The Expandable Solar Power System (Plug and Play)

[Maitland Gill]

My masterpiece is finally complete. Please check for any errors and let me know your thoughts on the subject.

[jflorey2]

My masterpiece is finally complete. Please check for any errors and let me know your thoughts on the subject.

You did not include battery cost in your payback calculations. At your rate you'll be replacing batteries every 2-3 years. What will that do to the breakeven time?

[Maitland Gill]

You did not include battery cost in your payback calculations. At your rate you'll be replacing batteries every 2-3 years. What will that do to the breakeven time?

Right on the bottom, it says "The total cost for Batteries, Charge Controllers, Solar panels, and other equipment) / $4,453 (365 days)"

[jflorey2]

Right on the bottom, it says "The total cost for Batteries, Charge Controllers, Solar panels, and other equipment) / $4,453 (365 days)"

Right. Now what about the cost of regular replacement?

In your calculations it states "A Battery should not be drained of more than 85% of it's total capacity and 15% of this Battery would be 27.45 Amps." Draining a lead acid battery that far will kill it quite quickly, likely within a year. So where are battery replacement costs figured in? How much, per year, are you allocating for regular battery replacements? You have spec'd out about $6000 worth of batteries, so there needs to be around $6000 a year going to battery replacements.

Or you could go to a more reasonable DOD - say 40%. Now your batteries will last considerably longer, but there will be twice as many. Might save a bit, but you are still going to have to allocate several thousand a year to replace your batteries regularly when they fail.

[Maitland Gill]

Right. Now what about the cost of regular replacement?

In your calculations it states "A Battery should not be drained of more than 85% of it's total capacity and 15% of this Battery would be 27.45 Amps." Draining a lead acid battery that far will kill it quite quickly, likely within a year. So where are battery replacement costs figured in? How much, per year, are you allocating for regular battery replacements? You have spec'd out about $6000 worth of batteries, so there needs to be around $6000 a year going to battery replacements.

Or you could go to a more reasonable DOD - say 40%. Now your batteries will last considerably longer, but there will be twice as many. Might save a bit, but you are still going to have to allocate several thousand a year to replace your batteries regularly when they fail.

No no no no no no. What I'm saying is that the Battery should be kept at 85% or above to make them last.

[Sunking]

No no no no no no. What I'm saying is that the Battery should be kept at 85% or above to make them last.

Makes no difference whatsoever. Battery cost alone wile be 3 to 5 times higher than the mean ole power company will charge you. You just volunteered a 400% or maore increase in electricity silly. You will never have an ROI.

[Maitland Gill]

Makes no difference whatsoever. Battery cost alone wile be 3 to 5 times higher than the mean ole power company will charge you. You just volunteered a 400% or maore increase in electricity silly. You will never have an ROI.

There are two differences.

(1) The cost of this system and the time until we get a Return On Investment.

(2.) Compared to the time it takes for us to save up so we can afford a Grid-tied system and get a Return On Investment.

[Sunking]

There are two differences.

(1) The cost of this system and the time until we get a Return On Investment.

(2.) Compared to the time it takes for us to save up so we can afford a Grid-tied system and get a Return On Investment.

I am typing slowly so you understand. There is no ROI on a battery system.

If you believe there is an ROI on a battery system, I have one heck of a investment you will love. It works like this; you give me $100 today, and in 5 years I give you $25 back. You will be so happy with that deal you will give me another $100 for 5 years. Both of us will be tickled pink.

Anything you invest today in an off grid system is money lost forever never to be recovered. All you are doing is fooling yourself throwing money away when you should be saving it.

[sensij]

I really like what you've done with detailing out the design and thought process that went into it. With a few more iterations, it could be a good reference for others wanting to follow in your footsteps.

However, there are a *lot* of errors. Some are just minor unit errors (183 Ah / 20 h = 9.15 Ah is wrong. 183 Ah / 20 h = 9.15 A is right).

Some are more significant, for example, this units in this statement are nonsense: "requires 132 Watt-Hours at 0.52 Amps per hour (Or 2,112 Watts for 16 hours)."

That pump is listed at 120 W. Somewhere you've applied a 10% factor to come up with 132 W. 132 W * 16 hours = 2112 Wh. "Amps per hour" and "Watts per hour" don't mean what you seem to think they do. Watts is power. Watt-hours is energy. You will need to understand the difference to really correct what you've written.

This statement is also hard to understand: "The Inverter needs to be designed for an Input of at least 878.4 Watts (96 Volts DC x 9.15 Amps = 878.4 Watts per hour)"

The load on the inverter is 132 W. The 9.15 A comes from the 20 hr discharge rate on the battery, but if you don't have loads that require it, there is no reason to size the inverter so large.

Your battery sizing section is kind of a mess. You want to supply 2112 Wh daily, bumped up to 2323 Wh to account for some battery loss, with discharge of only 15%. That requires 15488 Wh of battery capacity. The battery you selected is 183 Ah * 12 V = 2196 Wh, at the 20 hr discharge rate (9.15 A). However, your discharge rate would be expected to be more like 132 W / 12 V = 11 A / 2 banks in parallel = 5.5 A, so might get a little extra capacity, but you are still pulling more than the 100 hr rate, which has 210 Ah capacity (210 Ah / 100 hr = 2.1 A).

Let's stop here... buying 8 of these batteries (at >$8000) to create two 48 V banks in parallel is silly, even before you look more closely at the limitations of gel batteries. A better choice would be to build a single string of batteries with the necessary capacity... 15488 Wh / 48 V = 323 Ah. The Trojan L16RE-A is a 6 V battery with 325 Ah at the 20 hour rate. 8 of those gets you 48 V * 325 Ah... perfect. You can get them for around $300 ea, so your initial battery cost is only $2500.

