How Often Should I Clean My Solar Panels?

How Often Should I Clean My Solar Panels?

One of the relatively minor side effects of the wildfires in California is the layer of dust and ash that has coated virtually every outdoor surface — including over one million homes with rooftop solar panels. So there are literally millions of people wondering: “Should I clean my solar panels?”

Fortunately, with today’s accurate solar monitoring systems, a system owner can actually determine the energy lost from dirty solar panels — and calculate the savings that can be achieved by cleaning them periodically.

Wind-blown dust and dirt is the source of most soiling on solar panels. Just like your car or your windows, the dust accumulates on the surface and builds up over time. If you’re in a dusty area like a farm or near dirt roads, this dust accumulation may be worse. Pollen from trees is another source of solar panel soiling, particularly in the spring. Some people talk about cleaning up after birds, but bird debris is usually not a problem unless your name is Hitchcock and you live in Bodega Bay.

When solar panels get dirty, photons from the sun are absorbed or reflected by the dirt instead of being converted into electrons — thereby reducing system output. The amount of output decline varies based on the location of soiling on the panels and the thickness of the soiling layer.

Heavy rains do an OK job of cleaning light dirt and debris off solar panels. But if you are in a dry and dusty are, if you can see a layer of ash on your solar panels, or if your solar monitoring system shows a significant drop off in energy product, it may be time to get your panels cleaned.

Please Listen Up to this week’s Energy Show as we walk through the performance implications of dirty solar panels, and describe the best ways to safely and effectively clean your panels (hints: never hose them off, use deionized water and an environmentally safe cleaning solution).

The Myth of Whole House Battery Backup

The Myth of Whole House Battery Backup

Will batteries keep your AC cranking and electric vehicle charged up during an extended blackout? Probably not.

We like to believe the myth of whole house battery backup or the notion that our 21st century lifestyle will continue unabated despite fire hell or high water. The reality is different: Typical battery backup systems work best when they are designed to ration battery capacity and minimize the use of major appliances. These systems must also be integrated with rooftop solar so that the battery can be recharged as soon as the sun comes up.

There are two fundamental engineering limits that make it impractical to run a whole house on battery power alone. First, the energy capacity of typical lithium-ion battery systems is insufficient to power an entire house through a nighttime blackout. Second, battery backup inverters are not powerful enough to start and run many large appliances. Adding multiple batteries and inverters can overcome these engineering limits – but at a very high cost.

Nevertheless, a well-designed solar and whole house battery backup system can provide limited power almost indefinitely. To learn more about the reality of backup power in the event of a blackout or Public Safety Power Shutoff, please listen to this week’s Energy Show.

Energy Vampires in your Home

Energy Vampires in your Home

We’re talking about VAMPIRES on this week’s show — energy vampires.

I know, it’s not Halloween yet, but these little energy suckers are insidious. I guarantee that you have dozens of little devices plugged into your home that are using a small amount of standby power, sucking energy all day and night. It really adds up, and causes nightmares for energy geeks like me.

Research shows that these “plug loads” are about 1/3 of a home’s total energy consumption. We’re not talking about big appliances or lighting – but sneaky little things plugged in or wired in all around your home.

Think about what you have. Obvious vampire loads are devices like computers, routers, Wi-Fi repeaters, phone chargers, TVs, cable  boxes, cable modems, and entertainment consoles. Less obvious vampires are things like security systems, motion detectors, appliances (anything with a clock and an illuminated LED). The really sneaky devices that you might not see include doorbell and thermostat transformers, WiFi thermostats (Nest), hot water and furnace ignitors, garage door openers, irrigation systems, outdoor lighting control systems, cordless vacuum cleaners, and pool timers.

To get a handle on this infestation, I went to every room with a Kill-A-Watt meter to measure the power consumption of each device. It added up to over 250 watts of 24×7 power — over $500 per year.

To learn more about these energy vampires — how to identify them, calculate their costs, and stamp them out — tune in to this week’s Energy Show.

Second Biggest Energy Hog – Your Pool

Second Biggest Energy Hog – Your Pool

After your heating and cooling system, the next biggest energy hog in most homes is your swimming pool. I won’t feel bad if you skip this podcast if you don’t have a swimming pool — unless you’re an energy geek like me. My recent experiences addressing the energy problems in my old house really focused my attention on my swimming pool; in comparison, fixing my HVAC system was relatively easy (that’s the subject of another podcast).

