vas
Well-known member
not sure, this definitely applies for semi flex stuck on the coachroof, but most down here have rigid panels on SS framework so not sure they heat much more than the ambient (which can be high but not excessive imho!)
Inverter Size Compared to Your Boat Size?
- Thread starter YannikPronto
- Start date
noelex
Well-known member
An efficient system is certainly essential if you want to heat water using solar panels on a yacht.
Calorifers are ideal for heating water via waste engine heat, or shore power/generator 240v AC systems. These therefore are ideal for most boats, but as we have no generator, almost never plug into shore power, and don’t do many engine hours, then they are not a great system in our case. The biggest killer is that it is frequently several days between running the main engine. Starting the engine just to have hot showers is not ideal.
Calorifiers can be used to heat water via solar, but they are inefficient in this role. A large amount of heat is lost storing the hot water, transferring this heat to the shower, and perhaps most critically waiting for the water to in the shower rose to reach an acceptable temperature.
I have not checked all your calculations, but a quick check for this month (October) based on the insolation in Glasgow suggests 34L of 50° C (the table shows 22L) water should be theoretically possible. Our normal shower temperature is 41°C so this increases the production to 45L. Part of the secret of shower efficiency is to have all the water immediately available at the right temperature. If this is done you can have a great shower with much less than 45L of water, This leaves power for other uses.
However, at these lattitudes we are normally ending solar production of shower water around the end of September/early October (which fits in with the seven months of year that I estimated). Today, for example, (near the end of October) our solar panels charged our batteries to 100% with power to spare, but all our shower water was heated using our Reflex diesel heater. We find this fits in conveniently. By the time solar electric production is insufficient to heat our shower water the diesel heater is needed to generally heat the boat and so might as well be also used to heat our water.
Heating water does take plenty of electrical power, but if your solar system is sized to provide enough general electrical power to cover months where the solar insolation is poor then there will be loads of excess power available for much of the year. Efficient systems to make use of ths excess power, such as heating water, are worth considering.
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Mistroma
Well-known member
Figures are based on output in an average year and therefore take account of the weather. I suspect might be you are talking about insolation W/m2 at 55N in October without considering prevailing weather conditions. That would explain why it only shows 22 vs. your 34 litres. However, I have seen insolation figures worked out both ways. I suspect people selling PV kit would want to show maps with higher insolation values.
Or my calculations could be out. I fudged an old Excel sheet I made to work out predicted output and added a quick calc. to work backwards to give Water volume for predicted output. The predicted output has always been close to real world figures but I've never used it to convert output to volume of water you could heat.
PV jumped ahead of thermal because of simplicity, lifespan, feed in tariffs etc. I'd agree about solar thermal in Scotland not being great for many reasons. It does work well in Greece with a simple container on deck (or on a roof). High efficiency capturing heat (vs. 20%ish for PV), no parasistic losses from pumps and conduction/radiation losses aren't much in the middle of the day. I wouldn't waste my time trying that on a wet Scottish autumn day.
I often hear that solar won't work as well in Scotland and am forever telling them that they shouldn't waste money on a wind-gen. Many boats in Greece with 300W or more PV and relatively few in Scotland with even one decent sized panel. I would certainly fit 300-400W if back sailing in Scotland.
Good to see that it is working well for you, thanks.
legendraver
New member
Or put her head out the hatch while sailing
chrishscorp
Well-known member
Just had 2 weeks down in the SW UK, ended up mostly at anchor or on mid river pontoons, I had a trusty 300w mobitronic inverter 18-20 years old anyway we stopped for the night and I plugged in 2 I phones a Kindle and the handheld VHF without a lot of thought as to what I was pulling anyway sadly it killed it.
We have an engine battery and 2 house batteries so some 330AH all lead acid topped up by the engine and a Rutland wind gen, mid beer, thinking we will have to find a marina tomorrow, it occurred to me I might not have taken off the inverter I took out the works van and put down the back of quarter berth a couple of years ago, sure enough after a rummage I found it. A Ring heavy duty 3100W beast with 12V cables thicker than the ones to my electric windlass its a serious bit of kit and I had not wired it in as I thought I could end up canning the batteries, my current thinking is to now permanently wire it in to the 12v supply and plug in a cable with a commando socket and lead that through to the mains inlet we would normally connect in the marina.
We have an engine battery and 2 house batteries so some 330AH all lead acid topped up by the engine and a Rutland wind gen, mid beer, thinking we will have to find a marina tomorrow, it occurred to me I might not have taken off the inverter I took out the works van and put down the back of quarter berth a couple of years ago, sure enough after a rummage I found it. A Ring heavy duty 3100W beast with 12V cables thicker than the ones to my electric windlass
its a serious bit of kit and I had not wired it in as I thought I could end up canning the batteries, my current thinking is to now permanently wire it in to the 12v supply and plug in a cable with a commando socket and lead that through to the mains inlet we would normally connect in the marina.
