I am not sure what information most folks think they will find in a solar tutorial. Rain or shine we get a huge number of calls about solar power each day. We will attempt to answer the questions most often asked so we can save you a phone call.
Before we get started we think you need to know that solar power is not the cure all for replacing spent energy. For example some are trying to recharge batteries for a Trolling Motor, Boat, RV, House, Electric Scooter, Backwoods Cabin, etc. and they want it done in a very short time, usually in just a few days. Assume you take a discharged 100-amp hour battery and charge it with a 30-watt solar panel under ideal summer time light conditions. After a full week the battery will be just about fully charged. Using this example you can see that it will take at least 100-watts of solar power to recharge a 100-amp hour battery in a few days. Keep in mind that it takes direct sunshine on the surface of the panel to produce the maximum rated power of a solar panel. Conditions such as an overcast sky, shadows, improper mounting angle, equatorial direction or short winter days will reduce the actual solar panel output to below the rated values.
Most solar products offer are designed for 12 VDC, but we do have limited availability on a smaller 24 volt panels. Typically when 24 volts or greater is needed, solar panels may be wired in series, or we can special order solar panels that are made to deliver more DC Volts such as 24, 36, 48 etc.
Anytime you use a panel that is over 5 watts rated output, we recommend using a solar controller. Actually, a charge controller is a good idea in a majority of applications. A charge controller can provide several benefits such as preventing overcharge, improve charge quality, and prevent battery discharge in low or no light conditions. Some solar panels are made with blocking diodes pre-installed that prevent battery discharge during low or no light conditions. In most case where a 6-watt or larger solar panel is installed use of a charger controller is highly recommended. In a nutshell, solar charge controllersact like an on and off switch, allowing power to pass when the battery needs it and cutting it off when the battery is fully charged. Something to be aware of when selecting a controller is that they are typically rated in amps, while photovoltaic panels are typically rated in watts. So the morningstar SS-6, 6 amp controller will work with nearly every panel we sell right up to about 70 watts.
POWER RATING WATTS AND AMPS
Solar panels manufacturers rate solar output in watts. As a rule of thumb a rating of 15 watts delivers about 1 amp per hour in direct sunlight. As an example, the SP-5 panel can output one third of an amp per hour. This is a very popular panel for maintaining single and dual batteries for stand-by and storage applications. Typically this power output is stored in a battery for use when the panel is not producing energy. This energy is stored for later use and also allows the battery to act as a filter to prevent damage to any sensitive electronics you may be powering.
HOW DO I FIGURE SOLAR PANEL SIZE
The first thing to remember about solar power is that it is all a matter of numbers. The power you require, vs. power the panel can put out. Before you can even get started when purchasing a panel, you need to know how many amp hours or watts you will need to produce in a set period of time; This figure could be measured in hours or days. Since there are 24 hours in a day, we suggest you use that as a baseline. First, get your total electrical consumption in that time period. Then figure the amount of direct sunlight the solar panel will receive in that time period and come up with a total amount of watts-hours needed. You should always err on the side of caution and over-estimate your power needs. This will help compensate for variables like shade, clouds, panel angle, etc. Once you have a good handle on your power requirements, I suggest you go to our Solar Calculator
Solar panels ratings are calculated in bright direct sunlight. Conditions such as indirect sunlight, overcast and partial shade will decrease the output. We always recommend over-sizing the size of your solar array, as these conditions occur often. Also remember that the length of daylight in summer vs. winter can be quite different.
OPERATING A DEVICE DIRECTLY FROM SOLAR PANEL
This can be done as long as the device is designed for such an application and not sensitive to voltage variations. It is best to use a battery as a storage container for energy that will provide constant source of stable, reliable power.
ARE SOLAR PANELS WEATHER PROOF
Nearly all solar panels are designed for outdoor installation, as this is where they will recieve the best, most direct exposure to sunlight. Remember that anything less than that will cause the panel to produce less than it’s full rated power
DO I HAVE TO MAINTAIN SOLAR PANELS
A periodic inspection to remove dirt, debris and check electrical connections is all that is needed.Keeping the panel clear of snow and debris will allow for better results.
HOW LONG DO SOLAR PANELS LAST
Performance from a solar panel will vary but in most cases guaranteed power output life expectancy is between 3 and 25 years. This guaranteed life expectancy rating is usually 80% of the published rating of the Solar panel. Of course this will vary from manufacturer to manufacturer, and as always, you typically get what you pay for. Watch out for those cheap panels made in Pakichinastan.
USE OF AN INVERTER
Many folks use an inverter to convert 12 VDC to 110 VAC. Inverters, because whenever you change power from one form to another, are power gobbling monsters and should be avoided when possible. If you have a choice of a 12 volt dc powered device or 110 volt ac device, go with the 12 volt DC device. There are DC devices on the market that either step down or step up DC power and these also use significantly more power than otherwise.
FORMULA DC to AC via an Inverter
Formulas and Examples for 12 & 24 Volt DC Systems
This “Rule of Thumb” is intended as a general guide for estimating the DC amps required operating a DC to AC inverter. Since the calculations yield approximate values, an appropriate safety factor should be considered when designing and specifying system components, for example: wire, size, and length. This basicly is legalese for “oversise your system”
12 Volt DC Systems
Formula: 12 volt inverters require approximately ten (10) amps DC input for each 100 watts output power used to operate an AC load.
Example: How many DC amps will a 12-volt inverter require to operate three 500-watt quartz lights, or a 1500-watt electric heater?
1) Total watts = 1500
2) 1500 watts/100 (from formula) = 15
3) 15 X 10 amps (from formula) = 150 amps. This is the DC current the inverter will use to operate the 1500-watt load. Note; If these 150 amps are drawn from the battery for one hour, 150 amp hours of battery power will be used.
To support 150 amp hours of battery power 300 amps of battery capacity should be used for maximum battery life and performance.
24 Volt DC Systems
Formula: 24 volt inverters require approximately five (5) amps DC input for each 100 watts output power used to operate an AC load.
Example: How many DC amps will a 24-volt inverter require to operate three 500-watt quartz lights, or a 1500-watt electric heater?
1) Total watts = 1500
2) 1500 watts/100 (from formula) = 15
3) 15 X 5 amps (from formula) = 75 amps. This is the DC current the inverter will use to operate the 1500-watt load. Note; If these 75 amps are drawn from the battery for one hour, 75 amp hours of battery power will be used.
To support 75 amp hours of battery power 150 amps of battery capacity should be used for maximum battery life and performance.