Solar Energy Facts & Resources

Solar basics, tips, A solar glossary and just a complete background on everything solar power
Do you need to clean your solar panels?

Do you need to wash your solar panels?

It’s a good question and one with a lot of different answers. Companies specializing in cleaning solar panels generally say: Yes – you have to clean your rooftop solar panels and you have to clean them regularly. Some say panels need an annual scrub, others say quarterly. One company selling an automated washing system says panels should be washed every couple of weeks.

SMA Sunny Boy inverter

The solar inverter is like the switchboard operator or middle manager of a photovoltaic array. In a conventional PV system all the PV modules are wired or tied into a central inverter, also called a string inverter.

The inverter itself conducts several important functions. Most importantly it converts the direct current (DC) electricity produced by the photovoltaic modules into alternating current (AC) with the proper voltage that can be used by household appliances.

SolarMagic Power Optimizer

Relatively new to the solar marketplace are a new type of technology that helps boost efficiency and hence the output of solar PV systems.  Power optimizers help condition the electricity produced by photovoltaic modules and by wind turbines. They act as sort of a DC to DC converter for each module and use maximum power point tracking (MMPT) technologies. MMPT measures the output of all the cells or PV modules in an array and applies the proper resistance or electric load to produce as much power as possible in an array. As such, power optimizers allow each panel in an array to produce as much power as possible and increase or decrease the module’s output voltage to match the amount of voltage requested by the inverter they’re tied to.


Solar renewable energy credits, or solar renewable energy certificates, known as SRECs, are tradable energy commodities that represent the environmental benefit of producing one megawatt-hour of electricity using renewable solar technology. 

In the eight SREC states, the Renewable Portfolio Standard requires electricity suppliers to secure a portion of their electricity from solar generators. An SREC can be created for every megawatt-hour of solar electricity created.

An SREC is sold separately from the electricity and represents the “solar” part of the electricity produced. The market- supply and demand- determines the SREC value.

Solar micro-inverters, like their big brothers string inverters, convert the direct current (DC) electricity that solar panels produce to the alternating current (AC) energy we use to power our electronics. The difference is that they’re smaller.

Instead of converting electricity from an entire solar array or big groups of panels in a solar farm at once, micro-inverters convert DC to AC one or two panels at a time.


Micro-inverters are known to increase solar system efficiency by 5 to 25 percent. The reason is that they are concentrated on one or two panels instead of 100, so they can fine-tune a panel’s output. If there is a problem with one of the panels attached to a string inverter, it can greatly diminish the output of the entire system, depending on the inverter and how it’s configured.

Hybrid Solar System

The sun’s full spectrum of light produces two types of radiation that are useful for energy production. Most solar systems take advantage of one type of radiation, but some newer systems are now taking advantage of both. That’s why there’s an increase in the number of solar hybrid systems now becoming available on the market. They generally produce electricity via photovoltaics and then also solar thermal energy that can be used in other applications, like heating—and yes cooling—a home or building, or for heating a home’s or building’s hot water. 


In the past however, most solar systems had just been either a solar thermal system or a photovoltaic systems. The former takes advantage of the sun’s thermal or infrared energy, producing heat, which can be harnessed for solar hot water, like the solar thermal panels on rooftops—it can also be reflected and concentrated on a point. This is the type of solar used in most concentrating solar applications, like power towers and trough systems. 

Solar WarrantiesSolar installations are investments that deliver increasingly greater returns over time as grid electricity prices continue to rise while free energy from the sun remains a constant.  However, the lifetime ROI of a new installation largely depends on how long that “lifetime” actually is.  Consequently, any homeowner or business owner interested in switching over too solar must understand the actual manufacturing warranties backing whatever systems they explore.  These warranties typically cover the 3 main components of a standard PV installation – the panels, inverters, and batteries if you have them.

Most solar panels come with warranties guaranteeing 80% system performance or higher for 20 to 25 years – well beyond the warrantees typically attached to most electrical appliances, cars, and even diesel generators.  In addition, many manufacturers also segment their warranties, guaranteeing 90% system performance for the first 10 to 12 years.  It’s worth noting that the potential lifetime of a solar PV installation can be as high as 30 to 40 years, with many installations from the 1970s still producing clean energy. 

flexible solar

Thin-film solar photovoltaics are a class of photovoltaics that are also known as second generation photovoltaics. Thin-film photovoltaics came about as an alternative to silicon-based photovoltaics because the costs of the semiconductors used in thin-films were cheaper than silicon. However, increased production of silicon for solar and other uses has dramatically dropped its cost. That and a subsequent increase in the production of silicon-based photovoltaics have reduced the price of silicon-based photovoltaics, making it harder for thin-film photovoltaics, which are still generally less efficient than silicon photovoltaics. 

There are three main types of thin-film photovoltaics: Cadmium Telluride (CdTe): Copper Indium Gallium Selenide (CIGS); and amorphous silicon. Another type of photovoltaics using Gallium Arsenide could be considered thin-film, but are often called multi-junction photovoltaics since they use multiple layers of semiconductors to absorb more light than other PV cells. For a look at major thin-film producers as of July 2012, see the table at the bottom of the page.

power purchase agreementPower-purchase agreements are contracts, under which property owners (hosts) lease power-generating systems, financed by a third party, and use electricity generated by systems onsite.

PPAs are a powerful tool in the solar developer’s arsenal, a financier helps reduce the up-front costs of installing solar on a home or building. In exchange, the property owner—host—enters into a legal contract—essentially an equipment lease—with the installer or a third party (usually an investment firm, a bank, or a community) and pays a set monthly rate for the duration of the contract.

If you’re interested in renewable energy, you’ve probably heard the term wind-solar hybrid before and wondered what that really meant. On the surface, it's pretty straight forward; it’s a renewable energy system, generally small, designed to provide power for your home or small business.

But there’s a difficult side to this technology: How do you connect two or more different types of electric current, condition, and convert it into usable, stable electricity for your home or building? And why consider a hybrid system anyhow?