Newbie Needs Help For Off Grid System Or Brain transplant. HELP PLEASE !!!!!

Re: Newbie Needs Help For Off Grid System Or Brain transplant. HELP PLEASE !!!!!

Laura,

Just to give you some math that you can play with and start getting some prices for your system... Assume you will need around 4 kWatt*Hours per day (fridge+freezer+lights+deep well pump+clothes washer+computer+network+TV). And that you are reasonably energy efficient. Will use propane/other fuels for heating/hot water/cooking.

For Murica Spain, fixed array tilted to your latitude (52 degrees from vertical):

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

Murcia
Average Solar Insolation figures

Measured in kWh/m²/day onto a solar panel set at a 52° angle:
(For best year-round performance)

Jan
Feb
Mar
Apr
May
Jun


3.70
4.27
5.10
5.44
5.42
5.97


Jul
Aug
Sep
Oct
Nov
Dec


6.23
5.78
5.19
4.28
3.60
3.29


Full off grid home, 2 days of energy storage (no sun) and 50% maximum discharge (longer life for lead acid battery bank). Use 48 volts for relatively large off grid system:

• 4,000 WH per day * 1/0.85 AC inverter efficiency * 1/48 volt battery bank * 2 days storage * 1/0.50 max discharge = 392 AH @ 48 volt battery bank

(note any solar numbers +/- 10% range are "dead on" for solar predictions--I am just carrying out more digits so that you can follow the math and how I use the numbers)

We can estimate the "practical" size of solar inverter for the battery bank... for a 392 AH @ 48 volt battery bank, that would be a maximum of ~3.92 kWatt AC inverter (call it 4 kWatt or ~1kWatt per 100 AH @ 48 volt battery bank capacity)--Any larger inverter for that size battery bank would be a waste (you would "kill the batteries" with any higher current draw on a lead acid flooded cell storage battery type bank).

Next, we need to size the solar array... Two calculations. One is based on the size of the battery bank (larger battery bank, more solar array needed to meet charging requirements). Second is to size the array to the planned daily load.

First based on battery bank capacity and 5% to 13% rate of charge:

• 392 AH * 59 volts charging * 1/0.77 panel+solar charger deratings * 0.05 rate of charge = 1,502 Watt array minimum (suggested for weekend/seasonal cabin/home usage)
• 392 AH * 59 volts charging * 1/0.77 panel+solar charger deratings * 0.05 rate of charge = 3,004 Watt array nominal (minimum recommended for a full time off grid home)
• 392 AH * 59 volts charging * 1/0.77 panel+solar charger deratings * 0.05 rate of charge = 3,905 Watt array "cost effective" maximum (if you charge during day and use power at night)

The second array calculation is based on how much power you use over 24 hour period. From looking at the hours of "noon time equivalent sun" in your area, planning on your "break even" point for solar vs running a genset to make up for bad weather/winter sun, ~4.0 hours per day would cover 9+ months of the year on solar only.

• 4,000 WH per day * 1/0.52 system efficiency * 1/4.0 hours of sun = 1,923 Watt array minimum for "break even" solar vs genset.

So--The suggested array for your system (based on my made up/suggested power usage) would be around 1,923 watt array minimum--And for a full time off grid home, I would suggest a 3,004 to 3,905 Watt array.

A 3,004 Watt array and 4 hours of sun would generate around:

• 3,004 Watt array * 0.52 system efficiency * 4.0 hours of sun per day = 6,248 Watt*Hours = 6.2 kWH per day for ~9+ months a year, minimum average

Assuming that fuel costs are expensive in Spain/Europe, you will want to run your generator a minimum amount of hours per year. Also, you probably would want to run some extra loads during the summer day time (Air Conditioning, water pumping for irrigation, etc.)--So the "extra" summer energy can be used during the day (if there is good sun, run your "optional loads").

My suggestion is to not "over size" your battery bank. Batteries are expensive, heavy, and need maintenance, plus they can drive up the size of your array and have additional losses (an old fork lift battery can use upwards of 1-2% per day of its storage capacity as self discharge). Ideally, you want to size the system to your needs/loads.

