Calculation of storage and then how to build it

[Doug Hutcheson]

I am considering building an off grid aquaponics system with 12000lph air and 12000lph water being pumped 24x7x365.

Best use of energy seems to be 48v DC. I have found a 48v 12000lph water pump drawing 750w and a 48v 12000lph air pump drawing 202w. These are examples only and I am still looking.

Assuming these loads, I calculate my daily draw to be 22848w and I am in the Philippines where it is rainy so I estimate I need 4 days of storage, or 91392w hours.

At 48v this comes to 1904 amp hours. Allowing for LiFePO4 batteries at a discharge limit of 80% and rounding up a bit, it seems I will need 2500 amp hours of storage.

Am I on the right track so far?

If so, how do I source the cells I need and connect them to build this sized battery?

Furthermore, I am working on 5 sun hours per day. To charge 2500 amp hours of 48v storage in 5 hours seems to me to require PV supplying 5000 amps by 48 volts, or 240 kilowatts, but that doesn't sound right. What am I doing wrong?

 

[snoobler]

952W/.85*24h*4d/.8/48V = 2800Ah (0.85 is for DC-AC conversion efficiency)

Is that 5 sun hours or 5 hours of solar irradiance, from something like link #5 in my signature?

With panel selection, you size it based on your DAILY use and add a surplus for recharging sunless days.

952W/.85*24h/5h/day = 5376W

That's what you need to recover a full day's worth of usage. Then you decide, do you really want to charge all four days in one day, or do you want to charge 2 days worth of capacity/day, etc.?

 

[Doug Hutcheson]

952W/.85*24h*4d/.8/48V = 2800Ah (0.85 is for DC-AC conversion efficiency)

Is that 5 sun hours or 5 hours of solar irradiance, from something like link #5 in my signature?

With panel selection, you size it based on your DAILY use and add a surplus for recharging sunless days.

952W/.85*24h/5h/day = 5376W

That's what you need to recover a full day's worth of usage. Then you decide, do you really want to charge all four days in one day, or do you want to charge 2 days worth of capacity/day, etc.?

Thanks so much for the reply.

My location gets very close to 12 hours day 12 hours night year round as I am in the tropics. An educated guess says 5 of those 12 hours would be useful to the PV panels on a sunny day.

As I am planning on a purely DC installation, do I need to account for the .85 factor?

I see what you mean about the PV requirement. Maybe a 10kw system at the least would be a start point, to give 2 days worth of charge. That is starting to get expensive so I may have to redesign my aquaponics setup to reduce the power requirements. Time to sharpen the pencil.

 

[Hedges]

Water pump, 75% of your estimated load, is highly dependent on how much head you need to produce, elevation change or backpressure from pipes and filter. So double-check performance of equipment, etc.

12000 liters is 3000 gallons. Over 10 hours, that is 30,000 gallons, about the size of my 20 x 50 swimming pool.
Can you provide that much storage, or more, both above and below your aquaculture system?
If so, instead of a huge lithium battery or forklift battery (about 5 forklift batteries for $25k to $50K, I think), this would just be pushing some dirt around and laying pod liner.

PV panels can generate electricity for $0.025/kWh (amortized over a decade), while batteries cost on the order of $0.25/kWh over their lifetime. More or less, as there are several chemistries and some real cheap cells direct from China.

How frequently is it so rainy? Could fire up a fossil fuel generator on some occasions.
How much rain, and can you catch it? If it is falling from the sky and can be diverted to your pond, no need to pump the water you've got. (Why buy the pump when you get the rain for free?)

If you get a smaller volume of rain but can capture and discharge it at considerably different heights, e.g. 100' or more of head, a Pelton wheel turbine for micro-hydro can generate power on those days.

 

[snoobler]

Thanks so much for the reply.

My location gets very close to 12 hours day 12 hours night year round as I am in the tropics. An educated guess says 5 of those 12 hours would be useful to the PV panels on a sunny day.

As I am planning on a purely DC installation, do I need to account for the .85 factor?

I see what you mean about the PV requirement. Maybe a 10kw system at the least would be a start point, to give 2 days worth of charge. That is starting to get expensive so I may have to redesign my aquaponics setup to reduce the power requirements. Time to sharpen the pencil.

No .85 with DC only.

Link #5 in my signature will tell you your daily solar hours by month at your location, panel orientation and tilt.

 

[Doug Hutcheson]

Water pump, 75% of your estimated load, is highly dependent on how much head you need to produce, elevation change or backpressure from pipes and filter. So double-check performance of equipment, etc.

12000 liters is 3000 gallons. Over 10 hours, that is 30,000 gallons, about the size of my 20 x 50 swimming pool.
Can you provide that much storage, or more, both above and below your aquaculture system?
If so, instead of a huge lithium battery or forklift battery (about 5 forklift batteries for $25k to $50K, I think), this would just be pushing some dirt around and laying pod liner.

PV panels can generate electricity for $0.025/kWh (amortized over a decade), while batteries cost on the order of $0.25/kWh over their lifetime. More or less, as there are several chemistries and some real cheap cells direct from China.

How frequently is it so rainy? Could fire up a fossil fuel generator on some occasions.
How much rain, and can you catch it? If it is falling from the sky and can be diverted to your pond, no need to pump the water you've got. (Why buy the pump when you get the rain for free?)

If you get a smaller volume of rain but can capture and discharge it at considerably different heights, e.g. 100' or more of head, a Pelton wheel turbine for micro-hydro can generate power on those days.

Thanks very much for the reply.

This is a recirculating system, with six fish tanks each holding 1000 litres (those cubical IBC containers). The water in each tank needs to be changed every hour, so there is half the usage. Then there are the grow beds which will total perhaps 750 litres of water per fish tank and that needs to be changed every hour as well, so there is another 4500lph. Finally I am allowing for a 1.5 metre head lifting from the sump to the fish tanks and grow beds through 50mm smooth bore pipes kept as short as possible to reduce friction, so I allowed the equivalent of 1500lph losses for those factors. It is very 'rule of thumb', but is an educated guess.

The climate analyses for my town according to Google show rain on average 269 days per year, but that includes sun showers, so I am using another rule of thumb to say I want 4 days of storage.

I am planning on having a generator as a backup charge facility and I am on grid, although too unreliable for aquaponics, so in good times I could also charge from the grid if sunshine is inadequate.

Here in the Philippines we get plentiful typhoons and in bad cases these can knock the grid out for weeks so I cannot rely on that as a charge source. For the same reason, I prefer not to rely upon the availability of fossil fuels as roads may be impassable and tankers unable to deliver. It all comes down to the sun.

As to water, we get 1.6 metres of rain annually and I certainly plan to store as much as possible, supplemented from our deep well. There is a town supply but it is chlorinated which means I would have to clean it up before putting it into my fish tanks.

This is an interesting exercise and at the end of the day may be unaffordable, forcing me to scale it back, but I won't know unless I ask these beginners questions and I am very grateful for the terrific replies I am getting.