Solar Hot Water / Heating...

BB. · April 2006

Now that I have filled the roof of my home with 3kW (peak) of solar electric panels (I have broken about even in kWh during fall/winter--summer should be way positive for that electric car--when that comes...), what are your experiences regarding solar hot water for domestic hot water and space heating?

I have looked around and read about the various types of systems, and I have seen many installed locally... However, many of the local installations seem to have been disconnected and/or disused after more than a few years. The failures I have seen include leaks, clouding up, freeze damage, and a complexity of operation/maintenance/settings that owners (and subsequent owners) just don't seem to put up with.

In theory, a solar hot water system (upwards of 90-96% collection efficiency in some designs) is more efficient than a solar electric panel system (~15-18% collection) so--the size the panels can be much smaller for the same amount of "heat". And, hopefully, cost less to buy/install.

So, I live in the city (just south of SF CA, grid electrical and natural gas), not much "good" roof space left for sun, and I don't want a large tank/plumbing nightmare (home is relatively small, new building is expensive and planning/permits are a pain in the butt). We have a soft freeze every few years.

I have done a pretty good job of conservation (pulled lath and plaster walls to insulate, operating skylight in middle of home for light/ventilation, double pane windows, new energy star appliances, CPFL everywhere, new furnace--only 80%--should have done better at the time).

So, the last part of my in-home energy budget is the natural gas bill of $25-$65 / month (summer/winter).

I liked the design of the http://solarthermal.com "Mazdon" collectors (heat pipes w/ glass, copper, and vacuum construction). I am thinking I can scrap my current gas hot water heater and replace it with a closed loop heat storage tank and a backup gas tankless water heater (for cold days).

I have used a tankless water heater before (in-law's home overseas) and find it does work OK... But a tank of hot water is certainly nicer to shower with.

One thing that I missed during the remodel was Brock's brilliant idea of placing one of those waste water heat recovery pipes in the shower drain (and connect it to the shower's cold water inlet). I have seen those before, but I could not think of a good place to install one of those in my house that made sense (until reading Brock's post here).

So, what are your suggestions and experiences around Solar Hot Water?

Thanks,
-Bill

crewzer · April 2006

Re: Solar Hot Water / Heating...

Bill,

I'll sure be interested in the responses to your post. I'm looking to start building a new home later this year, and, while I think I have a good handle on the PV part of the design, I'm just starting to consider the solar water heater design. One site to research, if you haven't already done so, is Home Power (www.homepower.com). My recollection is that they've published numerous articles on solar water heating.

Good luck, and I'm looking forward to comments from others.

Regards,
Jim / crewzer

halfcrazy · April 2006

Re: Solar Hot Water / Heating...

we are off grid with close to 2 kw array of pv. so we went after the hot water panels i looked and looked but couldnt bring myself to spend the money so we made ours. we used a wooden frame and 2 inch foil faced foam. them soldered up copper manifolds 3/4 headers and 1/2 runners 4 inches on center then used the aluminum fins that are made for radiant floor and snapped them onto the tubing and painted it all black we then covered the wood with aluminum coil stock made for house trim and fixed a sliding glass door panel. we have 4 without the radiant flanges and 2 with for 6 panels and here in maine we get our 45 gallon water tank to 165F and get about 3 hours of heat in the radiant slab in the house. if any one is interested here is a link to a diary i made on otherpower www.fieldlines.com/story/2006/4/9/14621/53240

niel · April 2006

Re: Solar Hot Water / Heating...

along this line i've only experimented with it and i did make a small setup out of half inch copper pipes. what i did was i thought the best way to efficiently heat the water in the pipe was to slow the water down so that it could absorb the solar radiation better. i accomplished this by using a copper t and then from that t those outputs of the first t so that you now have four 1/2in copper pipes instead of one. the water flowing through will go at 1/4 the speed as the main 1/2in copper feed pipe. doing this one more time would have been even better, but i stopped at the 4 pipes. of course this was all painted flat black and was recombined back to an output 1/2in pipe. seemed to work ok, but i never fully instituted it because of it being a direct water heating method and that doesn't work well in pittsburgh in the winter. it may be ok in your part of california though.
always give yourself the option through good valves of bypassing or draining the system in an area protected from harm to the piping.

BB. · April 2006

Re: Solar Hot Water / Heating...

Niel and Half,

Years ago (before wife and kids), I probably would have tried to build my own too... But it just does not seem to be in the cards for me now. :-(

Half,

Looks like a neat job you did... Are you going back to do a little "panel surgery" and add the missing radiant flanges to those four units? The sliding door panels are a neat idea--wonder how good they are at passing the IR? Obviously, they are working well for you.

