Solar Power - A Guide

[BOAC]

You will have heard the saying 'You get what you pay for'.

 

This is very applicable to solar panels, so buy the best that your wallet will allow. Do not be fooled by cheap offers, they rarely exist in the solar panel world.

Knowing the UK weather and the general lack of sunshine you might think that there is no point in buying a solar cell of any description, but you are wrong. Cells produce electricity from light, not heat, but sunshine will increase the output. Many people buy a panel and find that it does not do the job they bought it for because they have not considered the required wattage or allowed for UK weather.

This article will help you to choose the solar cells to meet the requirements you demand of them.

There are three types of solar cells, Mono-crystalline and Polycrystalline which are both a silicone composition and the third type is Amorphous Solar Cell (Thin film.)


Mono and Polycrystalline Cells.

This type of cell is wired in series, with each cell producing approximately . 55 of a volt, so 36 cells are required to produce approx. 20 volts which are sufficient to charge a 12 volt battery under most conditions. For solar panels on caravans and motor homes, it is recommended to have glass-fronted mono-crystalline type that supply maximum power generation and lowest cost.


Although the theoretical efficiency of mono-crystalline cells is slightly higher than that of polycrystalline cells, there is little practical difference in performance. Crystalline cells generally have a longer lifetime than the third type of cells, the :-

Amorphous cells. (Thin Film).

An example of these is found on garden lights and calculators.

This type of cell is flexible and is less expensive to manufacture but is less efficient than the two types of crystalline cells and thin films have to be nearly double the size for the same output as crystalline. Their power output reduces over the first few months of use after which they become stable.

 

 

POWER REQUIRMENTS

Solar power panels are rated by how many watts per hour they supply.

To find the current output, divide the panels wattage by 17.

There are numerous power requirements, for example, caravan alarms discharging the main leisure battery in storage to requiring power on rallies. Solar Panels are great technology but for us caravanners they can be confusing.

Now, let us suppose you are requiring a solar panel to keep the leisure battery topped up and your alarm active when the caravan is in storage.

First, you have to find the amp-hour rating of the battery to be charged and you must plan for a wet-cell battery loosing about 0. 3 percent of its current per day, depending on the ambient temperature.

So, for a 75 Ah hour battery, the solar panel must be capable of supplying 0. 22 amps per day to maintain the charge. Add to this, say, 2 Amps per day the alarm is demanding then a solar panel should supply 2. 22 Amps per day at least.

Allow for a crystalline panel facing south and un-shaded to supply for a maximum of 2 hours of optimum output in the winter, and 4 to 5 hours in the summer. If the panel is going to be placed in the caravan, note that any window could reduce the amount of light reaching the solar panel.

So a 20 watt panel should produce:-

 

20 watts divided by 17 = 1. 18amps. per hour in optimum conditions.
In the winter approximately 2. 36 amps will be supplied, enough to keep a 75 Ah battery charged and to power the alarm.

A 20 watt panel is 300mm x 640mm x 26mm and weighs about 2. 3 Kgs.


POWER CONTROL

Sometimes there will be too much power output, and sometimes there won't be enough so the battery will be damaged if it is allowed to be overcharged or over discharged, so a controller is needed to protect it. Panels rated at 15 watts and greater will have to have some type of power control.

A solar charge regulator / controller, is a device that regulates the voltage and current sent from a solar panel to a battery.

The output of solar panels can vary. If a solar panel is listed as 8 volt, the output may be within a range of around 4 to 12 volts. If the battery requires less than this, it could be damaged from overcharging.

The charge controller prevents this by keeping the charging voltage at a safe level. Only if a very small solar panel such as a battery saver is used to charge a large battery is it possible to do without a controller.

Solar charge controllers are specified by the system voltage they are designed to operate on and the maximum current they can handle.


CALCULATING WATTAGE REQUIREMENT

For those of you who have not nodded off yet, and who want to calculate your own power requirements, read on.

Draw four columns on paper.

List all items that will use AC and DC electricity in column 1.

List all AC watts that appliances draw in column 2.

If you power AC appliances with a DC battery through an inverter, you will have to calculate an approximation of what the inverter may take. Find the power (wattage) rating of the appliance you are using with the inverter and divide by 10. This will give you the amps per hour that will be taken from the battery and this includes the running current of the Inverter.

So if you have a small TV taking 100w (watts at 240vac) you will be using approximately 10 amps an hour from your battery.

List how many hours in a 24 hour period you will use each item in column 3.
Make sure you list every item separately.

Multiply column 2 by column 3 to get the watt hours for each appliance and put the totals in column 4. Add together all the numbers in column 4 for the total watt hours.

