Posted by *Ben* on October 9, 2007, 1:31 am

Hello,

I'm sure this type of question gets asked here a lot so forgive me.

Interested in calculating the 5 year cost to power a water refrigeration

unit I assembled exclusively by solar panels / battery power to determine

cost effectiveness. If the numbers work out I'd like to construct it

myself.

The unit runs on 115v, 3.0 amp. I read that to calculate watts you multiply

the V x Amp so if that is correct the watts would be 345. I'm expecting the

average running time of the unit to be 8 hours per day to maintain

temperature so I'm guessing that's 2760 watts per day or 2.76 KwH right?.

It will be set up in SW Missouri unobstructed from dawn to dusk.

Wondering approximate cost of a generic (or recommended setup) including

panels, batteries, wiring, etc. How long it might last. What items (such

as batteries) might need to be replaced and at what interval.

Also where a good place to obtain the materials might be in Springfield, MO

or Kansas City, KS area.

Hope I've put enough info out to get an assist here. Thanks in advance for

any help.

=Ben

Posted by *Ron Rosenfeld* on October 9, 2007, 12:57 pm

*>Hello,*

*>I'm sure this type of question gets asked here a lot so forgive me. *

*>Interested in calculating the 5 year cost to power a water refrigeration *

*>unit I assembled exclusively by solar panels / battery power to determine *

*>cost effectiveness. If the numbers work out I'd like to construct it *

*>myself.*

*>The unit runs on 115v, 3.0 amp. I read that to calculate watts you multiply *

*>the V x Amp so if that is correct the watts would be 345. I'm expecting the *

*>average running time of the unit to be 8 hours per day to maintain *

*>temperature so I'm guessing that's 2760 watts per day or 2.76 KwH right?. *

*>It will be set up in SW Missouri unobstructed from dawn to dusk.*

*>Wondering approximate cost of a generic (or recommended setup) including *

*>panels, batteries, wiring, etc. How long it might last. What items (such *

*>as batteries) might need to be replaced and at what interval.*

*>Also where a good place to obtain the materials might be in Springfield, MO *

*>or Kansas City, KS area.*

*>Hope I've put enough info out to get an assist here. Thanks in advance for *

*>any help.*

*>=Ben *

The following assumes an off-grid system with high reliability.

The most SW corner of MO gets about 3.5ESH (effective full sun hours)

during the worst month, according to a map I have from BP Solar. So that's

the resource you need.

Your calculation for consumption is correct for your unit. However, an

inverter will not be 100% efficient. Depending on the ratio of load to

capacity, and quality, it *might* be better than 90% efficient, but for

safety sake, I would figure 85% efficiency which boosts your requirement to

3,247.06 watt-hours/day.

You then need to figure various system losses, and losses in your

batteries, which add about another 20% to the requirements.

Assuming a 24V system, one computes a total daily load (including all

losses and safety factors) of 162.35 ampere-hours.

Dividing that by the 3.5 ESH gives a required panel output of 46.39

amperes.

The Sharpe NE-170U1 seems to have specs compatible with your requirements.

It is a nominal 24V panel which, at maximum power, will put out 4.9

amperes. So ten of these in parallel will cover your requirements during

the worst month.

If you are putting the system together yourself, you should shop mail-order

rather than restricting yourself to just KC or STL. I see one price of

$10 so your looking at $,100 + shipping.

The next big (expensive) item will be batteries.

Most would recommend a 5 day reserve, although if your needs are very

critical, you might want a ten day reserve.

If you purchase high quality batteries, you can get away with allowing an

80% depth of discharge (DOD). With cheaper batteries, you should only

allow a 50% DOD so you'd have to buy more.

With your daily load of 162.35 Ah and 80% DOD you will need 1015AH capacity

at 24V (or 24.35kWh) for a five day reserve.

Surette 4KS21PS seems to be a good match at 1104Ah @ 4V. You would need

six of these wired in series. I see one price of $,009.49 each so the

batteries would cost $,056.94 and may include shipping.

