Hot water from Solar PV (resistance heated)

Xringer · 01-10-10, 01:47 PM

The government has studied this idea for years and have come to the
conclusion that it will be possible for home-owners, when PV is at $1-a-watt.

I've been thinking about the fact that I'm using #2 heating oil for hot water.
And if oil prices shoot up a lot.?. The $1-a-watt conclusion might be somewhat off the mark. (At least for me).
Maybe $2 a watt is workable?

If you included 35 years of maintenance cost, I'll bet that the typical Solar Hot-water system (coolant in panels)
would cost approximately the same (per BTU) as a PVHW (with no moving parts), IF you could find PV for $2 a watt.

The biggest negative with PVHW is the larger size of the array.
So, you would only go with PVHW if space was abundant.

PV array sizing would be based on your hot water usage.
In my case, hot water is a side benefit of using oil heat in the winter.
And the winter in MA isn't the best for solar anyways.
But, in the summer, we get lots of good solar, and we only need a little
oil to heat hot water for showers etc.

I checked out this dealer(importer?) and they told me that I could come by their NY location and pick up panels.
(Did not get any price info yet).
Cosmos Solar Energy

A pair of 210 watt panels would produce 1433 BTU (best case conditions)
which would provide a nice supplement to our oil-fired boiler.
Especially if the boiler heat-loss was less than 1433 BTU..

So, any PVHW project has to begin by eliminating boiler heat-loss in a big way.

Daox · 01-11-10, 05:48 AM

Interesting. Keep us updated.

Xringer · 01-11-10, 09:23 AM

The thing that worries me about PVHW, is my location in MA..
In the lower 48, the only place worse than here is Tacoma Washington!

Maybe I should move back home to west Texas..

Edit:
Wait a second! Maybe it's not so bad here after all.. Just need a better map..

Why does the south shore of MA look like south Key West??
Is somebody doctoring the data again?

wyatt · 01-11-10, 10:12 AM

I would guess you could home-build a solar hot water heater for way less than the cost of PV. I toured a house in Wisconsin that had a custom-one-off system that worked great. There were three panels on the roof, clear glass on top, black felt on bottom. It ran air through them and into the bottom of a gas water heater. The air would go up through the water heater and heat the water. They just had a small blower running the whole system, and it would stop blowing once the water temp got to a user defined temp, and start again below a certain temp. We were there in the dead of winter, the blower was not running, and water temp was 115degF (at about 2pm).

AC_Hacker · 01-11-10, 12:15 PM

Quote:

Originally Posted by Xringer

The government has studied this idea for years and have come to the
conclusion that it will be possible for home-owners, when PV is at $1-a-watt.

I've been thinking about the fact that I'm using #2 heating oil for hot water.
And if oil prices shoot up a lot.?. The $1-a-watt conclusion might be somewhat off the mark. (At least for me).
Maybe $2 a watt is workable?

If you included 35 years of maintenance cost, I'll bet that the typical Solar Hot-water system (coolant in panels)
would cost approximately the same (per BTU) as a PVHW (with no moving parts), IF you could find PV for $2 a watt.

The biggest negative with PVHW is the larger size of the array.
So, you would only go with PVHW if space was abundant.

PV array sizing would be based on your hot water usage.
In my case, hot water is a side benefit of using oil heat in the winter.
And the winter in MA isn't the best for solar anyways.
But, in the summer, we get lots of good solar, and we only need a little
oil to heat hot water for showers etc.

I checked out this dealer(importer?) and they told me that I could come by their NY location and pick up panels.
(Did not get any price info yet).
Cosmos Solar Energy

A pair of 210 watt panels would produce 1433 BTU (best case conditions)
which would provide a nice supplement to our oil-fired boiler.
Especially if the boiler heat-loss was less than 1433 BTU..

So, any PVHW project has to begin by eliminating boiler heat-loss in a big way.

As I recall, heating water in a flat plate collector is about 30% efficient, and using evecuated tubes is about 40% efficient. Producing electricity is about 15% efficient.

This would seem to favor direct heating of water in panels. The panels are cheaper per square foot, and you would only need about half as much area as with PV.

As an additional bonus, you can find used HW panels in your area on Craig's List for little or nothing. I got ten panels for $600 total, from C/L.

If you looked at it on a year-round basis, both types of panels produce maximum water or electricity during the sunnier summer months. If your HW panels are producing more hot water than you need, you can't sell the exccess to a power company, but you could possibly store the exccess in a reservoir of water or rocks or earth.

With commercial energy, if you are using energy you don't need, you are wasting it, with solar and wind energy, if you are not using the energy, you are wasting it, big difference.

