Solar water

[lewisericeric]

Hi

 

Some of you may know because of an earlier thread, that I've got 3 x 230w solar panels feeding the batteries. Anyway, I think this is more than enough for our battery bank. But I was wondering, is it possible to link up one of the solar panels to my calorifier to heat up hot water rather than having to have the engine on for it. If so, how can it be done? Does anyone have any ideas?

 

I'm guessing I don't just put the cables from the solar panel directly into the electrics on top of the calorifier

 

(that is a joke just to clarify!!)

 

It's a surcal calorifier I've got with an 1kw electric immersion

[Ex- Member]

Hi

 

Some of you may know because of an earlier thread, that I've got 3 x 230w solar panels feeding the batteries. Anyway, I think this is more than enough for our battery bank. But I was wondering, is it possible to link up one of the solar panels to my calorifier to heat up hot water rather than having to have the engine on for it. If so, how can it be done? Does anyone have any ideas?

 

I'm guessing I don't just put the cables from the solar panel directly into the electrics on top of the calorifier

 

(that is a joke just to clarify!!)

 

It's a surcal calorifier I've got with an 1kw electric immersion

 

 

Hi Lewis

 

You can get 12v elements for a calorifier so you could simply wire up from your battery bank via a switch and use it to heat water when your batteries reach full and your solar panels are still in daylight. I think 12v elements though take quite a long time to heat the water up and of course use a lot of power.

 

There are also dump systems for using excess solar energy when batteries are fully charged, I'm not too sure about these though and heard they are expensive.

 

As you know I'll be in a similar position to you as our 500 watts of solar would mean not having to run the engine much in the summer months so I have planned a solar collector that heats water in the summer. We have diesel heating in the winter that can also heat water in the calorifier, so that's my plan for hot water as we won't be running the engine in winter either as i'm fitting a small diesel engine in the engine room married to alternators that will charge batteries when solar doesn't.

 

There's also gas water heating which is probably the most efficient as it heats as you use, with hindsight I wish we had fitted one of these in the beginning of the build, fitting one now would be difficult as it would mean a lot of work and upheaval, if it was easier to do, that's what I would choose though.

Edited August 8, 2012 by Julynian

[Smelly]

You'll never get enough energy from a boat sized Pv installation to make a significant difference to the temperature of a calorifier full of water.

[Roger Gunkel]

A great idea at first glance, but probably pointless in practice. To get the equivalent of what your 1kw immersion gives you from a 230w solar panel is really a bridge too far. Your panels will only get anywhere near their maximum theoretical output under ideal conditions and that will only be for about 3 -4 hours in the height of Summer on a perfect day. If you look at the average output over a day from one of your panels, it will be way down on the maximum. It would take many hours to get any worthwhile heat into the tank, assuming that none of the output was being diverted to battery charging during the course of the day.

 

To try it, you should find that your controller has a direct load output, which would route surplus 12v to a load such as a 12v immersion heater, but personally, if I had that much surplus powe available, I would expand the battery bank to take advantage of it.

 

Of course if you have enough sunshine to give you that much surplus, you would get much quicker and more efficient water heating by putting a black flexible water storage bag on the roof, and feeding the output pipe via gravity to a suitable outlet.

 

Roger

Edited August 8, 2012 by Roger Gunkel

[DeanS]

Add more batteries, and go cruisin

[Ex- Member]

A great idea at first glance, but probably pointless in practice. To get the equivalent of what your 1kw immersion gives you from a 230w solar panel is really a bridge too far. Your panels will only get anywhere near their maximum theoretical output under ideal conditions and that will only be for about 3 -4 hours in the height of Summer on a perfect day. If you look at the average output over a day from one of your panels, it will be way down on the maximum. It would take many hours to get any worthwhile heat into the tank, assuming that none of the output was being diverted to battery charging during the course of the day.

 

To try it, you should find that your controller has a direct load output, which would route surplus 12v to a load such as a 12v immersion heater, but personally, if I had that much surplus powe available, I would expand the battery bank to take advantage of it.

 

Of course if you have enough sunshine to give you that much surplus, you would get much quicker and more efficient water heating by putting a black flexible water storage bag on the roof, and feeding the output pipe via gravity to a suitable outlet.