Buck Turgidson
Well-known member
None of the items you mention require AC power to charge. Why are you using an inverter to change DC to AC only for it to be rectified back to DC for the appliances? Just fit USB charge points to your DC system.Just had 2 weeks down in the SW UK, ended up mostly at anchor or on mid river pontoons, I had a trusty 300w mobitronic inverter 18-20 years old anyway we stopped for the night and I plugged in 2 I phones a Kindle and the handheld VHF without a lot of thought as to what I was pulling anyway sadly it killed it.
We have an engine battery and 2 house batteries so some 330AH all lead acid topped up by the engine and a Rutland wind gen, mid beer, thinking we will have to find a marina tomorrow, it occurred to me I might not have taken off the inverter I took out the works van and put down the back of quarter berth a couple of years ago, sure enough after a rummage I found it. A Ring heavy duty 3100W beast with 12V cables thicker than the ones to my electric windlass
chrishscorp
Well-known member
We did also have 2 laptops and a printer with us which definitely want AC hence me wiring it in.
12v USB yes i would be interested however I have yet to find any that are worth buying, if you have some you would recommend im all ears
GHA
Well-known member
These seem very good so far. PD is much faster than USB
https://www.amazon.es/-/pt/dp/B0CNPY4ZBS?psc=1
Very little onboard which isn't 12v, kitchen immersion blender the only one the gets any use. Some power tools which aren't cordless. Computers from a dc/dc boost converter to 19v, much more efficient than an inverter from 12v. Printer gets used once in a long while so inverter for that.
Gustywinds
Well-known member
Pretty much same as me. Wife has to have her hairdryer and kettle and I have to have my Espresso machine. I also use a CPAP machine and, although I have small portable one it’s not as effective as the full job.
So we replaced the existing 800VA inverter with a 2000VA Victron Multiplus and the 2 x 80VA house batteries with 3x100VA ( originally going to be 2x200 but they were very expensive and long lead). The BMS ( also Victron) has option for solar but I can’t see us fitting this.
So far it has worked faultlessly and it’s quite fascinating watching the monitoring on the app.
PetiteFleur
Well-known member
I've got a 150w invertor, just plugs into a 12v socket, only used for charging the 16v cordless drill and sometimes a small soldering iron which is much better than the 12v soldering iron.
mrangry
Active member
I currently dont have ac on board, I fitted a dc to dc converter for an LG tv which steps up from 12v to 19v and as others have said, why convert from dc to ac then back to dc. I now miss not having a toaster on board as the grill on the gas cooker is rubbish and considering an inverter for this and maybe a coffee machine.
mrangry
Active member
Arent these devices powered/charged by dc on a small brick transformer?
ChromeDome
Well-known member
I have a 30'. And a 1500w inverter carefully selected to be able to do what I calculated to need, pure sine, pc-compatible and what not.
I don't actually use it a lot. On rare occasion, but far and between as I'm mostly on shore-power when doing things that need this kind of power.
All the nav gear etc. is on 12 volt.
With the same requirements the same setup will do for any size boat. 10'-300' I'm sure.
I don't actually use it a lot. On rare occasion, but far and between as I'm mostly on shore-power when doing things that need this kind of power.
All the nav gear etc. is on 12 volt.
With the same requirements the same setup will do for any size boat. 10'-300' I'm sure.
noelex
Well-known member
We have a 49 foot yacht with a 2500 VA inverter. In the interests of electrical efficiency we try to run as much as possible from 24v either directly or via small local DC to DC converters if needed for devices such as our movie screen.
However, the inverter is needed for electric cooking, the washing machine and heating shower water. It also runs a small devices such as charging tool batteries that use such little power it is not worth devising a DC charging option.
One consideration when deciding on inverter size is the stand by current. This rises, often substantially as the inverter size increases. Try not to buy an inverter significantly larger than is likely to be needed, but make sure you take into account the start up current, the power factor and temperature deregulation. These factors mean a larger inverter than is obvious may be needed to power a load.
However, the inverter is needed for electric cooking, the washing machine and heating shower water. It also runs a small devices such as charging tool batteries that use such little power it is not worth devising a DC charging option.
One consideration when deciding on inverter size is the stand by current. This rises, often substantially as the inverter size increases. Try not to buy an inverter significantly larger than is likely to be needed, but make sure you take into account the start up current, the power factor and temperature deregulation. These factors mean a larger inverter than is obvious may be needed to power a load.
GHA
Well-known member
Sometimes there's more than that, like many HP laptops & no doubt others the have 3 pins in the charging lead so the laptop talks to the mains charger. My HP needed some time on google & a couple of resistors on the central pin to charge off 19.3V
geem
Well-known member
We run a 3kw LF inverter for large loads but we have a smaller 800w inverter dedicated to a double socket in the nav station for small loads for just this reason.
Gustywinds
Well-known member
A duck.
Gustywinds
Well-known member
That was my original plan but the two 200AH batteries were going to be a long lead ( and much more expensive) so we scaled back to the 2000VA one and 3x100AH and it’s been working fine.
Sea Change
Well-known member
3kva, 39ft boat. It's great having a proper wet and dry vac on board 
GHA
Well-known member
3000w pure sine on 33' boat, being able to weld in the anchorage is not a daily occurrence, but sooo useful if the need does arise 
