Sunday, May 10, 2020

My grid-tied solar power system and back up

My solar power system is grid intertied.  This means that I have no battery backup and the solar inverters shut down to prevent back feeding power into the grid in an outage.  This could harm line workers as they restore power and is a federally mandated safety system built into all grid connected solar equipment.

So I have 2 meters.  One that records incoming energy from the utility (the use meter), and the other records surplus energy that I export to the grid (generation).  My solar power offsets my usage, and in the summer and fall I generate more than I use so the utility credits me for the power I put into the grid.  The credits accumulate and I use them up in the late fall to cover a month or 2 of bills.

A lot of people assume that because I have solar I have power during an outage.  I don't.  I had 2 options when I built my system in 2009 - battery backup or an automatic standby generator.  The cost and maintenance of a battery bank would be prohibitive and it would not work well with the micro-inverters that I used.  Back then the only option was lead-acid batteries that were either flooded (filled with liquid acid) that require constant maintenance, or more expensive sealed batteries know as AGM (absorbed glass mat) batteries.  Nowadays lithium batteries are more common - like the Tesla Powerwall.  But that is also pricey and does not provide as much storage as I would like.

So I elected to install a Generac Guardian automatic backup generator powered by propane.  This unit starts within 15 seconds of an outage and is pretty reliable, as long as I do basic maintenance.  I already had a propane backup boiler for my solar heating system, so I had a propane storage tank right near my utility room.  I got mine from Home Depot for $2500 and installed it myself.  It cost less than half the cost of a modest battery bank that would be sufficient for my needs.  With a full tank (actually 2 tanks) of propane I can run for over 2 weeks on the generator and often need it for days at a time when we get big winter storms.  The generator does not power everything on my property, just the essential loads, so it can't charge my electric car and I can't run my table saw or wood lathe - both are big 240V machines!

I installed an hour meter for my generator in a box with 2 lights that indicate where my power is coming from and use this to record how long each outage is.

This last winter was brutal with 11 outages ranging from an hour to over 2 days.  We had a lot of hard wind storms with gusts topping out at over 45MPH as recorded on my weather station.  Yesterday (May 9, 2020) was a typical windy day that knocked power out for 10.5 hours.  You can see that the wind gusts went off the chart at 50MPH!  You can see where the power dropped out where the blue line goes flat at around 7:30pm.
 Click on the image to see my live weather station.

Here's a list showing generator run times per outage we had over the winter and spring:
So clearly it's a Faustian bargain for me.  Most of the time I'm using free and clean energy from the sun to power my home, workshop and Chevy Volt.  But then I have to deal with dirty, expensive propane when the utility power drops out.  I still think it's more cost effective than batteries.  But someday I'd love to install more solar and battery power to go fully off the grid.


UV Germicidal Sanitizing lamps and scams - the science and technology

UVC Germicidal Lamps - a tutorial

During the Covid-19 pandemic a large number of sellers on the internet are touting "UV Germicidal Sanitizing" lamp products.  Most of them are fake and do not produce useful UV light.  In the first week of May 2020 I noticed that Amazon has clamped down on these scam products and removed them, but they remain widely available on eBay and other sites.

So I though I would offer some guidance on how to distinguish real from fake products.  I'll start with the science behind UV, then talk about technologies that produce UV (ultraviolet) light and finally talk about what types of products are real, practical and usable.  Be advised that genuine germicidal UV lights produce dangerous light that can harm your eyes, burn your skin and product harmful amounts of ozone (O3).

UV light is broken into 3 categories, so first lets put it into context.
UV light is beyond the human visible spectrum - although parts are visible.  For instance long wave "black lights" are used to light posters and fluorescent minerals are UVA and are perceived as deep purple.  UVB light is used in bug lights and is seen as a pale lilac/white color.  These 2 types are commonly available in small fluorescent tubes and do not produce harmful UV although prolonged exposure to UVB (like those use in tanning parlors) can give you sunburn.  UVA penetrates glass and clear plastic while B and C do not.

UVC however is much more hazardous, but fortunately the ozone layer in our atmosphere blocks most of it.  It is UVC that has the germicidal and sterilizing properties.  This wavelength from 100 nanometers (nm) to 280nm breaks the molecular bonds in DNA preventing viruses and microorganisms from replicating.  UVC is harmful to humans and can give you skin burns quite quickly and if you look at this type of light your eyes can be harmed.  Welding arcs produce UV that welders sometimes see without safety goggles and the result is known as "arc burn".  Basically your eyes will feel like there is sand in them for hours and it can be quite painful.

UVC produces what is called ionizing radiation that directly disrupts the molecular bonds of oxygen (O2) and the free molecules join up to create ozone (O3 or 3 oxygen atoms) in the surrounding air.  Ozone is that "fresh air" smell you get from lightning in a thunder storm.  The lightning itself produces a lot of ozone.  In moderate amounts ozone is not bad for you, but too much will harm or inflame your lungs.

