Dump the plumbing and use PV to heat water?

Xringer · 12-29-09, 01:48 PM

This simple technology (DC heating of water using PV panels)
has been tested for a few years by the government.
BFRL: Solar Photovoltaic Hot Water System

And now that PV panels are available for under one dollar a watt,

http://ecorenovator.org/forum/solar-....html#post5341

it just might be cheaper to skip all the plumbing hardware and just wire some PV to a heating element in your HW tank.?.

I'm trying to get some of those cheap panels to try my hand at making some hot water.
I'm going to start with 4 panels, into a 75 ohm resistor, making about 240 watts of heat for my 76 gallon hot water storage.

240 watts per hour = 819 BTUh. Five hours of good sun, could mean 1.2 kWh or 4094 BTUh dumped into the tank daily.

I'm not sure how much that would help keep the oil burner from coming on,
but if the heat-loss is close to 819 BTUh, it could keep the tank coasting during the sunny part of the day at least.

I like the idea of cutting out the middle-man inverter (and/or battery) losses.

And the idea of just using a 75 ohm resistor and some PV panels is very attractive to the purist in me.

Years ago, I had a good working solar hot water system working. 3 big Novan collectors on the roof, made lots of hot water!
But, after about 10 years, the plumbing starting going. The city water supply eats copper. And loves tanks and heat exchangers.
The system worked well for about 15 years and was removed after a few years of collecting dust. A new tank and exchanger
was too costly and I knew we would be needing roof shingles again before too long.

If my guess is right, a PV driven hot water system, could last 30 years and still be working. Plus, it's going to be very low maintenance, if the parts count is kept low.
Less things to go wrong, the longer they last.

Piwoslaw · 12-29-09, 02:12 PM

What about efficiency?
Just the PV's are 10%-15% efficient, plus resistor efficiency.
I'm guessing that solar hot water systems can be 30% efficient (BIG ?).
On one hand, I'm an efficiency buff, on the other, there are other things to consider...

Xringer · 12-29-09, 03:21 PM

The efficiency is in the long term cost, IF you can get the cheap panels.

An it appears the day of the cheap panel isn't here yet..

I just got off the phone with the dealer and it turns out that Solar Panels : Solar Panels Direct $1.74 per watt
is pulling a bait-n-switch with their shipping cost.

It was:

$58.80 USD 4 $235.20 USD
Shipping and handling $101.74 USD
Total $336.94 USD

And now, they want $240 for shipping. More than the price of the panels..

I think maybe I'll wait until they have $1-a-watt panels at Lowes..

Ryland · 12-30-09, 10:42 AM

This is why when I was talking to a solar hot water installer about heat pump water heaters he got worried, 550 watts to run the heat pump, they claim with the other elements it's around 5kwh per day... seems kind of high so with those specs you would need over a kw of pv, but compared to the cost of solar hot water panels, pumps, plumbing, fluid... and they still recommend having a back up for those, this the back up would be a switch.

gt390 · 07-25-13, 03:13 PM

Quote:

Originally Posted by Xringer

The efficiency is in the long term cost, IF you can get the cheap panels.

An it appears the day of the cheap panel isn't here yet..

I just got off the phone with the dealer and it turns out that Solar Panels : Solar Panels Direct $1.74 per watt
is pulling a bait-n-switch with their shipping cost.

It was:

$58.80 USD 4 $235.20 USD
Shipping and handling $101.74 USD
Total $336.94 USD

And now, they want $240 for shipping. More than the price of the panels..

I think maybe I'll wait until they have $1-a-watt panels at Lowes..

Thread got off topic, but I was just browsing around this thread and some others on build it solar. Noticed this for 95cent/watt solar panels. I have not looked into availability or shipping cost.
Home - American Solartechnics, LLC.

Xringer · 07-25-13, 06:10 PM

Quote:

Originally Posted by gt390

Thread got off topic, but I was just browsing around this thread and some others on build it solar. Noticed this for 95cent/watt solar panels. I have not looked into availability or shipping cost.
Home - American Solartechnics, LLC.

Yeah, somehow this thread lost it's way. 95 cents a watt sounds really good to me.
Plus, I'm only about 215 miles from the dealer in Maine. I could drive up there.
215 mi, 3 hours 36 mins on I-95 N. I could build a giant PV farm in my back yard!

I would never see the fry pan coming towards my noggin..

I just looked at Home Depot and found $1.36 per watt.
Grape Solar 235-Watt Polycrystalline PV Solar Panel-GS-P-235-Fab1 at The Home Depot
Lower than I expected to see..

PV prices are coming down into the DHW heating range.
My PV DHW stuff is still working surprisingly well, considering the way it's wired up.
Summer sun is keeping my A7 ASHP from getting much chance to run.

Today was rainy, so it should run after my shower this evening.. At least an hour.

Thanks for posting. I will alert my local buddies. One friend is getting ready
to retire up in Maine, and he might be very interested in some cheap PV.

