Batteries needed for startup?

Just to run some numbers for a 8x 6 volt @ 230 AH per battery bank. Charging:

• 230 AH * 58 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 866 Watt array minimum
• 230 AH * 58 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 1,732 Watt array nominal (minimum recommended)
• 230 AH * 58 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 2,252 Watt array next step up

Your proposed array:

• 12 * 250 Watt panels = 3,000 Watts
• 3,000 Watts * 0.77 panel+controller derating * 1/58 volts charging = 40 Amps charging
• 40 amps / 230 AH = 0.174 = 17.4% rate of charge (usually a maximum of 20-25% rate of charge)

With >13% rate of charge, make sure you have a solar charge controller with a remote battery temperature sensor. With high(er) rates of charge, it is possible to overheat the battery bank (battery bank gets hot, charging voltage falls, controller "thinks" batteries need more charge, and they get hotter).

At 2.0 hours of sun per day in deep winter, your system will produced an average of:

• 3,000 Watt array * 0.52 off grid system eff * 2 hours of sun per day (winter) = 3,120 WH per day (rough estimate)

That is probably enough to keep an energy efficient refrigerator going, some LED lighting, running an LED TV, laptop computer a few hours per day, and a bit of water pumping... It an be done, but you have to be very careful about your loads vs battery bank state of charge.

There are battery monitor systems... Some that are voltage only. Others that you install a large precision resistor in the negative battery lead and it will keep track of the AmpHours into and out of the battery.

None of these devices is "fool proof". The ones measuring battery current in/out can "drift". So, you still need to watch the voltage (typically not fall under ~50-48 volts resting and not under ~46 volts under load (can drop lower for starting surge of water pump, etc.).

Just some product links to review--What is available in France may not be what you see here:

https://www.solar-electric.com/midnite-solar-mnbcms.html (simple voltage monitor only)
http://smartgauge.co.uk/smartgauge.html (voltage monitor)
https://www.solar-electric.com/victron-energy-bmv-712-smart-battery-monitor.html (with current resistor, fancy, very nice)

You can also find lots of meters (AC and DC) on Amazon and eBay:

https://www.amazon.com/s?k=dc+amp+hour+meter&crid=3VPQW322DC9IK&sprefix=dc+amphour+m%2Caps%2C232&ref=nb_sb_ss_sc_1_12 (DC Meters)
https://www.amazon.com/s?k=ac+watt+meter+240v&crid=WHE1AALAG49H&sprefix=ac+watt%2Caps%2C234&ref=nb_sb_ss_ts-ap-p_6_7 (AC meters)

If you have appliances and AC power already--You can also get plug in Power Meters so you can better measure/plan your daily loads:

https://www.amazon.fr/s?k=kill+a+watt+meter&__mk_fr_FR=%C3%85M%C3%85%C5%BD%C3%95%C3%91&ref=nb_sb_noss

Regarding water heating... Certainly when it is sunny weather, solar water heating systems can work very nicely. More or less, 40 gallons of hot water per day per person, is something like a minimum of 40 sqft (~4 sqmeters) of solar collector per person (very rough estimate).

The problem with solar hot water--Is you become the plumber and electrician (water pipes, electric pump, etc.). And do it yourself solar (if you have the land) has been done in very cold climates too... Some things to read:

https://solarroofs.com/
https://www.floridasolarhotwater.com/do-it-yourself
https://www.builditsolar.com/Projects/SpaceHeating/SolarShed/solarshed.htm

Note that there are several major types of "hot water" systems... One is a simple, put fresh water in, circulate through panels, store in hot water tank (open loop system), a variation of open loop is the drain back system--In cold weather, drain water from solar panels so they don't freeze. Another uses antifreeze in solar panels (won't freeze overnight in winter) and an anti-freeze/fresh water heat exchanger (closed loop system).

There are wood stove water heating systems too... HOWEVER, anything using a wood stove and boiler can be very dangerous. There have been multiple steam explosions from improperly designed/installed/maintained boiler systems.

Using propane (or other fuel based heater--Tanked or tankless) in winter, and using solar heat during the other 6-9 months of the year is always an option.