There are a number of inverters on the market in your power range. You'll

need to check the start-up surge on your refrigeration unit and be sure

that your inverter can handle that, as well as the running watts. Motors

will run hotter, and draw more power, if you get other than a "sine wave"

inverter, so that needs to be taken into account, also.

In addition, you will need a controller, wiring, mounts, etc. which may run

another few thousand dollars.

You should also check to see if your state provides any rebates.

If you were going to be grid-connected, the calculations would be

different.

The batteries I recommended come with a 10 year warantee, and might last

longer with good care.

Panel life is unknown, but they do have a 25 year warrantee and will likely

last quite a bit longer.

Good quality inverters have a long life-span; cheap ones not so long.

--ron

Posted by *Ben* on October 9, 2007, 9:12 pm

[insert]

Thank you Ron for your very thorough and thoughtful reply. This gives me

the information I was after. Just using a *rough* calculation I come up

with the following total cost at an annual rate:

Panels: $,000 / 25 year life = $20 per year

Batteries: $,000 / 10 year life = $00 per year

Inverter + Misc wiring, etc: $,000 / 25 year life = $20 per year

---------------------------------------------------------------

Total Cost Per Year = $,040

This verses another *rough* estimate for grid at $00 per year so we're not

saving anything .

Will need to brain storm some more and will likely have more questions.

Once again thanks for the reply.

