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Are solar panels efficient in winter?

post #1 of 19
Thread Starter 
I live in Lake Tahoe, CA, and I'm thinking about installing solar panels. Winter concerns me. How does snow and decreased daylight hours affect the efficiency of solar panels? I don't want to install the panels if they will be problematic in winter.

Any input would be appreciated.
post #2 of 19
Hi jmiller, Welcome to the Ecohuddle!

Same longitude as Sacramento so the same hours of sun of watts/square meter/day = the same output from a panel. You still have to be careful of shading and orientation toward the sun plus inclination.

The panels would need to be inclined due to the snow cover - your installer should have this well in hand.  

The farther north you go the less total sun power available but you are probably in a good place.

For insolation levels you can check the following URL - Sacramento is the closest I found but it is on the same longitude.  http://photovoltaics.sandia.gov/images/Sacramento.gif
post #3 of 19
Summer is much better for sure.

Insolation levels for South Lake Tahoe are as follow (from gaisma):

Jan    Feb   Mar   April  May  June  July   Aug   Sept   Oct    Nov   Dec  
2.06  2.97   4.35  5.55  6.73   7.38  7.31  6.39   5.16    3.68  2.37  1.90

Sandia gives an annual average of approximately 5.91 kW/m2/day annual average for Sacramento.

Another source for solar data is http://www.gaisma.com/en/location/south-lake-tahoe-california.html

post #4 of 19
Russ sometimes this kind of data such as Insoltaion Levels (Nth America) don't take in factors like sea level one sun or 1.5 suns during the peak of the day. South Lake Taho near Incline Village, NV has some very different problems. Lake Taho is a volcanic lake. It is fully circled by mountains. The mountains create shade because they are much higher than the lake. Well having said this I need to explain more about sun days. The earth is 360 degrees. It turns at 15 degrees a hour. A fixed solar system must be pointed true south and not magnetic south. Remember the mountains? Well these figures are wrong unless the solar panels are in the middle of Lake Tahoe. The mountains will shade land installed solar panels just after 4-4:30 PM every day during the summer months. I know we did a energy survey for a customer there about 20 years ago. We discovered that the top of a mountain was the best place for solar. In Reno Nevada it is different and Sacremento was not as good for sun as Reno. California is a good state but it is very hard to use off grid solar systems there because of permits. It seems like the power companies control the state government over permits. This is why you never hear of off-grid solar systems in California. Besides the biggest scam is selling electric power to the grid. The truth is the grid can not handle the power it gets now. Almost 40% of all grid power except hydro power is wasted. Hydro power is the only form of renewable energy (the oldest and biggest Renewable Energy in the United States that can regulate the output of power) can reduce its power output by just turning off the water valve or lowering the current to the generators. Nuclear, Coal and gas power plants make steam to run a turbine. You can not shut them down. Thank God peak periods happen during daylight hours. This makes solar a better solution but near mountains it is not so good.  
post #5 of 19
Hi Jim,

Good to have the expertise aboard. Regards the insolation levels the net numbers are only a starting point - if they are bad then you can probably forget it but if they are good you need to do more research. I have a weather station with a solar sensor which does just that.

I mentioned orientation and shading - both important factors. Off grid solar is fine where you don't have access to a power line but I am not impressed with it otherwise. Too many losses in efficiency plus having to maintain batteries. Much better to let the power company act as your battery. It is up to them to be as efficient as possible.

About hydro - agreed - it is easy and convenient - unfortunately it is difficult to build any more large size projects. In a gas fired power plant the hot gases drive a turbine and at the outlet of that unit it is customary to place what is called a 'combined cycle' unit which is a boiler to recover otherwise wasted energy.

Turndown on gas turbines is not prefered as it forces the operator to move away from the most efficient operating point, adding cost per unit produced.  
post #6 of 19
post #7 of 19
I had a similar inquiry before regarding solar powered homes in Alaska. One of my colleagues referred me to spheresolar.com and I found it really useful. They have a section in their site that can guide you in determining if solar panel installations is right for your home. It's a very user friendly and informative source, I must say. Check it out: http://www.spheralsolar.com/issolarrightforme.html
Edited by lunRay - 8/21/09 at 8:39pm
post #8 of 19
I've been wondering about the efficiency of solar panels during winter as well. I've looked at the sites you've mentioned and I've gathered quite a bit of information about it already. I'd like to ask, are there any particular solar panel brands that are more effective than most during winter? Can anyone recommend any brand/s?
post #9 of 19
There is just plain less watts per m2 per day falling on the earth's surface in the winter - less power available.