Anyways, here's my current solar hotwater hack.. Currently using about 7 cents a day off the grid..

Daox · 12-30-09, 07:25 AM

Yikes, yeah... that'll get people excited over nothing. Too bad too.

Xringer · 12-30-09, 02:10 PM

A heat pump hot-water heater is the best way to go for my setup.
I can get hot water from my boiler during the winter months,
but don't like the waste of running the boiler in the summer..

A heat pump hot-water heater would cool and dehumidify my basement during the summer. And, from what I've read, they don't use a lot of kWh,
when compared to heating elements.

What would be idea, is a 24 volt DC heat pump hot-water heater! That would
work way better than PV into resistance.. But, it would cost much more
and be more prone to breakdown.

According to the government studies that I've skimmed, the break-even for resistance hot-water heaters is the $1-a-watt panel..
Without a low priced panel, it's just something that most folks would not go for.
Except those guys who buy a new Prius with the built in solar roof..

They have mandated PV hot water on new houses and large renovations, in many areas down in Australia.

"
Hot water systems
A typical 1kW solar photovoltaic hot water system avoids around 1200-1500kWh of grid
electricity per annum, contributing to around 20% of residential sector greenhouse gas
emissions (The Nous Group 2007).
The Federal Government is currently giving consideration to a proposal to impose a
nationwide ban on electric hot water systems (HWS) in new housing in all States from 2010,
and for replacement HWS from 2012. Some States have already introduced such a ban, with
South Australia placing a ban on electric HWS for both new homes and replacement units in
existing homes on 1 July 2008, although the bans are conditional. This ban does not however
apply to homes in remote areas, multi-unit dwellings or a unit replacing one which services
only a shed or pool.
A ban on electric HWS in Queensland (implemented 2006) currently applies only to new homes
and substantial alterations and additions. It will be extended to apply to replacement units
from 2010. The ban will initially be voluntary for those without access to reticulated gas.
The NSW Building Code places an effective ban on the use of electric HWS in new housing and
for alterations and additions requiring planning approval. It is difficult to reach the BASIX
planning requirements without installing a low emissions hot water system.
"
http://www.caf.gov.au/documents/Acce...PRSReport3.pdf

I guess they are doing more than just studying PVHW Down Under

NeilBlanchard · 12-30-09, 02:27 PM

Vacuum tube solar heat collectors can be as much as 80% efficient!

Solar Water Heaters: Solar Hot Water Heaters For Home, Commercial & Industrial Solar Water Heating

They are used all over China, in great numbers. The latest designs AFAICT are a glass tube with a copper heatpipe inside and a (near) vacuum in between them. The top of the heatpipe has contact with the water in the header.

If one of the tubes is broken, it can be unplugged and replaced.

Xringer · 12-30-09, 03:33 PM

If there is more efficient technology, I wonder why the Australian government is supporting PV HW ?

Maybe they think something with no moving parts will last longer.?.

12-29-09, 01:48 PM	#1
Xringer Lex Parsimoniae Join Date: Feb 2009 Location: Woburn, MA Posts: 4,918 Thanks: 114 Thanked 250 Times in 230 Posts	Dump the plumbing and use PV to heat water? This simple technology (DC heating of water using PV panels) has been tested for a few years by the government. BFRL: Solar Photovoltaic Hot Water System And now that PV panels are available for under one dollar a watt, http://ecorenovator.org/forum/solar-....html#post5341 it just might be cheaper to skip all the plumbing hardware and just wire some PV to a heating element in your HW tank.?. I'm trying to get some of those cheap panels to try my hand at making some hot water. I'm going to start with 4 panels, into a 75 ohm resistor, making about 240 watts of heat for my 76 gallon hot water storage. 240 watts per hour = 819 BTUh. Five hours of good sun, could mean 1.2 kWh or 4094 BTUh dumped into the tank daily. I'm not sure how much that would help keep the oil burner from coming on, but if the heat-loss is close to 819 BTUh, it could keep the tank coasting during the sunny part of the day at least. I like the idea of cutting out the middle-man inverter (and/or battery) losses. And the idea of just using a 75 ohm resistor and some PV panels is very attractive to the purist in me. Years ago, I had a good working solar hot water system working. 3 big Novan collectors on the roof, made lots of hot water! But, after about 10 years, the plumbing starting going. The city water supply eats copper. And loves tanks and heat exchangers. The system worked well for about 15 years and was removed after a few years of collecting dust. A new tank and exchanger was too costly and I knew we would be needing roof shingles again before too long. If my guess is right, a PV driven hot water system, could last 30 years and still be working. Plus, it's going to be very low maintenance, if the parts count is kept low. Less things to go wrong, the longer they last.

12-30-09, 07:25 AM	#7
Daox Administrator Join Date: Aug 2008 Location: Germantown, WI Posts: 5,525 Thanks: 1,162 Thanked 374 Times in 305 Posts	Yikes, yeah... that'll get people excited over nothing. Too bad too. __________________ 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.