I have heard of people with solar & wind using resistance heated water heating as a cheap way to capture otherwise lost energy.

Using a heat pump would capture more.

Regards,

-AC_HAcker

%%%%%

NeilBlanchard · 01-11-10, 05:52 PM

Hi,

The new vacuum tube solar heat collectors are about 80% efficient -- I don't think you can beat this or even come close, with solar PV --> electricity --> hot water.

Xringer · 01-11-10, 09:06 PM

IF I could buy 450 watts of PV for 900 bucks,
and IF, 1,535 BTU could actually do the job of keeping my boiler warm enough (during the summer) to keep from burning oil..
(To make up for ordinary heat loss, plus a few BTU), I'm not seeing that as too costly.

Considering the life span of the panels (and zero maintenance cost),
together with the always increasing price of #2 heating oil,
break-even might occur within 10 or 15 years..

The Thermomax Evacuated Tubes and Manifold Kit for about $3,000
after you add in a few odds-and-ends for installing.. Seems high..
Solar Water Heat. Thermomax Solar Water Heating Solar Collectors with Mazdon Manifold Kit. Thermomax Solar Hot Water System.

Regular hot water panels aren't cheap either..
Stiebel Eltron Solar Panels for Solar Water Heating, Solar Radiant Heat, Solar Indirect Storage Hot Water Tank

But, putting efficiency aside (as hard as that may be), if PVHW works and it doesn't cost an arm & leg,
what would be the problem?

People who live off-grid use resistance hot water heaters all the time.
Granted they are doing it as a last resort, but it works. It helps them
make hot water.

One thing I find interesting about PVHW is that it's easy to upgrade.
If I wanted more BTU, I could add more PV or better insulation on
the water storage, the feed pipes etc..
It would be pretty easy to improve output.

I don't want to set the world on fire, I just want a warm shower

(Without hearing the oil burner running too much).

Anyways, if someone can point me to a $1,000 solar assist hot water system,
I'll be happy to look at it before making any buying decisions.

AC_Hacker · 01-15-10, 12:55 AM

Quote:

Originally Posted by NeilBlanchard

Hi,

The new vacuum tube solar heat collectors are about 80% efficient -- I don't think you can beat this or even come close, with solar PV --> electricity --> hot water.

About 80% efficient, I think that's remarkable.

What is your source for this information?

Regards,

-AC_Hacker

AC_Hacker · 01-15-10, 01:04 AM

Quote:

Originally Posted by Xringer

Anyways, if someone can point me to a $1,000 solar assist hot water system,
I'll be happy to look at it before making any buying decisions.

* * * Cheap Solar HW Panels for Sale, $75 each * * *

Regards,

-AC_Hacker

%%%%%%%

NeilBlanchard · 01-15-10, 06:46 AM

I saw some at the Build Boston show in November, and that is the number the person in the booth mentioned. I have also heard from any number of sources that solar heat collectors are far more efficient than solar PV -- because PV only uses a small portion of the spectrum, and the mechanism is not as effective. These new (near) vacuum tube systems work very well because virtually all the light enters the tube, and most of the heat that is created (infrared) is kept in because of the vacuum. The heatpipes are efficient because they have a state change material inside. I'm sure that the greatest inefficiency is in the heat exchanger at the top of the tube.

The parabolic solar heat collectors are also very efficient, but they have to do vertical tracking.

01-10-10, 01:47 PM	#1
Xringer Lex Parsimoniae Join Date: Feb 2009 Location: Woburn, MA Posts: 4,918 Thanks: 114 Thanked 250 Times in 230 Posts	Hot water from Solar PV (resistance heated) The government has studied this idea for years and have come to the conclusion that it will be possible for home-owners, when PV is at $1-a-watt. I've been thinking about the fact that I'm using #2 heating oil for hot water. And if oil prices shoot up a lot.?. The $1-a-watt conclusion might be somewhat off the mark. (At least for me). Maybe $2 a watt is workable? If you included 35 years of maintenance cost, I'll bet that the typical Solar Hot-water system (coolant in panels) would cost approximately the same (per BTU) as a PVHW (with no moving parts), IF you could find PV for $2 a watt. The biggest negative with PVHW is the larger size of the array. So, you would only go with PVHW if space was abundant. PV array sizing would be based on your hot water usage. In my case, hot water is a side benefit of using oil heat in the winter. And the winter in MA isn't the best for solar anyways. But, in the summer, we get lots of good solar, and we only need a little oil to heat hot water for showers etc. I checked out this dealer(importer?) and they told me that I could come by their NY location and pick up panels. (Did not get any price info yet). Cosmos Solar Energy A pair of 210 watt panels would produce 1433 BTU (best case conditions) which would provide a nice supplement to our oil-fired boiler. Especially if the boiler heat-loss was less than 1433 BTU.. So, any PVHW project has to begin by eliminating boiler heat-loss in a big way.

