When it comes to the point, that you decide to empower your devices with solar power, a lot of questions come to your mind. It’s not only about the amount of devices, you want to run with solar power, also the necessary hours are important, the place you live in or aim to use your solar system, the season(s) and much more.
Let’s have a look at these points to help you when it comes to deciding which kind of system you should choose and how much wattage and accu capacity you need:
Solar panels and Off grid systems – Capacity
First of all, you have to have a look at all your devices, you’d like to be empowered by solarpower.
So you will find on every item a plate with informations as voltage and ampere hours.
→ Make a list (best in excel) where you enter the device, how many hours per day you need it to be empowered, the voltage and ampere hours.
To figure out, how much wattage you’ll need, you use this formula:
Powerage in ampere = wattage/volt
Now, a further step is needed to calculate: The time
Consume in Ampere hours = Powerage in ampere x Period of time each day
A place to live – Solar powered systems
Next, you need to know how many hours the sun will shine each month in your favourite/needed area or country.
For example, I live in spain, exactly in andalucia. The Costa tropical has more than 300 days of sunshine every year, what means around 2900-3000 sun hours.
For comparison: UK has 1493 sun hours averagely per year – and especially in winter, you will struggle to empower your home by pure solar power. It would be too expensive, so for these months, it’s recommended to add a further empowering device, especially for heating up rooms and water.
The four seasons – a solar challenge
Living in Spain makes it more easy, to decide which capacity and wattage your solar off grid system would need.
It’s much more easy to achieve the necessary sun hours also in winter with a fairly small wattage and capacity then in any other european country.
In most cases, you need at least double time bigger system in winter times than in summer times; depending on your country, also in spring and autumn.
Solar panels – where can you place them?
A further point to define the exact needed wattage lies in this aspect: In best cases, you can put them on a house’s roof that is southern directed and has an 30 degrees angle. Important is also, if trees or other buildings are shadowing the planned solar area, for you know, the su ist higher in summer than in winter.
Make your research carefully, otherwise you will be very surprised – but not in a funny way…
For sure, it’s different, when you’re on the road with a campervan. You must realize, that you never can’t choose a road, where optimal conditions for charging your solarpanels are given. So it’s recommended, to choose a higher capacity than with your exact calculation.
(Unnecessary to mention, that the same problem exists, if you fix your solarpower on a boat)
Back to calculate your needed wattage
When you’ve read the article up to this point, you will have noticed, that it’s not that easy to calculate the needed capacity for every season and situation very well. So either, you make a list, which uses you can reduce during low power times, or you increase your capacity – but especially when you drive a campervan, there’s only a limited surface on top of your van, you can use for panels.
Under normal circumstances, for some LED-Lights, 4 hrs radio and running the water pump, around 80 W should be enough. But when you also want to run your TV or laptop and maybe also the heating, this will increase exorbitantly up to 200-300 W – depends on the hours you need power for heating and TV/laptop, of course.
Mono- or polycrystallin panels or CIS-Modules?
It’s important to know, that with higher rays and heat, the performance decreases. But monocristalline panels have a higher output than polycristalline ones.
CIS-Modules will be more and more part of the market, for they are used in thinlayered modules and do not age as much through incoming light as mono- and polycrystalline silicium cells do.
They also have a higher output in winter, but the costs are actually higher than of mono- or polycrystalline modules.
So if you drive a campervan, an 18V Module will be the right one, when you use a 12V Battery.
If you have a 24V Battery, you combine two 18V or directly choose a 36-48 V module.
Also, a huge difference in your needs is the point of waterproofness.
There are panels (as my own ones), that are not only waterproof, but can also be used on boads and ships, or beachbuildings close to the ocean. Not many panels are capable to cope with saltwater. So if you want to power your ship or sailboat, you should look for solarpanels like this one: http://www.lensunsolar.com/Flexible-solar-panel/Lensun-100W-12V-Flexible-Solar-Panel,Sunpower-Back-Contact-Solar-Cell-for-12V-Battery-charge-motorhome,boats
They are slim, and additionally, you can walk on them with soft boots – very important, if you place them on the surface of your sailboat to power your electricity.