 

Roger

 

Hi Roger

 

A few years ago I fitted a 240 volt 1KW 27 inchlong immersion heater element in our calorifier. It's only be used thus far from a mains supply but our inverter 3KW would easily power it. When we get on the boat it takes around 20 minutes for the calorifier water to heat up, it's not set at a very high temperature but plenty hot enough to do washing up and just too hot for for a shower so a good temperature.

 

We've got 500 watts of solar ready to be fitted. so assuming when on he water and panels up and working, If by lunchtime my batteries were fully charged on a sunny day and we had 8 hours daylight remaining, I switched on the water heater for 20 minutes via inverter to heat the 60 litres of water, I'm sure should the remainder of he day stay reasonably sunny, that that 20 minute use of 1 kw might well be replenished by a further 8 hours of charging from solar panels.

 

However that's just an assumption, I don't know the maths of this, but if the panels averaged say 20 amps for that remaining 8 hours (just under half of rated amps) would that replenish the heating of the water.

 

Lewis who was he original poster has 750 amps of solar, so would fair even better.

 

Also it's difficult to know what to do with excess energy, adding batteries would be expensive assuming you have the space anyway. But even if you do that, you're likely to be in the same situation again with excess energy, so you can't just keep adding batteries.

 

So dumping excess charge into anything you can utilise is better than losing it altogether. So using a method of dumping the energy in to heating water, even though it might not heat it up fully but would mean using less energy from elsewhere to heat it up further.

 

Edited August 8, 2012 by Julynian

[Roger Gunkel]

I understand your logic regarding the solar, but Lewis the original OP, did say he thought about using one of his 230w panels, which is way below the average of 20ah that you mention

 

I am also surprised that a 1kw immersion heater was able to get 60 litres of water to a hot showering temperature in 20 minutes, but I will take your word on that as I don't have an immersion. I am certainly not an electrician, but I would have thought that putting the best part of 100a continuous load on your battery bank for a least 20 minutes on top of any other power that you may be using is quite a load.

 

The question about what to do with surplus power is also an interesting one, as I would have expected that if you need 500w of solar in the first place, as I do, that you presumably have a reasonably high daily load expectation. I certainly wouldn't want to put energy into heating water in the height of Summer if I could store it in my batteries instead. If you assume an average of 20-25 amps per hour from 500w solar for 8 hours, then you are expecting 160-200 amps into your batteries over one day. I would consider that a very optimistic figure averaged over several days and the reality is likely to be considerably lower. Even if we take that figure, by the time you allow for putting back 50% more than you use, to take into consideration inefficiencies in the batteries, inverter etc, you are still only getting 110-130 useable amps back in. I wouldn't want to waste 30amps of that for a shower, and if you are running a fridge, you will already be taking 40-50 amps out.

 

When you take into consideration the fact that a couple of cloudy or rainy days will drastically reduce the solar output, then solar PV water heating in my opinion becomes a wasteful use of hard gained energy. If anyone can honestly say that they have been able to get useful hot water on a regular basis whilst running the boat on solar Pv, then I would love to hear how they have set it up.

 

If you really want to heat water from solar energy, then rather than using solar PV, which is about 15% efficient, then why not look at evacuated tube panels which convert solar energy to heat at an efficiency of over 80%. You will also get useable water temperature all year round and not just for a few scorching days in mid Summer.

 

If the pv water heating theory worked, I would be the first to use it, but I think it is sadly a non starter.

 

Roger

[Arthur Brown]

Driving ALL of your solar output into a 12 or 24v (according to your system volts) 1Kw immersion heater element for a couple of hours WILL make a difference to your hot water levels. If you are finding that you have full batteries than either a manual or automated switch will allow you to power the immersion heater from the panels directly. HOWEVER 1Kw at 12v is close on 100 amps so please use appropriate wire etc. and be certain tht your controller will supply this load.

 

Unless your calorifier has two heater threads then fitting a 12v heater means that you need a big transformer to heat from hookup any other time, while your summer PV output may leave you surplus the winter output may not!

[Grace and Favour]

Hi

 

Some of you may know because of an earlier thread, that I've got 3 x 230w solar panels feeding the batteries. Anyway, I think this is more than enough for our battery bank. But I was wondering, is it possible to link up one of the solar panels to my calorifier to heat up hot water rather than having to have the engine on for it. If so, how can it be done? Does anyone have any ideas?

 

I'm guessing I don't just put the cables from the solar panel directly into the electrics on top of the calorifier

 

(that is a joke just to clarify!!)

