With the exception of a small group of properties next to the river, no homes in Queensland’s Daintree have access to grid connected power. And yet, a large percentage of Daintree residents appear to have put off-grid renewable energy power systems (RAPS) in the “too hard basket.”
This is partly because many existing solar systems in the area were installed in the mid-90’s – as part of the Daintree Rescue Package – at a time when knowledge of solar (and especially of the climatic and environmental conditions here) was in its infancy.
This has resulted in a general dislike and distrust of solar RAPS in the area and continuous agitation for grid connected supply.
Thankfully, things have changed a lot in off-grid solar and storage technology since 1995. But there is still a lot of detail to get across and choices to be made.
A well designed and operating solar RAPS here can supply most households’ needs easily, even in the wet, but without understanding of how it works and its limitations, it can be a source of immense frustration.
Basic design principles for off-grid solar and storage:
1) Solar panels are now cheap, and reliable, and it is wise to have a bigger panel array than you think you need. In grey or wet weather this will pay dividends, and the back-up diesel generator run-time will be significantly reduced (or maybe eliminated altogether).
2) Don’t get a battery bank larger than you need. Work on it being big enough to give you one day’s supply. Discharging lead acid batteries regularly by more than 30 per cent of their capacity leads to rapid failure. Remember, the bigger the battery bank, the harder it is to recharge if it goes ‘flat’.
3) Minimise your energy wants, determine your (real) energy NEEDS!
4) Understand the principles of solar RAPS enough so you can talk intelligently with your installer/supplier.
Other renewable energy sources:
Unfortunately, very few properties in the Daintree have sufficient permanent water flowing through them for mini-hydro to be a viable option, and even if they do, the ‘head’ (that is the height drop between the upstream entry to the property and the exit from the property) is usually too low to extract meaningful energy, except at times of very high rainfall (when there maybe significantly large trees and branches flowing down as well).
Our wind resource is also very limited unless your property is on a ridgeline or very near the beach. Really, there is no effective wind generating capacity. It is recommended that if you REALLY want to have wind power, that you monitor your site for at least a year with a recording anemometer set on a tower at least 30 metres high. If your average windspeed is less than 40km/h… forget it.
Solar panel installation:
Solar panels require direct sunlight to produce maximum power, but can produce significant power in light overcast conditions. Shading of any part of a panel (even though the rest is in full sun) will drastically reduce its output, a fact that needs to be borne in mind when choosing a location for your array.
Conventionally arrays are roof mounted and in timbered areas this is often the only option. As it is wise to have a clearing of at least 50 meters around a dwelling (for cyclone protection and air movement – and maybe a garden) this should allow the array to get maximum solar exposure.
If you have a larger cleared area, mounting the array at ground level is a good option as it allows ease of maintenance, cleaning and adjustment, whereas roof mounts can be difficult for many to access.
The array must face north, but if possible, it should allow for easy adjustment of the sun angle – from almost horizontal in summer (when the sun is actually in the south at midday, here in the tropical North) to about 30 degrees north in the winter, when the sun is in the north. This greatly optimises the effectiveness of the array throughout the year.
Tracking arrays (which follow the sun during the day) increase the effectiveness of the panels even more, but given the current low cost of panels, and the greatly increased complexity of trackers, it is cheaper (and simpler) just to install more panels.
If your roof faces east and west, then two identical arrays on both sides will give you the best result (just like a tracker). As solar panels are becoming cheaper – this is a very effective option (and
as the two arrays should be connected in parallel when one loses the sun the other will gain it).
Some installers have a “sun path” analyser, which allows them to determine which trees and at what season, you might have shading problems (usually during winter and with trees to the north of the array).
Please remember, installation can become a major cost especially if your location is ‘difficult’.
Batteries:
Lead-acid batteries have the advantage of being a known technology, (although constantly improving), and are (theoretically, at least) almost totally recyclable (not that you’d ever guess looking around properties here!).
Flooded “wet cell” lead acid batteries are being phased out for RAPS use, being replaced with the AGM (Adsorbed Glass Mat), or “gel-cell” design. These are totally maintenance free, there is nothing to fill, and they don’t vent hydrogen gas when charging, so they don’t have to live outside. They can be installed in any position – even on their sides in a rack! Set and Forget! – a big load off your mind. (However not all AGM batteries are the same – you get what you pay for.)
Other battery technologies:
These are being rolled out at an amazing rate, but not all will last the distance. Early adopters beware! Lead acid – while large, heavy and not that efficient is a tried and true technology.
Lithium-ion is being hyped – and we’ll have to wait and see. Flow Cell (Redflow) has potential – as it has no capacity or discharge limits (only limited by electrolyte tank size) – but requires sophisticated controls – and it still has to be recharged.
Solar charging:
Modern batteries (AGM) require modern solar charge controllers. The best, and the only ones recommended for the Daintree (or anywhere else) are MPPT’s (Maximum Power Point Trackers) – aka “Maximisers” (first commercially developed in Queensland by AERL).
