500watt vs 1000watt solar...... difference?

[jenevers]

Is the main difference that a 1000 watt system is a quicker charging system or a more effective system in low sunlight or both or something else?

[matty40s]

about 500w.....

[Phil Ambrose]

The 1000 watt panel has the potential to produce twice as much power than the 500 watt panel. Only you can decide which suits you best. I would suggest you do a power audit to get an idea of your daily requirements.

Phil

[RubyTuesday]

Yes, in theory the 1000W will charge your batteries twice as fast as a 500W system.

Get the most you can for the space that you have available for them.

 

Panasonic have just released some very nice 330W modules (N330) but they are a devil to get hold of thanks to the solar cartel we seem to have.

 

They are 1000mm wide and 1600mm long which fits nicely length ways along a roof of a narrowboat.

Edited April 20, 2016 by RubyTuesday

[matty40s]

In winter, even 1000w will only provide a 10th of what it does in summer on a really sunny day - cloud or worse and the return will be marginal to nil.

[Punk Stig]

Someone with better knowledge may come along and correct me but the wattage isn't the important part of the equation, it's the amps. Different makes of panels that have the same wattage can have different amperage, not forgetting the other important factor of the charger- if you have a 40 amp charger and the 500w panels put out an optimum 35 amps, upping the panels to 1000w but having the same charger you'd only get an extra 5 amps at twice the price unless you change the charger!

[Phil Ambrose]

Someone with better knowledge may come along and correct me but the wattage isn't the important part of the equation, it's the amps. Different makes of panels that have the same wattage can have different amperage, not forgetting the other important factor of the charger- if you have a 40 amp charger and the 500w panels put out an optimum 35 amps, upping the panels to 1000w but having the same charger you'd only get an extra 5 amps at twice the price unless you change the charger!

But watts divided by volts equals amps plus a charger is not involved, what is used is a solar charge controller which must match the output of the panels, trying to put 50amps through a 40amp controller is not going to end well, magic smoke may well escape.

Phil

[Arthur Brown]

Wattage is important, so is the control gear (charger etc). You really need the best MMPT charger for the panel array that you have. However even with a smaller MPPT controller you will get better charging in the winter, spring and autumn months although you will not make best use of the summer charge available.

[Paul C]

P = V x I

 

Meaning that power is inextricably related to current, so if the system voltage is a constant, doesn't really matter if you discuss amps or watts.

 

Solar power is like grass growth - highly seasonal. Grass grows in the winter - very slowly, but it shoots up like bamboo in conditions of hot soil temperature and med-high humidity - a nice warm late spring day, for example. Unlike grass though, you can't ensile solar energy.

 

Anyway....in summertime, solar panels will generate an excess of power on a typicall installation. Of course, the seasonal variation of power requirement is probably the inverse of solar output, albeit a shallower variation. And in winter, a solar installation typically generates 10% of its rated power on average. And some days, generates 2/3 of naff all (think, dull, probably raining, short day).

 

What this pragmatically means is that for some of the year, the solar generates "enough" or "exess" power; and for some, it generates too little. The bigger the solar installation, the more months/year it generates "enough". If you have enough roof space and money, you could fit enough solar panels to cover 98% of the year. There's always going to be rubbish days, so you need some kind of alternate generating capability.

 

Its just a case of doing a cost-analysis to find out the ideal size of solar bank, given the %age of the year you'd need to generate the shortfall and its generating cost, vs the capital outlay of the panels etc. And of course there may be other contraints such as available roof space, etc.

 

We made do with 200W of solar and it fitted well with the boat's usage, respecting that in the winter we had to run the engine. Other boaters seem to have a bit more on average, eg 300-400W it seems; and a few have 1000W+. Lots seem not to have any though, which I've never quite understood?

[Punk Stig]

But watts divided by volts equals amps plus a charger is not involved, what is used is a solar charge controller which must match the output of the panels, trying to put 50amps through a 40amp controller is not going to end well, magic smoke may well escape.