 

It's a surcal calorifier I've got with an 1kw electric immersion

 

If I recall correctly you've had your PV panels running for two or three months now . . . . .

 

so will have had the opportunity to observe and monitor the charging regime...... how much energy are you collecting each day?

 

At what point in the day are your batteries (fully-ish) charged.

 

However, as others have said, a 230w panel will make marginal difference to a calorifier full of water, (there are easier ways to heat water)

[canalowl]

I have 360 watt of solar power and this produces more than I need on a very good day i.e. the smart Guage is showing 100% by mid afternoon sometimes.  I have a lister HA3 which is air cooled and so I often put the 1 kw 240 volt immersion heater on when cruising in the summer. I estimate that the heater draws around 100 amp on the 12 volt side allowing for losses and for the first hour or so the battery loses about 10% of charge but then starts charging as the water heats up.  This means in effect that the alternator plus the 360 watt solar isn't able to keep up and so I concluded its a waste of time to think about dump load.  I would like to install solar water at sometime if and when I become convinced its worth it.  In the meantime I just turn the diesel heater on for half an hour if not cruising or the diesel generator on if the batteries need a good charge as well as heating the water.

[Roger Gunkel]

Driving ALL of your solar output into a 12 or 24v (according to your system volts) 1Kw immersion heater element for a couple of hours WILL make a difference to your hot water levels. If you are finding that you have full batteries than either a manual or automated switch will allow you to power the immersion heater from the panels directly. HOWEVER 1Kw at 12v is close on 100 amps so please use appropriate wire etc. and be certain tht your controller will supply this load.

 

Unless your calorifier has two heater threads then fitting a 12v heater means that you need a big transformer to heat from hookup any other time, while your summer PV output may leave you surplus the winter output may not!

 

Arthur, your post is really factless waffling, and while I appreciate that you want to give useful advice, you give absolutely no information to back up your assertions. You state that 'drriving ALL of your solar output into a 1kw immersion element for a couple of hours WiLL make a difference to your hot water levels' . OK I'll agree with that, BUT, based on your own experience of solar and maths, how much difference will it actually make? I degree increase, 10 degrees, 50 degrees? How often will the conditions be right to give any increase in water temperature at all? If you are offering advice, it needs to be based on facts, and the facts are that if the OP has fully charged batteries and can output his entire solar array to an immersion heater, has no other drain whatsoever, and has continuous optimum sunshine to drive the panels at their maximum, then useable results will likely be obtained. HOWEVER, anyone living on a boat and having a solar array of that size, is likely to have a fairly high continuous power requirement, so the chance of all the parameters being right on a regular basis to make any significant difference is slim to say the least.

 

The wiring, cost and effort involved to produce minimal difference for the odd day in the Summer makes it a pointless excersise in my opinion. Immersion heaters are only of real use when you have access to grid electricity, or want to run a generator with a high enough output to power other devices and run an immersion at the same time. A costly way to heat water though.

 

Roger

[RLWP]

 

I'm surprised that solar hot water isn't more common on boats. It is far easier to do the electricity

 

I suppose you would have to do some plumbing instead of just running a few wires about the place

 

Richard

Edited August 9, 2012 by RLWP

[Ex- Member]

I understand your logic regarding the solar, but Lewis the original OP, did say he thought about using one of his 230w panels, which is way below the average of 20ah that you mention

 

I am also surprised that a 1kw immersion heater was able to get 60 litres of water to a hot showering temperature in 20 minutes, but I will take your word on that as I don't have an immersion. I am certainly not an electrician, but I would have thought that putting the best part of 100a continuous load on your battery bank for a least 20 minutes on top of any other power that you may be using is quite a load.

 

The question about what to do with surplus power is also an interesting one, as I would have expected that if you need 500w of solar in the first place, as I do, that you presumably have a reasonably high daily load expectation. I certainly wouldn't want to put energy into heating water in the height of Summer if I could store it in my batteries instead. If you assume an average of 20-25 amps per hour from 500w solar for 8 hours, then you are expecting 160-200 amps into your batteries over one day. I would consider that a very optimistic figure averaged over several days and the reality is likely to be considerably lower. Even if we take that figure, by the time you allow for putting back 50% more than you use, to take into consideration inefficiencies in the batteries, inverter etc, you are still only getting 110-130 useable amps back in. I wouldn't want to waste 30amps of that for a shower, and if you are running a fridge, you will already be taking 40-50 amps out.

