PV - Batteries - DC generator coupling for islanded operation

Dauren

Hi everybody!
Planning to build a house with no grid connection and an LPG tank for heating, HDW, cooking purposes and a small DC air conditioning system for modest day use (house internal layer has high heat retention rate) during 1 - 1,5 month a year.
I wonder if it's possible to connect to the PV - Charge controller - Batteries system a DC generator (like www.alpha.com/index.php/outside-plant-power/generators/item/alphagen-dcx-3000 or www.whisperpower.com/4/2/285/products/generators-(programmable-rpm)/dc-generator-24v-300a-mobile.html). Without taking into consideration the specific size of PV system, battery system and loads (planning to adjust the PV and Battery system capacities according to needs cause I have the possibility to order them quickly.
The question is how to connect such (or any other)  DC generator (variable speed permanent magnet) to the the DC bus bar and what components would I need (apart PV, battery set, inverter and generator)for following scenarios:
1. charge the battery bank only;
2. charge the battery bank and power the load through the PV inverter at the same time;
3. power excessive load with the battery bank in parallel.
The priority list: 
1. keep the batteries charging cycles correctly in order to maximize the their life cycle;
2. have the possibility power the peak loads at any time.
I wonder if this is a feasible system?  
Any help would be desirable
  

mike95490

Concern: how to bring the DC genset on-line and off-line without a big arc ? 
 
What is the AC inverter you are using, does it not include a AC/Gen powered charger ?

oil pan 4

What type of battery are you using and how many amp hours do they hold?
If you have a 24 volt system I would say just get the 24v generator and hook it directly up to the bank that way you can take care of bulk charging. A simple generator isn't going to provide full range battery maintenance but it will keep the batteries charged.

BB.

Just to add some information from Dauren's post in another thread:

Thank you Bill, for your comment.
Sure, before buying I have to pass through the estimate-calculate-design process. For now I'm just willing to understand possible issues in the power supply system of the projected house. I guess, it's better to start with a smaller PV system with a properly sized storage bank and a DC generator and then to size it by adding modules and batteries. So the inverter and charger have to have higher capacities for such extension. I'm from Almaty (Kazakhstan) and the solar radiation rate is about 3,5.
What do I want - to couple a DC generator like DCX3000 (there's not a lot of options for variable speed DC generators) with the charger and the PV inverter so it will supply the energy in following scenarios (cloudy days and/or exceeding loads connected):
1. charge the battery bank only;
2. charge the battery bank and power the load through the PV inverter at the same time;
3. power excessive load with the battery bank in parallel.
The priority list:
1. keep the batteries charging cycles correctly in order to maximize the energy passed through them;
2. have the possibility power the peak loads.
I wonder if this is a feasible system? What components would I need (apart PV, battery set, inverter and generator)? 
Please refer to the correct topic where it was already discussed if so. 
Thanks in advance

And here is the solar radiation for Almaty Kazakhstan:

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

Almaty
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 47° angle from vertical:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
3.06	3.70	4.21	4.81	4.99	5.28
Jul	Aug	Sep	Oct	Nov	Dec
5.39	5.62	5.47	4.58	3.45	2.69

-Bill

Dauren

For now I'm just studying possible issues on connecting DC genset.
Planning to buy 72 cell modules of 300 Wp, starting with 10-12 modules in parallel and battery lead acid flooded batteries of 12 or even 6V connected in series of 48V, with total capacity of 150-160Ah. To the average DoD of 50%.  
mike95490 What the arc you mean - do you mean start surge? I hove to study if that is the problem.
Looking for a simple 6kW china made inverter and to cuople the DC generator with the DC bus bar. No battery charging function.
Instead to use a separate DC-DC charger.
Thank you Bill for the information, I got some historical data on radiation from local weather station, perhaps for the horizontal surface and no information on measuring unit calibration, cleaning etc.
Question still open:
Is this a feasible system?
What components would I need (apart PV, battery set, inverter and generator)? 
What kind of issues can arise during the operation?
Thanks for any info/help.

BB.

Dauren,

In general, no, the system you have proposed is probably not feasible (i.e., it will not function to the "capabilities" of the various pieces.

In some ways, with specialized batteries (like LiFePO4 or other Li Ion type), you could get some higher surge power from a small battery bank--but for most homes, this is not how a system would operate (6 kWatts, then shutdown from dead batteries in 30 minutes).

Mike is probably talking about your usage of DC gensets and switches... DC current is much more difficult to switch without drawing large arcs. DC arc welders are common for a reason--They are great at making sustained arcs.

This is a neat example where you have everything identical except one example with AC power and the second with a rectifier and DC power through the switch instead.

In any case, we keep coming back to how much power you need, and how you use it (day/night/shop/home/etc.).