Crewzer,

I have read the on-line version of home power a few times over the last few years... That is, part, of why I went with the Grid Tie system for my home. The other part that made it "economical" for my grid tie system was the constant drum beat of conservation in Home Power Mag. I will never get to the low numbers that they recommended oh those many years ago for solar power (less than 100 kWh/month)--but it was nice to have a goal for conservation (I did hit under 200 kWh/month quite a few times though).

I know that our gas usage is not that high relative to our neighbors (we are always under baseline--except for this last rainy/cold March/April when the summer baseline kicked in while it was still "winter" for us)--but it is nice to be a little bit competitive (even if they don't know you are "competing" with them).

-Bill

halfcrazy · April 2006

Re: Solar Hot Water / Heating...

Bill yeah we are going to build 4 new ones and change them out this summer then over the winter i will repair the 4 and make two more so we will have 12 if i have done the calculations with 12 i should be able to heat the house most of the year here in maine maybe 2-3 months in the dead of winter i will need to assist them with the wood boiler. it seems like 3 of these would make our hot water needs for our family of 4 about 45 gallons a day. we put the original 4 up in febuary here in maine and they would almost completely make the tank of water just fell a little short but i feel that was the missing radiant panels.

BB. · April 2006

Re: Solar Hot Water / Heating...

By the way, Home Power has a free article reprint up that talks about salvaged hot water panels and what to look for... In it they talk about the good and bad construction materials and some of the brands (again, the good and not so good). Nice summary of what worked and failed over time.

A couple of interesting things that I did not think about--anti-freeze starts to break down at 280F and they recommend Fiberglass bats or other foam (polyisocyanurate/Thermax) that withstands upwards of 300F. Same warnings about the type of Caulk/etc. used...

http://www.homepower.com/files/featured/112_68.pdf

They also have a nice description of solar hot water systems and their various strengths and weaknesses.

http://www.homepower.com/files/beginner/SolarHotWaterBasics.pdf

-Bill

BB. · May 2006

Re: Solar Hot Water / Heating...

The following is a stream-of-thought as I am looking at solar hot water... Please feel free to comment on anything that I have missed or should look at differently. It isn't perfect but does show the decisions that I am trying to weigh as I go through the evaluation process.

Well, I see that the first link about Used Solar Panels has been taken down--probably have to subscribe to Home Power to get the back issue PDF file...

But, after cruising through the web (and not even really looking at any hard prices), I have come to the following conclusion/concerns:

I was looking to keep the size of the tanks small and getting rid of my current 50 gallon gas water heater (probably 8+ years old) as inside my garage I don't have a lot of free space (if I wish to park cars there).

But, any solar hot water system is going to need, roughly, 20 gallons of storage per user--for me, 4 people is 80+gallons. One manufacturer recommended 1.5 to 2 gallons per sq. foot of solar collector (a 4x10 foot unit would require, again roughly 80 gallons of storage). So--realistically, I am looking at 2-3x more hot water storage vs my current gas domestic hot water heater. So now, I would need to look at alternative tanks and/or outside tanks/heat exchangers (not great, but an OK possibility).

So, panel wise, I like some of the features of the vacuum insulated glass with heat pipe collectors (should not overheat because of thermal cutoff, can repair/replace individual glass/heat pipe collector if damaged--There is also a possibility of loss of vacuum failures, which were more common on older installations???, but no real information about current failure rates)--but realistically, my outside air temperature is not low enough to really need their type of insulation--and it is possible that a standard flat panel collector of equal size will out perform (at probably lower costs) than the vacuum/heat pipe collector.

Next question is the type of water storage tank... It seems that tanks with internal heat exchangers are becoming more of a thing of the past and what is becoming more popular is a system with an external, double walled heat exchanger (to prevent a leak of anti-freeze back into the domestic water system). So, the "standard tanks" are typically, more or less, standard electric water heater tanks which can help keep costs down, and even use an electric element for make-up hot water heating. There are also options where you get hot water at the top of the tank, or where the whole tank is heated (a tank full of 90F water instead of a 1/3 tank of 110F water).

And the question of open loop, closed loop, and freeze protection… I would like to compare real costs, but in terms of service life—I would probably tend to go with a closed loop / anti-freeze type system to have a very low maintenance system—no scaling; no drain back complexity, use lower powered recirculation pumps (kind of a pain given the few hard freezes we have here).

