Solar Water Heating in Cold (Colorado) winters?

[duncanshannon]

Hi-

I'm contemplating radiant floor heating for a yurt I'm about to build. I love the idea of DIY solar water heating...and I have two main questions to get started.

1) how can I determine the feasibility of such a thing in Colorado winters? Lots of sunshine, temps rarely below -5 F. But I don't know how to calculate / size to see if it's reasonable.

2) are there good DIY friendly / lower cost water storage tanks? Got a quote for a 50 gallon and it was $1400

Thanks in advance...sorry if these are FAQ. The solar water forum is pretty small and I did review it!

 

[chrisski]

I'm sure you've seen the cheaper 50 gallon water tanks. I'll bet the $1400 is quality. Did that include intallation?

Around here, there's quite a few used, large water storage containers that cycle through Craigslist at real reasonable rates if you're willing not to go new.

 

[duncanshannon]

I'm sure you've seen the cheaper 50 gallon water tanks. I'll bet the $1400 is quality. Did that include intallation?

Around here, there's quite a few used, large water storage containers that cycle through Craigslist at real reasonable rates if you're willing not to go new.

Nope! $1400 for the 50 gal tank. Not even shipping.

I guess I'm not even totally sure of the brand. It was quoted thru radiantcompany.com

So much to learn!

 

[chrisski]

Nope! $1400 for the 50 gal tank. Not even shipping.

I guess I'm not even totally sure of the brand. It was quoted thru radiantcompany.com

I mentioned a basic water tank. I'm sure those aren't suited to what you need.

I'm not sure how you would heat the water in -5F with solar. Electric Water heaters really draw a lot of power. Just for an idea, the 600 watts of panels and 4 golf cart batteries I am putting in my RV are certainly not suited for heating water. Once this is done, I will be able to brew a couple of cups of coffee in a 700 watt single cup coffee maker. If I were to go to six golf cart batteries and 24 volts, I may be able to boil water a couple of times a day in a 1700 watt kettle.

There may be something you can do for solar water heating. I don't know anything on that subject.

 

[fat_old_sun]

Hi-

I'm contemplating radiant floor heating for a yurt I'm about to build. I love the idea of DIY solar water heating...and I have two main questions to get started.

1) how can I determine the feasibility of such a thing in Colorado winters? Lots of sunshine, temps rarely below -5 F. But I don't know how to calculate / size to see if it's reasonable.

2) are there good DIY friendly / lower cost water storage tanks? Got a quote for a 50 gallon and it was $1400

Thanks in advance...sorry if these are FAQ. The solar water forum is pretty small and I did review it!

What's the size of the yurt you'd like to build? length, width, height? how many windows & the directions they would face? what kind of insulation are you planning to use? Once you have all this info compiled, there are a number of on-line calculators that will help you figure out the energy needed and how to go about collecting it.

 

[Craig]

This is something that has interested me for a while. The common thinking around here by the pointy heads is that it cant be done. I disagree I think it can be done although how economically is the question. Seems to me that you do not need to heat the wqater from freezing to 65 degrees or whatever you just need to maintain the temperature at 65 degrees.

My thoughts are this. You do not need a $1500.00 50 gallon water tank. Find something in the 200-300 gallon range and burry it deep in in the ground below the frost line. This will do two things A. Since it is above the frost line it will never freeze and potentially stay well above freezing. B. It will have more thermal mass being 200 gallons vs 50 gallons. When the sun is shining throw the solar to it to get it as hot as possible.

2000 watts of solar will heat 300 gallons 10 degrees in less than 4 hours. So if you can keep the water relatively warm it can be done.

 

[newbostonconst]

I looked into this solar water heating because my house has pex radiant floors with GeoThermal. It is cost prohibitive to use water to store heat. I know many are doing this but they are missing the very low cost of batteries today.

My calculations are for 165 gallon tank. You can store 6657 watts in that tank raising the water temp from 110 to 176 degrees. $1500 for a tank to do that?

For batteries you can buy them now for $100 per kWh, so for that $1500 you can buy 15kWh of battery storage which is half the cost of using water. So, with the equipment I have, it was better to buy batteries.

Tell us more about the place you want to build. Is there going to be a grid? Is there solar? Is there an inverter? If you give this info I can help calculate it out to see what is best.

Another fact is that now mini splits have passed Natural Gas for being cheaper way to heat. There is 4.5 times the energy in Natural Gas then in straight electric. So 16 seer heat pump is 4.5 COP.....what that is saying is that if you have a 16 seer heat pump is will multiply the heat 4.5 times per unit of electricity. There are now heat pump mini splits that claim 42 seer.... Thus an all electric house is now the best way to go, even better then natural gas....

I have a 7000+ sqft house (3700 sqft on main floor of ranch and basement of 3700 sqft with half of the walls exposed walkout into the side of a hill) We are net zero except for a $40 month Natural Gas bill. We plan to get a couple more panels to get us below net zero. Just mentioning this because I have a lot of experience in the last two houses we have built and designed completely ourselves. We are in Michigan (Ann Arbor).

 

[fat_old_sun]

My calculations are for 165 gallon tank. You can store 6657 watts in that tank raising the water temp from 110 to 176 degrees. $1500 for a tank to do that?

I get 29 kWh. Something's not right with your calculations, besides the units for energy.

 

[Hedges]

Evacuated tube thermal collectors?
Heat-pump water heaters?