Remember solar power panels are rated by how many watts per hour they provide. Let us assume your panels produce 100 watts an hour. If you average four hours of sunlight a day, each panel will produce 400 watts a day at the Solar Panel working voltage, (around 17 Volts) which will equate to approximately 23 amps that could possibly put back into the battery (if the battery requires it).

 

I hope the above allays some of the confusion surrounding solar panels.

Happy touring,

Pete


With thanks to Sunshine Solar for their technical support

Edited January 4, 2021 by BOAC
Text modification

[mechs]

What a great help! I was confused setting up my solar panel with what one to get, regulator etc but now i've got it up and running find it was easy to follow than at first.

 

I have a 20w solar panel and the regulator charging 2 leisure batteries, they stay charged fine and the green lights are usually on when it starts to get dark to show they're charged which is good, however when I went up last time a couple of week ago for a quick check on the caravan after the bad weather it wasn't dark but the green lights weren't on so either it wasn't dark enough or the batteries have discharged, I didn't have time to take a multi meter reading but to be fair my batteries are old and don't hold a charge as well as they used to so might be on the look out for another couple soon.

 

Cheers

[Surf01]

A few questions if I may. Our Sky HD box is 42watt and the TV is about 60watt. Does this indicate that the battery will drain 10amp per hour? In effect will it only last about 5 hours? Due to rising cost we are considering using CLs with no EHU, but both of us like to watch TV in the evenings. Just concerned that with a flat battery in the morning no water from the 12v pump.

Secondly if the caravan is in storage, how would you go about connecting it to the battery to recharge the battery? Obviously you do not want other people to see wires trailing down the side of the caravan indicating a "free" solar panel available!

[Lefthand Down]

if the caravan is in storage, how would you go about connecting it to the battery to recharge the battery? Obviously you do not want other people to see wires trailing down the side of the caravan indicating a "free" solar panel available!

 

If you are considering solar charging in storage then you need to bite the bullet and have the panel fixed on the roof.

Others have temporally fixed a maintenance panel in the Heki.

 

Our Sky HD box is 42watt and the TV is about 60watt. Does this indicate that the battery will drain 10amp per hour? In effect will it only last about 5 hours? Due to rising cost we are considering using CLs with no EHU, but both of us like to watch TV in the evenings. Just concerned that with a flat battery in the morning no water from the 12v pump.

 

You need to remember the panel is replacing the used power from Dawn to Dusk. The correct size could replace the power you use.

[Surf01]

You need to remember the panel is replacing the used power from Dawn to Dusk. The correct size could replace the power you use.

What is a suggested size?

[Lefthand Down]

What is a suggested size?

 

http://rvsolarpanels. wordpress. com/category/rv-solar-power-calculator/ BO used this link to provide the answer.

[Surf01]

Thanks.

[Richiebuoy]

I'm a bit confused on solar power, we bought a small top up Solar Power panel rated at 4 watts. It says because of its low power there is no need for a voltage regulator, fair enough, when I put my volt meter on the panels terminals on a sunny day it hit 21 volts which I'm told is enough to damage my leisure battery. So should I use it or not ?

[JTQ]

I'm a bit confused on solar power, we bought a small top up Solar Power panel rated at 4 watts. It says because of its low power there is no need for a voltage regulator, fair enough, when I put my volt meter on the panels terminals on a sunny day it hit 21 volts which I'm told is enough to damage my leisure battery. So should I use it or not ?

 

Whilst you see 21 volts 'off load' you will not see anything like that if coupled to a substantial capacity lead acid battery.

The voltage must be well above 12 volts to even start a charge current flowing, and with it 'belting out' its full 4 Watts it will never give more than 0. 3 Amps.

IMO this will occur here in the UK so infrequently and is in itself low enough that it will not damage any 70 Ahr plus battery.

[Richiebuoy]

Thanks JTQ, that's reassuring.

[thewelshman]

So I know it says don't buy cheap but a certain auction site has been selling 20 Watt panels with the regulator for about 65 squids. Is this too cheap and nasty? Can anyone recommend one to me that isn't going to break the bank?

[dreadly]

http://www. ebay. co. u. ..=item564697b1b1

 

A friend of mine purchased two of these, good quality and no problems.

 

They also do a 30w version

 

http://www. ebay. co. uk/itm/30-Watt-Solar-Panel-PV-Monocrystalline-12V-30W-T-/370577902185?pt=UK_Gadgets&hash=item56482a0a69

Edited January 18, 2012 by dreadly

[thewelshman]

Thanks but I don't see a regulator with that - I was looking at this:

http://www. ebay. co. uk/itm/20W-monocrystalline-solar-panel-12V-5a-regulator-charge-controller-No-tax-/220854695088?pt=UK_Gadgets&hash=item336bf734b0

[BOAC]

http://www. ebay. co. u. ..=item564697b1b1

 

A friend of mine purchased two of these, good quality and no problems.