Phil

Yep- but different makes of panels have different maximum voltages which can be taken advantage of!

A decent system will have an output power and current limiter so that the panel output won't exceed the controller's (charger in layman's terms, as we're charging batteries) maximum.

[Wanderer Vagabond]

P = V x I

 

Meaning that power is inextricably related to current, so if the system voltage is a constant, doesn't really matter if you discuss amps or watts.

 

Solar power is like grass growth - highly seasonal. Grass grows in the winter - very slowly, but it shoots up like bamboo in conditions of hot soil temperature and med-high humidity - a nice warm late spring day, for example. Unlike grass though, you can't ensile solar energy.

 

Anyway....in summertime, solar panels will generate an excess of power on a typicall installation. Of course, the seasonal variation of power requirement is probably the inverse of solar output, albeit a shallower variation. And in winter, a solar installation typically generates 10% of its rated power on average. And some days, generates 2/3 of naff all (think, dull, probably raining, short day).

 

What this pragmatically means is that for some of the year, the solar generates "enough" or "exess" power; and for some, it generates too little. The bigger the solar installation, the more months/year it generates "enough". If you have enough roof space and money, you could fit enough solar panels to cover 98% of the year. There's always going to be rubbish days, so you need some kind of alternate generating capability.

 

Its just a case of doing a cost-analysis to find out the ideal size of solar bank, given the %age of the year you'd need to generate the shortfall and its generating cost, vs the capital outlay of the panels etc. And of course there may be other contraints such as available roof space, etc.

 

We made do with 200W of solar and it fitted well with the boat's usage, respecting that in the winter we had to run the engine. Other boaters seem to have a bit more on average, eg 300-400W it seems; and a few have 1000W+. Lots seem not to have any though, which I've never quite understood?

I'm one of those . My rationale so far (it may change) is that looking at, for instance, Onboard Solar, for my usage they recommend a 300W system with a fitting cost of £882. Now accepting that during the winter with low light levels and short days it isn't going to reduce my engine usage much (I still travel in the winter). During the summer however we use the lighting less and usually travel for a few hours, normally sufficient to re-charge the batteries. So I don't really need anything much in the summer as the engine charges the batteries, and in the winter there isn't enough light to make much difference. How long would it take to recoup the installation cost by the minimal reduction in engine usage in the winter? Quite a while I would suggest.

[Paul C]

I'm one of those . My rationale so far (it may change) is that looking at, for instance, Onboard Solar, for my usage they recommend a 300W system with a fitting cost of £882. Now accepting that during the winter with low light levels and short days it isn't going to reduce my engine usage much (I still travel in the winter). During the summer however we use the lighting less and usually travel for a few hours, normally sufficient to re-charge the batteries. So I don't really need anything much in the summer as the engine charges the batteries, and in the winter there isn't enough light to make much difference. How long would it take to recoup the installation cost by the minimal reduction in engine usage in the winter? Quite a while I would suggest.

 

I think you'd need to do the calculations yourself using your own power audit and also your own best estimate of £/kWh it costs to generate electricity using your boat's diesel engine. Remember that during travelling, the electricity for charging batteries is not "free", it will place an additional load on the motor and use extra diesel. And if not travelling, the engine--> alternator --> battery charging efficiency is really bad.

[Wanderer Vagabond]

 

I think you'd need to do the calculations yourself using your own power audit and also your own best estimate of £/kWh it costs to generate electricity using your boat's diesel engine. Remember that during travelling, the electricity for charging batteries is not "free", it will place an additional load on the motor and use extra diesel. And if not travelling, the engine--> alternator --> battery charging efficiency is really bad.

