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Old 11-13-2013, 01:40 PM   #1
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Shore Power Independence

Shore Power Independence- Load Analysis


About a week ago a discussion on the practicality of operating a household size refrigerator solely with the power from a set of solar panels was started. After several dozen posts the conclusion was that “yes” it’s probably possible but “no” it’s probably not practical. A day or so ago we found a commercial refrigerator manufacturer of eutectic plate refrigerators who makes fridges that might be able to operate on the power from solar cells. The price of these fridges and whether they would actually work has not been determined. I think the forum discussion has gone as far as it practically can so now it’s up to those who are interested in solar powered refrigerators to buy one and see whether it really works.
Good luck guys. Let’s hope it doesn’t cost too much.

Over the past five years, I and a number of the members of the Murray Chris Craft Constellation forum (the Connie Forum) on the Boat US Manufacturer’s Forum site have been kicking around the concept of Shore Power Independence. Shore Power Independence means making your Connie capable of operating for long periods (days or weeks) without any connection to shore based power sources. Operational, in this case, means both providing a reasonable living environment on board as well as actually cruising. The conclusion of the forum was again that while the concept was possible it was not practical. And so far no one has attempted to actually make their Connie Shore Power Independent.

In order to determine whether shore power independence is practical the first requirements are to make an accurate determination of how much power a Connie uses when away from the dock and whether the generator and/or other power sources can provide it.

None of us had much experience in long term offshore operation but we were able to obtain some very good information from The Voyager’s Handbook; a 570 page tome on ocean crossing and round-the-world-circumnavigations. Sailors who do that obviously need boats equipped for operation for long periods far from shore power cords. The Handbook is a treasure trove of information on offshore operation.

On page 232 we found Table 9-6 which describes the electrical needs of “Highlife” a 52’, eight year old, cutter rigged ketch. The table indicated that the daily DC demands were 115 Ah for House Loads, 75Ah for Activities, and 312 AH for AC loads supplied to the battery bank via an inverter. The peak load is 502 Ah. But not all of these loads occur at the same time so the average load from these three sources is about 301 Ah.
In addition one must add in the power for the refrigerator/freezer which running 24/7 at 12 amps burns about 280 Ah per day. It is the largest power consumer on the boat. The total and average for the day is now 581 Ah.
There are also the inverter loads which include the washer/dryer, hair dryer, toaster, coffee maker, microwave, vacuum cleaner and TV/DVD. They add up to 312 Ah but average out to about 187 Ah. The total and average for the day is now 768 Ah which at 12 volts is 9.22 kWh. This completes the compilation of DC loads.

But there are also AC loads powered by the generator and delivered directly to the loads at 120 volts. They include battery charging at 5 kWh, AC watermaker at 3.4 kWh and a small amount of air conditioning at 5.4 kWh (about enough to cool down the master stateroom so that you can sleep at night). The AC load total is 15.3 kWh.

The total, DC plus AC, load is 9.22 +15.3 = 24.5 kWh which requires 1.2 hours of generator operation at full load, burns about 1.9 gallons of fuel and costs $7.68 at $4.00/gallon.

This is an enormous load and on page 235 the Handbook gives a table which states that the maximum realistic output for solar cells on a 52’ boat is about 100 Ah which at 12 volts is 1.2 kWh. This in turn is not even 5% of the boat’s requirements. There is no chance that solar cells or wind generators are going to generate 24.5 kWh. The only practical source is a diesel generator. The owners of Highlife ran their generator 20 hours a day.

So what can I do? The answer is not much. I could replace the 27 year old refrigerator with a new more efficient one which would reduce the refrigerator and battery charging loads to about one third of their previous levels. But that saves only about 5 kWh (about 1/5 of the total load) which would reduce the daily fuel costs by only $1.53. The old fridge/new fridge swap out would probably cost about $2,000 so at 30 days per year (estimated average use in the Shore Power Independent mode) it would take about 43 years to recover the cost. Not practical!

Sorry this analysis didn’t come out with a more positive answer that indicated solar cells or wind generators would work but that’s the way the cookie crumbles. At least it may have allowed you to avoid a lengthy excursion down a blind alley. In my next post, I’ll try to find a practical way to accomplish Shore Power Independence.
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Old 11-13-2013, 01:41 PM   #2
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Shore Power Independence

In my last post I analyzed the loads that I might have in the Shore Power Independence mode and came to the conclusion that it was about 25 kWh per day. That’s far more than solar arrays or wind generators can provide so I am are going to have to find another solution. At 25 kWh I have to generate an average of about 1 kWh per hour (1000 watts).

Let’s think about what we are trying to do. We aren’t trying to reduce power consumption because we can generate all the power we need for only about $8 per day. That’s not going to be a big financial strain on any of us.

The main objection seems to be the noise and vibration.