The thin film types are less efficient than the older types - as much as 50% less. They also cost less but tend to degrade more quickly losing further efficiency.

The only thing I know to do is look at the panel efficiencies and warranties. 
Edited by Russ - 8/13/09 at 2:05am
post #10 of 19
To: J Miller
Fm: Jim McKirdy
Subject: Solar Panels for winter use and snow.

Dear sir: There are two types of solar cells available. Standard silicon solar cells and Low light CIG cells. Silicon solar cells will work everywhere but the amount of power is limited in time. Silicon Solar panels must have sun light angles of 45 degrees to 90 degrees back over to 45 degrees.This is a total of 90 degrees.  The earth turns at 15 degrees in a hour. This means that a silicon solar panel at best can produce 6 hours a day in the summer months. In the winter months this time can be shortened by up to 50%. The reason is simple in the winter months we have shorter day light hours. Now CIG low light cells start at 20 degrees and back over to 20 degrees. This is a total of 140 degrees. In the summer months you will see 9.3 hours. In the winter months you will see 4.2 hours a day of electric production. Snow does cover solar panels no mater what the solar cells are made out of. The biggest difference is how much light is available thru the snow. Some other solar experts and I argue this point all the time. Here is what I know happens. If snow sticks to any solar panels it reduces the light being absorbed by the solar panels. The thicker the snow the less light is absorbed. Ice and snow is very refective. This can reduce the light needed by solar panels buy 80%. Silicon solar cells will not produce any power under these conditions. Also the power produced by CIG cells is reduced by 80% also. There is a company in Denver that is developing a new solar panel that will even produce power during moon light nights. These new cells are very powerful. I feel that it will take another 6 months before the new solar cells are ready. These new cells really absorb light and the entire spectrum of light. Visible, UV and IR light. Silcon and other compound solar cells can only absorb visible light. As a mater of fact UV light weakens the output of silicon solar panels due to heat almost 8%. This is why some people get upset with the performace's of imported solar panels. China, Japan, Taiwan all make claims of outputs. These claims are in lab conditions only. Say for expample 200 watt solar panel. Well here in Florida you may get 200 watts but more than likely you will only get 180 watts due to heat. At Incline Village, NV. You have much cleaner air quality so you may get 190 watts because the air is cleaner, dryer and you are closer to the sun. But never let someone tell you that a 200 watt solar panel will produce 1,200 watts in 6 hours. They really don't know what they are talking about. I have seen the new solar cells working in the real world. The unique thing about these solar cells is the high volts and low amps that they put out. I can tell you this about the new solar cells. Open volts is 6.2. The size of the solar cells is 20mm by 55mm. The AMPS are .018 amps. The main reason why the low amps is to reduce the cost of wire sizes. These new solar panels may not be less expensive as the standard silicon solar panels. But they will produce more power under normal conditions per day than silicon solar cells. These are going to be the next generation solar panels. If you are very interested in wanting to get off the grid and make your property energy independent and sustainable I suggest that you continue the way your at and when this company from Denver is ready you can be one of their customers. It might just be the solution that will make your life better.
post #11 of 19
Russ, The first commercial application for off grid solar was to reduce the cost of maintaining batteries. Back in 1968 I was ordered by my captain to report to Boston to develop a new type of aids to navigation. Back then there were no solar cells or solar panels. We set out to build our own. We called the units solar plates. This reduced the cost of maintaining aids to navigation by over 600% per year. So instead of changing batteries every 90 days now the batteries stay in place for at least 5 years. The solar lights (red or green) have been working every 4 seconds for many years. There are still some of the orginal solar plates still working for over 40 years. These solar aids to navigation have been showing mariners for may years safe passages. I guess it is about saving lives and property. At least these are the results for the last 40+ years. Now for homes. There are homes today that are independent of the grid, the reasons are simple. There is no grid available, or some people don't want to pay for electric power. I agree with you about if you have the grid use it as a stand by generator. You see electric usage is not fixed at all. It is proven by DOE reports that the average home increases it electric usage by 8% a year. What this is really saying is we buy more products to plug into our homes. The standard mode of grid tied homes is their electric bills over the year will increase by 8%. Plus the local utility electric company will also have a increase. Here in Florida we are paying Progress Energy $4.51 each month for a nuclear power plant that is not even built. Imagine that! At this time my total electic bill is $.14 a KW. My parents live in Henderson NV. They pay $.17 a KW. My folks power comes from the Hover Dam. My power comes from a coal fired Jacksonville, Florida power plant. My bill includes the fuel cost. My parents bill does not have a fuel cost. These ongoing cost for electric power is cheap compaired to buying a solar PV system. But over time the electric billing system will cost 900% over solar PV. Solar PV only real advantage is maintaining cost. I look at this as the best renewable energy systems because it is affordable now.
post #12 of 19
Thread Starter 
Thanks everyone for your help. I've been checking out the recommended sites and like the additional info, especially Solar Sphere's Learning Center.