These function a bit like an automatic gearbox between your panels and your battery bank, with about 95 per cent efficiency. In fact they can increase the effective output of your panels by up to 30 per cent in overcast weather and correctly charge your battery bank. There are quite a number of manufacturers now. However, as with everything else, you get what you pay for, especially in the service and warranty department!
One great advantage of MPPT’s is that they convert a high voltage input from the array (which can be over 100V with the panels connected in series) to the voltage of your battery bank. This allows the same amount of power to be delivered from your array over much smaller (and far less expensive) cables and over longer distances without significant losses, ideal for the array mounted outside in the field. Cabling costs can be quite significant, especially at low voltages, as more copper is required to transfer the same amount of power. (Do understand that in this situation one shaded panel (or part thereof) will greatly reduce the output. Watch that shading!)
Monitoring your system:
This is CRITICAL for the long term survival of your very expensive battery bank. More PV systems fail because of poor battery/charge controller performance.
Lead acid batteries should not be allowed to discharge below 30 per cent of their rated capacity on a regular basis. So for a 1000AH battery, that means maximum amount of power, is limited to 330 AH. So two-thirds of your battery bank capacity is invisible – you can only access it in emergencies, and then it has to be recharged immediately.
Deep discharging of any lead acid battery (wet cell or AGM) reduces its capacity. and if they are left discharged, they can die fast.
While there are many options for remote (web) or computer based monitoring of your system – it is best to stick with the KISS principle (Keep It Simple, Stupid!).
Battery capacity:
This is normally expressed as Amp-Hours (usually at the C10 rate, that is its capacity discharged over 10 hours from full charge to a specified final voltage). So theoretically a 1000 AH battery should be able to deliver 100A current for 10 hours (- don't try it!). But as described above, 330 AH is all that is useable from that battery without causing damage.
The less current you take from the battery, the greater the capacity, the more you take, the less the available Amp Hours. This relationship is called the Peukeut relationship.
Amp-Hours (AH) has nothing to do with the voltage of the battery bank, just the amount of current it can deliver for so many hours. The amount of power that the battery bank can deliver, IS dependent on the voltage and the current.
Power (watts) = Volts x Amps
So a 12V 100 AH battery can theoretically deliver 1.2 KWH, a 24V 100 AH – 2.4 KWH and a 48V 100 AH – 4.8 KWH (all at the C10 rate of 10 A over 10 hours). 1kWh is the same as 1 unit of commercial grid power. But only one-third of that potential power is available without damaging the battery.
So to ensure you don’t take too much out of you battery bank, you need an AMP-HOUR meter – basically it’s your battery’s fuel gauge.
Some inverters have one built in – but that will only record the amp hours that the inverter has consumed, not much help if you are also running DC loads. Similarly solar controllers will also display amp-hours, but this is usually only the charge into the system.
So understanding the complete picture requires a dedicated Amp-Hour meter which monitors the total power flowing into the battery and flowing out.
There are a number of types available, the Austrop Foundation has found one of the simplest and basic units, the Trimetric 2020 (Bogart Industries) to be the most effective.
It can be mounted anywhere in the house and shows the amp-hour status in large red glowing friendly numbers, so you can see battery charge status at a glance (without having to push buttons). It also enables you to see the battery voltage and charge/discharge current – very useful for detecting faults.
Having a monitor such as this Trimetric ensures that all members of the household can easily become monitors of their power usage. This unit is telling me that my battery is almost charged..(17.7 AH left to go).
Where to house your system:
When the systems were first installed in the Daintree, they were all installed in some kind of basic enclosure outside or under the building, as there were quite real concerns about hydrogen explosions when the flooded cell batteries were “gassing” in their final stage of charging.
Naturally the electronics and power controls were placed next to them in an equally basic cabinet, with the result that the local wildlife soon moved in, and inverter and charger failures due to cockroaches and gekkoes were very common.
Plus, in heavy rain everything got very damp and failures were common from that source.
Now, with AGM batteries, there is no reason why the whole system cannot reside inside the house. The whole system generates quite an amount of heat, which in the Daintree can be used to good effect to keep clothes, linen and books dry (and in the process deter cockroach and gekko invaders).
A small 2m square room, well sealed and insulated will suffice, and your goods will not get mouldy or acquire the distinctive “Daintree pong” during the wet. The power system can be mounted on one of the walls, where it is easily accessible and the batteries on the floor, or on a suitably sturdy rack.
A plus, is that modern electronics perform best in a slightly warm and dry (and hopefully clean) environment, which is exactly what your Power Room will provide!
Inverters:
Basically, all an inverter does is convert the DC power from the battery bank into 240V alternating current (AC) at 50 Hz, to run the conventional household appliances and lights.