If we go the solar panel route we are going to have to generate 25 kWh in about eight hours. That’s a rate of about 3,000 watts. At $360 an 85 watt solar panel will provide only about 25 ampere hours per day and at 12 volts that’s 300 watt hours (0.3 kWh). That’s based on the average daily insolation. So we’re going to need 25/0.3 = 83.3 panels at a cost of about $360 x 83.3 = $30,000. Way too expensive and I doubt that you could even find space for them. In summary it’s too expensive and impractical.

An alternative would be to buy a small 4kW diesel generator for $4,000, spend $1000 to install it and buy an inverter system consisting of a 3000 watt inverter, a 100 amp battery charger and about 600 Ah of golf cart batteries for another $1,200. Total cost about $6,200. I’d run the genny at ¾ load 2 hours at breakfast, lunch, dinner and midnight snack generating about 24 kWh. A small 4kW diesel can be very quiet so it won’t disturb your meals and you need to run the genny anyway at those times to handle the heavy galley loads. The rest of the day the loads would be carried by the inverter system and you can relax in total silence.

If you already have a genny, as I do, just eliminate the cost of the genny ($5,000) and the remaining cost is only $1,200 for the inverter system. Guess which approach I’m going to take?

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Old 11-13-2013, 01:58 PM   #3
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Great post! Recommend as a sticky.
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Old 11-13-2013, 09:45 PM   #4
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[QUOTE=Pete37;191438][
On page 232 we found Table 9-6 which describes the electrical needs of “Highlife” a 52’, eight year old, cutter rigged ketch. The table indicated that the daily DC demands were 115 Ah for House Loads, 75Ah for Activities, and 312 AH for AC loads supplied to the battery bank via an inverter. The peak load is 502 Ah. But not all of these loads occur at the same time so the average load from these three sources is about 301 Ah.[Quote]

I am confused by the prior two sentences. Would not the daily demand expressed in amp hours be the total amps hours over the day. Thus the peak load would be expressed in amps as well as the average load.

Also it is confusing to me that if the daily Ah is 502, then would it not mean an average hourly use of 502/24?

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Old 11-13-2013, 11:49 PM   #5
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Hi Marty,

Peak load is the load you get if you add up all the loads and assume they all occur simultaneously. Average load is what you get if you assume they occurred randomly so that not all loads were on at the same time. For random events the ratio is about 0.6.

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Old 11-13-2013, 11:59 PM   #6
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Quote:
Originally Posted by Pete37 View Post
After several dozen posts the conclusion was that “yes” it’s probably possible but “no” it’s probably not practical.
Possibly what you meant to say is it is not practical for YOU, from what I can gather, because you cant get your head around converting a soft top bimini into a hard top covered in panels
And as far as "possible", well no possible about it, there are people on this very forum (rjtrane) that are running them and he said he is using this $1000 fridge here


Mitsubishi-MRC375CSTA-Refrigerator
And there are several other forum members who also said they run household refrigeration.

Quote:
A day or so ago we found a commercial refrigerator manufacturer of eutectic plate refrigerators who makes fridges that might be able to operate on the power from solar cells. The price of these fridges and whether they would actually work has not been determined. I think the forum discussion has gone as far as it practically can so now it’s up to those who are interested in solar powered refrigerators to buy one and see whether it really works.
Of course they work, but at what expense?
Like I mentioned in the other post, 300 litres of decent 12 volt fridge freezer in Australia (iceer) will cost about $10,000
This mob Ozefridge do the eutectics, but you have to build a box so I could see that costing $5k at least if not more for the box and another few grand for the eutectics.
Quote:
Good luck guys. Let’s hope it doesn’t cost too much.
Well that is the issue isnt it

$5000 to $10,000 for 12 volt/eutectic Vs $1000 for modern 240v
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Old 11-14-2013, 12:06 AM   #7
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At $360 an 85 watt solar panel
LOL, you're doing it wrong
Solar panels can be had for as little as $1 / watt
Ebay is full of 200 watt panels for under $200 delivered to my door

In the US, first click found this place doing 0.85c/watt http://www.wholesalesolar.com/
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Old 11-14-2013, 12:51 AM   #8
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We spent five months in Maine last summer on the hook. Never saw shore power. No solar. 110V Ice maker, 110V cheap dorm style fridge, all elec galley, 110V WH, lite like a Christmas tree every night, three kids and wife. Didn't move the boat much at all. Ran the genny long enough in the am to make coffee and breakfast and long enough in the pm to cook dinner. 1100AH battery bank 160A/MSW inverter/charger.

Just do it!
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Old 11-14-2013, 02:29 AM   #9
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Hi Mark,

Guess that shows that the job can be done by an old fashioned diesel generator. No need for any high tech solar panels.

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Old 11-14-2013, 02:36 AM   #10
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Hi Parmenter,

Any system which requires a special $10,000 12 volt DC refrigerator and a $5,000 custom built box ($15,000 total) is impractical when the same job can be done better for $1,200 if you have a generator or for $6,200 if you dont.