=Ben

*>>Hello,*

*>>*

*>>I'm sure this type of question gets asked here a lot so forgive me.*

*>>Interested in calculating the 5 year cost to power a water refrigeration*

*>>unit I assembled exclusively by solar panels / battery power to determine*

*>>cost effectiveness. If the numbers work out I'd like to construct it*

*>>myself.*

*>>*

*>>The unit runs on 115v, 3.0 amp. I read that to calculate watts you *

*>>multiply*

*>>the V x Amp so if that is correct the watts would be 345. I'm expecting *

*>>the*

*>>average running time of the unit to be 8 hours per day to maintain*

*>>temperature so I'm guessing that's 2760 watts per day or 2.76 KwH right?.*

*>>It will be set up in SW Missouri unobstructed from dawn to dusk.*

*>>*

*>>Wondering approximate cost of a generic (or recommended setup) including*

*>>panels, batteries, wiring, etc. How long it might last. What items (such*

*>>as batteries) might need to be replaced and at what interval.*

*>>*

*>>Also where a good place to obtain the materials might be in Springfield, *

*>>MO*

*>>or Kansas City, KS area.*

*>>*

*>>Hope I've put enough info out to get an assist here. Thanks in advance *

*>>for*

*>>any help.*

*>>*

*>>=Ben*

*>>*

*> The following assumes an off-grid system with high reliability.*

*> The most SW corner of MO gets about 3.5ESH (effective full sun hours)*

*> during the worst month, according to a map I have from BP Solar. So *

*> that's*

*> the resource you need.*

*> Your calculation for consumption is correct for your unit. However, an*

*> inverter will not be 100% efficient. Depending on the ratio of load to*

*> capacity, and quality, it *might* be better than 90% efficient, but for*

*> safety sake, I would figure 85% efficiency which boosts your requirement *

*> to*

*> 3,247.06 watt-hours/day.*

*> You then need to figure various system losses, and losses in your*

*> batteries, which add about another 20% to the requirements.*

*> Assuming a 24V system, one computes a total daily load (including all*

*> losses and safety factors) of 162.35 ampere-hours.*

*> Dividing that by the 3.5 ESH gives a required panel output of 46.39*

*> amperes.*

*> The Sharpe NE-170U1 seems to have specs compatible with your requirements.*

*> It is a nominal 24V panel which, at maximum power, will put out 4.9*

*> amperes. So ten of these in parallel will cover your requirements during*

*> the worst month.*

*> If you are putting the system together yourself, you should shop *

*> mail-order*

*> rather than restricting yourself to just KC or STL. I see one price of*

*> $10 so your looking at $,100 + shipping.*

*> The next big (expensive) item will be batteries.*

*> Most would recommend a 5 day reserve, although if your needs are very*

*> critical, you might want a ten day reserve.*

*> If you purchase high quality batteries, you can get away with allowing an*

*> 80% depth of discharge (DOD). With cheaper batteries, you should only*

*> allow a 50% DOD so you'd have to buy more.*

*> With your daily load of 162.35 Ah and 80% DOD you will need 1015AH *

*> capacity*

*> at 24V (or 24.35kWh) for a five day reserve.*

*> Surette 4KS21PS seems to be a good match at 1104Ah @ 4V. You would need*

*> six of these wired in series. I see one price of $,009.49 each so the*

*> batteries would cost $,056.94 and may include shipping.*

*> There are a number of inverters on the market in your power range. You'll*

*> need to check the start-up surge on your refrigeration unit and be sure*

*> that your inverter can handle that, as well as the running watts. Motors*

*> will run hotter, and draw more power, if you get other than a "sine wave"*

*> inverter, so that needs to be taken into account, also.*

*> In addition, you will need a controller, wiring, mounts, etc. which may *

*> run*

*> another few thousand dollars.*

*> You should also check to see if your state provides any rebates.*

*> If you were going to be grid-connected, the calculations would be*

*> different.*

*> The batteries I recommended come with a 10 year warantee, and might last*

*> longer with good care.*

*> Panel life is unknown, but they do have a 25 year warrantee and will *

*> likely*

*> last quite a bit longer.*

*> Good quality inverters have a long life-span; cheap ones not so long.*

*> --ron *

Posted by *Ron Rosenfeld* on October 10, 2007, 12:13 am

*>[insert]*

*>Thank you Ron for your very thorough and thoughtful reply. This gives me *

*>the information I was after. Just using a *rough* calculation I come up *

*>with the following total cost at an annual rate:*

*>Panels: $,000 / 25 year life = $20 per year*

*>Batteries: $,000 / 10 year life = $00 per year*

*>Inverter + Misc wiring, etc: $,000 / 25 year life = $20 per year*

*>---------------------------------------------------------------*

*>Total Cost Per Year = $,040*

*>This verses another *rough* estimate for grid at $00 per year so we're not *

*>saving anything .*

*>Will need to brain storm some more and will likely have more questions. *

*>Once again thanks for the reply.*

*>=Ben*

I would probably be figuring the panels at closer to 50 years, and the

batteries at 15 years.

The things that makes an off-grid solar system worthwhile from a purely

economic point of view are:

1. Very high electric rates

2. Grid extension costs

3. Subsidies

With a grid-tied system, you don't need as much in the way of batteries; so

if you have state subsidies, that might be an option to consider.

--ron

Posted by *Eeyore* on October 11, 2007, 9:40 am

Ron Rosenfeld wrote:

*> I would probably be figuring the panels at closer to 50 years,*

By which time they will be producing less output of course.

*> and the batteries at 15 years.*

Depends heavily on battery type and typical regular depth of discharge.

Graham

>Hello,>I'm sure this type of question gets asked here a lot so forgive me.>Interested in calculating the 5 year cost to power a water refrigeration>unit I assembled exclusively by solar panels / battery power to determine>cost effectiveness. If the numbers work out I'd like to construct it>myself.>The unit runs on 115v, 3.0 amp. I read that to calculate watts you multiply>the V x Amp so if that is correct the watts would be 345. I'm expecting the>average running time of the unit to be 8 hours per day to maintain>temperature so I'm guessing that's 2760 watts per day or 2.76 KwH right?.>It will be set up in SW Missouri unobstructed from dawn to dusk.>Wondering approximate cost of a generic (or recommended setup) including>panels, batteries, wiring, etc. How long it might last. What items (such>as batteries) might need to be replaced and at what interval.>Also where a good place to obtain the materials might be in Springfield, MO>or Kansas City, KS area.>Hope I've put enough info out to get an assist here. Thanks in advance for>any help.>=Ben