 

When you take into consideration the fact that a couple of cloudy or rainy days will drastically reduce the solar output, then solar PV water heating in my opinion becomes a wasteful use of hard gained energy. If anyone can honestly say that they have been able to get useful hot water on a regular basis whilst running the boat on solar Pv, then I would love to hear how they have set it up.

 

If you really want to heat water from solar energy, then rather than using solar PV, which is about 15% efficient, then why not look at evacuated tube panels which convert solar energy to heat at an efficiency of over 80%. You will also get useable water temperature all year round and not just for a few scorching days in mid Summer.

 

If the pv water heating theory worked, I would be the first to use it, but I think it is sadly a non starter.

 

Roger

 

I am also surprised that a 1kw immersion heater was able to get 60 litres of water to a hot showering temperature in 20 minutes

 

Hi Roger

 

I'm on the boat later today so will time this more accurately. Using the 27 inch elements is essential if heating a vertical calorifier though. I also super insulated the calorifier cocooning it in 5mm thick polypropylene sheet and filling the additional 1 inch cavity with another layer of spray foam.

 

 

This is a very interesting subject, and excess energy used for heating water I have to agree isn't going to be the most efficient. It was more of a question if you have no other ways of using excess power dumping to heat water might be a bit better than not utilising at all.

 

We'll soon be on the water so will be experimenting with different things. I do have a plan for a water solar collector and have all the bits required to build one, probably a project that will be finished when on the water as it isn't priority.

 

Our 500 watts of solar is calculated to cope with our usage through 8 warmer months, calculated to cope on the worst 2 months of the top 8, our power usage isn't that high although we will run a 240 volt fridge through inverter, it is an A+ rated fridge though.

 

Of course this summer hasn't been that great so we might well have struggled with 500 watts, we do have the capability of adding another 250 watt panel though should we require, and this could simply be added to the array as the controller will be rated high enough to accept the additional panel.

 

Our battery bank is already 700 amps all brand new and all neatly and newly installed, adding more batteries is possible but I reckon 700 amps is probably about the limit taking in to consideration our original audit. The bank size is designed to last 2 to 3 full days whilst still maintaining a 50% state of charge, this calculated assuming a minimal 10% output from solar over the same period.

 

Me and Lynn have been thinking of excess energy and when this occurs using our Twin Tub washing machine would be a viable way of using additional power at 160 watts wash and 180 watts spin. We even have a small 700w halogen oven which we would use for cooking should excess power be available, that would only save some gas usage though, although a saving is a saving.

 

Some solar output figures from lewis would be very helpful especially as the weather's been so poor, the figures would be very realistic in these circumstances and offer a good average guide.

 

c/mon Lewis

 

Also have you had many occasions where you have produced excess power????

 

 

 

[BEngo]

Arthur, your post is really factless waffling, and while I appreciate that you want to give useful advice, you give absolutely no information to back up your assertions. You state that 'drriving ALL of your solar output into a 1kw immersion element for a couple of hours WiLL make a difference to your hot water levels' . OK I'll agree with that, BUT, based on your own experience of solar and maths, how much difference will it actually make? I degree increase, 10 degrees, 50 degrees?

 

SNIP

 

 

Roger

OK.

 

Assumptions:

 

Heat loss from the calorifier and pipes is negligible

Heat transfer from the heater to the water is perfect

 

140F is shower temperature

40F is inlet water temp

 

Calorifier heats 60lb of water

 

Effect:

 

To raise 60 lb of water through 100F requires 6000 BThU.

 

6000 BThU is approximately 1758 Wh

 

So if 230W was available to heat the tank it would take about 7.6 hours to heat the tank. 500W would achive the same effect in about 3 1/2 hours.

 

Julynian probably has a 3kW heater so that should take about about 35 minutes.

 

HOWEVER,

 

The heat transfer is not perfect and it becomes more difficult to heat the water as it gets warmer-this will slow things down.

The calorifier WILL lose heat to the outside, more insulation means more slowly, but it still happens. This will also slow down the heating of the water.

 

The heater should match the panels output. ie a 12V 230W heater will only work properly when the panel (and any fancy controller) is feeding it 230W at 12 v. I can only guess what will happen if the panel produces less than 230W- either the voltage at the heater will fall or the immersion will become very inefficient at transferring heat to the water because its temperature has fallen because it is under voltage or under current.

