Solar panels

[roaringgirl]

When cooling: it takes 4200J/degree/litre to cool water plus countering any heat that gets through the insulation.

When maintaining: it only has to counter any heat that gets through the insulation.

 

[roaringgirl]

If your fridge is insulated enough to stop your food going off overnight (because you're not opening it) then it'll barely use any energy if you leave it switched on, if you see what I mean.

 

[Baggywrinkle]

If your fridge is insulated enough to stop your food going off overnight (because you're not opening it) then it'll barely use any energy if you leave it switched on, if you see what I mean.

Interesting point ... I'll check that next time I'm on the boat. I used a watt meter to measure the power consumption of my fridge over a number of days, from initial switch on when I arrived to leaving a week later - then averaged to find consumption over a 24 hr period - my intention was to spec the batteries/solar to be able to leave it on 24/7 anyway, but it would be interesting to test your assertion.

 

[ip485]

Some very interesting comments, but as I said previously, there is the totally practical side to this, which apart from all the calcualtions will say that 300W is probably confortable for the standard comforts and for all singing all dancing with big chest fridge and freezer, sat TV etc you need 800 to 900W, all the permutations in between the more things you have. Thats is the range that I think is proven to work. Less than 200W and it will be a real struggle to all but impossible.

 

[roaringgirl]

If you're going to measure it, watch the first 2 hrs that you switch it on and compare that with a couple of hours before you open it to make breakfast.

 

[RobF]

I found this one to be reasonably effective & cost effective. However, I did go for the Victron controller rather the controller which can be bought with the panel as part of a kit. The panel folds down into a reasonably small unit when not in use.

 

[Graham376]

....... - my intention was to spec the batteries/solar to be able to leave it on 24/7

Our fridge draws 7 amps (BD50F) and 200w of solar was "only just" enough to be able to leave it running, along with usual devices charging, some TV etc. 24/7 living aboard 6/12, in Algarve. Lots of good sunshine but 30+ degrees below deck at times. Changing panels to 320w last winter has made a hell of a difference, batteries usually full before lunch time.

 

[roaringgirl]

It's not how much your fridge draws that is the key thing here, it's how much of the time the compressor is running.

 

[geem]

It's not how much your fridge draws that is the key thing here, it's how much of the time the compressor is running.

Fridge insulation thickness, size of fridge, temperature of the compartment all determine compressor run time, assuming the fridge is gas correctly and the compressor isnt worn.
If you have a large battery bank and lots of solar then there is not really a problem. We are adding a second fridge for fruit and veg that we will run at circa 10degC. Current fridge runs at 4degC. We will have no issues running them and leaving them on at night with our 1000Ah of battery capacity and 760w of solar.
If you are running a small amount of solar and a small battery bank then getting the fridge right will pay dividends. If you have a large fridge then keep it full. This will reduce compressor cycling. Bottles of water help this especially if you have a small battery bank but lots of solar. Supercooling the fridge during the day with lots of solar then turning it off at night and using the stored coolth in the water bottles will keep food cool whilst the compressor is off. The bottles will function like a holding plate.
I dont think there is a one size fits all solution. It is very much dependant on the particular arrangement on any one particular boat.
For us we use four large solar panels. They are wired in pairs in series on to their own Victron 75/15 per pair. This gives us 40v at the panels. Its a good compromise between low sun conditions and shading issues. The same can be applied to relatively small panels. We have a roving panel that we hook up to the engine batteries. It is a pair of framed 20w panels bolted together and wired in series to give us a 40w 40v panel to feed through an MPPT reg. it works well and is small enough to throw on the front bunk when we are at sea.

 

[roaringgirl]

I can't think of a scenario where it would be more efficient to switch the fridge off overnight.

If switching it off overnight doesn't result in the contents rising to atmospheric temperature and staying there for a few hours (hello food poisoning & off milk!), then the overnight compressor run-time would have been minimal, had you left it on.

 

[wiggy]

I’ve got 30ft boat and our 100w panel covers all our needs including the fridge which is left on. Mine hangs on the guard rails and is moved for the afternoons as the sun moves, I put it in the morning position once the sun sets. Usually by 9am batteries are back to 100%, later if is very cloudy. I bought the panel with an mppt controller from Mid Summer Energy, they extended cables as needed. I made legs from broom hand to allow me to angle the panel, my battery bank is 250AH of sealed lead acid.

 

[Red Panda]

Can you please point me to this information as I have not seen anything mentioning it whilst researching a solar panel set up for myself?

