- Flexible Solar Panels
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- Rigid Frame Solar Panels
- Rigid Frame Solar Charging Kits
- Dual Battery Solar Kits
- Folding Solar Charging Kits
- Solar Charge Controllers
- Battery Accessories
- Household Solar Systems
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Great bit of kit charged up a battery in only a few hours. Fast delivery
Bob (Abingdon, Oxfordshire, UK) - July 2012
We are a trusted supplier to thousands of UK clients
Can Solar Panels Store Energy?
Do Solar Panels Work in Cloudy Weather?
Can I Use a Solar Panel Inside my Caravan / Boat Next to the Window?
What Size of Solar Panel Should I Choose?
What is the Difference between Monocrystalline and Polycrystalline Solar Panels?
How Quickly Will a 50W Solar Panel Charge my 70Ah Leisure Battery?
How does Ambient Temperature Affect Solar Panels?
Can I Connect 10W Solar Panel to an Electric Heater in my Caravan/Boat to Power it Directly?
Solar charge controllers
Do I Need a Solar Charge Controller / Regulator?
Can I Connect a Solar Charge Controller to my Battery When it Remains Connected to the System of my Boat / Vehicle?
What is an MPPT Solar Controller and When Should it be Used?
Why is my solar charge controller not showing any output from battery terminals?
Solar panels generate electricity when they are exposed to light. When this exposure is no longer available (e.g. if a cover is placed on a solar panel or during the night) they stop generating electricity immediately. Solar panels can not store energy - they always require a battery / battery bank for power storage.
Solar panels achieve maximum output in direct sunlight, but they work in normal daylight and cloudy weather too. The amount of power a 12v solar panel or charging kit generates in cloudy weather will be lower compared to direct sunlight. If your solar panel is being used to charge batteries, the charging time will be longer in cloudy weather.
Even if it looks as if there is a lot of light inside the caravan / boat it is actually much better if a solar panel is located outside. Even in the middle of the day, a caravan solar panel is going to get more direct sunlight when it is situated outside where the efficiency and power generated by the solar panel will be higher.
Besides, if a solar panel is kept inside, even next to the window, it is quite likely that some solar cells will be shaded. This reduces the efficiency of the solar panel and puts some strain on shaded solar cells to pass current generated by sunlit solar cells which is not recommended.
If you simply need to trickle charge your battery to compensate for self-discharge then a small 5W-10W motorhome solar panel or charging kit will be sufficient.
If you use your battery from time to time to draw power for small loads such as energy saving lighting, stereo equipment or charging your mobile phone etc , we would recommend 40W-50W solar panel or charging kit. These kits are normally sufficient for electric fencing and off-grid lighting systems too.
For larger loads / heavier use including non-energy saving light bulbs, TV’s and water pumps we recommend 80W-100W solar panels or charging kits.
If you constantly use an electric fridge 24h a day, then you will need 100W-150W solar panel or charging kit for the fridge alone.
If you are using solar panels for caravans, motorhomes and boats consistently for a number of appliances with a heavy load, then the total of all consumption requirements should be added together to discover the true size of the solar panel required. For more information please check our article explaining how to choose the right solar panel for your motorhome, caravan, campervan, boat 12V leisure battery.
Small 5W-10W caravan solar panels can sometimes be connected to large batteries without a regulator for trickle charging as long as they are fitted with a blocking diode to prevent reverse current (when power flows back to the solar panel from the battery at night). Solar panels of 20W or more always require a regulator.
As a rule of thumb, it would be safe to use 5W solar panels without a regulator with batteries starting from 50Ah, 10W starting from 100Ah battery capacity.
We recommend using a regulator even for small panels to gain important benefits:
- Your battery will never overcharge (a regulator stops charging automatically when the battery is full and resumes when it's discharged)
- The regulator will use pulse charging (PWM) instead of constant charging, an improved method which prolongs the life of your battery
- The charging voltage will be optimised for your battery (solar panels typically have voltage 18V and higher)
Can I Connect a Solar Charge Controller to My Battery When It Remains Connected to the System of My Boat / Vehicle?
Yes, generally it is possible. However there are some points which you need to take into consideration:
- When your battery remains connected to the system of your boat / vehicle, there might be some power drain from the battery, which means the efficiency of charging by solar panel may be reduced
- When you start an engine with a generator or use an external mains charger to top up your battery, then the voltage in the battery circuit will increase. As a result, the solar controller might treat this as if the battery was fully charged and cut the solar panel off temporarily. When the engine / external mains charging stops, the solar controller will resume charging by solar panel
- If you use a dual battery solar controller designed to charge 2 batteries independently, then at least 1 of them should not be connected to the system of your boat / vehicle, otherwise they will be in the same circuit and the dual battery solar controller won't work properly
The differences between these two types of solar panels relate to the manufacturing process used rather than product characteristics. Monocrystalline solar cells are produced from a single crystal of silicon while polycrystalline solar cells are produced from a piece of silicon consisting of many crystals.