Cause they are semi-flexible, on my own small car I don’t have the problems, I would have with inflexible ones. (But this concrete build up will be part of my next story).
Best of all, this solar panel is resistant against being damaged by saltwater – and the air here close to the beach is always full of salty humidity.
How to choose your solar charge controller
For the panels deliver – depending on the sunrays – 0 – 22 V of power, you need a device that controls the optimal income and output automatically.
This is a solar charge controller. He knows and controls, how charged your board battery or supply battery is and regulates the in- and outcome in an optimized way.
These chargers are offered in two varieties: MPP-Controller and Shant controller.
MPP means Maximum power point, these are mostly chosen when you work with more than 36V and bigger systems as 200 W.
The Shant controller work also efficient and handle the in- and outcome of your system.
More important is the point, that the controller fits to your chosen battery – an extra aspect in your calculation, for mostly, you collect sunpower during the day, but mostly need it afterwards at night or in the evening.
Most of them can be set up, depending if you use a lead, gel or AGM battery.
And note please, that you should not overload the controller. If your system produces 10A, your controller should be capable to handle 15-20 A.
In clear words about the function of a solar regulator: Since the sunshine is changeable, the output of solar panel is different every second. So we need solar controller to adjust the solar panel to be stable for your battery. And solar controller will protect the current from returning to solar panel at the night and disconnect solar panel and your battery automatically to protect from overcharging to damage your battery, when your battery is charged full.
Important note: Please have an eye on the self-consumption of power, for some are using around 12,5 mA. That means 3W each day, simply for working!
When you decide, to choose a series connection instead of a parallel connection, this is also important for your controller’s choice, for it doubles the production of solarpower, while choosing the parallel connection doubles the voltage.
(You may find a great variety of controllers here: http://www.lensunsolar.com/Solar-regulator-controller)
Which kind of battery should you choose?
When it comes to the point to decide, which battery you should choose, there is a variety of possibilities: The lead-acid battery, AGM Battery, gel battery or solar battery – but all of them are also available in different sizes and capacities.
This capacity is mentioned in ampere hours, so if the type plate says, it has 90AH (20A), 75AH (5h), this means, you can use for 20 hrs devices, that need 54 W. That could be two lamps of 20W and a radio of 14 W. Or you can use for 5 hours devices up to 180 W.
Some simply choose theirs car batteries, but these are produced to offer short but high output to make the car starter step into action. They are not meant to be used for enduring but lower output, so they will be much sooner not charging any longer. AGM batteries or gel batteries are a better choice, for gel batteries can be placed in every position. In an AGM Batterie, the lead is in a fleece that reduces sipping. But lead-acid and lead-fleece batteries need to be inspected, water needs to be filled up. Gel batteries are in a closes system, where you need not to look up and inspect them. So you can place them better in a place, you can’t reach very well – only when they need to be completely replaced.
When you calculate the capacity of your battery, it’s important to add all points, where performance gets lost, e.G. the cables, the converter, the controller. Then, you should also be aware, that some batteries can’t be unloaded further than 50 %.
So when you need 50 Ah/day and your battery should not go under 50 %, you need not only 100 Ah, but add around 30 % for performance loss or cloudy days. In this case, your battery should have a capacity of 130-150 Ah.
So when you plan your offgrid living, you should add some days for your own security to the capacity of your battery. There could always be some cloudy or rainy days – even at the sunny coast of andalucia.
Assembly of panels, controller, battery
When you put up the system, you should choose a place for the controller, that is not very far from the battery, you aim to charge, to reduce the loss of power due to the length of the cables.
Some place it in the back garage of theirs campervans, but I, as I possess a Volkswagen Polo, need different solutions.
But this story, how to assembly such a system in and on a small car to achieve most possible autarchy, will come during the following months.