If you want to avoid fuel usage for cooking/hot water... Look at solar hot water systems or even various "heat pump" systems (take the waste heat from an A/C system and use it to heat water, or there are Heat Pump based water heaters that are ~2-3x more efficient than standard "resistance" type water heaters:

http://water.nyle.com/residential/ (US brand--I am sure you can find European brands that will work well for you)

Neat thing about heat pump water heaters is that take hot air as input and output cold/dry air as "waste"--Great if you need A/C for your home... Not so good if you live in a colder region (in cold regions, heat pump water heaters need outside air to keep from over cooling the room/building they are in--especially in winter).

In the end, how much energy you use is the result of a highly personal set of choices you will make. We can give you estimates as too how much power you will use--But they are little more than guesses. We have people here that live off a 300 Watt AC inverter and 4x golf cart batteries are are ecstatic over having any electricity at all without having to fire up a generator.

And others run their full home+business entirely off of solar (plus generator usage in bad weather) will full A/C, additional water+pumps for fire fighting, etc...

Even if the system generates 4kWatt*Hours per day in early November--You cannot use 4.000 kWH per day--Some days there will be a little more sun, others less... You should plan on using around 66-75% of your "predicted loads" as your "base load", and if you have the extra energy, then turn on some optional loads (cooking/canning, doing the wash, vacuuming, run some extra water into the cistern, etc.).

Your first step should be to know your loads. And it is almost always cheaper to conserve power than it is to generate power. Refrigerator/Freezers, Computers, Well Pumps (and of course A/C and Heat pumps) are usually the huge consumers of power. Sometimes lighting can be too (lights for work, greenhouse, etc.).

And do not spend too much on your first battery bank... It may be the "wrong size" for you (need larger/smaller after a few years of living there) and/or most people murder their first set of batteries (under charging, forget to water with distilled/filtered rain water, guests/kids come by for a visit and kill the battery bank by leaving everything turned on, using hair driers and curling irons, etc.). Your second (or third) bank, you will have learned more about your own needs and will be able to make better choices/take care of issues before they kill your bank.

-Bill

Re: Newbie Needs Help For Off Grid System Or Brain transplant. HELP PLEASE !!!!!

Laura,

Unfortunately, it is a bit like buying a vehicle... Vehicles run from motor cycles to cars to pickups to box vans to semi-tractors+trailers. You cannot buy a mini-cooper and grow it into a box van. And if you buy a semi-tractor, it will not make a good vehicle to go shopping in.

You have several ways to go... You can build the house (conservation rules--lots of insulation, skylights, efficient appliances) and run the home on a genset for a month or so--Measure your loads and then install a system to support those loads (probably another month or so on a genset)...

Or you can can build out a smaller system that meets a minimum set of needs (say 3.3 kWH per day for a base system, and if you have any special needs--Say a 2nd freezer, add ~1 kWH per day, etc.)... Buy "cheap" set of batteries and see how it goes for a couple of years (run more generator power as needed)--Then redesign the system (if needed), toss/sell the cheap batteries, and then buy/build the system that meets your needs.

Or visit some folks around you that have solar and see how their systems and life style work for you... Then build accordingly.

Power usage is the result of a highly personal set of choices. What works for me may not work for you.

Let's look at your original quote and figure out how much power it would produce. Note that the price does not include batteries--In the USA that would be ~USD$10,000 worth of fork lift batteries that would last ~15-20 years (if well taken care of):

24 x Amerisolar 250W solar panels
2 x Outback FM80 MPPT Solar Charger (48V)
1 x Outback Radian 7kW (48V) Peak DC>AC Inverter

1 x Mounting kit (2 rows of 14 panels in portrait)

24 x 2V 1000AH Solar Batteries (48V System) (BATTERIES TO BE SUPPLIED BY THE CUSTOMER)
1 x All cables, clips, isolators needed for the installation
1 x Dedicated delivery within mainland UK (excluding the Highlands)

Using rules of thumbs for a "typical/optimum" off grid grid home:

• 1,000 AH * 48 volt batteries * 1/2 days of no sun * 0.50 maximum battery discharge * 0.85 AC inverter eff = 10,200 WH = 10.2 kWH per day (306 kWH per month)

That is a pretty large off grid power system... About 3x what I would call a minimum system of 3.3 kWH per day (and 3x as expensive). I could run my grid connected home off such a system very nicely.

