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19-07-2020, 12:03   #1
 
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A solar power question?

I'm in self isolating for the next two weeks in our old static caravan after coming home from the UK. Its got me thinking about going off grid with it as far as possible.

First of all I thought it would be nice to have a decent radio built in and having a spare nearly new 12V car radio from a recently scrapped car I though why not install that and some decent speakers. Along with the internet, Bluetooth on a mobile phone and laptop that gives me access to all the audio content I want.

I then realised that it might be easier to power the car radio (12V 10Amp) from a 12V battery than make up a power supply. OK so then I lost the plot a bit and thought if I'm using a battery why not charge it from solar panels and if I'm doing that why make the whole thing off grid.

Currently the static caravan (30ft) is connected to the mains. Heating, hot water and cooking is all gas so that eliminates some big power hungry uses for electricity. That leaves fridge, toaster, electric kettle and microwave as items that probably use more power than I may be able to accommodate. Apart from the fridge which is always plugged in, the toaster, electric kettle and microwave are only used for a few minutes a day. I'm even thinking of getting rid of the microwave as its rarely if ever use. I can dump the toaster and use the grill on the stove and similarly the kettle but I do like their convenience. Items I'd like definitely like to power from solar/battery are, LED lights for the whole caravan, laptop computer (will get 12 V psu for it), router, wireless link (PoE), TV, Security system (12v), USB charging (phones, tablets, torches), car radio (12V). A bonus would be to be able to charge 18V Dewalt XR batteries I can't find a car charger for the 4 Amp ones I use so would have to hack something.

Getting PoE working as directly from the batteries is possible an issue. I don't see the point in charging batteries, then using an inverter to power a 24V PoE adapter, but I'd like some form of charge limiting or intelligent controller for the PoE as I don't like the thought of a short at the end of a Ethernet cable being a short across the batteries - would a fuse be enough protection? The PoE is worth the effort because we are the last house on the circuit in our area and I'm connecting for the internet to a neighbor whose power comes from a different county so if we go off they often still have power.

So to start me off what is a sensible amount of power to be trying to generate and what would be a sensible amount of storage?

First thoughts are I have room for 600 Watts of panels (4 x 150Watt?) but might be able to squeeze in more and was thinking about a 24V system with either 2 x 12V 100Amp leisure batteries or 4 x 12V and having a 24 Volt system (there is plenty of well ventilated space for batteries). Which leads to the question of what charge controller? 24V seems more sensible to keep cable size down but then how do I power my 12V car radio that started me down this road?

This is a hobby project so I'm not looking for a return on investment but don't want to waste money on stuff I really don't need. I tend to be a bit excessively belt and braces so would prefer to over rather than under specify.
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19-07-2020, 23:56   #2
Sir Liamalot
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24V system. Forget leisure batteries get 4 x crown or trojan 6vs. They're industrial traction batteries. Leisure batteries are engine starting with expensive stickers.

Use 60 cell domestic panels. Double the power for half the price.
MorningStar PWM controllers are ideally suited to 60cell panels on 24v systems in our climate.
You won't beat them with MPPT.

Do not get a cheap charge controller.

Store a week to a month of energy. Design to 10% use per day average. Have enough solar to supply your daily average in the worst climate conditions.
1000W of solar seasonal minimun = 3000Wh per day

Last edited by Sir Liamalot; 19-07-2020 at 23:59.
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20-07-2020, 10:00   #3
 
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Thanks thats a great start.

I've already downloaded the MorningStar PWM TS-60 manual, to take a look at it, which poses the question why does the info you find on a casual google of the internet about charge controllers seem to indicate that MPPT is more efficient?

I'm thinking 600W of panels so assume I only need a 30Amp PWM controller but is there any harm in using a 60Amp in case of future expansion?

About the only thing I've really decided on is that I will have a 24 Volt system. I'll do some calculations of possible power use and see how that works against a 10% use per day average.
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21-07-2020, 19:40   #4
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If panels are closely matched to the charging voltage for the bank the gains with mppt add up to very litttle of significance at all.

Cheap Domestic 60cell panels would typically be in the 260-290w range and as little as €100-€120.