-Bill

Money wise, deep cycling to 50% vs 25% of battery capacity (50% state of charge vs 25% state of charge) for lead acid batteries--More or less the 50% batteries will last 1/2 as long as the 25% discharged batteries--But you have 2x more batteries at 25% discharge lasting (usually a bit more) 2x as long. So--Cost Wise--It is about the same (i.e, 4 batteries lasting 3 years deep cycled, vs 8 batteries lasting about 6 years less deeply cycled--made up numbers to show the point).

The bigger issue for me is that Lead Acid batteries need a lot of time on charge (simply something like 6-10 hours per day if disharged to 50%). So one day's worth of discharge takes a bit more than 1 day of "day light/sun above horizon" to recharge. So that if you discharge to 50% the first day and recharge to 90% the next day, then discharge by 50% to 40% the day after to 80%, etc... You can end up with "deficit charging" (basically taking a bit more energy out of the bank when you recharge)--It may take days or a week or more, but you end up with a very deeply discharged battery bank and possibly a damaged battery bank.

The 50% discharge can work--For example people that have a weekend place--They deeply discharge for a couple days, then let the bank recharge over the next 5 days -- and ready for the next weekend use.

So the 25% discharge vs 50% discharge costs you the same in batteries (4 batteries in 3 years, vs 8 batteries in 6 years), but it is hard to fully recharge the deeply cycled bank in 1 day without using a generator/grid power/etc. to get back to full for next days use.

Of course, the above is "worst case" estimate of usage... Basically charge during the day and discharge during the night.

If, however, much of your energy use is during the day (running computers, trade tools, something like 1/2 of your refrigeration) is during the day--The solar panels carray a good part of the load during the day (plus battery charging).

But this does ignore the couple of days of bad weather where your harvest could be 10% or less during "dark weather", and you still need power... So I usually just assume the "worst case design" of all energy used "at night" (or in the "dark"), and you want to recharge fully the next sunny day or two.

The sad fact is, with any renewable energy supply, you have to "over design" the power source... Whether Wind, Solar, etc. You usually want power when needed--And not stop your business during dark weather, calm winds, or whatever.

That is where you decide what energy is needed every day (refrigerator, some LED lighting, perhaps a laptop and cell phone), and have optional loads (running an electric cooker, water pumping for irrigation, washing clothes, vacuuming) that can be done during the next sunny day (or you fire up the backup generator).

Speaking of which--Will you have a backup genset or not? I understand the price of fuel is very high in much of europe due to taxes. But you can trade off between solar panels vs genset runtime during bad weather/and some during deep winter... Over sizing your solar array is a pretty good solution (panels last 20+ years, no maintenance or other costs) to keep generator runtime down... But if there is "no sun" or very poor sun for many days/weeks at a time, you still need alternate power sources and/or to reduce energy usage.

Some folks like to use wind turbines for winter backup (storms = dark = wind)--But that is something that I suggest as a last resort... In the end, turbines are cheap, but towers, concrete, yearly maintenance is not--And the wind is much less predictable/consistent for power generation.

Anyway, looking at your proposed system:

• 48 volts @ 220 AH flooded cell lead acid battery bank
• 48 volts * 220 AH * 0.85 inverter eff * 1/2 days storage * 0.50 max discharge = 2,244 WH per average day (2 days storage/50% planned discharge)

Assuming you use 50% to 65% of your storage for "base loads" (load that must run such as a refrigerator):

• 2,244 WH per day storage * 0.50 base load fudge factor = 1,122 WH per day (just a refrigerator during bad weather)
• 2,244 WH per day storage * 0.65 base load fudge factor = 1,459 WH per day (fridge+some LED lights, etc.)

Just for the sake of argument... You use a generator when needed... Roughly a gasoline genset sized to your loads is a bit less than 4,000 WH per gallon... (or around 1,000 WH per liter). If you needed another 1,000 WH per day for a few days of bad/winter whether, would a few liters of petrol be "acceptable" (Diesel gensets are more efficient so diesel fuel costs may be less--But diesel gensets are more expensive to purchase and service, and can be pretty noisy and smelly). Just trying to look at what "backup power" is worth to you.

