Switching between solar and mains

[ThrilloPads]

I'm installing some solar panels, mainly for the purpose of having charged batteries when out and about.

However, most of the time I'm plugged into shore power, as a live-aboard. I was wondering, in the summer, is there a way to ensure that the solar panels are saving me money and I'm using the electricity they are generating? The problem is that many things on board are AC, so the normal float charge wouldn't work... If I'm making sense?

I have a multiplus for inverter and charging. Is there perhaps a way to tell the inverter to use the batteries for AC if there is an incoming charge or if it's over a certain percentage. I want to make sure all this solar power is being used and not wasted....
Thanks!

 

[lw395]

I'd suggest working out how much power is at stake and whether it's worth messing about with costly inverters.
The obvious way to do it would be a 'grid tie inverter', using your panels like a conventional system on a house, to feed into the mains at your boat's consumer unit.

 

[PaulRainbow]

The danger with having mains and solar on at the same time is that the mains charger will keep the batteries charged up and leave nothing for the solar array to do. Not sure what AC equipment you have, but i'd get as much of it onto DC as i could, DC-DC converters are more efficient than an inverter.

 

[duncan99210]

The info on the Victron website seems to suggest that the Multiplus will adjust the battery charging output to take account of solar input: in other words that it does what you want it to. I'd talk to Victron and ask them if this is in fact the case.

 

[ThrilloPads]

Thanks all for the help so far.

Paulrainbow - completely agree, this was my concern. I'm slowly switching more things to DC, but it's a bit of a long process with lots to work through.

Duncan - thanks for pointing that out, much appreciated. I'll speak to Victron and see what they say

 

[Hadenough]

The danger with having mains and solar on at the same time is that the mains charger will keep the batteries charged up and leave nothing for the solar array to do. Not sure what AC equipment you have, but i'd get as much of it onto DC as i could, DC-DC converters are more efficient than an inverter.

Why should that be a problem? In the winter we have the mains charger on 24/7 (livaboard). It floats the batteries at 13.4v and puts in whatever Amps it needs to meet the DC load. Sun comes out - sometimes and the solar controller sees that the batteries are happy and dumps its charge. I have noticed that we sometimes get a brief, maybe 5mins, blip of charge from the solar but it soon goes to float at 13.4V. Or have I got it wrong?

 

[PaulRainbow]

Why should that be a problem?

Because you are not getting any useful yield from the solar panels, although i'm not sure i'd use the word "problem".

In the winter we have the mains charger on 24/7 (livaboard). It floats the batteries at 13.4v and puts in whatever Amps it needs to meet the DC load. Sun comes out - sometimes and the solar controller sees that the batteries are happy and dumps its charge.

Which is exactly what i said.

I have noticed that we sometimes get a brief, maybe 5mins, blip of charge from the solar but it soon goes to float at 13.4V. Or have I got it wrong?

You are seeing exactly what i described and exactly what i see from my own system. I also leave my mains charger on 24/7 in the Winter, as the solar yield isn't enough to keep up with demands and i can't be bothered to worry about it. In the Summer i can turn the mains charger off and the solar will keep up, easily.

In the Spring/Autumn, there is some useful solar yield to be had, but if the mains charger is on 24/7 you don't really get much from it. I have a Victron battery monitor the has a built in relay, the relay is configured to trigger a 12v/240v relay that turns the mains charger on if the voltage falls below a set level. So i get some solar yield when it's available, without over cycling my batteries.

 

[William_H]

I'm installing some solar panels, mainly for the purpose of having charged batteries when out and about.

However, most of the time I'm plugged into shore power, as a live-aboard. I was wondering, in the summer, is there a way to ensure that the solar panels are saving me money and I'm using the electricity they are generating? The problem is that many things on board are AC, so the normal float charge wouldn't work... If I'm making sense?

I have a multiplus for inverter and charging. Is there perhaps a way to tell the inverter to use the batteries for AC if there is an incoming charge or if it's over a certain percentage. I want to make sure all this solar power is being used and not wasted....
Thanks!

You have o think in terms of relative power. Your AC usage as a live aboard is likely to be for heating, hot water, perhaps cooking all very high power stuff in terms of Kilowatts. It is very unlikely that you can avert some electricity charges from a small solar array on the boat. You need perhaps 2kw of solar which takes up a garage roof area to do any cost saving. Things like lighting are easily done with low power from 12v system.
Any solar charging you achieve in lieu of running a battery charger is perhaps worth doing but will save almost no electricity charges. Typically your charger will supply 2 or 3 amps on float or about 20 to 40 watts. A bit more for inefficiencies and you are taking about perhaps 1 Kwh of electricity which costs perhaps 10p per day. A very small part of your other 240v AC usage.
So solar for when you are cruising, yes very desirable although an engine run can do the same thing. Solar at mooring in lieu of mains battery charger yes but won't save much. Hardly worth doing. olewill

 

[PaulRainbow]

You have o think in terms of relative power. Your AC usage as a live aboard is likely to be for heating, hot water, perhaps cooking all very high power stuff in terms of Kilowatts. It is very unlikely that you can avert some electricity charges from a small solar array on the boat. You need perhaps 2kw of solar which takes up a garage roof area to do any cost saving. Things like lighting are easily done with low power from 12v system.
Any solar charging you achieve in lieu of running a battery charger is perhaps worth doing but will save almost no electricity charges. Typically your charger will supply 2 or 3 amps on float or about 20 to 40 watts. A bit more for inefficiencies and you are taking about perhaps 1 Kwh of electricity which costs perhaps 10p per day. A very small part of your other 240v AC usage.
So solar for when you are cruising, yes very desirable although an engine run can do the same thing. Solar at mooring in lieu of mains battery charger yes but won't save much. Hardly worth doing. olewill

Sorry, but your assessment of savings by using solar power could not be further from reality Will.

Sure, if he's using electricity to heat the boat or heat water then that'll realistically need to be supplied by mains, but most loads on a boat, even a liveaboard can be supplied by DC. My own boat is almost exclusively 12v, apart from a toaster i use once in a blue moon, a printer and a mains kettle. I use the mains kettle as it's much cheaper than gas, which i use for cooking.

During the Summer my solar yield is enough to run the whole boat. Last Summer, from May to Oct, i used £15.70 in mains electricity, the mains charger was off for the whole time. TV, soundbar, laptop, phone charger, tablet charger, LED lights, water pump, fridge, all 12v or run via DC-DC converters.

 

[Hadenough]

Because you are not getting any useful yield from the solar panels, although i'm not sure i'd use the word "problem".



Which is exactly what i said.



You are seeing exactly what i described and exactly what i see from my own system. I also leave my mains charger on 24/7 in the Winter, as the solar yield isn't enough to keep up with demands and i can't be bothered to worry about it. In the Summer i can turn the mains charger off and the solar will keep up, easily.

In the Spring/Autumn, there is some useful solar yield to be had, but if the mains charger is on 24/7 you don't really get much from it. I have a Victron battery monitor the has a built in relay, the relay is configured to trigger a 12v/240v relay that turns the mains charger on if the voltage falls below a set level. So i get some solar yield when it's available, without over cycling my batteries.

OK, thanks just down to semantics. We both run our systems in pretty much the same way although I don't have the 12v/240v relay.