Solar @ MPPT's

[[2574]]

Solar @ MPPT\'s

I'm just about to spend about three times the price of my first car on Solar panels! I'm being recommended Sunware Compact (69w) panels. This is a polycrystaline semi-flexible panel. I've been reading that Multiple Power Point Trackers (MPPT's) are the way to go as regards regulation but the supplier of the panels advises that these are too pricey relative to the benefit derived therefrom and proposes a non-MPPT regulator.

I'd welcome any views on either the panels, the regulator or any other relevant pearls of wisdom.

thanks

rob

 

[alan]

Re: Solar @ MPPT\'s

The Sunware panels seem to be OK from a price/watt comparison. I have never used them; I have used and fitted to other peoples boats Solara semi-flex panels and have been satisfied with their performance ..... a bit on the expensive side though.

As for the regulator: yes in theory the MPPTs are more efficient and offer better control but I have found in practice that the PWM regulators work fine and I doubt if in practice you would be able discern any difference between the two.

Pearls of wisdom: remember that the 69W quoted is the peak at the max ouput volts of the panel (around 17 - 21V); so actual peak power at 12v would be more like 48W (4A). Just something that is not always made clear when the dealer is selling you panels. Also you can only expect 4A when panel is orthogonal to the sun, perfect atmospheric conditions e.t.c. [I would guesstimate, from experience, that you can expect to get 2.5A to 3A at noon time on a nice sunny day]

Alan.

 

[pappaecho]

Re: Solar @ MPPT\'s

I have used solar panels for several years. Yes they provide a trickle charge to the batteries, and yes they work better in the summer months for obvious reasons. But the rated output is much over stated. These are based on near perfect lab conditions, and do not take into account, shading due to masts, booms or even sails. Just a small shadow across the panels will reduce its output by more than 50%. The correct angle of dangle is the azimuth, which is clearly very different from mid summer to mid winter. so there are a series of compromises. In the end I elected for two cheaper panels and a proper controller, and they keep the batteries ( 400 amps) at between 13.5 and 14.0 v when they switch off.

 

[William_H]

Re: Solar @ MPPT\'s

Well I advocate in most cases no controller. As has been pointed out the actual power from solar panel is a lot less than you might imagine.
If you really want rapid recovery from discharge then you need lots of panels and a controller. But if you are looking for battery maintenance or recover over a week or more then less panels and no controller is much cheaper.

Most batteries will take about 1% of Amp hour rating in current on a continuous basis without harm. So 100AH battery can be connected to 25 watt panel that gives a bit more than 1 amp when in the sun.
If you have a continuousor a predictable load on the system then that should be added to the solar current capability. If you are worried you can provide a kind of manual regulation by leaving consumer devices turned on. ie radio

One of your 69 watt panels should be safe on 250AH of batteries.
Remember it is easy to split the charging to multiple isolated batteries using diodes.

In my humble opinion a regulator will end up wasting much of your solar capability so avoid the regulator if you can. Or maybe have a switch to switch it out. Just to be contrary olewill

 

[[2574]]

Re: Solar @ MPPT\'s

thanks everybody, the subject is a minefield and i think i'll have another look at a wind generator + smaller solar option.

rob

 

[Robin]

Re: Solar @ MPPT\'s

Don't be put off of solar for summer UK use. Yes the output can be less than number of hours x rated amps but then wind generators suffer similar losses overall from hunting and stop/starting. We have both a large wind generator (Aerogen 6) and large solar panels (1 at 75W, 1 at 110W) and all outputs are monitored by ammeters and battery volts too so I feel I can comment from real use.

I once saw a table of expected daily average slar outputs at various locations around the world, taking into account cloudy days and number of daylight hours etc. If I remember correctly, the (average) figure for a 60W panel on the IOW was about 19/20Ah per day in June/July/August.

Our wind generator IS regulated and it's output split 3 ways to 2 main battery banks and the engine battery and switchable so that we can chose which gets what.

We have a 75W fixed but unregulated solar panel on a gantry that is connected via a switch and we can chose which of the 2 sevice banks to charge, usually the fridge one. This is normally enough for summer season weekends away from shorepower, up to 2 or 3 nights of running whatever we wish yet not dropping battery volts below 50% charge, actually my limit is 12.5v. When away longer we will use the 110W panel as well whilst at anchor and because this is moveable it is very effective. Usually it just lays on one side of the coachroof and we will move it at some stage to the other side as the sun moves round but it lays flat not aimed at the sun. Again this panel can charge either of the 2 main banks simply connecting via 2 different deck sockets in the cockpit and again it is unregulated. Using the 2 panels on our summer cruises at anchor we have had to switch off or unplug one or other panel after 5/6 days of no other charging (wind genny tied off) to avoid overcharging.

Remember we have ammeters showing the individual outputs of our panels and the wind generator and we have voltmeters on each battery bank. Without monitoring our high output panels could damage the batteries, but under normal conditions living aboard on a cruise it is no hassle to keep an eye on the state of charge.

Our panels are both rigid aluminium framed glass ones, not flexible or semi-flexible. The big 110W moveable one justs lays on a spare stern cabin bunk when not in use with a protective cover made from a padded tablecloth.

Our high output Aerogen6 is very capable but gets very little use in practice because the solar panels in summer are coping on their own and in total silence, not that the Aerogen is noisy.

IMO small solar panels are very expensive per Ah and do little other than maintain batteries when the boat is left, which is fine if that is all you need. Bigger panels can be very effective (we often see over 10A from our two and even 2A early and late in the day) but for winter UK use solar would lose out for sure to a wind generator.

 

[ccscott49]

Re: Solar @ MPPT\'s

we have 4 x 80w panels, wired for 24 volts with a regulator in the meddy, they keep up with all our power requirements during the day, when at anchor, which is mainly two fridges and a freezer! They are rigid aluminium framed and are easy to move around to get the best out of them. Wouldn't go for a wind genny in the med, just not efficient, not enough reliable wind, plus noisy at night, well anytime really.

 

[npf1]

Re: Solar @ MPPT\'s

FWIW I tried several types of solar panels side by side a couple of years ago before deciding which to install. The outputs varied considerably: for example, on type of 48W panel (can't remember the make) was putting in 1.6A at the same time that a 32W Unisolar flexible was putting in twice that amount. This was in Southampton. The Unisolar was also better when partially shaded and had some output in cloudy conditions too.

On the basis of the above practical trial, I bought two 64 Unisolar rigid panels which are now fitted on the top of the pilothouse - so horizontally and partially shaded by the boom. I regularly see 8 amps per hour going into the batteries (12V system) and even on dullish days there is around 2A to 4A going in.