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Old 11-14-2013, 03:40 AM   #11
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Quote:
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Hi Parmenter,

Any system which requires a special $10,000 12 volt DC refrigerator and a $5,000 custom built box ($15,000 total) is impractical
Thats not what I said

Quote:
when the same job can be done better for $1,200 if you have a generator or for $6,200 if you dont.

Pete37
But here it cant, not even close

And define better?
Solar doesn't use diesel daily, or cause noise and vibrations.
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Old 11-14-2013, 03:51 AM   #12
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We are all in different boats. What works for me, doesn't suit the next guy.
I like to keep it simple, so solar would be best for me. I have limited space for a generator, and enjoy my peace and quiet. Going solar is simple and cheap as I have very little load. (gas stove, LED lighting, no A/C, small fridge freezer and large icebox) I need to add a couple panels and batteries to use the fridge while I'm on the hook, but that's it. Easy.
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Old 11-14-2013, 06:37 AM   #13
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Quote: "The total, DC plus AC, load is 9.22 +15.3 = 24.5 kWh which requires 1.2 hours of generator operation at full load, burns about 1.9 gallons of fuel and costs $7.68 at $4.00/gallon."

Pete what size generator supplies 24.5 kWh in 72 minutes?

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Old 11-14-2013, 09:44 AM   #14
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Hi Marty,

The Onan MDL4 I have on my Connie produces 20 kWh in one hour or 24 kWh in 72 minutes. That's pretty close to 24.5 kWh. I guess I should have said 73.5 minutes (1.225 hours) but I rounded it off to 1.2 hours. It weighs 1025 lbs. (465 kg) and is quiet as a mouse.

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Old 11-14-2013, 10:17 AM   #15
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Hi Parmentor,

I'm sorry that things are so expensive in Australia but I have no control over that. I and most of the people posting on this forum live the the USA so I'm quoting US prices.

I'm surprised that so many of those posting are so sensitive to noise. The $6,200 system I proposed is absolutely quiet for 16 hours of the day (it's working on batteries) and with a bigger battery bank I could probably get that up to 20 hours. For the 4 to 8 hours the genny is on(during mealtimes) it has a slight hum. It's so quiet that the only way I know that it has conked out is when I notice the exhaust water noise has quit (or when the lights go out).

As for fuel, it costs less than $8 per day. Is that a problem for any of you?

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Old 11-14-2013, 12:17 PM   #16
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Pete

I calculated a 20kw generator from what you said. Thanks for confirming that. Just haven't seen many that large. Are you able to load it when it is running?

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Old 11-14-2013, 06:31 PM   #17
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As for fuel, it costs less than $8 per day. Is that a problem for any of you?
Possibly

Fuel in US rises 10% (approx) a year historically


$8/day x 365 days/year = $2920/year

Year 1) $2920 a year in diesel Vs cost of 14 x 200watt solar panels CLICK
Year 2) $3212 a year (+10%) Vs zero for solar panels
Year 3) $3533 a year (+10%) Vs zero for solar panels
Year 4) $3886 a year (+10%) Vs zero for solar panels
Year 5) $4275 a year (+10%) Vs zero for solar panels
Year 6) $4702 a year (+10%) Vs zero for solar panels
Year 7) $5172 a year (+10%) Vs zero for solar panels
Year 8) $5689 a year (+10%) Vs zero for solar panels
Year 9) $6258 a year (+10%) Vs zero for solar panels
Year 10) $6884 a year (+10%) Vs zero for solar panels

Total = $46,531 for diesel Vs $2920 (initial cost) for solar panels

The above are approximate numbers for illustrative purposes
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Old 11-14-2013, 07:18 PM   #18
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I have a genset, and some panels. The panels will happily run a 12v fridge. But when I use the eutectic fridge and separate eutectic freezer, I need and use the genset twice a day.
They are not mutually exclusive power solutions. I see battery bank size capacity as more limiting than panel capacity. Panels keep getting better and cheaper.
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Old 11-14-2013, 07:21 PM   #19
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". So we’re going to need 25/0.3 = 83.3 panels at a cost of about $360 x 83.3 = $30,000. Way too expensive and I doubt that you could even find space for them. In summary it’s too expensive and impractical."

I bought four 120 watt panels for $190 each. So your numbers are nowhere close to realistic. But aside from the math, I think that 99% of people who would not change their lifestyle so as not to need a 20-24 KW generator aren't going to be spending very long away from a dock, restaurants, mall, and Starbucks anyway. Usually anyone who wants to set up their boat for extended anchoring is more than will to sacrifice some things for the freedom that brings.
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Old 11-14-2013, 08:41 PM   #20
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Hey Parmenter,

Get real! Nobody uses their yacht 365 days a year. 36 days a year would be more realistic.

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