 

N

[RLWP]

<snip>

 

So if 230W was available to heat the tank it would take about 7.6 hours to heat the tank. 500W would achive the same effect in about 3 1/2 hours.

 

Julynian probably has a 3kW heater so that should take about about 35 minutes.

 

<snip>

 

N

 

Is that right? Even if the heater is 3KW, there is still only 230W (or 500W) going into it. And if there is less power, won't the temperature of the heater be lower, the heat transfer worse, the final temperature lower and so on

 

Richard

[Roger Gunkel]

Hi Julian,

 

Firstly regarding surplus power, that is a tricky one to answer, as we have 200w of solar at present but our residential mooring has a 240v hookup. We are on our mooring for most of the time as our business is run from the boat, but we use the solar to supplement the 25per Kw cost of our hookup. We tend to switch to battery power during the day until the batteries reach 65-70%, then back to 240v. The solar always brings the batteries back to 100% on the SOC meter, so in the duller or Winter times, we simply switch back to 240v earlier than on the brighter days. We haven't used a mains charger for nearly 3 years.

 

Coming back to your own situation, I agree that the 27" element will be the most effective, but the problem with surplus output utilisation is that it will vary depending on the varying load on the batteries from other devices, time of day, clouds etc, so it would be very unpredictable as far as I can see.

 

Your 700ah bank sounds good for normal use, but again it depends on how you intend to use it. So if you intend to run down to no lower than 50%, then you will have 350ah available if you expect a possible 3 days use to allow for dull days, then that would only give you around 90amps per day allowing for losses in the system and replacing more than you take out. To that you would add the output from your solar, so adding an average of 160 amps per day on the best days, would give you 250w, which is more than enough during the good Summer days. If you intend to preserve battery life by not discharging so far on a regular basis, then you will considerably further reduce the available power. I feel that any surplus power is best used to keep your batteries as high as possible.

 

Of course when you start taking out your power, the picture is again very variable. Our fridge freezer is A+ rated, and when I tested the consumption at the unit over 7 days, it averaged about 48amps per day, but to that I would have to add at least 10% loss from the inverter, plus putting back lets say 25% more than used. That would take us into the region of 70 amps per day just for the fridge. If you are also using the occasional other high power appliances, the you will quickly use up the daily quota. During the days that the solar ouput is very low, it is easy to see how the balance swings backwards and forwards.

 

You also mention items such as a twin tub etc, so be aware that the fridge and other motor driven and sensitive 240v electrical equipment will need a pure sine wave inverter and of course the cost of these escalates rapidly with the output requirement. You should allow at least 5 times the wattage of any motor driven appliance for startup loads.

 

So coming back to the water heater element, I really think that it is pointless, and if you really want to use surplus power, look at ways of driving your fridge from the load output of the controller rather than just from your batteries, as that will help to keep your batteries at as high a charge level as possible.

 

Roger

[BEngo]

Is that right? Even if the heater is 3KW, there is still only 230W (or 500W) going into it. And if there is less power, won't the temperature of the heater be lower, the heat transfer worse, the final temperature lower and so on

 

Richard

 

 

Indeed. My calculation was on the basis that Julynian currently has National Grid behind him for immersion heating so his 3kW heater gives just that (or maybe a bit more if National Grid have the volts up). If he hasn't then there is no way he's going to get 27 litres of hot water in 20 minutes from any realistic boat sized solar array. That would actually require a bit more than 5 1/2 kW.

 

In the absence of a thermostat the final temperature is determined by the heat input rate and the insulation of the calorifier. Provided the calorifier does not boil first(!) the water will get hotter until the heat loss rate is exactly the same as the heat input rate.

 

N

[lewisericeric]

Hi everyone

 

Sorry for the delay in my reply, just not had much chance to respond lately. In answer to your question, with my 690w of power, on sunny days I am at 100% by lunch or mid afternoon at the latest usually with the outback going into float mode not long after it hits 90% on the smart gauge.

 

Sometimes that though I'm not reaching 100% up until late afternoon or early evening and sometimes I do pop the engine on anyway just to get it up to around 100.