Based on the above, there are probably errors in the solar panel sizing section as well, but this is enough for now.

Edit:
in the payback section:
If 1 kW per hour costs $5.87 and the 16 Solar panels produce 2.08 kW per day, then $12.20 is removed from the electric bill each day.
($5.87 x 2.08 = $12.20)

I think you've badly misunderstood the price of grid electricity. Here in southern california, running 1000 W for 1 hour results in 1 kWh of energy consumption. 1 kWh costs about $0.20.

At our pricing, the 2.1 kWh of energy to run the pump is less than $0.50 / day. Do you really live somewhere that energy costs 20X that?

[Maitland Gill]

I am typing slowly so you understand. There is no ROI on a battery system.

If you believe there is an ROI on a battery system, I have one heck of a investment you will love. It works like this; you give me $100 today, and in 5 years I give you $25 back. You will be so happy with that deal you will give me another $100 for 5 years. Both of us will be tickled pink.

Anything you invest today in an off grid system is money lost forever never to be recovered. All you are doing is fooling yourself throwing money away when you should be saving it.

Are you saying that the Batteries would not last long enough to make up for what they cost?

[Maitland Gill]

(183 Ah / 20 h = 9.15 Ah is wrong. 183 Ah / 20 h = 9.15 A is right).

I want to keep the Ah, even if it's not how people normally do it, because it makes sense and is requied for the other calculations.

this units in this statement are nonsense: "requires 132 Watt-Hours at 0.52 Amps per hour (Or 2,112 Watts for 16 hours)."

If two of the three measurements of electricity (V | A | W) are known, the third can always be found. But Electricity, being similar to light, needs a value of time, otherwise these numbers become meaningless.

I did change the Watts into Wh though: "(120 Wh - 10% efficiency = 12 Wh) + (120 Wh) = 132 Watt-Hours"

This statement is also hard to understand: "The Inverter needs to be designed for an Input of at least 878.4 Watts (96 Volts DC x 9.15 Amps = 878.4 Watts per hour)"

The load on the inverter is 132 W. The 9.15 A comes from the 20 hr discharge rate on the battery, but if you don't have loads that require it, there is no reason to size the inverter so large.

I said: "the Inverter (Being the load) will need to be able to receive an input of 96 Volts DC | 9.15 Amps"
(96 Volts DC x 9.15 Amps = 878.4 Watts per hour)

The air-pump requires 132 Watt-Hours, which makes the Amperage larger (132 Watts / 240 Volts = 0.55 Amps per hour), so I'll need to change that.
But are you saying that an Inverter that's rated for 200 Watts will be able to have a larger Input of 3.66 Amps at 240 Volts per hour flow through it?
So its ok as long as the Amperage rating is up to standard?

The battery you selected is 183 Ah * 12 V = 2196 Wh, at the 20 hr discharge rate (9.15 A). However, your discharge rate would be expected to be more like 132 W / 12 V = 11 A / 2 banks in parallel = 5.5 A

Won't the Inverter supply the number of Amp-hours as they're needed?

At our pricing, the 2.1 kWh of energy to run the pump is less than $0.50 / day. Do you really live somewhere that energy costs 20X that?

Welcome to Australia...

Also, while this is off-topic, I heard the Central Bank in America is going to raise the rates on Monday. So I suggest you buy some Silver before inflation goes up.

[foo1bar]

I want to keep the Ah, even if it's not how people normally do it, because it makes sense and is requied for the other calculations.

It doesn't make sense.
And if you're using that value with "Ah" as the unit in another calculation with that value as the input, then you must be doing something wrong in that calculation too. AmpHours/Hours = Amps. Or at the very least "Ah/h".

If you're not showing the right units in your calculations it makes me believe you're sloppy elsewhere in your calculations.

[Mike90250]

i have to agree with sunking and sensij on their comments.

You DO NOT have a grasp on the basic math or units you are throwing about. You can't call Amps AmpHours because you need to use Ah someplace else.

You do not feed 96V into any inverter because it's a round number for math someplace else.

I said: "the Inverter (Being the load) will need to be able to receive an input of 96 Volts DC | 9.15 Amps"
(96 Volts DC x 9.15 Amps = 878.4 Watts per hour)

Gel batteries are not suitable for solar applications, AGM batteries are, but are quite expensive.

You will have a mighty surprise when you connect batteries to the solar inputs of of the MPPT controllers,
no matter how good your intentions are.

You can build it, and it will smoke badly. Or just plain stink when it all melts down.

You have a bad habit of transposing units and devices around, so much it's really impossible to list all of what is wrong, here is my list of what is right.
2 x Schneider Electric MPPT 80 600 Solar Charge Controllers = $3,799.32

there may be more, but I advise you to label your web page as a DRAFT and I do not recommend anyone build it yet.

[Maitland Gill]

i have to agree with sunking and sensij on their comments.

You DO NOT have a grasp on the basic math or units you are throwing about. You can't call Amps AmpHours because you need to use Ah someplace else.

You do not feed 96V into any inverter because it's a round number for math someplace else.

Are you saying that the notion of (183 Ah / 20 hours = 9.15 Ah) is wrong?
But then how else do we determine the number of Ah that a battery can give out at a desired percentage?

[Sunking]

Are you saying that the Batteries would not last long enough to make up for what they cost?

Yep and coupled with your huge errors.