There are basically 2 ways to produce UV light, gas discharge tubes (like fluorescent tubes) - and LEDs (Light Emitting Diodes).  Here's a typical UVC tube:
It is made from quartz glass and filled with a low pressure gas such as argon and a tiny amount of mercury.  It is the incandescent mercury vapor that produces the UVC light when high voltage is applied to the tube.  This image represents what you see - a pale light blue glow. The glass must be quartz because regular glass or plastic will block up to 90% of UV light.  

The other way to make UV light is with LEDs these are solid state devices that can produce UVA (black light) and UVC.  Black light LEDs are used in discos and you see CSI techs on TV waving them around to detect blood etc.  But UVC LEDs are very expensive to make.  They typically cost from $3 to $150 each!  Here's what they look like:

This component is about 1/4" (5mm) square.  They are made from metal or ceramic with a quartz glass window.  They are quite efficient electrically so some battery powered UVC products are available that use these LEDs.  But here is where the scam comes in.  There are also a lot of LEDs that create light that has a strong white/blue cast that looks like UV but isn't.  Those parts look like this:
As you can see this is made from white plastic which - if it did produce UVC - would degrade quickly.  Not to mention that the plastic window would block most of the UVC light.

Lets start with the fake products.  Here are some pictures of various ones that I found on the web:

As you can see these are constructed with dozens of white plastic LEDs that cannot be UVC emitting devices.  Some do emit UVA "black light" however. One give-away is that these products retail for under $50.  If they used genuine UVC emitting LEDs they would cost HUNDREDS of dollars!

And there are small battery powered "UV sanitizing" wands too:
In these pictures they have colored the image to make it look like the light is purple when in fact it looks white with a blue cast.  (Although some may be using inexpensive "black light" purple LEDs that produce UVA light).  Many of these fake products will lure you in with the bold keywords of: "Germicidal", "Sanitizing", and most egregious: "UVC".  They are flat out lying!  While there may be one or two products that do use genuine UVC LEDs, I would generally advise against risking a purchase unless they sell for well over $100.  But the best option is to get the real deal which are actually quite affordable.

Products that do produce UVC will look like this:

The one on the right correctly states "with ozone".   These lamps do not produce dangerous amounts of ozone unless used in a small space. There are also portable UVC sterilizing wands like these:
If you look closely, you can see the quartz glass tube inside - as opposed to the LED dots in the wands above.  These units are fine for sterilizing small items like breathing masks or light switches, and can accomplish good results if used for several minutes.

Larger, more powerful tubes are wall powered and are more effective and do produce the distinct odor of ozone when operating.  Here's a good example of an 11 Watt lamp:
This type of lamp is encased in a quartz glass tube and can be rated up to 30 Watts.  Some however use a regular glass tube that blocks the ionizing radiation that produces ozone.  Some some will feature "ionizing" and some will say "non-ionizing" if they are ethical.

Hospitals use much larger UVC lamps in operating rooms and to sterilize patient rooms and they need to air out the room to remove excess ozone before it can be used after being sterilized.

There are no clear-cut guidelines for use of UVC lights but generally speaking using small (under 20W) units for several minutes to sterilize small items should work.  If you want to sterilize a room of more than 100 square feet you would need a big lamp rated at over 30 Watts and leave it on in the the room for over an hour.

This article from NPR suggests that there really is no clear "dosage" or exposure duration.  And small lamps will not illuminate every part of an object of room

Some lamps come with timers that allow you to walk away and let them work unattended.  Some even have a start button you press, and there will be a delay before they come on so you can leave the area before it lights.  All these lamps advise that the room needs to be aired out after use to reduce exposure to unhealthy levels of ozone.

Be advised that UVC sterilizing lamps are dangerous and should not be left in the hands of the inexperienced or children.  If you are sterilizing a room it should be closed and locked and then aired out afterward.  NEVER look directly at these lamps with the naked eye!  The lenses in most prescription glasses do block UVC but don't trust that as a safe practice.  Never expose your skin for more than a few seconds!  Keep in mind the inverse square law that states that as your distance doubles the amount of light diminishes dramatically, so touching or looking at these lamps up close is dangerous, but is somewhat safer as you get farther from it.

If you want to shop for these lamps, try this link to get started - and just ignore anything that looks like it uses LEDs.  As of this writing (May 10, 2020) they are hard to get from US suppliers.  But Chinese suppliers will ship them by air post to arrive in 4 to 6 weeks.

I hope this is helpful and useful for those of you who may be considering the purchase of a sterilizing light.  Please leave comments if you have questions, corrections or experiences to share.