Still wondering--is there is a way to maximize efficiency during the winter time? Also, is there any way to protect panels from snow or keep snow off the panels altogether?
post #13 of 19
Available sunlight decreases in winter, effecting efficiency. It take a few years to see a return, but solar is a worthwhile investment. I think you should talk to an expert. The Solar Sphere site mentioned above has a call number.
post #14 of 19
@jdsouthall, Welcome to the EcoHuddle!

Your advice about talking to an expert is correct and someone that knows the local area as well. The only problem is to find someone who is either very honest or has no commercial interest in making a sale.

Some of the panel and thin film suppliers are exceedingly optimistic to the point of being deceiving in their claims.   

The PV panels are big in Germany where snow is rather normal - I expect that with the relatively steep inclination and dark color of the panel the snow cover does not last long.

With the incentives/subsidies the panels/systems are more attractive than ever.

You are fixing your electric rate for years to come with the panels which is a good thing as it can only get more costly. The down side is that you are also prepaying the electric bill for a good many years.  
post #15 of 19

For the best quality solar panels for your roof go to globalsolarcenter.com for free and helpful info on solar. Global Solar Center stores energy it is given  by the sun on hot days. This provides you with backup energy on those snow days... Snow is also the first to slide off your roof because it's slippery. They provide roofing for both residential and commercial customers! When I started using their panels I was extremely pleased and I'm advising you to rush and check this website out. After using them you'll never want to use anything else! Hope you'll be as happy as I am with this product!!!! 

post #16 of 19

Interesting post. Where I come from the son don't shine that often and when it does we have a street party. (just kidding). Anyway, I installed solar panels last october (after summer) and I was holing for results this summer however I was amazed to find that I have saved 9% on electricity when compared to last years winter so I'm encouraged and excited to find out how the summer will work out.

post #17 of 19

Hi guys, This probably adds little to the discussion but may be of interest. Here in Canberra, Australia we have a system where you sell all of the electricity generated straight into the grid and use all your electricity straight from the supplier. When you get the bill it shows what you ought less what you sold. The advatage is I am paying between 13 cents to 21 cents for what I buy and selling as a special Govt deal for 45.7 cents. My panels were connected last week. Its May and almost winter here (no snow and 2000 feet up) and the 3 kw system seems to still generate 500 watts when cloudy and around 1,600 watts when sun comes out. Of course it will be better in summer. My panels are at 20 degrees (normal roof alignment) and on a sub-optimal west north west roof cause north was too shaded and small. (Equivalent to ENE in your hemisphere.

post #18 of 19

If solar electric was cost effective, we'd all have it. I'm not really convinced that it's even all that environmentally benign.  Solar water heating makes more sense to me. As well as investing in new homes and retrofits that use less energy from existing sources. By the time the things are paid for they will be degraded beyond use and likely obsolete. We already have power plants that deliver

pretty good value and we can impact the emissions at the source. Why encourage people to pay the personal and environmental cost of each having their own power plants if the grid is available?

Seems like an unnecessary waste of resources with the solar technology that's currently available. Just a hunch, but I think we will probably have better options in a few years.

post #19 of 19

In my experience around half or a little more energy was generated during a cloudless winter's day, when compared with the energy generated during a cloudless summer day.

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