Solar Panel use FAQs

Do Solar Panels Work?
Yes they do......these are some of the most successful examples where they provide power away from a mains supply, communications satellites in space, illuminated navigation buoys, irrigation pumps in remote areas, radio and monitoring equipment in remote areas, power for caravans, motorhomes and camping applications.

What are the different types of Solar Panel? / Solar Cell and how will these affect my Caravan, Motorhome or Narrowboat?
There are two basic types of cells used in the manufacture of most modern general purpose solar panels, these are crystalline (monocrystalline / polycrystalline) or thin film. Both produce similar outputs in sunny conditions, although thin film cells generally perform better in overcast weather. The only down side of thin film solar panels is their size and weight, a much greater area is required to equal outputs of crystalline panels. Monocrystalline Solar Cells are the most efficient at converting the suns power to useable electricity. Monocrystalline Solar Panels tend to have a smaller foot print and last longer than the cheaper Amorphous and Thin film Solar Panels.

Will a solar panel produce electricity on a cloudy day?
Yes, a solar panel does produce electricity even when it is not placed in bright sunlight. On a normal cloudy day there is always enough so-called diffuse light, by which the panel will produce electricity. However, the production of electricity is not as high as when the panels are placed in bright sunlight.

Will solar panels work in the winter?
Yes, solar panels work on light not heat. The amount of sun hours will be less in the winter, as the sun rises later and sets earlier.

How can they help on my Caravan, Motorhome or Narrowboat?
Quite simply by charging the battery(s) during daylight hours. They work at their best in bright clear sunshine, most high quality solar panels will still produce a useful charging current even in cloudy conditions.

What size solar panel is required on a Caravan or Motorhome?
To some degree this is the "How long is a piece of string" question. .As a general guide, most owners would want to try to balance the power produced by a solar panel with their average daily 12 volt power consumption. Average consumption is also a wide question, generally it is in the region of 10 - 20 ampere hours (Ah) per day from the leisure battery. (Batteries are rated in ampere hours, 45, 60, 75, 90, 150 amp hour, this describes the storage capacity of the battery). A 80 watt solar panel will produce up to 3-4 amps (A) per hour in bright sunny conditions. On a good sunny day, allowing for the changing position of the sun in the sky, low in the morning and evening, overhead in the middle of the day, you might expect this 80 watt panel to produce 14 to 18 Ah of battery power. The solar panel needs to supply approximately 30% more than your needs to compensate for variables, such as cloudy days etc. Obviously the winter will have shorter sunlight hours per day than the summer, but you can work on an average of approximately 5 hours sunshine a day in the UK over a year

What is a blocking diode?
This is a component connected within the cable that prevents the solar panel discharging the battery when there is no sunlight. All Free Solar Energy Uk Solar Panels come fitted at the factory with blocking diodes, we recommend using Solar Panel charge controllers for all panels above 10 Watts.

What is a charge controller?
This device controls the charge to the battery. When the battery is fully charged the controller disconnects the solar panel from the battery. We offer two ranges of solar panel charge controllers both budget and professional.

Do I need a charge controller?
We recommend that charge controllers are used with 10watt solar panels and above.

What is an inverter?
An inverter takes the DC (direct current) from the solar panel and creates a useable form of AC (Alternating current). Inverters are power hungry, so it is best to purchase (if possible) a product that operates on 12vdc.

Can equipment be used directly from solar panels?
Yes, solar panels will run equipment direct, these could be loads such as fans & pumps, but make sure the load of the equipment is not equal to the output of the solar panel, as overcast or cloudy days will reduce the output. Solar panels with not run TV's or radio's (without battery backup), as they require a more stable voltage.

Is maintenance required on solar panels?
Clean using a non-abrasive cleaner. In the long term check the sealing especially in marine use and reseal with a silicon sealant if damage is suspected. Check battery connections periodically when you check battery levels and if it is mounted on the roof check the security of the panel mounts. Fuse holders and connections should be kept dry and clean.

What problems might there be with mounting a solar panel?
Make sure there is an air gap beneath the panel. Panels will have reduced efficiency in hot weather - having an airgap between the panel and the Caravan, Motorhome or Narrowboat helps reduce this. We offer a range of fixed solar panel mounts.

How to calculate your solar panel needs
Battery Ampere Hour: The amp hour (ah) rating of a battery tells you how much amperage is available when discharged evenly over a period of time. The amp hour rating is cumulative, so in order to know how many constant amps the battery will output for a given period, you have to divide the amp hour rating by the amount of hours the load will be used.

Example: If a battery has an amp hour rating of 85, and it will be used for 20 hours dividing 85 (ah rating of battery) by 20(hours of load) = 4.25. Such a battery can carry a 4.25 amp load for 20 hours before dropping to 10.5 volts. (10.5 volts is the fully discharged level, at which point the battery needs to be recharged.) Please be aware that it is not a good thing to discharge the battery fully. If the battery is fully discharged the solar panel may not be able to start the recharge, so add at least 15% more to you battery needs.

The ratings of Solar panels are calculated in bright direct sunlight. Conditions such as indirect sunlight, cloudy, hazy conditions and partial shade will decrease the output. Also the length of daylight i.e.: summer vs. winter. Figures quoted for example only.

Calculating power using current and voltage
There are three ways of writing an equation for power, current and voltage:

Power = Current x Voltage so:
P = I x V
or
I = P divided by V
or
V = P divided by I

Where:
P = power in watts (W) P = power in milliwatts (mW)
V = voltage in volts (V) V = voltage in volts (V)
I = current in amps (A) I = current in milliamps (mA)

A milliwatt is a 1000th of 1 watt
A milliamp is a 1000th of 1 amp

Example: A 12 volt 15 watt solar panel in peak light conditions will give approximately the following current using one of the above equations. We have the 2 variables, volts and watts so the following equation can be used:

I = P divided by V
I = 15 divided by 12 =1.25 amps

So as the formula states that a 12 volt 15 watt solar panel in peak light conditions will supply a current of 1.25 amps.

Example: If we say that a 12 volt 15 watt solar panel will supply 1amp-hour (average) for a period of 6 hours (in the summer) it will replenish the battery with 6amps in a day. If you have equipment which is connected to the battery that use more than 6amps per day then the solar panel you have may not be sufficient for your needs. The best way to assess your needs is to consider what load do you have connected - i.e what do you have connected thats pulling power from your batteries?

These examples are for guidance only. The ratings of Solar panels are calculated in bright direct sunlight. Conditions such as indirect sunlight, cloudy, hazy conditions and partial shade will decrease the output. Also the length of daylight i.e.: summer vs. winter. When sizing a solar panel for your needs you need to consider will it be used all year round or for seasonal use i.e summer only. If all year round use is needed you will need to oversize for summer use to accomodate the lower light levels, and less dailylight hours in winter to accomodate your winter use. If seasonal summer use - then a smaller solar panel will probably suffice, its use only being to trickle charge in winter when no load applied.