If we use our typical Off Grid cabin/home rule of thumbs... A 160 AH @ 48 volt battery bank would be good for:

• 1,600 Watt AC inverter
• 3,200 Watt Surge (starting well pump as an example)
• 1,600 Watt of Solar Panels (rough maximum recommended)
• 160 AH * 48 volts * 1/20 hour discharge rate * 0.85 inverter efficiency = 326 Watts of AC power for 5 hours per night for 2 nights average load
• 1,600 Watts * 0.52 off grid system eff * 3.5 hours of sun per day = 2,912 Watt*Hours of AC power per "average" day (enough ot run a small, very efficient home--Refrigerator, LED lighting, laptop computer, washing machine, "off grid friendly" well pump, cell phone charging...
  

Most people when they first get involved in solar/off grid power tend to underestimate their loads and overestimate how much power a pure off grid solar power system and supply (for a "reasonable" amount of money).

There are options (common suggestion is a small solar+battery system for overnight lights, computer, cell phone charging, TV, etc. loads) and a generator for daytime loads (washer, well pump to cistern, vacuum cleaner, shop tools, electric cooking appliances, etc.).

I am very "big on":

1. Define your loads
2. Reduce your loads and go back to one (conservation)
3. Paper design of a balanced system (Loads->battery bank; Battery bank->solar array/backup genst/etc.).
4. Pick hardware and batteries to support those needs. Estimate total costs. Review #1 and #2 before buying anything
5. Buy stuff.
   

-Bill

mike95490

Just what BB so exquisitely said with that video.  Connecting and disconnecting the DC generator will be rough.  Even DC rated breakers will be hard pressed to do that switching

Dauren

Thank you Bill for your clarifications.
1. I'm I right - the arc problem is not solvable even for 48V system? Consequently is it better (more efficient) to get couple of "genverters" like i2000EU or i3000? Same question: is it possible to use those genverters for charging (through AC/DC charger) and power AC loads at the same time?
2. It is not a problem to increase the 48V battery capacity up to 320 even 400Ah and the PV array to 20-22 units. But I don't wont to get an over-sized system, so the significant part of solar energy will not be used. Is it a stupid idea - to increase the battery system so one part of it could charge other part and work for the load?
3. Regarding loads - I don't have yet exact equipment list with specifications, can enlist common main apparels and differentiate usage time:
regular every day and night use
- home heating and water supply pumps bout 6-8 pieces;
- invertor refrigerator and freezer(trending more for a separate freezing and cold rooms);
- thermo pot,  coffee machine;
- kitchen blender;
- multicooker;
- microwave;
- hair dryer;
- 3 TV sets, 2 PCs, Hi-Fi amplifier, LTE modem, phone and tablet chargers.
regular (3-4 times a week) use only sunny days:
- invertor direct drive washing machine;
- iron; 
- vacuum cleaner;
- air compressor;
- water pump;
- meat hasher;
not regular (not more than 2 times a month):
- different electric tools.
I know that the total load is very high and some of them has the automatic switching and working regulation, but as I said I'm ready to upgrade the system. Also I think I have to to plan loads connection according to available mount of energy and develop some rules and habits for it. 
Last good news I have learned (not yet officially approved) that I can connect to the 10kV grid which is 500m far from my land plot and next year there will be special connection tariffs for farmers (the land has such designated purpose). Regular price is about 800$ per kW + equipment and works. So if the total grid connection budget will economically make sense - I will do it.
Sure it will be more reasonable to have a grid connected PV, battery, generator system, and opt for time differentiated rates. As I calculated the cheapest energy is the night tariff, then the PV energy, then generator energy, then stored energy. Anyway I'm considering the PV-battery-generator system as a pure investment asset (I know that such property will be more attractive on the market).

BB.

Dauren said:

Thank you Bill for your clarifications.
1. I'm I right - the arc problem is not solvable even for 48V system? Consequently is it better (more efficient) to get couple of "genverters" like i2000EU or i3000? Same question: is it possible to use those genverters for charging (through AC/DC charger) and power AC loads at the same time?
DC Arcing is "an issue" when the voltage across the switch is >12 volts (very difficult to sustain arcs at less than 12 volts, in general). Like all problems, they can be solved--But takes engineering, proper parts selection, and money to solve. We try to avoid "pitfalls" where possible, but sometimes, we do have to make do with less than optimum solutions.

Inverter-Generators like the Honda (and others) are lightweight, pretty reliable, and quiet--Very nice for campgrounds and residential areas. But, they are for backup power usage--Not great for long term off grid use (i.e., use some during the winter, not for 12 or 24 hours per day, 7 days a week--at that usage level, you would need a new Honda genset every 1-2 years).

In any case, if your make your battery bank to 400 AH at 48 volts, a minimum of 10% rate of charge would be 40 amps * 59 volts ~ 2,360 Watts--You would need > 4 kWatt genset (and could justify a 8 kWatt genset minimum) for such an installation.

