Solar Tutorial

I am not sure what information most folks think they will find in a solar tutorial. Rain or shine we get a ton of phone calls about solar power every week. We will attempt to answer the questions most often ask so we can save you and us a phone call.

First we think you need to know that solar is not the cure all for replacing spent energy. For example we have folks trying to recharge batteries for a Trolling Motors, Boat & RV House, Electric Scooter, Backwoods Cabin, etc. and they want it done in a  very short time,  usually less than several days. Assuming you  take a dead 100-amp hour battery and charge it with a 30-watt solar panel under ideal summer time light conditions, the battery would be nearly charged within 7 days. With this you can  see that it will take at least 100-watts of solar power to recharge a 100-amp hour battery in several 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 overcast, shadows, improper mounting angle, equatorial direction or short winter days will reduce the rated solar output.

VOLTAGE RATING
Most solar products we are involved with are designed for 12 VDC, if 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.

POWER RATING WATTS AND AMPS
Solar panels manufactures rate solar output in watts. As a rule of thumb rating of 15 watts delivers 1 amp per hour in direct sunlight. Typically this output is stored in a battery. The battery stores this energy for use also the battery also acts a filter to prevent damage to sensitive electronics. Our very popular Pro 5-Watt for instance 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.

HOW DO I FIGURE SOLAR PANEL SIZE
This is all a matter of numbers power in vs. power out. You need to know how many amp hours or watts hours you are using based on a period of time; this figure could be measured in hours or days. Then figure the amount of direct sunlight the solar panel will receive in a day and come up with a total amount of watts-hours output. Output should exceed consumption by about 20% to compensate for efficiency variables.

USE OF AN INVERTER
Many folks use an inverter to converter 12 VDC to 110 VAC. Inverters are power gobbling monsters and should be avoided whenever 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 steps down or up dc power and these also use significantly more power.

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.

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?
Answer:
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?
Answer:
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.

CHARGE CONTROL (REGULATION)
A charge controller is a good idea in the 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 they prevent battery discharge during low or no light conditions. In most case where a 6-watt or larger solar panel is in use a charger controller is highly recommended.

OUTPUT CONDITIONS
Solar panels ratings are calculated in bright direct sunlight. Conditions such as indirect sunlight, overcast and partial shade will decrease the output. Over-sizing the solar output should be considered if any of these conditions occur often. Another situation to consider is the length of daylight summer vs. winter.

OPERATING A DEVICE DIRECTLY FROM SOLAR PANEL
Yes, 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 reliable power.

ARE SOLAR PANELS WEATHER PROOF
Yes, most are.

DO I HAVE TO MAINTAIN SOLAR PANELS
A periodic inspection to remove dirt, debris and check electrical connections is all that is needed.

HOW LONG DO SOLAR PANELS LAST
Performance of 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.