Monocrystalline cells therefore have a continuous and unbroken structure, with an even external colour. In contrast, polycrystalline silicon has visible grain boundaries and a "metal flake" look.
Solar panel properties for these two types of cells are very similar, however polycrystalline solar panels require slightly more space than monocrystalline with the same power rating.
MPPT stands for Maximum Power Point Tracker. This is a new highly efficient technology of solar charge controllers which allow them to track the Maximum Power Point (peak of the current-voltage curve) of solar panels as it varies with sunshine exposure and temperature.
In other words, it allows solar controllers to extract as much power as possible from the solar panel in the current conditions.
MPPT solar charge controllers can also boost the charging current. For example, if the maximum current of a solar panel is 5A, a standard solar charge controller would always charge 12V leisure battery at 5A or less (depending on light), while MPPT solar charge controller would increase this current to about 6A-7A or sometimes even more.
MPPT solar controllers are more expensive than standard controllers, however for certain solar systems they are the only choice. The most common example of this is in systems where the nominal voltage of solar panels is significantly higher than the battery voltage (e.g. using a 36-60V solar panel to charge a 12V battery). In this situation an MPPT would be the only solution, because a regular solar charge controller will have very low efficiency in such systems.
A 50W motorhome solar panel generates a maximum current of approximately 2.5-2.8A in direct sunlight. However it is wise to assume some energy losses in cables or solar controller, as well as some clouds. Therefore the charging current for a leisure battery might be lower, about 2.0A each hour.
So as a rough estimate, to charge a 70Ah battery from 0% to 100%, a 50W solar panel will need 70Ah / 2.0A = 35 hours of charging. This period will be longer in cloudy weather.
Of course, this is only a high level estimate - in reality many factors play a role in this process, such as temperature, the angle of the solar panel relative to the sun etc.
In contrast to popular opinion, mono and poly crystalline solar panels work with higher efficiency and output in cold temperatures. The difference between the power output in +25°C and +50°C can be as much as 5-10%. The warmer the surface of the solar panel, the less energy it is able to generate.
Power rating of solar panels is assigned in so called "Standard Test Conditions" which normally assume +25°C temperature. If a solar panel is rated at 100W in Standard Test Conditions, in higher temperatures you should expect it to produce less output (approximately 90W when the surface of the solar panel increases to +50°C).
For this reason mounting brackets and mounting systems typically allow some space under solar panels for motorhomes to enable ventilation and cooling.
In addition to a solar charging kit for your 12V leisure battery which typically includes a solar panel plus a solar charge controller, you will need another device called a power inverter. It converts 12V battery DC power to normal household electricity 240V DC and has one or two mains power sockets where you can just plug your household appliances. We recommend purchasing pure sine wave inverters - for more information on different types of inverters and how to choose the right one please see our review of 12V DC to 240V AC off-grid power inverters.
No, it's not possible. A 10W solar panel is simply not powerful enough. The power required by your heater is at least 1000W (typically 2000W) - this is 100 - 200 times more than a 10W solar panel can produce in 1 hour. So it would be a major mismatch between the power output of your solar panel and power consumption of your heater.
In addition, only a few appliances can be connected to a solar panel directly without a battery. These are appliances not sensitive to changes in input voltage and power (output of the solar panel constantly goes up and down due to changes in sunlight exposure). One example of such appliances would be a 12V fan which can be connected to 10W solar panel directly. Most other appliances will require a battery and solar charge controller to stabilise power.
Properties and advantages of Gel and AGM batteries are very similar, however there are some slight differences. AGM batteries are better for applications which sometimes require higher than average power consumption, while gel batteries are better in applications with steady or constant low-current discharge. Gel batteries have wider operating temperature range typically from -10C to +50C, while AGM batteries work best in temperatures from +10C to +40C. AGM batteries can accept slightly higher charging current so they can normally be charged a bit faster than Gel batteries. AGM batteries also have slightly higher self-discharge rate. In terms of costs, Gel batteries are typically more expensive.
Our solar charge controllers are very intelligent. Before they transmit any power from the solar panel to the battery terminals, they must decide on three things:
- Charging voltage
- Charging current
- Programme of charging (stages)
The controller can only decide on these when you connect the battery to its battery terminals. Then the controller will measure the battery voltage, assess its state of charge (approximately) and start transmitting power from the solar panel to the battery terminals. The solar charge controller should have a working battery connected to its battery terminals at all times, to enable charging. If you simply connect your multimeter to the battery terminals with no battery connected, don't be surprised that the output is 0.
For the same reason solar charge controllers cannot be used for regulating power provided directly to appliances - if they cannot detect a battery, they will simply not work.
... More questions and answers coming soon...
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