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Old 15-05-2022, 09:11   #1
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sizing my solar / battery / invertor system.

Greetings, I have a "new to me" 53 ft. Royal Cape Catamaran in very bad condition that I am refurbishing. I am based close to the RCC factory in Durban, South Africa. I need help with sizing the invertor. I have not calculated a detailed power requirement spreadsheet for the vessel. However, its a standard luxury cat with 5 cabins. The vessel has 4 fridges & freezers, ( chillers ) an ice maker, a washing machine and aircons in the cabins and saloon. It also has a 220V AC water maker that makes 220 l / hr. The vessel is equipped with an old 8 KVA diesel generator and can be connected to shore power if necessary. In South Africa, we run a 12 Volt system and our AC power is 220 Volt. On rare occasions, I will have a maximum of 9 people on board at any one time. With todays technology, I am hoping that I will be able to run my water maker and one, or if I'm lucky, 2 aircons off my battery & invertor system. I understand that the new Victron equipment has built in soft start capabilities to enable 220V equipment to be run if supported with the correct hardware. I am hoping that I will never ever need my generator again and this is what I'm trying / hoping to achieve, if at all possible. Given the relative cost effectiveness of solar panels, I will install the maximum panels and work backwards with my power specifications and hope that it meets my needs. I will install 8 x 550 Watt solar panels with one MPPT controller per two panels so will install 4 MPPT controllers. I will install 7 x 300 Amp hour Sunray Lithium Lifepo4 batteries from China. All my electrical components will be Victron. However, I'm unsure of what size & configuration of the Victron Multiplus invertor to install. My thinking is to install two 12 V / 3000 W Multiplus Victron Charger controllers. Is the 2 as suggested the optimal choice? If so, should they be connected in parallel? Should I rather be installing only one 12V 5000 or 6000 ( or 8000 even ) Watt invertor. Do the 5000 / 6000 exist? I notice that sine invertors exist. Is a sine invertor necessary or recommended? I will appreciate any comments on the above Invertor queries as well as any general comments from the gurus out there on my whole proposed system. Does 7 x 300 AHr batteries makes sense. I've tried my best to come up with a balanced system with very limited knowledge and lots of time spent on the web. Any criticism and advice will be most welcomed. Thank you immensely in advance.
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Old 15-05-2022, 09:41   #2
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Re: sizing my solar / battery / invertor system.

That is a very ambitious power system.

To wire a 12v system that can deliver that amount of energy in a safe manner is going to difficult.

It sounds like you are starting from scratch with your electrical installation. The first thing I would look at is moving to a higher voltage house system.
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Old 15-05-2022, 11:36   #3
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Re: sizing my solar / battery / invertor system.

I'm inclined to suggest that you explore installation of a second genset with extensive sound insulation. Those power demands are going to require the battery bank from hell between charges.

Backing up a moment. Start with a careful calculation of your energy needs. How many air conditioners running at how many watts for how many hours per day for how many days, then the refrigerators, then the water heaters, and so on. You will end up with two numbers, immediate draw (the inverter) and battery capacity. I use a 3000 watt inverter on a much smaller budget than yours. I suspect that you are going to find yourself outside what you can expect an inverter and battery bank to supply for long (you don't say how long). I would also guess that the solar panels aren't going to do the job; remember that their rated production is at noon on the equator on a sunny day with perfect alignment.

At any rate, the information you've shared is not enough to answer your question - just raise the question of your finding enough energy for a very heavy load.

Best of luck with your very big project.

Full sine wave inverters cost more, but produce AC like from shore, not stepped square waves. Our microwave oven doesn't like them.
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Old 16-05-2022, 10:01   #4
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Re: sizing my solar / battery / invertor system.

Agree that you need to better define your energy needs and at what duty cycle. However right off the top, for your complete “new build” of your electrical system which has heavy demands, definitely get rid of an “old 8KVA” genset, and, consider a 48vdc house bank.
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Old 16-05-2022, 10:23   #5
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Re: sizing my solar / battery / invertor system.

Quote:
Originally Posted by YPSILANTI View Post


1. I need help with sizing the invertor. I have not calculated a detailed power requirement spreadsheet for the vessel.

2. I am hoping that I will be able to run my water maker and one, or if I'm lucky,

3. I am hoping that ... and this is what I'm trying / hoping to achieve, if at all possible. ... and hope that it meets my needs.

4. Is the 2 as suggested the optimal choice? If so, should they be connected in parallel?

5. I've tried my best to come up with a balanced system with very limited knowledge and lots of time spent on the web.

6. Any criticism and advice will be most welcomed. Thank you immensely in advance.

1. The very first thing you need to do is an ENERGY BUDGET. Moving along without one is a recipe for disaster. It's like trying to balance your checkbook without knowing how much income and what you are spending. Here's how to do it:


The All-Important Energy Budget:

http://c34.org/bbs/index.php/topic,3976.0.html


You could also Google "boat energy budget" and read others' contributions, but you'll learn they are all the same.


2 & 3. Without an energy budget, the ONLY thing you can continue to do is hope.

4. You simply cannot make ANY choice(s) without doing a budget first.

5. You simply cannot balance anything without a budget. The amount of time on the boat is meaningless.

6. It should be clear to you by now that this is an ENGINEERING exercise, not a "feel good and hope" endeavor. You have to roll up your sleeves and PLAN. There is simply no way to throw equipment at any challenge and just hope for the best. Sorry to sound so tough and judgemental, but the reality is what we have all learned over the years. Earlier comments have mentioned it, but an energy budget is a critical first step in being able to even begin to size any electrical components.
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Old 21-05-2022, 08:07   #6
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Re: sizing my solar / battery / invertor system.

Thank you so much for the honest and informative replies. I will do my homework.
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Old 22-05-2022, 23:11   #7
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Re: sizing my solar / battery / invertor system.

Just piling on here, but as Stu says, an energy budget is the place to start. For a system of this size you will want to consider designing with 24v at minimum. It will keep cable sizes manageable.

If you haven't done one, list your consumers (all of them, there are more than you think at first) and your power sources, then consider your various use cases: under way, at anchor, at the dock, or on a mooring. Ambient temps also impact power consumption for heating, cooling and refrigeration.
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Old 22-05-2022, 23:29   #8
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Re: sizing my solar / battery / invertor system.

I'll also add that your Victron dealer will be responsible for support of your purchased components, so choose wisely.
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