Any advice on solar panels for boats?

[PaulRainbow]

Say a 2kW microwave for easy maths.

If you get a 105Ah LiFePO4 battery, that will give you about 1kWh of usable power after losses.

Therefore it could run the microwave for about 30 minutes before flattening the battery.

To charge the battery back up again you need to put about 1.2kW back in again.

With a 100W solar panel, in the middle of summer, you will generate around 10kW a month in the summer, and perhaps 3kW in the winter.

So it would kind of work assuming you only used the microwave for a few minutes at a time.
I would just take the battery home with you when you leave the boat and charge it up again.

Typical microwave for an 8m boat would be 800w, maybe 1000w. So at least twice as long from the battery than above.

As you say, would likely only be used for short bursts. If so, an additional SLA battery, in parallel with the current domestic battery/s would give enough power for a few short uses.

I would expect a 100w panel in a reasonably unshaded spot would charge the battery back up from a pretty depleted state in a couple of days.

@Victoriana A little more info would be useful, size of microwave, how much use expected, current batteries etc

 

[Victoriana]

I'm afraid the answer from me is that I use the generator.
You might like to check what your engine alternator can provide and if you would do any damage to it if yo connect an inverter to your DC system.
A friend with a sailboat changed his engine alternator to provide more power - maybe thats an option (alternative to a generator).
But taking Croftis's point, you need to size your DC cables carefully and keep their length down.

Thanks for all the advice. What size generator would you suggest?

 

[jakew009]

Thanks for all the advice. What size generator would you suggest?

Something like this for a little 700W microwave: https://www.amazon.co.uk/Hyundai-HY...r+generator&qid=1672773406&s=outdoors&sr=1-19

It's totally impractical though.

 

[Hurricane]

Something like this for a little 700W microwave: https://www.amazon.co.uk/Hyundai-HY...r+generator&qid=1672773406&s=outdoors&sr=1-19

It's totally impractical though.

He should be VERY careful where he operates with regard to the exhaust outlet.
But, yes, that would be the cheapest option.
The safest way would be to use a properly installed marine generator.

 

[jakew009]

He should be VERY careful where he operates with regard to the exhaust outlet.
But, yes, that would be the cheapest option.
The safest way would be to use a properly installed marine generator.

As I said, totally impractical

 

[PaulRainbow]

He should be VERY careful where he operates with regard to the exhaust outlet.
But, yes, that would be the cheapest option.
The safest way would be to use a properly installed marine generator.

Perhaps a little OTT to install a generator on an 8m boat to run a microwave ?

 

[PaulRainbow]

Thanks for all the advice. What size generator would you suggest?

You still have not revealed the size of microwave and your intended usage pattern. This would help to provide you with better suggestions.

 

[Bouba]

Best Campervan Microwave - read this guide before you buy

 

[PaulRainbow]

Best Campervan Microwave - read this guide before you buy

The claim in that link, that "The stated output power of a microwave oven (900W for example) is only approximately half the amount of power the microwave requires. A 900W microwave will actually need around 1800W of power (or approximately 7.5 amps). " is way over the actual figure.

A modern inverter microwave is over 90% efficient, not 50%

 

[Bouba]

The claim in that link, that "The stated output power of a microwave oven (900W for example) is only approximately half the amount of power the microwave requires. A 900W microwave will actually need around 1800W of power (or approximately 7.5 amps). " is way over the actual figure.

A modern inverter microwave is over 90% efficient, not 50%

They might be talking about the start up

 

[Victoriana]

You still have not revealed the size of microwave and your intended usage pattern. This would help to provide you with better suggestions.

Sorry, its an 800w microwave for occasional use like heating up jacket potatoes, beans etc.

 

[PaulRainbow]

Sorry, its an 800w microwave for occasional use like heating up jacket potatoes, beans etc.

No problem.

In that case, see post #11.

Add another battery and as much solar as you can. With sensible use of the microwave and your engine, you should be OK. Just keep an eye on battery voltages so as not to kill the batteries.

 

[jrudge]

OK so if I get a 3kw inverter with a 230ah AGM battery, would that work if I keep the engine running whilst using the microwave?
[/QUOTE]

I did exactly this. The microwave was Ok on batteries ( to a point ) but the low wattage kettle and toaster would only run for about a minute before the low voltage alarm sounded.

I used to run one engine ( that connected to the house batteries) at about 1200 RPM and whilst the battery was still taking a hammering it didn't trigger the low volt alarm. I then used to reduce the throttle to idle while I had breakfast.

This would not have fully replaced the current used, but given this was breakfast time it was fine by the next time I wanted to use it.

The inverter was not a sine wave one but a cheap eBay and the microwave did make a funny buzzing noise!

Will work fine for occasional use.