Off Grid Solar at $0.16/kWh - Small Cabin Forum (2)

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Small Cabin Forum / Off-Grid Living / Off Grid Solar at $0.16/kWh

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electrodacus
Member

# Posted: 29 Mar 2015 15:09
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Quoting: Steve_S

We determined last year that I need to setup for 1200-1500 watts panel capacity, likely using this basic config:
* 4x Canadian Solar CS6X-305P.
* Outback Flex-60 or 80 (have no need for 240v power)
* 8 Surrette S-550 Lead Acid Batteries setup for 48v
* 2000w Inverter / 3000w max. PURE SINE.

So how would I determine a comparable system using the LiFePO4 batteries ?

Hi Steve,

I try to make a comparison and cost analysis try to keep things simple. I made a video about almost exactly this setup
https://www.youtube.com/watch?v=cKrh9tdXDX8
The battery's are not included in this video since I was talking about the obsolesce of MPPT and other technologies related to the cost of PV panels.

So here is a complete comparison for you. I will not include the inverter since that is your choice and will work for both versions.

* 4x Canadian Solar CS6X-305P.
305W x 4 x $0.8 = $976 (1220W)
* Outback Flex-60 or 80 (have no need for 240v power)
about $540 for FM80
* 8 Surrette S-550 Lead Acid Batteries setup for 48v
best price I found $340 (Capacity is 428Ah at 20h rate 300Ah at 5h rate and 253Ah at 3h rate). Since is 6V is about 1.5kWh to 2.5kWh depending on discharge rate x 8 = 12kWh to 20kWh
Batteries will last about 2000 cycles at 20% DOD and charge discharge efficiency is realy bad for the top 20% SOC can be as low as 50% but I will use 70% in this calculation. And I will use the 10h rate value of 2.2kWh

2000 cycles x 0.2 x 0.7 x 2.2kWh = 616kWh over the life of the battery can be stored so cost of storing energy in this battery is
340$/616kWh = 55 cent/kWh just for the battery.

For LiFePO4 equivalent system you need

5x 255W Canadian solar PV panels
255 x 5 x $0.8 = $1020 (1275W)
SBMS100
$339 but not so important since this will last 25 year or more no electrolytic capacitors as the MPPT version and allows you to upgrade up to 3kW of PV panels.

Then battery the most important part related to cost.
An equivalent battery that is probably way overkill for that PV panel array is 8x 200Ah but is not important what choice do you make cost per energy stored will be the same for this Winston brand. So if you decide to use 400Ah for double the numbers of autonomy the cost per kWh over the life of the cell will be the same.

The 200Ah cell is about $280
This WB-LYP200AHA cells will last 7000 cycles at 70% DOD with a charge discharge efficiency of at least 95%
Capacity is the nominal one 200Ah at two hour rate.
3.2V x 200Ah = 0.64kWh

7000 cycles x 0.7 x 0.95 x 0.64kWh = 2979kWh
$280 / 2979kWh = 9 cent/kWh

You see this battery cost is 6x lower than Lead Acid based on spec but in reality things can be even better for LiFePO4

In order to calculate the real cost /kWh I will need to know the power consumption.
Basted on your location and about 1200W PV panels I expect about 100 to 120kWh/month as your average energy usage with fixed array and south facing exposure with no shadows as extrapolation from my data.

Your most energy will be used for the refrigerator about 25 to 30kWh/month + the inverter standby that can add another 15 to 20kWh/month depending on the inverter
There rest should be more than sufficient for LED lights and some computers and some occasional other devices like the water pump vacuum cleaner a hair dryer things of that nature.

If you decide to go with LiFePO4 I recommend just an 8 cell 200Ah battery and eventually increase the PV array to 1500 or 2000W do not increase the battery size it will not help.
A 2000W array will produce close to 1kWh/day even in the worst cloudy and short winter day as long as you clean the snow of course

Set the array for most gain in winter at about 65 to 70 degree tilt.

Dacian.

Steve_S
Member

# Posted: 29 Mar 2015 19:35 - Edited by: Steve_S
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Thanks Dacian,

I'm situated about 150 kms from Ottawa northwards up the Valley, close to CFB Petawawa. Snow is a fact of life out here in the bush country, therefore I've always considered snow clearing off the panels as a must. I'm undecided as to which mounting method I will use, ground mounted VS building side mounted (using the top side of my 20' Sea Container). Either of these will have the ability to be readjusted for Winter / Summer inclination to optimize. I have a nice Southern Exposure on the property which is on the southern face / side of a hill. I do lose a bit of Westerly due to the forest but it's only about 30-45 minutes at the end of the day. I won't be cutting any more pine & cedar trees down. I cannot attach to Cabin as it is surrounded by old pines & cedars and well tucked in.