 

The last few days have been strange though, as I've been getting roughly 8-10amps thru the panels and had only tv and fridge on, and using water pump etc occasionally throughout the day but not getting anywhere near 100%. I'm currently at 89% and have just switched the engine on to top up and to get some hot water for washing up later and hot water tomorrow. This is despite having quite a bright and intermittently sunny day. I'm a little concerned about this but putting it down to it coming up to the end of aug and the sun being different in the sky plus the weather not being the best at certain times throughout the day .

 

I don't really want to put what my total amps were on here on a day to day as I don't feel that they are that accurate off the outback logger as I'm going into float mode usually by lunchtime (up until the last few days) so it drops the ampage figures down quite a bit obviously, which doesn't show the full amount of amps I could be getting if I were in full charge all day.

However, depending on circumstances I can get around 50-200 amps a day.

 

Some days I've played around and dropped the batts down to about 70%'by putting the immersion on and then letting solar recharge again. Usually putting the immersion onaround 11 or 12pm For half hour or so and then solar charges batts back up toabout 90% by 5'or 6pm. Again on days ive done that ive had the engine running later for about Half hour or so just to top up. However I'm nervous about doing this with the immersionn too often as have read that rapidly discharging batts can shorten their life.

So that's it in a nutshell. How are yours Julian , are they all connected to batts and charging now?

Edited August 20, 2012 by lewisericeric

[Ex- Member]

Hi everyone

 

Sorry for the delay in my reply, just not had much chance to respond lately. In answer to your question, with my 690w of power, on sunny days I am at 100% by lunch or mid afternoon at the latest usually with the outback going into float mode not long after it hits 90% on the smart gauge.

 

Sometimes that though I'm not reaching 100% up until late afternoon or early evening and sometimes I do pop the engine on anyway just to get it up to around 100.

 

The last few days have been strange though, as I've been getting roughly 8-10amps thru the panels and had only tv and fridge on, and using water pump etc occasionally throughout the day but not getting anywhere near 100%. I'm currently at 89% and have just switched the engine on to top up and to get some hot water for washing up later and hot water tomorrow. This is despite having quite a bright and intermittently sunny day. I'm a little concerned about this but putting it down to it coming up to the end of aug and the sun being different in the sky plus the weather not being the best at certain times throughout the day .

 

I don't really want to put what my total amps were on here on a day to day as I don't feel that they are that accurate off the outback logger as I'm going into float mode usually by lunchtime (up until the last few days) so it drops the ampage figures down quite a bit obviously, which doesn't show the full amount of amps I could be getting if I were in full charge all day.

However, depending on circumstances I can get around 50-200 amps a day.

 

Some days I've played around and dropped the batts down to about 70%'by putting the immersion on and then letting solar recharge again. Usually putting the immersion onaround 11 or 12pm For half hour or so and then solar charges batts back up toabout 90% by 5'or 6pm. Again on days ive done that ive had the engine running later for about Half hour or so just to top up. However I'm nervous about doing this with the immersionn too often as have read that rapidly discharging batts can shorten their life.

So that's it in a nutshell. How are yours Julian , are they all connected to batts and charging now?

 

 

 

Hi Lewis

They're all ready to go as soon as the boat's on the water. Unfortunately some further delays again due to another family bereavement, just not our year. So now heading for mid to end Sept, not the best time to start using solar panels

All is ready to fit though and the array works great in it's SS bowl in box, I'll try to get some more photo's of it later this week. Haven't bought the Outback yet either, hoping it'll come down in price, will be he 80 amp though and funds are safely set aside for said item.

Yours seem to be performing pretty well though (fully charged by lunchtime, pretty damned good on sunny days then ) but I think running your engine in the way you are describing is wasteful and unnecessary.

 

 

Personally I would let the solar panels top up my batteries and not engine running. You'll be getting very few amps into to your batteries when at 90% running your engine for a few measly amps really is a waste of diesel. he evening light say from 6pm to 8/9pm would probably do this even this late in he year and even if they didn't then batteries at 90% is easily going to last the evening anyway.

I plan to assess solar input at lunchtime 12.00 noon, if by then my batteries are at say 60% I'll assess depending on the weather if the solar panels will charge the batteries fully through the rest of the day. On a nice hot day they would most probably do so, but on a not so good day I would run the engine/generator at 12 noon and get the batteries up to 80/85% as they're at a low SOC then they'll get more amps out of the alternator up to that level or SOC, so I might have to run the engine for a couple of hours, but then let the solar top up as the low amps it's likely to produce in poorer weather are just about right for topping up. OK this will take some time and experience to get right and good short term weather prediction, but I won't be burning lots of diesel for topping up batteries that only require minimal amps to do so.