 

They also do a 30w version

 

http://www. ebay. co. u. ..=item56482a0a69

 

As long as they state monocrystalline they should be fine.

 

And they do - well found oh dreaded one

 

BO

[Lefthand Down]

I'm a bit confused on solar power, we bought a small top up Solar Power panel rated at 4 watts. It says because of its low power there is no need for a voltage regulator, fair enough, when I put my volt meter on the panels terminals on a sunny day it hit 21 volts which I'm told is enough to damage my leisure battery. So should I use it or not ?

 

You are seeing the open circuit voltage. Clip in on a battery and you will the proper voltage. The meter is not a load.

[Bar Steward]

A very helpful guide, Pete. With the ever increasing price of EHU

many (myself included) will be trying to save a few quid and go solar. You may also stop fellow

'vanners being taken in by scammers on that "certain on-line auction site"!

Thanks,

Marc.

[neil and lena]

A very helpful guide, Pete. With the ever increasing price of EHU

many (myself included) will be trying to save a few quid and go solar. You may also stop fellow

'vanners being taken in by scammers on that "certain on-line auction site"!

Thanks,

Marc.

 

Your not wrong there, the C&CC are now charging somewhere in the region of £3. 75 per night extra for EHU which is why we have invested in a 80 watt solar panel plus regulator .

Will be using non EHU pitches this year to save a few quid when the weather permits

[dreadly]

Thanks but I don't see a regulator with that - I was looking at this:

http://www. ebay. co. u. ..=item336bf734b0

 

20w is too low, it won't give you much power at all. I would go for a larger panel, IMHO minimum 50w - even that will only give you around a 3. 5amp charge at peak sun times.

 

Regulators here :- http://www. ebay. co. uk/itm/12V-10A-PWM-Solar-Panel-Power-Charge-Regulator-Controller-Compatible-10A-/270853616069?pt=UK_Gadgets&hash=item3f102231c5

 

Your not wrong there, the C&CC are now charging somewhere in the region of £3. 75 per night extra for EHU which is why we have invested in a 80 watt solar panel plus regulator .

Will be using non EHU pitches this year to save a few quid when the weather permits

 

Book a couple of nights on EHU to charge the battery

[BFM]

Just a little bit of advice; this RV calculator is for 120v for the US, so the wattages will not change but the current is half that quoted.

[Surf01]

These look to be good and a reasonable wattage

[dotntel]

Hi all i have fitted on the roof an 80watt panel with a regulator fitted under the bed near as possible to the battery compartment, we have a 115 amp leasure battery, this system worked for a weeks stay on a cs with no hook up at all, heating run on gas as was the fridge and hot water, we watched our avtex tv for a couple of hours every night and used the radio as normal showered every day (12v pump) at the end of our stay the battery was fully charged according to the regulator, we used more gas as was expected but on the whole we are very pleased with the system.

The holiday was taken in sep 2011 with dull windy weather as the norm throughout the week , under these conditions everything was fine, it has also kept the battery charged through the winter to run our alarm and tracker so far this winter, hope this helps anyone thinking of going solar.

 

Cheers

Terry

[sirjohnfaulkner]

Terry

 

Did the site have hookups. How much did you save on electric hook up. How much gas did you use. How much are the 80watt panels, is it connected to the caravan battery.

 

Sorry about the question rush, I typed them as I was thinking.

 

I was interested in where the break even point was although I appreciate there are other [ green ] issues involved. .

[dotntel]

Hi John

 

No the site did not have hookups and cost us £6 per night.

 

After seven nights on site we had used about a third of a bottle of calor lite.

 

I paid £250 for a complete kit, and it is permanently connected to the battery through a controller so as not to over charge the battery.

 

Personally we enjoy quiet caravanning and this was a cs at Woebley castle, and we were the only van on site, its why we fitted the panel, if you enjoy solitude the panel will pay for itself very quickly.

 

Hope this helps. ....

 

 

Cheers

Terry

[Surf01]

The only concern I would have with visiting a non EHU site is security as quite often you may be the only caravan on site. We are debating whether to get a solar panel as a 80w one seems to set you back £400+ at Maplins. It may be cheaper and better for us to buy a small Honda generator or one that is very quiet anyway. I wonder how long it would take a generator like the small Honda one to charge a 110amp battery which has been used for about 5 hours the previous day for a TV and sat receiver?

[Guest Rita]

Surf We have a free standing solar panel and often only ones on remote sites never had a problem in 6 years

 

If your worried why not get the flexi one and have it fitted on the roof out of sight

 

There are a lot of sites now not allowing Generators

 

We have a fav site thats banned them and he is always fully booked