I fully expect to resume building in the next couple of weeks and with fingers crossed and a touch of luck, have the cabin completed for living in by July 1st. At that point, the solar system will have to be fully operational. For now, I have a 7.2kw gas generator which will also act as backup power if/when needed.

One problem I have is the distance between the Sea Container & House. See attached Site-Plan. I have dual 4" O-Pipes running from the Pump House to the Cabin itself, one is for the water line & the other is for power. These are buried 5' deep inside 2-1/2" thick Blue Foam boxes to prevent freezing. I could install Panels @ the pump house which also has very good exposure but is lower on the hill than the Sea Container and subject to a bit of winter shade due to the tall pines.

I haven't got a hair drier (that would require hair) nor a vacuum but I do have a microwave (1200w) which is used minimally. Sadly, I'll have to minimize my Desktop Wk-Station use as it uses 183w idling (it's an 8-core 4-ghz graphics wk-station), so I'll be playing with my dodgy Dell i7 laptop, which is far more frugal on power.

Ideally, it would be nice to have the batteries, electronics etc located inside the cabin, which would be roughly a 40-45' run from the Pump House to Cabin. DC Volt drop & wire sizing could be an unpleasant expense.

Unfortunately, I am unable to locate a dealer for the batteries you mention... I even looked @ Total Battery who carry pretty much any kind of battery one can imagine. (they aren't discounted in any way there)

Attached file: Site-Plan-NOV-2014

electrodacus
Member

# Posted: 29 Mar 2015 20:05
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Quoting: Steve_S

One problem I have is the distance between the Sea Container & House. See attached Site-Plan. I have dual 4" O-Pipes running from the Pump House to the Cabin itself, one is for the water line & the other is for power. These are buried 5' deep inside 2-1/2" thick Blue Foam boxes to prevent freezing. I could install Panels @ the pump house which also has very good exposure but is lower on the hill than the Sea Container and subject to a bit of winter shade due to the tall pines.

Those distances are not bad at all. With LiFePO4 you will need to have the battery inside a heated building you are not allowed to charge those batteries below freezing.
You can use individual AWG12 wires from each 255W panel based on those distances or you can use a single thicker cable for all in parallel your choice. The cable is not realy that expensive.

Quoting: Steve_S

I haven't got a hair drier (that would require hair) nor a vacuum but I do have a microwave (1200w) which is used minimally. Sadly, I'll have to minimize my Desktop Wk-Station use as it uses 183w idling (it's an 8-core 4-ghz graphics wk-station), so I'll be playing with my dodgy Dell i7 laptop, which is far more frugal on power.

My hair is also very short it take me about 0.02kWh my wife usually needs 10x more 0.2kWh still not that significant.
I also have a microwave about 1000W AC and a convection oven 1400W that I use quite often to make bread this is on the sunny days during the day. A small bread 500g takes about 0.4kWh and a pizza about 0.3kWh
On computers is preferable to use laptops they are designed to be way more efficient.
I have two laptops my wifes is a core i5 second generation using about 10W idle and I have a Dell older dual core low voltage same 10W idle both directly used with a 24V to 19V DC-DC converter.
When not in the winter months starting with February usualy I have more sun and use my All in one ASUS P1801 with a core i7-3770 and a mobile version of GT730 and this uses about 30W idle getting close to 90W at full load or 60W if I keep the frequency lower this includes the 18" HD LCD
Computers are used usually 12h or more/day.

You have quite a bit less solar there than I have here with the worst month November about 41kWh with my array where I get around 60kWh in the worst month.
Still getting 50% more PV panels will not be a big problem to get the same as I have.
You need to have panels somewhere accessible and easy to clean.

MtnDon
Member

# Posted: 3 Apr 2015 21:22
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Quoting: groingo

What law? They are both in everything from anti freeze to wood sealers.

Most states have laws that regulate the disposal of ethylene glycol. Yes EG is used in auto anti freeze; and the laws apply to that stuff. Disposal rugulations can also be interpreted to mean accidental disposal / spills or leaks. Where I am if a heating system uses anti freeze it has to be a non toxic variety or the system must be designed to be able to contain any spills or leaks.

Because EG and PG both transfer heat less effectively than plain water it is best to not use an anti-freeze unless it is absolutely necessary, such as might be the case in a heating system that is in an unoccupied, unattended structure. PG is worse than EG on the transfer of heat. Plus both EG and PG are thicker than plain water and require more pumping pressure / power. Both EG and PG can find leak points that plan water will not leak through.

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