Its still only going to pay for itself if you go offgrid, from your post its sounds like you're planning on keeping the power for the fridge, you' be better off putting your connection costs towards enough panels to keep the lot going.
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21-07-2020, 22:36   #5
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I run a 60 cell on an MPPT controller it tells me the maximum power point of this panel is the same as what a PWM controller would deliver.
The internet claims say MPPT is 30% more efficient.
The truth is 10% to 15% if you go with traditional panel to battery voltage couplings.

If you couple a 30Vmp panel to a 24volt battery with an absorption voltage of 29V > 30V there are no losses for the MPPT controller to recuperate from the system.

It works in Ireland where the panels don't derate from heat. If your motor takes 10w-40 / 15w-30 then it's an ideal climate for this arrangement.

The controller is not inefficient, the installation configuration is. Conventional wisdom advises us to fit panels that are 15% redundant and then pay for expensive controllers to rectify the losses.


I'm getting 60 cells for €50 > €90 ranging €250Wp to €310Wp
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22-07-2020, 13:40   #6
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Hi, If have limited space why dont you install 2X400 plus solar panels which will give you plenty of power for your load. In respect to a charge controller you have several options. Yes Morningstar is good, but you have can have a Steca, Phocos (D) or a Victron (NL) as well.
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22-07-2020, 19:02   #7
Sir Liamalot
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MorningStar are the only genuine manufacturer.

Victron are spoofers.
Steca are rebranders.
Phocos I've never heard of.

I can assure you MorningStar will charge a battery to 1.28 specific gravity. I pray recommendations of other manufacturers can be validated by similar evidence.

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22-07-2020, 19:39   #8
 
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Don't panic morningstar is up there top of the list.

The TS-45 seems to be the obvious option for 600 Watts of Solar. Would the TS-60 be worthwhile in case I decided to increase the number of panels? On the other hand I doubt I would.

But I really can't justify the price of Trojan batteries, which means I might go back to the plan of powering a car radio off a leisure battery, 100 Watt panel and a cheap controller
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22-07-2020, 20:29   #9
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If you use the system every day you don't need a charge controller if the panel VOC is 32V or less to battery 24V.

Trojans are cheaper than the alternative if you get 10 years outtov them which is possible. They're genuine traction batteries. Crown are better but harder to source.

Leisure batteries are consumables. I'd save money on a sticker and buy a starting battery over a leisure battery.

The lowest grade battery in production ought to last 300 cycles. I know of many can't get two years from one with 6 weeks use a year. If that's where the charge system is don't buy expensive batteries.
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22-07-2020, 20:30   #10
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TS-45 does 1.2kW @ 24v
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22-07-2020, 20:33   #11
 
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Quote:
Originally Posted by Sir Liamalot View Post
TS-45 does 1.2kW @ 24v
My bad, was calculating the current at 12V.
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22-07-2020, 20:47   #12
 
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Quote:
Originally Posted by Sir Liamalot View Post
If you use the system every day you don't need a charge controller if the panel VOC is 32V or less to battery 24V.

Trojans are cheaper than the alternative if you get 10 years outtov them which is possible. They're genuine traction batteries. Crown are better but harder to source.

Leisure batteries are consumables. I'd save money on a sticker and buy a starting battery over a leisure battery.

The lowest grade battery in production ought to last 300 cycles. I know of many can't get two years from one with 6 weeks use a year. If that's where the charge system is don't buy expensive batteries.
What do you call a cheap battery? I was originally looking at Yuasa's Leisure batteries because I can get them cheaply in the UK - but then noticed Yuasa's number of charges cycle rating, the UK ones had the lowest rating. Then found this rebadged Yuasa L36-AGM https://www.halfords.ie/camping-and-...00-682097.html supposed to be rated to 400 cycles to 50% with AXA discount €140.

Going off on another tangent is there a cheap charge controller that would be effective with that battery and a single 150 Watt panel? Its the cheapest way I can see that will allow me to learn from my mistakes
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23-07-2020, 00:03   #13
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I was about to say anything in halfords...but yuasas are amazing. I've a set that are performing 40% overspec.


A 150W 22Voc 36 cell "12volt panels" are nearly three times as expensive as 260W 34Voc 60 cell panels.
A 36 cell 150W panel on a 12volt PWM controller is a 130W panel.
That's not cheap to me.

Price per watt.
MS make lots of controllers. Buy a used one they're ridicously reliable. I have 10 all used, all bargains, never an issue.
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