Looking at the solar array:

• 24x 250 Watt panels * 0.77 panel+controller derating * 1/58 volts charging = ~80 amps peak charging current
• 80 amps charging current / 1,000 AH battery bank = 8% rate of charge

We recommend 5% to 13%+ rate of charge... 8% is a bit on the small side for a full time off grid home--10% to 13%+ rate of charge would be better (especially for tall/fork lift type batteries which usually need ~10% minimum rate of charge).

If we assume 1.25x larger array for 10% rate of charge:
24 panels * 1.25 larger (10% minimum charge) = 30 panel array (approximately) = 7,500 Watt array (nominal)

Now, how much energy could such an array supply for 9+ months of the year? Using the Murica numbers from earlier in the thread:

For Murica Spain, fixed array tilted to your latitude (52 degrees from vertical):

http://solarelectricityhandbook.com/...rradiance.html

Murcia
Average Solar Insolation figures

Measured in kWh/m²/day onto a solar panel set at a 52° angle:
(For best year-round performance)

Jan
Feb
Mar
Apr
May
Jun


3.70
4.27
5.10
5.44
5.42
5.97


Jul
Aug
Sep
Oct
Nov
Dec


6.23
5.78
5.19
4.28
3.60
3.29

The "break even month" (when you may need generator for bad weather) would be February at 4.27 hours of sun average (typical weather average of ~20 years usually). And lets use a 7,500 Watt array (10% rate of charge):

• 7,500 Watt array * 0.52 average system efficiency * 4.27 hours of sun (Feb) = 16,653 WH = 16.7 kWH per day (500 kWH per month)

You can run the math for summer and winter months to see where that puts you vs your power needs.

A 1,000 AH @ 48 volt battery bank would supply:

• 1,000 AH * 48 volts 0.85 inverter eff * 1/20 hour discharge rate = 2,040 Watts for 5 hours per night (average power)
• 1,000 AH * 48 volts 0.85 inverter eff * 1/8 hour discharge rate = 5,100 Watts for 2 hours per night (recommended max continuous load)
• 1,000 AH * 48 volts 0.85 inverter eff * 1/5 hour discharge rate = 8,160 Watts for minutes to hour or so (short term max load)
• 1,000 AH * 48 volts 0.85 inverter eff * 1/2.5 hour discharge rate = 16,320 Watts for seconds to minutes (starting pump loads, etc.)

So, your 6-7 kWatt of AC inverters looks practical for the battery bank you are looking at.

Note that you will (on average) need to purchase new AC inverters and Solar Charge Controllers around every 10+ years. And a new battery bank after ~15 years (if good quality forklift batteries that have not been abused).

Very roughly--On average assuming you use ~66% to 75% of your generated solar power (you cannot use 100% of solar power every day with an off grid solar power system):

• 7,500 Watt array * 4.86 yearly average sun * 0.52 system eff * 365 days per year * 0.70 usage = 6,918,210 = 6,918 kWH per year

Assume that you spend something like $10,000 USD to install the system:

• ($20,000 for hardware + $10,000 for batteries + $10,000 labor to install + $10,000 for replacment inverter+controllers + $10,000 new battery bank) / (20 years * 6,918 kWH per year) = $0.43 per kWHour

That is not bad at all for off grid power costs over 20 year life of system... Of course, I made some guesses and did the calculations in USD$--You need to do the same calculations in your currency and with your assumptions.

Anyway--A different way of looking at your questions.

-Bill