Frequently Asked Questions- Solar Power

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.

Will a solar panel supply electricity 24 hours a day?
No, solar panels convert light into electricity. So as the light reduces in the day so does the output of the solar panel.

What size solar panel do I need?
This depends on the load you have connected to the battery. You will need to calculate the watt-hour or amp-hours you are using in a period of time (see FAQ How to calculate your solar panel needs), then having a rough idea of the amount of direct sunlight your solar panel will receive each day. The solar panel needs to supply approximately 20% 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 4 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.

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.

Do I need a charge controller?
We recommend that charge controllers are used with 15watt 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. Fuse holders and connections should be kept dry and clean.

What are the possible problems?
Failure of a solar panel is normally due to water damage to the panel itself or the connections. Also damage to the sealant around the frame could cause failure. Mounting the panel incorrectly. If it is fixed horizontally it may be able to collect water. Not a sufficient air gap beneath the panel can also cause damage.

What problems might there be with mounting a solar panel?
Try not to fix panels horizontally as rain will collect in the frame and not cleaning the panels will reduce the output. Make sure there is an air gap beneath the panel.

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.

Please remember that 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.

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, as it will eventually drain your battery.

Please remember that 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.

Appliance Test Information
The following 240V appliances were tested using a 12v leisure battery and a Power Inverter High Quality 400-800 Watt to find out their approximate power consumption when using an inverter, as a guide for our customers when working out what solar panels and equipment to use:

# 240V Radio Cassette Player = 700mA
# 240V Home Computer (base unit) = 8 amps
# 240V Computer Monitor = 6 amps
# 240V Light Bulbs - for every 10 watts allow 800mA
# 240V Small Marshall practice amp & electric guitar = 900mA

We will be adding to this section as and when more appliances are tested.

We hope these FAQ,s have helped and please feel free to contact us via e-mail or telephone if you require any further assistants.

Sunshine Solar Technical Team.