And at those power levels (and possibly higher fuel usage), a diesel genset may make more sense (more noise, more fumes--You do not want right next to a neighbor's house, or probably even right next to your home).

Lots of design choices to make--Don't buy any hardware until you have done a paper design and costing of the system.
2. It is not a problem to increase the 48V battery capacity up to 320 even 400Ah and the PV array to 20-22 units. But I don't wont to get an over-sized system, so the significant part of solar energy will not be used. Is it a stupid idea - to increase the battery system so one part of it could charge other part and work for the load?
On average, you will probably only use 50% of your array's daily output (if you try really hard, you may get 65 to 75% of array output). It is simple the nature of using solar power.

Most people want to run loads when needed. If your life style is such that you can adjust your loads to match available sunlight (i.e., put off clothes washing for sunny days, pump well to tank during sun, etc.)... You can better make use of a smaller battery bank and solar array.

Energy usage is a highly personal set of choices--I (we) try not to tell you what is right or wrong--Just how those choices in power usage will affect your design and costs.

These days, in general, solar panels are "cheap" and batteries are "expensive" (and need to be replaced every 5-8 years, and can be damaged if over/under charged, poor maintenance, etc.).

Suggest battery bank "sized" to loads, and "over size" solar array to get the batteries quickly recharged the next sunny day--And/or use a genset when you need power and do not have sun.
3. Regarding loads - I don't have yet exact equipment list with specifications, can enlist common main apparels and differentiate usage time:
regular every day and night use
- home heating and water supply pumps bout 6-8 pieces;
- inverter refrigerator and freezer(trending more for a separate freezing and cold rooms);
- thermo pot,  coffee machine;
- kitchen blender;
- multicooker;
- microwave;
- hair dryer;
- 3 TV sets, 2 PCs, Hi-Fi amplifier, LTE modem, phone and tablet chargers.
regular (3-4 times a week) use only sunny days:
- inverter direct drive washing machine;
- iron; 
- vacuum cleaner;
- air compressor;
- water pump;
- meat hasher;
not regular (not more than 2 times a month):
- different electric tools.
I know that the total load is very high and some of them has the automatic switching and working regulation, but as I said I'm ready to upgrade the system. Also I think I have to to plan loads connection according to available mount of energy and develop some rules and habits for it.
That is a lot of power... And you could end up paying USD $100,000 or more for such an installation vary easily (this is just a wild guess--Trying to figure out if you are "willing" to pay $100,000--Or you are more able to afford a $10,000 system with 1/10th the power capabilities.

In general, solar electric off grid power is not very "cost effective" for "heating" applications (better off using propane/oil/or in some cases, solar thermal systems. And for powering "things that move" (water pumps, air pumps, heating and air conditioning, etc.)--Off Grid Solar can be done, but you want the "most efficient" equipment you can find--In general, spending money on conservation is much less costly than spending money on a larger solar+battery system.
Last good news I have learned (not yet officially approved) that I can connect to the 10kV grid which is 500m far from my land plot and next year there will be special connection tariffs for farmers (the land has such designated purpose). Regular price is about 800$ per kW + equipment and works. So if the total grid connection budget will economically make sense - I will do it.
That seems to be pretty reasonable for equipment/power line costs. Of course, you need to look at the $/kWH pricing too--But it will, on average, probably be 1/2 to 1/5 the cost of an off grid solar power system (overall 10+ year cost for power).

You might be better off getting a diesel genset and, if you want, a small solar power system for nighttime loads (quiet time) and when a "large" genset is not "cost effective" to run the small nighttime loads. Save the extra money to pay for bringing power to the farm.

Please note--That even utility power can be expensive to more "remote" areas... Even in the US, some farmers find it cheaper to run gensets (during harvest season) for water pumps/driers/food processing equipment than to buy utility power (especially if your usage is not uniform (high loads for a couple of summer months, low loads for the rest of the year).
Sure it will be more reasonable to have a grid connected PV, battery, generator system, and opt for time differentiated rates. As I calculated the cheapest energy is the night tariff, then the PV energy, then generator energy, then stored energy. Anyway I'm considering the PV-battery-generator system as a pure investment asset (I know that such property will be more attractive on the market).
I would humbly suggest that you do not look at PV+battery+genset as an "investment"--Unless you find the exact right buyer--Most folks will probably (at best) "ignore" those costs you have sank into your properly. At least that is what is seems like over here in the states (residential, not so sure about commercial farming--But I would suggest that PV+ costs are not going to raise the price of  the land very much, if at all).

If you sell the farm as an ongoing "business"--Businesses themselves have "value"--But it is (many times) based on cash flow--I.e., 2-3x the yearly cash flow of the business--Not really based on assets).

I am not an accountant--But batteries have a ~5-8 year life, charge controllers and inverters have a ~10+ year life. For gensets, their capital costs are relatively low, but fuel costs can be high (much higher for fuel costs over life of genset vs asset+maintenance costs).

-Bill