Charging battery pack with AC diesel generator

Where will the system be installed--Somewhere in Norway? What is the area like... Deep fjords that get little winter sun? Lots of Marine Layer?

Do you want 100% of the power to be solar+batteries for ~9 months of the year?

Or do you want to just reduce diesel fuel and maintenance costs--But still plan on running the diesels a few hours a day or every other day (and near constantly in winter)?

More or less, you can have solar=>GT Inverters=>Diesel AC and cut back on daytime fuel usage...

Or, for 4x more expensive solar system, Solar=>charge controllers=>battery banks=>AC inverters=>AC powered pumps (water/air). With Gensets connecting through hybrid solar AC inverters (support both GT and Off Grid operations and have integrated AC to DC battery chargers).

Looking at pumps and motors--Have you picked motors that are efficient (permanent magnet motors+VFD--Variable Frequency Drives tend to be more efficient than standard AC induction motors). And different pumps have different efficiencies too (water pumps that have their pump body below the water line--positive inlet pressure--tend to be more efficient than pumps that "draw/suck" water into pumps above the water level (negative inlet pressures).

The basics can be done--But you are talking about some pretty large battery banks, gensets, and inverters.

We can possibly help with the basics, but you would need to get some serious power engineers involved for a safe and reliable system (in my humble opinion).

For example--Just a simple 48 volt lead acid battery bank. 2 days of stored energy and 50% maximum discharge... Basically the battery bank is 4x the daily load (and tends to be a closer to "optimum" design for charging and daily use system):

• 1,000,000 WH per day * 1/0.85 AC inverter eff * 1/48 volt battery bank * 2 days storage * 1/0.50 max discharge = 98,039 AH @ 48 volt flooded lead acid battery bank
  

That is a pretty large battery bank... And if we go with sizing for 13% rate of charge (full time off grid) for a "happy" battery bank:

• 98,039 AH * 59 volts charging * 1/0.77 panel+controller deratings * 0.13 rate of charge = 976,570 Watt array "nominal"

And based on amount of sun in Norway with a south facing, adjustable tilt array:

http://www.solarelectricityhandbook.com/solar-irradiance.html

Oslo
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel where the angle is adjusted each month to get optimum sunlight. Jan Feb Mar Apr May Jun 0.97   2.06   3.21   4.26   5.40   5.71   Jul Aug Sep Oct Nov Dec 5.40   4.67   3.52   2.13   1.31   0.75

Toss the bottom 3 months, gives us February with 2.06 hours of sun per day:

• 1,000,000 WH per day * 1/0.52 off grid AC system eff * 1/2.06 hours of sun = 933,532 Watt array for "break even" February

Sizing the genset... Assume 100 kW load + 10% minimum charging and run at 80% of rated output:

• 100,000 Watts AC load + (98,039 AH * 59 volts * 1/0.80 AC battery charger eff * 0.10 rate of charge minimum) = 823,038 Watts total load (note the AC battery charger may have power factor issues---Watts /= VA ratings)
  
• 823,038 Watt load * 1/0.80 genset nominal rated load = 1,028,796 Watts ~ 1 MWatt genset
  

My guess is that you do not need all of this power in one location/for one application... Say you have 20 "fish pens", then design 20 separate systems so you can move them around where needed plus a few for backup/spares/servicing back on shore....

Also--Inverter-Chargers are (more or less) synchronous rectifiers for charging (more efficient than a standard AC to DC rectifier/battery charger). And tend to be "cheaper" because the synchronous switching is used both for inverting (DC to AC power), and charging (AC to DC power)...

Basically, the inverter-charger is "bi-directional". It supports power flow in both directions depending on how the electronics are configured and what "mode" is needed at the time. And they can do things like "AC Support"--Where you have (for example) a 5 kWatt load that takes 2.5 kWatts from the genset and 2.5 kWatts from the battery bank (+solar if available).

Or, take 10 kWatts from the genset and supply 5 kWatts to the AC load and 5 kWatts to charging the battery bank...

In the end, if I did not get the math wrong (always a possibility that I slipped a decimal point)--This is a large system that will need a power engineer and very careful system design and seeing what equipment (inverters and such) are available for your scale of system (one large system or 20x smaller independent systems).

And there are other ways of possibly solving the problems... For example, setup DC solar system and DC powered pumps (typically a version of VFD--Variable Frequency Drive--That takes Solar DC in and outputs, typically 3 phase power to Induction or Permanent Magnet motors). VFDs are another "magical" electronic device--Can support "soft start", efficient PM motors, and also vary frequency based on amount of sunlight and loads required (i.e., runs slower RPM in morning and evenings, and rated RPM during day). And run diesel at night (skip the whole battery thing). Some VFDs have been designed to take both AC and DC inputs to their VFD... See www.grundfos.com for one mfg.

Or hybrid systems... Lots of power during the day, and a limited amount of battery power needed at night. I try to reduce the usage of batteries as much as practicable... They tend to be the "weak and expensive" point of most system designs.

Good Luck!
-Bill