel which isn't actually available on the island.

[bpratt]

All that said, we're talking about an island and there's no point buying something that needs any fuel which isn't actually available on the island.

Good point, all the more reason to lean towards LPG powered generator as there's a lot of places that do the 'Swap and Go' deal. A 9kg bottle should give a bit of time.

[Wadepee]

Petrol's not a drama, because we live on an island we usually have around 100L in the shed at any one time and it get's rotated between three cars and two boats on a monthly basis'. Plus if there's a hint of a cyclone coming their all topped up we'll in advance to beat any "rush".

[Cherokee Solar]

Hi Wadepee,

A lot of the comments here focused on cost but didn't explain why. What they have not mentioned is that the reason you should use 24v or higher (48v) is because it uses cheaper wire and cheaper components than 12v. It's that simple.

It works this way - as the amps increase in a system so too does the thickness of the copper cables required to carry those amps. So, as you increase the voltage, the amps decrease. Copper wire is expensive.

Low voltage = high amps

High voltage = low amps

You've said that you want to install 3 x 300w solar panels for a 12v system. They probably put out about (at a guess) 20A = (300w / 15v) each. So 3 of them together will produce about 60A. Now 60A requires quite thick cable and a reasonably grunty regulator. If you use cheaper/thinner cable, then this will inevitably melt and/or catch fire.

But for a 24v system, the panels probably put out about 30v, so each panel puts out about 10A = (300w / 30v) each. So the 3 of them together will produce about 30A. The requirements for 30A cables is thinner and cheaper than for 60A.

You'd have to use 4 panels for a 48v system, but this would halve the required amps (A) again to 15A (at a guess).

As a general note, the Latronics inverter is a good bit of kit, it hasn't let me down yet. I use a 3,000w 24v continuous model and it seems to handle all the peaks I throw a it (I think it can go all the way to 9,000w for a short burst). You may also find that it uses less energy from the batteries in - on but idle mode - than the bigger 4,000w units. The 3,000w model uses 0.6Ah in on but idle mode. I leave it on all the time so for 24 hours it uses 14.4Ah/day which is about 10% of my daily usage.

A 240v refrigerator represents good value for money over DC fridges. I have a new frost free Whirlpool model 310L and it uses only about 1kWh/day. Nothing really, although it is much cooler here than Magnetic Island, QLD.

Incidentally, I think that you will find that most 300w solar panels are wired so that they are suitable for a 24v system. You can wire two of them together in series for a 48v system.

Hope this helps!

Regards

Chris

[Cherokee Solar]

Hi Wadepee,

Petrol can be a bit of a drama. Even the little Honda inverter generators use about 1L/hour.

So with 100L you've got 100L / 24 hours = 4.16 days of generator use. This also assumes that you don't use the fuel for vehicles / chainsaws etc.

Bigger generators use much more petrol / diesel per hour.

You mentioned cyclone Yasi. Well, I get bushfires up this way and one of the things I noticed after these is that everyone is asking for fuel diesel or petrol.

Batteries and an inverter are a good form of insurance.

Regards

Chris