There are an enormous number to chose from, all that is important is that they can deliver the power peak wattage that you need, and for how long. (This last consideration is important).
This is where your power demand management calculations are important. If you run a small household – a 1,500 watt (continuous, 2,000 watt 10 sec peak) inverter may be fine (and run a vacuum cleaner) – If you want to run a small welder, then a 3,000/4,000 peak might do the job – (or buy a gene for the welder!).
Again, you get what you pay for.
Generator:
Again, it’s a trade-off – if you have a big PV array, and enough battery to give you one-day’s carry-over, then a 2kW back-up power generator is probably all you need. 5kW is usually the maximum size generator for a conventional household, but if you use a dedicated charger, then a 5kW generator will probably run lightly loaded, which isn’t very good for it.
Diesel generators are highly reliable, but the price advantage of diesel has gone (unless you have an endless supply of fryer oil). We now have “inverter-generators” Honda, Yamaha etc, which have an inverter integrated with the generator which can be very efficient (run in “eco” mode) – but there are lots of cheap “knock-off” models, and as always you get what you pay for. Keep your generator well housed in a dry environment.
Even if you hardly use your generator, run it from time to time and keep it full of fuel and oil – as you may need it in a hurry when it is cascading rain!
Energy efficiency:
A difficult subject. If you are experiencing lots of fine weather, and your AH meter says 000 by early afternoon, don’t eschew using electricity for some cooking. But not the hot-plate variety, which is horribly inefficient! Many modern electric cookers and jugs are well insulated, which vastly increases their efficiency. Boiling an electric jug for tea or coffee doesn’t take that much power – and even less if you fill it from your solar heated hot water system! Making toast does not use that much either. A new electric pressure cooker on the market can cook soups, stews, vegies or whatever your imagination can come up with – and is so well insulated that it will complete cooking once the pressure is up, and you pull the plug! Microwave ovens are also quite an efficient method of cooking.
And you use no gas!
But you must ensure that the devices you buy are well thermally insulated. Simple devices such as a “box” or “straw box” cooker – a large basket and a pile of old blankets – can save enormous amounts of energy, gas or electric, and you can’t burn the food!
Washing machines use fairly little power – but hot washes are seldom needed, modern enzyme laundry detergents in fact work better in cold water (and our water isn’t really that cold!). Vacuum cleaners are energy hogs.
Maintenance:
This where everything rapidly comes unstuck. By adopting a Stand Alone Remote Area Power Supply, YOU become largely responsible for its operation and management. This is why it is critical that you understand as much as you can about the operation (and limitations) of your system – by doing so you can save a fortune in repair costs ($100 per hour – and this includes to-and-fro and ferry charges) – OK – if you are renting to tenants – you will have to “eat” these charges – but as a householder they can become horrendous. If you understand your system, when something does go wrong you can intelligently explain what the problem is – and maybe you can fix it with advice over the phone. I’m sure your installer has better things to do than travel 300km for a blown fuse (even if you are paying for it).
So … have a collection of necessary spares – fuses etc. Get a multimeter and learn how to use it. If you can – have a spare inverter, battery charger and solar charge controller – and learn how to install them. This means you have power – even while the other one is being replaced/repaired. They don’t have to be identical – their job is to hold you over.
Cleaning solar panels is a pain – especially on a pitched roof (why have pitched roofs in the Daintree – no snow!) – but should be done at least once a year, as a nice brown algae can start growing and drastically reduce your panel output. Use straight bleach and a ‘silver’ washing up scrubber to clean it all off – and rinse off.
Inspect all visible DC connections – if they are discoloured – and especially if the insulation is looking unhappy and melted- you need to fix them fast – as they can fail quite dramatically.
Make sure you have a suitable tool kit to allow you to carry out repairs – suitable wrenches, screwdrivers, wire cutter and insulation stripper.
CAUTION – solar wiring can carry significant current (you can get some spectacular sparks) – and in the case of MPPT system, significant voltage (100V) – MAKE SURE ALL THE BATTERY AND PANEL ISOLATION BREAKERS ARE OFF BEFORE YOU DO ANY REPAIRS.
Hot water:
Traditionally Daintree residents have relied on instantaneous gas hot water systems – almost all of which require a continuously burning pilot light, which in small households with not much hot water use, could account for half the gas consumption. Propane is becoming expensive (and produces GHG’s).
Again technology has changed and developed. The conventional solar flat-plate collector has given way to the evacuated tube collector, which is about two times more efficient than a newly installed flat plate, especially in grey weather.
A modern evacuated tube collector like the above (Run On Sun) is capable of producing very hot water even in grey weather, and needs minimum maintenance.
Evacuated tube collectors have the great advantage that the collector tubes cannot leak, and the tanks and frame are stainless steel, so do not degrade with time.
Dr Hugh Spencer is from the Australian Tropical Research Foundation, Cape Tribulation Tropical Research Station