I think I'm reasonably OK with the Onboard Solar audit since we currently have a 240v fridge (the biggest consumer of power!). The electricity generated whilst travelling is effectively 'free' since I don't have an option not to generate power whilst travelling (unless I want to go through all the faff of taking the drive belt off the domestic alternator, which rather defeats the object of having one ). The engine burns 0.87 litres per hour just charging the batteries or 1 litre per hour travelling so it is going to take me over 7.5 hours to burn one extra litre of fuel (currently costing about 65p) or an extra 8.6p per hour, I think I can probably manage that

 

If the solar generation during the winter was better I'd seriously consider it but. looking at the solar generated over last winter at a land based address I have (it was so bad we thought it had somehow disconnected, it hadn't!) I still remain to be convinced.

[GoodGurl]

I'm one of those . My rationale so far (it may change) is that looking at, for instance, Onboard Solar, for my usage they recommend a 300W system with a fitting cost of £882. Now accepting that during the winter with low light levels and short days it isn't going to reduce my engine usage much (I still travel in the winter). During the summer however we use the lighting less and usually travel for a few hours, normally sufficient to re-charge the batteries. So I don't really need anything much in the summer as the engine charges the batteries, and in the winter there isn't enough light to make much difference. How long would it take to recoup the installation cost by the minimal reduction in engine usage in the winter? Quite a while I would suggest.

i have 1000w and it cost less than £500 inc wires,connecters,controllers (2) and panels, self fitted.

[Paul C]

Its not free. An alternator generating little/no power is easy to spin. An alternator generating lots/max power is much more difficult to spin, it will consume engine power in doing so, and the fuel pump will recognise this demand, allow more fuel in, and maintain the desired rpm according to throttle position. Think of the "energy balance" - you can't make energy for free, it can only be converted from one form to another. In this case, the chemical energy within fuel, to electricity, then stored as (a different kind of) chemical energy in the batteries.

I think I'm reasonably OK with the Onboard Solar audit since we currently have a 240v fridge (the biggest consumer of power!). The electricity generated whilst travelling is effectively 'free' since I don't have an option not to generate power whilst travelling (unless I want to go through all the faff of taking the drive belt off the domestic alternator, which rather defeats the object of having one ). The engine burns 0.87 litres per hour just charging the batteries or 1 litre per hour travelling so it is going to take me over 7.5 hours to burn one extra litre of fuel (currently costing about 65p) or an extra 8.6p per hour, I think I can probably manage that

 

If the solar generation during the winter was better I'd seriously consider it but. looking at the solar generated over last winter at a land based address I have (it was so bad we thought it had somehow disconnected, it hadn't!) I still remain to be convinced.

[Phil Ambrose]

Yep- but different makes of panels have different maximum voltages which can be taken advantage of!

A decent system will have an output power and current limiter so that the panel output won't exceed the controller's (charger in layman's terms, as we're charging batteries) maximum.

Which is exactly what I said, match the size of the controller to the size of the PV array.

Phil

[jenevers]

Someone with better knowledge may come along and correct me but the wattage isn't the important part of the equation, it's the amps. Different makes of panels that have the same wattage can have different amperage, not forgetting the other important factor of the charger- if you have a 40 amp charger and the 500w panels put out an optimum 35 amps, upping the panels to 1000w but having the same charger you'd only get an extra 5 amps at twice the price unless you change the charger!

So having 2 x 40amp controllers, each with 500watts of panels, running side by side to the batteries will charge the batteries TWICE as fast and collect TWICE as much sunlight (therefore create twice the amperage) in winter, than a single 40amp/500watt setup?

[Paul C]

So having 2 x 40amp controllers, each with 500watts of panels, running side by side to the batteries will charge the batteries TWICE as fast and collect TWICE as much sunlight (therefore create twice the amperage) in winter, than a single 40amp/500watt setup?

Yes and no. If the batteries will accept more current than the charger (any charger) will generate, then yes. But batteries don't do this except for the relatively short initial time during charging. Towards the latter stage of charging, the current is limited by he battery bank's acceptance, not the size of the charger.