Thanks

Gladly - it's not clear from any of the datasheets, I only learnt this after buying the controller.
It's in the Smart Solar user manual, section 3.3:

3.3. PV configuration (also see the MPPT Excel sheet on our website)
.....
● PV voltage must exceed Vbat + 5V for the controller to start. Thereafter minimum PV
voltage is Vbat + 1V.
● Maximum open circuit PV voltage: 75V respectively 100V
For example:
12V battery and mono- or polycristalline panels connected to a 75V controller
● Minimum number of cells in series: 36 (12V panel).
● Recommended number of cells for highest controller efficiency: 72
(2x 12V panel in series or 1x 24V panel).
● Maximum: 108 cells (3x 12V panel in series).

 

[roaringgirl]

For reference, we have 350w of solar, and due to dead batteries, 50Ah of useable capacity. We kept the fridge running for 3 days (and nights) and it was fine. This was on a 3 day passage from the Scilly Isles to Spain.

 

[GHA]

Gladly - it's not clear from any of the datasheets, I only learnt this after buying the controller.
It's in the Smart Solar user manual, section 3.3:

3.3. PV configuration (also see the MPPT Excel sheet on our website)
.....
● PV voltage must exceed Vbat + 5V for the controller to start. Thereafter minimum PV
voltage is Vbat + 1V.
● Maximum open circuit PV voltage: 75V respectively 100V
For example:
12V battery and mono- or polycristalline panels connected to a 75V controller
● Minimum number of cells in series: 36 (12V panel).
● Recommended number of cells for highest controller efficiency: 72
(2x 12V panel in series or 1x 24V panel).
● Maximum: 108 cells (3x 12V panel in series).

As mentioned in previous post, the 5v above battery voltage for the regulator to go into charge mode makes no difference to the amount of charge going into the batts in the real world. Panels in series is more often than not a bad idea as even just a tiny shadow on one panel can hammer the output of both panels. Even in perfect sun on both panels if you switch between series & parallel there's just a tiny difference, slightly less voltage drop along the cables between the panels & regulator in series.

 

[GHA]

I’ve got 30ft boat and our 100w panel covers all our needs including the fridge which is left on. Mine hangs on the guard rails and is moved for the afternoons as the sun moves, I put it in the morning position once the sun sets. Usually by 9am batteries are back to 100%, later if is very cloudy. I bought the panel with an mppt controller from Mid Summer Energy, they extended cables as needed. I made legs from broom hand to allow me to angle the panel, my battery bank is 250AH of sealed lead acid.

You must use next to no power overnight then From 80%SOC would be something like 4 hours minimum to get back to really 100% no matter what size charge source you have.

 

[noelex]

Gladly - it's not clear from any of the datasheets, I only learnt this after buying the controller.
It's in the Smart Solar user manual, section 3.3:

3.3. PV configuration (also see the MPPT Excel sheet on our website)
.....
● PV voltage must exceed Vbat + 5V for the controller to start. Thereafter minimum PV
voltage is Vbat + 1V.
● Maximum open circuit PV voltage: 75V respectively 100V
For example:
12V battery and mono- or polycristalline panels connected to a 75V controller
● Minimum number of cells in series: 36 (12V panel).
● Recommended number of cells for highest controller efficiency: 72
(2x 12V panel in series or 1x 24V panel).
● Maximum: 108 cells (3x 12V panel in series).

The high start up voltage programmed into the Victron controller does not seem to be a problem in practice, but it would nice to hear reports from people with “12v” panels that have a lowish voltage output, especially if living in hot climates.

For the moment I would recommend for marine applications wiring the panels in parallel.

 

[wiggy]

It’s only the fridge on overnight and maybe a phone being charged. Lights are LED, and draw didleysquat. Key thing I recon is moving panel with the sun, fixed panels will always be a compromise.

 

[GHA]

It’s only the fridge on overnight and maybe a phone being charged. Lights are LED, and draw didleysquat. Key thing I recon is moving panel with the sun, fixed panels will always be a compromise.

Still sounds unlikely by 9am, what tells you it's full?

On my 2 x T105's, 225Ah, full is under 2A going in at 14.9V, varies a bit with temperature.

 

[wiggy]

NASA BM1

 

[Red Panda]

I've only tried 2x50W in series - and to confirm what various others have mentioned, although that brings the voltage well above the controller startup voltage, in practice it didn't greatly increase the charging current.
I'd previously been convinced that parallel wiring was the way to go, but I'm going to configure my own setup so that I can easily switch between parallel and series.
I certainly don't live in a hot climate, though!