Sizing the solar array--First based on battery bank capacity (5% to 13%+ rate of charge):

• 220 AH * 58 volts charging * 1/0.77 solar panel+controller derating * 0.05 rate of charge = 829 Watt array minimum (weekend use)
• 829 Watt array / 250 Watt panels = 3.3 (3 to 4 panels)
• 220 AH * 58 volts charging * 1/0.77 solar panel+controller derating * 0.10 rate of charge = 1,657 Watt array nominal (full time off grid)
• 1,657 Watt array / 250 Watt panels = 6.4 (6 to 7 panels)
  
• 220 AH * 58 volts charging * 1/0.77 solar panel+controller derating * 0.13 rate of charge = 2,154 Watt array "typical" cost effective maximum
• 2,154 Watt array / 250 Watt panels = 8.6 (~9 panels)
  
• 220 AH * 58 volts charging * 1/0.77 solar panel+controller derating * 0.20 rate of charge = 3,314 Watt array oversized
• 3,314 Watt array / 250 Watt panels = 13.3 (13-14 panels)
  
• 220 AH * 58 volts charging * 1/0.77 solar panel+controller derating * 0.25 rate of charge = 4,143 Watt array "maximum" oversize suggested
• 4,143 Watt array / 250 Watt panels = 16.7 (17 panels)
  

Note that you have to "match" the solar panels in your array to your solar charge controller. Depending on the specifications of your panels and the MPPT solar charge controller you choose, you are probably looking at ~3 panels in series to have the "correct" operating voltage for your MPPT solar charge controller... That means your array would be in groups of 3 (3/6/9/12/15/18) to match a generic MPPT solar charge controller.

And Sizing the solar array to your loads... For Caen Fr, fixed array facing south:
http://www.solarelectricityhandbook.com/solar-irradiance.html

Caen
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 41° angle from vertical:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
1.45	2.35	3.33	4.55	5.15	5.18
Jul	Aug	Sep	Oct	Nov	Dec
5.16	5.03	4.04	2.68	1.74	1.16

Use 2.0 hours per day minimum. And say >4.0 hours per day for "non-winter" average:

• 1,732 Watt / 250 Watt panels = 7 panels, round up to 9 panels
• 9 panels * 250 Watts per panel = 2,250 Watt array
• 2,250 Watt array * 0.52 off grid AC system eff * 2.0 hours per day (Karen's winter number) = 2,340 WH per day (winter)
  
• 2,250 Watt array * 0.52 off grid AC system eff * 4.0 hours per day (Bill's non-winter number) = 4,680 WH per day (non-winter)

A 9 panel @ 250 Watts per panel for 2,250 Watt array is not a lot of energy... More or less, enough to run a 1,000-1,500 WH per day refrigerator and some lights, plus maybe a small water pump during the winter.

During non-winter, such an array will give you more power for other things--But you still have to be very energy efficient and manage your loads.

Your title said "startup" in it... Are you looking to run a Bed and Breakfast, or small farm/home?

Note that the above numbers are all approximate values.... Anything within 10% in solar power is pretty much "the same" (a 10 panel vs 9 panel array is a very small difference).

And I am making lots of assumptions and guesses here... In the end, power usage/needs are highly personal. What may work for me, may not work for you (and I am on grid in a major population center--So off grid is not my lifestyle and more of an engineering/academic exercise to frame answers that, hopefully, can meet your needs).

Is there anyone near your place that has similar power needs and is off grid (solar/generator/wind) that you can talk to about what is working (or not) for them?

Looking at energy usage--Conservation is critical here. Most efficient/least amount of energy usage to meet your needs.

System design... Something like $250 (Euros?) per 250 Watt panel (watch for shipping costs--can be more costly to ship panels vs the cost of panels themselves). Is 3 or 6 more solar panels ($250*3=$750; 6x is $1,500; plus other costs) vs reduced or no generator runtime? Will you still have a generator for backup (don't lose food in fridge, no power for business, etc. during bad weather)? Or pay a few euros per day for genset when needed.

Not saying my answers are correct for you--Just trying to help looking at the problem(s) from different perspectives.

-Bill