Here is a summary of my annual pool expenses: $1,300 for pool pump electricity ($0.45/kwh), $1,800 for pool maintenance, $500 for evaporative water loss (1.5 cents/gallon), $100 every time I want to heat up the pool in the spring/fall for the weekend ($1.75/therm), and $10 every time I want to heat up the spa. I’m too busy on weekends to do the pool maintenance myself, and the pool’s oval shape is not conducive to a pool cover. So I focused on reducing my pool’s electricity and gas consumption.

It was surprisingly easy to cut my $1,300 electricity cost down to about $130 per year. First I installed a variable speed pump (about $1600) — if you have a pool, do this now. Second, since this pump is so quiet I run the pump at night during off-peak rates — currently $0.13/kwh. Third, with solar power on my roof my costs are down to about $65 per year ($0.07/kwh for solar electricity amortized over 25 years).

Keeping the pool at a comfortable temperature is usually more problematic…except for our family since my wife and I don’t swim, and the kids generally don’t care how cold the water is. But if you want to keep your pool comfortably warm in the spring and fall, the best option is a solar pool heating system that uses black plastic collectors mounted on your roof through which pool water is pumped. Note that if you have this type of system you will need to run your pool pumps during the middle of the day — which may be during peak electric rate times. Another option is a pool heat pump. Air to water heat pumps are good in warm and humid climates (not always best in hot and dry climates). If you are more concerned about heating a spa, a water to water heat pump (cooling the pool and heating the spa) might make sense.

For more about reducing your pool’s total operating costs so it’s no longer an energy hog, Listen up to this week’s Energy Show.

Whole House Electrification with Howard Wenger

Whole House Electrification with Howard Wenger

To slow the global warming trend, a number of states have committed to the aspirational goal of 100% carbon-free energy. As a species that literally evolved from burning wood and hydrocarbons, how can we possibly run our modern lives and economy without fossil fuels?

We can indeed achieve this transition quickly and economically. First, by converting all power generation to renewable, non-carbon sources. And second, by converting all fossil-fuel burning vehicles and appliances to electricity. Steady progress towards these conversions is being made. For example, 32% of California’s retail power came from renewable energy in 2018. The state is well on the way to converting to 100% renewable electricity. Use of EVs is growing steadily, and new building codes mandate the use of rooftop solar and electric appliances instead of natural gas.

The challenge is with the existing stock of residential and commercial buildings. Homes and businesses predominantly use natural gas for space heating, hot water heating and cooking. That’s where the concept of Whole House Electrification come in. Whole House Electrification is conceptually simple: replace gas appliances with electric appliances. In reality, one needs an energy audit to prioritize these conversions, then hire five different specialty contractors to do the work: insulation, solar, HVAC, plumbing, electrical and pool. It can be a daunting task.

Fortunately there are some pioneers out there – one of whom is my friend Howard Wenger. Howard was also a pioneer in the solar industry, with stints at AstroPower, PowerLight and SunPower. Please listen up to this week’s Energy Show as Howard discusses his experiences as he converted his house to 100% electricity, supplied — naturally — by solar.

Weather Impacts on Solar Power Systems

Weather Impacts on Solar Power Systems

This past winter season has been the rainiest I have ever experienced in California. The good news is that the state is no longer in a drought condition. The bad news is that severe weather is occurring around the country. We are likely to continue on this trend: a polar vortex recently hit the Midwest, heavy snows on the east coast, and even Seattle was devastated with big snow storms. 2018 was the 4th hottest year on record globally. On average, the summers are getting hotter and the winters are not as cold. 

But this is a show about energy — particularly solar. Although the output of solar systems can be predicted fairly accurately, weather has the biggest impact on annual energy fluctuations [side note: the biggest monetary fluctuations come from your local utility as they raise electric rates]. Several of our customers were concerned about lower energy output from their solar system in November, December and January. We pointed out that rainy weather — including smoke from wildfires — obscured the sunlight enough to make a noticeable difference in energy output. Even our customers who had battery backup systems contacted us, but for different reasons. Many of them had multiple weather-related blackouts this winter. These customers were delighted that their refrigerators, TVs, lights and heat were all still working even though their power was out. 

While one cannot change the weather (unless your name is Dr. Evil), we can prepare for a changing climate. Please listen up to this week’s Energy Show as we discuss how weather impacts solar power system performance.