01-11-10, 09:23 AM	#3
Xringer Lex Parsimoniae Join Date: Feb 2009 Location: Woburn, MA Posts: 4,918 Thanks: 114 Thanked 250 Times in 230 Posts	The thing that worries me about PVHW, is my location in MA.. In the lower 48, the only place worse than here is Tacoma Washington! Maybe I should move back home to west Texas.. Edit: Wait a second! Maybe it's not so bad here after all.. Just need a better map.. Why does the south shore of MA look like south Key West?? Is somebody doctoring the data again? Last edited by Xringer; 01-11-10 at 10:50 PM..

01-11-10, 05:48 AM	#2
Daox Administrator Join Date: Aug 2008 Location: Germantown, WI Posts: 5,525 Thanks: 1,162 Thanked 374 Times in 305 Posts	Interesting. Keep us updated. __________________ Current project - To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. & To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

01-11-10, 10:12 AM	#4
wyatt Helper EcoRenovator Join Date: Jan 2009 Posts: 75 Thanks: 3 Thanked 1 Time in 1 Post	I would guess you could home-build a solar hot water heater for way less than the cost of PV. I toured a house in Wisconsin that had a custom-one-off system that worked great. There were three panels on the roof, clear glass on top, black felt on bottom. It ran air through them and into the bottom of a gas water heater. The air would go up through the water heater and heat the water. They just had a small blower running the whole system, and it would stop blowing once the water temp got to a user defined temp, and start again below a certain temp. We were there in the dead of winter, the blower was not running, and water temp was 115degF (at about 2pm).

01-11-10, 05:52 PM	#6
NeilBlanchard Journeyman EcoRenovator Join Date: Dec 2009 Location: Maynard, MA Eaarth Posts: 383 Thanks: 78 Thanked 39 Times in 32 Posts	Hi, The new vacuum tube solar heat collectors are about 80% efficient -- I don't think you can beat this or even come close, with solar PV --> electricity --> hot water.

01-11-10, 09:06 PM	#7
Xringer Lex Parsimoniae Join Date: Feb 2009 Location: Woburn, MA Posts: 4,918 Thanks: 114 Thanked 250 Times in 230 Posts	IF I could buy 450 watts of PV for 900 bucks, and IF, 1,535 BTU could actually do the job of keeping my boiler warm enough (during the summer) to keep from burning oil.. (To make up for ordinary heat loss, plus a few BTU), I'm not seeing that as too costly. Considering the life span of the panels (and zero maintenance cost), together with the always increasing price of #2 heating oil, break-even might occur within 10 or 15 years.. The Thermomax Evacuated Tubes and Manifold Kit for about $3,000 after you add in a few odds-and-ends for installing.. Seems high.. Solar Water Heat. Thermomax Solar Water Heating Solar Collectors with Mazdon Manifold Kit. Thermomax Solar Hot Water System. Regular hot water panels aren't cheap either.. Stiebel Eltron Solar Panels for Solar Water Heating, Solar Radiant Heat, Solar Indirect Storage Hot Water Tank But, putting efficiency aside (as hard as that may be), if PVHW works and it doesn't cost an arm & leg, what would be the problem? People who live off-grid use resistance hot water heaters all the time. Granted they are doing it as a last resort, but it works. It helps them make hot water. One thing I find interesting about PVHW is that it's easy to upgrade. If I wanted more BTU, I could add more PV or better insulation on the water storage, the feed pipes etc.. It would be pretty easy to improve output. I don't want to set the world on fire, I just want a warm shower (Without hearing the oil burner running too much). Anyways, if someone can point me to a $1,000 solar assist hot water system, I'll be happy to look at it before making any buying decisions.

01-15-10, 06:46 AM	#10
NeilBlanchard Journeyman EcoRenovator Join Date: Dec 2009 Location: Maynard, MA Eaarth Posts: 383 Thanks: 78 Thanked 39 Times in 32 Posts	I saw some at the Build Boston show in November, and that is the number the person in the booth mentioned. I have also heard from any number of sources that solar heat collectors are far more efficient than solar PV -- because PV only uses a small portion of the spectrum, and the mechanism is not as effective. These new (near) vacuum tube systems work very well because virtually all the light enters the tube, and most of the heat that is created (infrared) is kept in because of the vacuum. The heatpipes are efficient because they have a state change material inside. I'm sure that the greatest inefficiency is in the heat exchanger at the top of the tube. The parabolic solar heat collectors are also very efficient, but they have to do vertical tracking.