12-29-09, 02:12 PM	#2
Piwoslaw Super Moderator Join Date: May 2009 Location: Warsaw, Poland Posts: 961 Thanks: 188 Thanked 110 Times in 86 Posts	What about efficiency? Just the PV's are 10%-15% efficient, plus resistor efficiency. I'm guessing that solar hot water systems can be 30% efficient (BIG ?). On one hand, I'm an efficiency buff, on the other, there are other things to consider...

12-29-09, 03:21 PM	#3
Xringer Lex Parsimoniae Join Date: Feb 2009 Location: Woburn, MA Posts: 4,918 Thanks: 114 Thanked 250 Times in 230 Posts	The efficiency is in the long term cost, IF you can get the cheap panels. An it appears the day of the cheap panel isn't here yet.. I just got off the phone with the dealer and it turns out that Solar Panels : Solar Panels Direct $1.74 per watt is pulling a bait-n-switch with their shipping cost. It was: $58.80 USD 4 $235.20 USD Shipping and handling $101.74 USD Total $336.94 USD And now, they want $240 for shipping. More than the price of the panels.. I think maybe I'll wait until they have $1-a-watt panels at Lowes..

12-30-09, 10:42 AM	#4
Ryland Master EcoRenovator Join Date: Mar 2009 Location: Western Wisconsin. Posts: 913 Thanks: 127 Thanked 82 Times in 71 Posts	This is why when I was talking to a solar hot water installer about heat pump water heaters he got worried, 550 watts to run the heat pump, they claim with the other elements it's around 5kwh per day... seems kind of high so with those specs you would need over a kw of pv, but compared to the cost of solar hot water panels, pumps, plumbing, fluid... and they still recommend having a back up for those, this the back up would be a switch.

12-30-09, 02:10 PM	#8
Xringer Lex Parsimoniae Join Date: Feb 2009 Location: Woburn, MA Posts: 4,918 Thanks: 114 Thanked 250 Times in 230 Posts	A heat pump hot-water heater is the best way to go for my setup. I can get hot water from my boiler during the winter months, but don't like the waste of running the boiler in the summer.. A heat pump hot-water heater would cool and dehumidify my basement during the summer. And, from what I've read, they don't use a lot of kWh, when compared to heating elements. What would be idea, is a 24 volt DC heat pump hot-water heater! That would work way better than PV into resistance.. But, it would cost much more and be more prone to breakdown. According to the government studies that I've skimmed, the break-even for resistance hot-water heaters is the $1-a-watt panel.. Without a low priced panel, it's just something that most folks would not go for. Except those guys who buy a new Prius with the built in solar roof.. They have mandated PV hot water on new houses and large renovations, in many areas down in Australia. " Hot water systems A typical 1kW solar photovoltaic hot water system avoids around 1200-1500kWh of grid electricity per annum, contributing to around 20% of residential sector greenhouse gas emissions (The Nous Group 2007). The Federal Government is currently giving consideration to a proposal to impose a nationwide ban on electric hot water systems (HWS) in new housing in all States from 2010, and for replacement HWS from 2012. Some States have already introduced such a ban, with South Australia placing a ban on electric HWS for both new homes and replacement units in existing homes on 1 July 2008, although the bans are conditional. This ban does not however apply to homes in remote areas, multi-unit dwellings or a unit replacing one which services only a shed or pool. A ban on electric HWS in Queensland (implemented 2006) currently applies only to new homes and substantial alterations and additions. It will be extended to apply to replacement units from 2010. The ban will initially be voluntary for those without access to reticulated gas. The NSW Building Code places an effective ban on the use of electric HWS in new housing and for alterations and additions requiring planning approval. It is difficult to reach the BASIX planning requirements without installing a low emissions hot water system. " http://www.caf.gov.au/documents/Acce...PRSReport3.pdf I guess they are doing more than just studying PVHW Down Under

12-30-09, 02:27 PM	#9
NeilBlanchard Journeyman EcoRenovator Join Date: Dec 2009 Location: Maynard, MA Eaarth Posts: 383 Thanks: 78 Thanked 39 Times in 32 Posts	Vacuum tube solar heat collectors can be as much as 80% efficient! Solar Water Heaters: Solar Hot Water Heaters For Home, Commercial & Industrial Solar Water Heating They are used all over China, in great numbers. The latest designs AFAICT are a glass tube with a copper heatpipe inside and a (near) vacuum in between them. The top of the heatpipe has contact with the water in the header. If one of the tubes is broken, it can be unplugged and replaced.

12-30-09, 03:33 PM	#10
Xringer Lex Parsimoniae Join Date: Feb 2009 Location: Woburn, MA Posts: 4,918 Thanks: 114 Thanked 250 Times in 230 Posts	If there is more efficient technology, I wonder why the Australian government is supporting PV HW ? Maybe they think something with no moving parts will last longer.?.