When I say engine/generator I mean a separate generator from the main engine run from a small Kubota diesel engine, I don't ever intend to use the main engine for battery charging unless I'm cruising or in an emergency. Also running your engine in day time is less intrusive for other boaters and you can relax the entire evening not having to listen to it yourself. Of course you need to be on the boat in the daytime to use my approach but when we are living aboard one of us will be there in the daytime.

I would try o only charge from engine between 50 and 80% SOC

 

[onionbargee]

The idea of heating water from a solar panel is insane, full stop.

 

a solar water heating panel is used for that...

 

 

Collectors used in modern domestic SWH systems

 

Main article: Solar thermal collector

Solar thermal collectors capture and retain heat from the sun and use it to heat a liquid. Two important physical principles govern the technology of solar thermal collectors:

Any hot object ultimately returns to thermal equilibrium with its environment, due to heat loss from the hot object. The processes that result in this heat loss are conduction, convection and radiation.[20] The efficiency of a solar thermal collector is directly related to heat losses from the collector surface (efficiency being defined as the proportion of heat energy that can be retained for a predefined period of time). Within the context of a solar collector, convection and radiation are the most important sources of heat loss. Thermal insulation is used to slow down heat loss from a hot object to its environment. This is actually a direct manifestation of the Second law of thermodynamics but we may term this the 'equilibrium effect'.

Heat is lost more rapidly if the temperature difference between a hot object and its environment is larger. Heat loss is predominantly governed by the thermal gradient between the temperature of the collector surface and the ambient temperature. Conduction, convection, and radiation all occur more rapidly over large thermal gradients.[20] We may term this the 'delta-t effect'.

The most simple approach to solar heating of water is to simply mount a metal tank filled with water in a sunny place. The heat from the sun would then heat the metal tank and the water inside. Indeed, this was how the very first SWH systems worked more than a century ago.[3] However, this setup would be inefficient due to an oversight of the equilibrium effect, above: as soon as heating of the tank and water begins, the heat gained starts to be lost back into the environment, and this continues until the water in the tank reaches the ambient temperature. The challenge is therefore to limit the heat loss from the tank, thus delaying the time when thermal equilibrium is regained.

ICS or batch collectors reduce heat loss by placing the water tank in a thermally insulated box.[21][22] This is achieved by encasing the water tank in a glass-topped box that allows heat from the sun to reach the water tank.[23] However, the other walls of the box are thermally insulated, reducing convection as well as radiation to the environment.[24] In addition, the box can also have a reflective surface on the inside. This reflects heat lost from the tank back towards the tank. In a simple way one could consider an ICS solar water heater as a water tank that has been enclosed in a type of 'oven' that retains heat from the sun as well as heat of the water in the tank. Using a box does not eliminate heat loss from the tank to the environment, but it largely reduces this loss.

Standard ICS collectors have a characteristic that strongly limits the efficiency of the collector: a small surface-to-volume ratio.[25] Since the amount of heat that a tank can absorb from the sun is largely dependent on the surface of the tank directly exposed to the sun, it follows that a small surface would limit the degree to which the water can be heated by the sun. Cylindrical objects such as the tank in an ICS collector inherently have a small surface-to-volume ratio and most modern collectors attempt to increase this ratio for efficient warming of the water in the tank. There are many variations on this basic design, with some ICS collectors comprising several smaller water containers and even including evacuated glass tube technology, a type of ICS system known as an Evacuated Tube Batch (ETB) collector.[21]

 

 

Flat-plate solar thermal collector, viewed from roof-level

Flat plate collectors are an extension of the basic idea to place a collector in an 'oven'-like box with glass in the direction of the Sun.[21] Most flat plate collectors have two horizontal pipes at the top and bottom, called headers, and many smaller vertical pipes connecting them, called risers. The risers are welded (or similarly connected) to thin absorber fins. Heat-transfer fluid (water or water/antifreeze mix) is pumped from the hot water storage tank (direct system) or heat exchanger (indirect system) into the collectors' bottom header, and it travels up the risers, collecting heat from the absorber fins, and then exits the collector out of the top header. Serpentine flat plate collectors differ slightly from this "harp" design, and instead use a single pipe that travels up and down the collector. However, since they cannot be properly drained of water, serpentine flat plate collectors cannot be used in drainback systems.