 

The reason solar is good is because of this. It can charge pretty much all day long, for £0, silently. An engine or generator can't do that.

 

Also factor in that a bigger solar array in winter can run electrical loads AND have excess generating power left over to charge a bit too, where a smaller array may not; indeed it may even not supply enough to run the daytime winter loads.

[Punk Stig]

Which is exactly what I said, match the size of the controller to the size of the PV array.

Phil

Not quite Phil, you may have missed what I was saying, you gave the formula for working out power- my original post pointed out that different makes of the same wattage panels give out different amps, this is because some have a higher maximum voltage output- something I was saying should be taken into consideration more than just the wattage of the panel, maybe you are unaware of this which is why your post appears to disagree with me saying that wattage isn't the important thing to factor!

And if the adequate regulators are fitted then no, the controller won't go puff!

[Punk Stig]

And I'm now understanding why I've read this forum for several years and refrained from posting on it!

[Phil Ambrose]

Not quite Phil, you may have missed what I was saying, you gave the formula for working out power- my original post pointed out that different makes of the same wattage panels give out different amps, this is because some have a higher maximum voltage output- something I was saying should be taken into consideration more than just the wattage of the panel, maybe you are unaware of this which is why your post appears to disagree with me saying that wattage isn't the important thing to factor!

And if the adequate regulators are fitted then no, the controller won't go puff!

Your OP stated that using a 40amp controller and using a 1000w panel would only give a marginal increase in power over a 500w panel, I'm saying doing that will produce magic smoke.

Still, not here to argue, been running successfully on solar for the last 12 years so I must be doing something right.

Phil

[Top cat]

Having double the power wont halve the battery recharge time, once the batteries hit the max voltage the current ramps down . Also assuming your controller and charger can take the extra power will your batteries accept the higher current? As others have suggested a full power audit is a good next step.

 

Top Cat

[RubyTuesday]

As far as I am aware as long at the controller can cope with the maximum PV voltage, the charge controller can be matched to the charge current capability of your batteries.

 

The controllers current rating is the limit for how much current can be moved from the PV side to the Battery side.

Just like any mains charger. It may connected to a 16A mains socket but only draw 10A, it doesn't go bang...

 

Because of P=IxV the voltage will be high if the array is of higher Wattage but you are only drawing low current. So the wiring of the solar array must keep the open circuit voltage within the maximum working voltage of the charge controllers input.

 

Solar charging is another good reason for Lithium batteries as they are 40% more efficient at charging and have a much lower internal resistance so can charge far faster... And utilise more of the Suns energy... Just saying...

[Jambo]

Is the main difference that a 1000 watt system is a quicker charging system or a more effective system in low sunlight or both or something else?

 

I would say the main difference is the proportion of the year for which you're self sufficient for electricity. Here are two curves of generation, one for a 500W installation and one for a 1kW installation (south facing, 30 degree inclination, no obstructions - i.e. not on a canal!, data from PVGIS and for a grid tied system):

 

 

Let's say the cut off point for self sufficiency is 1.5kWh/day, then double the capacity will add a month or two of extra self sufficiency either side of the summer months.

 

Note that there are complexities that can't be represented such as battery performance dropping off in cold weather which probably means that the actual generation required for self sufficiency would go up during the winter months, but the thrust of that chart is broadly correct. Another interesting upshot is that cutting your demand substantially in winter (say by switching off your fridge) can make a big difference to self sufficiency.

[Alan de Enfield]

Apologies in advance to whoever took all the trouble to produce this spreadsheet - I kept it bit did not keep a note of the author.

 

It is an excellent piece of work for calculations regarding solar requirements.

 

1) Do your electrical usage audit, entering the information on the left of the table.

2) Enter your battery bank size

3) Enter the size of your solar array

4) Enter your location

 

The spreadsheet will tell you

1) How many months the solar will supply your usage

3) Alternative solar requirements.

 

 

Solar Panel Calculator Sea Wolf.xls