Backyard Aquaponics
A place to discuss aquaponics

I paid the usual retail price that anyone else would pay from an EV place in WA




Operating a generator at 80%-> 5% isn't good for it, nor an efficient use of fuel. PV panels and a regulator will do it much better, and zero marginal cost. PV power is also much less expensive than diesel power, and vastly more environmentally friendly.
You are generally better off to oversize the PV array and not the battery- PV modules are a lot less expnsive than batteries, and an oversized array can help a lot in mostly cloudy weather.



As a rough guess without calculating anything, for an off-grid system I reckon a 25kW PV array arranged as per my Virtual Tracker design and a 100kWh battery should mean minimal generator usage for most of the year in Victoria, to run 5kW of continuous load.





Dependent on what you are wanting to run... I'm happy with the performance of the pump I'm testing, it runs at a nominal battery voltage of 48V, but best max power performance is at 58.5V. The controller converts this to 3phase AC, and there are higher voltage versions available. What voltage would your air pumps be?

What about installation and associated costs?


The system would be designed to run the generator at ~80% of capacity or not at all. I've been told that this is the point of peak fuel efficiency. In emergencies (battery failure or some other catasrophe) the generator could be run to power the system directly but this would be a last resort.


The problem is that to be confident you are never going to run short of power the PV panel array and the battery bank have to be relatively large. Since a generator is essential for redundancy it makes sense to have it integrated with the system.

If someone can show me that it is more cost effective to only have the generator for emergency backup and the PV panel array and battery bank 100% of primary power then I'd invest in that system.


Do you have a rough idea of how much that would cost?



The water and air pumps are available "bare" as in you just get the pump without a motor to make it work. THat means I can put whatever motor I want on them from a tractor PTO to 3phase electric to DC. I have looked at DC motors so as to do away with an inverter (at least a large one anyway). The trouble there though is finding the right motor and getting a system to run at the right voltage. As I understand it low voltage systems need seriously fat cables to get enough power through them but high voltage DC systems are not so common so can't be just bought off the shelf.

The preliminary conclusion I came to was that it was better to run standard 3 phase kit because it was available off the shelf.

You were going to send me the details on that pump. What is it capable of? What are its efficiencies?

I'm still working on that! I've only had it running a few days, but with only 5 beds connected I can only run at just above the minimum speed that will pump to 5m head. Once I get a few more beds ready and connected I'll be able to run it faster and do some efficiency tests etc. The 500W version I have will pump 15.3m^3 per hour at zero head, and there is a 900W 48V version, and a 1200W 72V version that pumps 27.9m^3/hr.
I'll send the brochure.

I installed it myself, cabling etc costs would depend on the particular installation, so hard to put a number on that.




We're only talking about a 6kW generator, which isn't very large. With a system as I described you wouldnt need to run it very often. I think the best way to convert 6kW @230V to your battery voltage would be via a welder transformer and large capacity rectifier.




Yes, and save money by not going overboard on battery capacity, it's just too expensive. Size it to minimise generator use, not eliminate it, based on BOM solar radiation data over a long period.





Roughly- good quality panels such as Yingli can be had for $1.20/watt these days, 20kW = $24K Mounting depends on roof, and what sort, angle etc, or ground mount, but its going to be several thousand I would guess. LiFePO4 cells were going for about $1.80/AH last I saw, but would probably be less for a large quantity, so for 100kWh, say $50-60K. $5K for charge controllers, and perhaps another $3K for BMSs. Probably looking at close to $100K including installation.
Lower voltage equipment can easily be catered for with DC to DC converters.

There are DC motors around, but sourcing a large number of a particular voltage and various kW ratings may prove to be quite a challenge. However, the pump I have, or other varieties of it, may be suitable.

Re cabling- if you were talking about ~1kW motors, then at 50V you'd need cabling to carry 20A with minimal volt drop- 16mm^2 would be fine if your runs were ~20m. Of course you could arrange the systems to minimise cable runs- maybe radial layout with larger pumps near the centre.

For someone only using batteries for a backup. Say in a tropical climate where hurricanes and Typhoons are possible. 3 to 6 days without power possible. Wouldn't it be more cost efficient to charge a battery bank with a trickle charger off mains power. That way you could bypass the need to buy solar panels and even a generator if you were willing to risk it. And the battery bank was sized properly.

Solar panels are much less expensive than batteries. For off-grid domestic systems, oversizing the PV panels and not having a huge battery is the most economical way to do it. Having a huge battery capacity that gets used maybe once or twice per year wouldn't be the best way to go about it IMO.

Thanks

If you were going to use a battery purely for backup, one of the gel cells that claims 400 cycles of running to flat would be the way to go- that way you don't have to worry so much about very deep discharges, which will damage most batteries. I'd give it a top up charge ~once per month, or just before nasty weather is forecast, rather than have it trickle charging all the time though.

That makes a big difference to the costs. For something like this because it is so crucial I'd want someone else to do the work. There are only so many things I can do myself


Ok so now I'm confused again. Didn't you say that your ~20kWh battery bank could be charged in about an hour? Assuming its from 50% charge at a rate of 1C a 25kW generator running at 80% would take 1/2 an hour to top the batteries off.

Is this right or have I missed something?



Yeah good idea.

Yes I did, but I hate generators and don't have one myself However, you were talking about running a 5kW system from a generator, so you'd only want a ~6kW generator to run a 5kW system, not a 20kW generator running at 25% capacity.




So you dont have to listen to the generator and pay for fuel for days on end in winter.
If you put in a 20kWh battery, you'll only get 3 hours use from it, so lots of generator starts overnight. What if something breaks in the genny at 9pm and you cant get the replacement part needed to start it until 9am or 2 days later if it happens on Friday night- lots of dead fish is what happens!


You should be able to lease batteries in the not too distant future- zero capital outlay. You can lease PV panels & inverters now for zero outlay for grid-connected systems. My Employer, SunEdison, does 24hour monitoring on their leased grid-connected systems, so they'd know in near real time if say an inverter decided to pop.

I'd think seriously about a leased grid-connected solar system to start, with battery backup for blackouts, and a diesel generator as a backup to the backup if the outage lasts too long. I'd be happy with 20kWh of battery in that case. You would only need a 6kW generator and would rarely need to use it. Buy 100% green power for your grid imports!

I think this is going to be the way to go. Rules out a bunch of sites but such is life. My only concern would be power companies objecting to solar installation and/or attempting to add surcharges for solar connections.

We (well my work, not me personally) often do zero export installations- the power companies dont like solar, often because it messes with their undersized transformers and wires.

You might be interested in this: http://reneweconomy.com.au/2015/trina-s ... rage-31674

Article really argues that it would be a good idea to minimise the money you spend on batteries.

http://rameznaam.com/2014/10/05/solar-wind-plunging-below-fossil-fuel-prices/

How's it going with the Li-Ion batteries? Have you chosen a particular battery to test yet?

http://www.homepower.com/articles/solar-electricity/equipment-products/lithium-ion-batteries-grid-systems
I don't know much about them. Your post has me thinking more and more about Li-Ion as a storage call for my pumps.