The type of glass used in flat plate collectors is almost always low-iron, tempered glass. Being tempered, the glass can withstand significant hail without breaking, which is one of the reasons that flat-plate collectors are considered the most durable collector type.

Unglazed or formed collectors are similar to flat-plate collectors, except they are not thermally insulated nor physically protected by a glass panel. Consequently these types of collectors are much less efficient for domestic water heating. For pool heating applications, however, the water being heated is often colder than the ambient roof temperature, at which point the lack of thermal insulation allows additional heat to be drawn from the surrounding environment.[26]

Evacuated tube collectors (ETC) are a way in which heat loss to the environment,[21] inherent in flat plates, has been reduced. Since heat loss due to convection cannot cross a vacuum, it forms an efficient isolation mechanism to keep heat inside the collector pipes.[27] Since two flat sheets of glass are normally not strong enough to withstand a vacuum, the vacuum is rather created between two concentric tubes. Typically, the water piping in an ETC is therefore surrounded by two concentric tubes of glass with a vacuum in between that admits heat from the sun (to heat the pipe) but which limits heat loss back to the environment. The inner tube is coated with a thermal absorbent.[28] Life of the vacuum varies from collector to collector, anywhere from 5 years to 15 years.

Flat plate collectors are generally more efficient than ETC in full sunshine conditions. However, the energy output of flat plate collectors is reduced slightly more than evacuated tube collectors in cloudy or extremely cold conditions.[21] Most ETCs are made out of annealed glass, which is susceptible to hail, breaking in roughly golf ball -sized hail. ETCs made from "coke glass," which has a green tint, are stronger and less likely to lose their vacuum, but efficiency is slightly reduced due to reduced transparency.

[edit]Heating of swimming pools

[Grace and Favour]

Well chaps . . . .

 

My panels are now up'n'running - - and we are slowly learning how to operate and utilise them to their optimum

 

Over the last few days we've had as much as 248Ah in a day, and as little as 110Ah . . . . .

 

(in fact, today we received 225Ah, and the day was overcast and raining until 12:30!)

[Ex- Member]

Well chaps . . . .

 

My panels are now up'n'running - - and we are slowly learning how to operate and utilise them to their optimum

 

Over the last few days we've had as much as 248Ah in a day, and as little as 110Ah . . . . .

 

(in fact, today we received 225Ah, and the day was overcast and raining until 12:30!)

 

 

Hi G & F

 

That's quite impressive, I recall you were putting up a KW of panels, did you get the Outback sorted, you had some query with wiring I recall?

 

 

 

[Grace and Favour]

Hi G & F

 

That's quite impressive, I recall you were putting up a KW of panels, did you get the Outback sorted, you had some query with wiring I recall?

 

 

 

 

Aye, I sorted the Outback, (though I haven't yet studied it well enough to alter any of the default settings. - it'll take me a year to understand the manual!)

 

Have managed to mount the mppt in such a way that it hides in a cupboard until such time as I need to read it

 

The panels are 4 x 240w Sanyo HIT's, and I have a set of mounting brackets made that fix them parallel to the roof (basically for security), and following advice on here - finally decided to use unique security bolts into 8mm stainless rivnuts. Cabling is 6mm² Solar cable, panels wired in series/parallel.

 

Must say I'm happy with the way they look, and all seems extremely sturdy

 

 

As they say in Ikea - - sofa, so good

[Ex- Member]

Aye, I sorted the Outback, (though I haven't yet studied it well enough to alter any of the default settings. - it'll take me a year to understand the manual!)

 

Have managed to mount the mppt in such a way that it hides in a cupboard until such time as I need to read it

 

The panels are 4 x 240w Sanyo HIT's, and I have a set of mounting brackets made that fix them parallel to the roof (basically for security), and following advice on here - finally decided to use unique security bolts into 8mm stainless rivnuts. Cabling is 6mm² Solar cable, panels wired in series/parallel.

 

Must say I'm happy with the way they look, and all seems extremely sturdy

 

 

As they say in Ikea - - sofa, so good

 

Nice one well done, you should get some photo's uploaded for us to admire your good work.

 

The Outback sounds complicated and I'm hopeless with technology and instructions I'l have to hand this part of solar installation over to Lynn I think