Tossing out those ideas because they aren't in the list yet.
Each of course has its potential issues.

Just for domestic hot water, not as heat storage for the building?
How much water do you want per day?

$1400?
Here's 50 gallons, $379, Home Depo:

Rheem Performance 50 gal. 4500 -Watt Medium Electric Water Heater with 6 Year Tank Warranty and 240 volt Connection XE50M06ST45U1 - The Home Depot

The Rheem Performance 50 Gal. Electric Water Heater takes up less space than competing models, making it the perfect for replacement of an existing water heater. Provides ample amount of hot water for

www.homedepot.com

So it costs $1031 for the option "delete electric heating element" so they can market it as a "hot water storage tank"?

I picked up a 30 gallon there a few years ago. They offered an extended warranty.
"How much?" I asked. "$175" she replied.
"No thanks, I'll just take two water heaters" I said. (It was only $130 for the one I bought)

 

[rin67630]

Forget electricity. Use vacuum tubes solar collectors. They are 50 times more efficient than electrical solar panels get warm water even with frost outside.

 

[snoobler]

Forget electricity. Use vacuum tubes solar collectors. They are 50 times more efficient than electrical solar panels get warm water even with frost outside.

PV panels typically convert 20% of the solar radiation to electricity. How does a vacuum tube solar collector collect 50 * 20% = 1000% of the available solar?

 

[Hedges]

Forget electricity. Use vacuum tubes solar collectors. They are 50 times more efficient than electrical solar panels get warm water even with frost outside.

50 times more? no way.
PV panels are around 20% efficient now. That means they convert 1/5th of the sun's energy which falls on them to electricity.
With charge controllers, inverters, etc. you can deliver maybe 3/4 of that to water.

50 times more efficient would be 1000% efficient, meaning for every 100W of sunshine you get 1000W of heating.

Heat pumps can deliver more than 100%, maybe 200% to 300%, by getting the other couple hundred percent from another energy source. For instance, heating your house in the winter with warm water from underground.

 

[chrisski]

I think 50 X more efficient is said for effect. I was just trying to find out how efficient these evacuated tubes are. I’m sure that aside from the 20% efficiency of the solar panels, there’s a pretty huge loss of taking this electricity and converting it to heat, but now enough to make the 50 X efficiency that’s claimned. Anyway, that google research will come later.

I’m also wondering if these Tubes are used for the Canadian winters, I understand the vacuum tube not freezing, but how about the copper pipes between the tubes? Some pretty cold nights up there. The problem was overcome somehow because people are using these, I just don’t know how. FOr me, that’s google research for later.

 

[rin67630]

Your 20% are an optimistic maximum under ideal conditions and 90° solar incidence. Most of the time they run far below that efficiency, especially under diffuse light.

 

[Hedges]

I'll give you "50% more efficient"

This article:

Why Evacuated Tubes Heat Pipe Solar Collectors are among the most efficient in Nordic Climates?

Most Canadian Cities and Businesses are located in Nordic Extremely Cold Climate areas. Living in such a harsh climate requires significant resources to provide space heating as well as domestic hot water heating for buildings. This blog will explains why Vacuum Tube Solar Panels are the best...

hydrosolar.ca

Has a graph showing various thermal collectors. Evacuated tube ranges from 28% to 52%
So with best case of fluid temperatures it peaks at 150% or 2.5x efficiency of my nominal single-crystal silicon PV figure.

No loss to speak of converting electricity to heat. Some loss in MPPT, battery, inverter.
You can buy an (expensive) heat-pump water heater, which delivers heat > 100% of electric input. It steals the heat from the room air.

 

[chrisski]

Your 20% are an optimistic maximum under ideal conditions and 90° solar incidence. Most of the time they run far below that efficiency, especially under diffuse light.

To save me from doing the research myself, how efficient are these vacuum tubes?

 

[Hedges]

Your 20% are an optimistic maximum under ideal conditions and 90° solar incidence. Most of the time they run far below that efficiency, especially under diffuse light.

True.
How much light enters your evacuated tubes when it hits the glass off of 90 degree incidence?

 

[Hedges]

To save me from doing the research myself, how efficient are these vacuum tubes?

I'll save you the "research" (sorting google results), but not the reading.
There is a graph in the page I linked. You then need to consider fluid inlet temperature and flow rate.

 

[rin67630]

I think 50 X more efficient is said for effect. I was just trying to find out how efficient these evacuated tubes are. I’m sure that aside from the 20% efficiency of the solar panels, there’s a pretty huge loss of taking this electricity and converting it to heat, but now enough to make the 50 X efficiency that’s claimned. Anyway, that google research will come later.

I’m also wondering if these Tubes are used for the Canadian winters, I understand the vacuum tube not freezing, but how about the copper pipes between the tubes? Some pretty cold nights up there. The problem was overcome somehow because people are using these, I just don’t know how. FOr me, that’s google research for later.

I have experienced them on a sailing camp in late September. Whole day casted clouds and 16°C outside.
The 15 participants got each a hot shower without problem.

I do not know if the shower water flew directly into the tubes or if they used a transmission fluid with heat exchanger.

 

[rin67630]

True.
How much light enters your evacuated tubes when it hits the glass off of 90 degree incidence?

The reflectors are providing a very large band of incidence, more than 60° i guess.
Anyway also that tops solar electricity by lengths