So, comes the issue of make-up hot water heating... Electric or Gas. I currently have excess electricity available (maybe 10+ kWh/day May-September) and with Net Metering/Time of Use billing from my utility, I might be able to juggle the numbers to justify using electricity for, some or much, my make-up heating. However, with the way home energy is priced in the US over the last ~30 years (thanks to Pres. Carter), there is a huge penalty for going much over baseline energy usage. I am not sure that I want to weekly (or maybe even daily) track and adjust my electricity/gas-backup energy mix. I am sure that it can be done--but I would need to instrument everything, plus forecast the weather, to avoid any nasty surprises... Which violates one of my goals of having a, relatively, use and forget hot water system. Plus, I would like to use Electricity for a car in the next couple of years as, to me; this is a better use of electricity I am generating.

So, I don't want to use electricity, then I would use gas. And, if I am trying to get rid of, or at least reduce, my hot water storage tanks (costs and room in the garage), then I looked at a tankless hot water heater.

Bosch/Aquastar has a new tankless hot water heater that can supply 2 major uses (~5 gallons per minute) of hot water. Looking at using a tankless water heater then gets into if it can boost solar hot water or not--turns out, that many (if not all) gas tankless water heaters only can support a minimum flow (0.5 gallons to 0.8 gallons per minute) or they turn off. So, Bosch does have a unit that has a 0.5 GPM minimum flow rate, but can take any input temperature (but only ~2.5-3+ GPM max flow or one major use). And, it has a standing pilot light (thereby reducing it energy factor back down towards a standard high-eff tanked gas water heater)...

Ok, now I start reading about tankless hot water heaters. I have used one for a few weeks over seas, so I do now that they work, but they are a bit of a pain in the butt to balance water temperature. So, I read around for some reviews (like the big Bosch unit) and found people that like them and those that do not. Those that don't like them complain that it needs 0.8 GPM minimum flow (like many other tankless water heaters), takes the better part of a gallon of water for the unit to heat up, every time you turn off a faucet, it takes another gallon of water before it turns on and heats up again--so you are either left leaving the tap on--wasting hot water or getting a jolt of hot/cold/hot water every time you cycle the hot water. Not the best situation if you are trying to save water during the droughts we sometimes have here.

Also, because they use about 2-3x the amount of natural gas (or propane), I would need to redo the exhaust stack (and on the big unit, install a fresh air feed too), plus I would have to install 20' of 1" or larger gas pipe from the meter to the water heater. Also, a few people have complained about the noise of these units. And lastly, with the higher complexity of some of these units, you may be down for, at least, a few days waiting for replacement parts.

Now, I am looking at the expenses of installing Solar Hot Water heating with 80-120 gallons of water tanks (and still keeping my current gas hot water heater for winter/high use periods), or using an electric make-up (worried about e-bills even with solar PV), or installing a tankless hot water heater (more complexity, more installation costs), or scraping the solar panels and storage tanks (don't have roof space, so I would need to tack on overhang on the house--probably looks ugly), and use gas tankless water heater but with questionable energy cost savings, huge installation costs (possible $300 rebate on some tankless and/or solar hot water system) and the issues of a small simple unit or a larger complex unit just a failure away from a week or more of no hot water (plus Bosch may be changing their repair policies that I would have to pay a plumber to do warranty repairs--more costs and loss of time to repair)...

I am thinking--Forget the Solar, forget the tankless water heaters. Too much money for parts, installation, service issues, long time to repair (if needed). I don't use that much hot water and probably, at best would only save $10-$20 per month (at current gas rates) and I am not quite ready to drop $3,000 or more to see if even those savings would be real. Plus, I would either have to keep my old, tanked gas water heater (and its losses), or drop another couple thousands of dollars to install a good sized tankless water heater.

Now, I look at the tanked water heaters. A.O. Smith has a couple of interesting ones:

First is a fan forced air condensing 50 gallon unit that is 90% efficient (better than tankless) and has 1/3 the standby heat loss (of those units that I could find numbers for) of other natural gas hot water heaters). Looks very interesting, but if a standard 50 gas water heater costs a bit less than $400 (parts, not installed), how much does this one cost (plus piping and flue changes). Also, needs AC power for hot water during a power failure (not a huge problem--but is something to think about).

Other efficient tanked units from AO Smith look OK--but, as always, they don't publish the same numbers for both models (no energy factor for the condensing water heater), so it is very hard to compare standby losses (US Gov uses energy factor to account for burner eff. and standby loss--I think). Their energy factors are around 0.63 which is not much less than a tankless water heater with a pilot light (around 0.69 for the Bosch Solar Assist model).

A.O. Smith Residential Water Heater page:
http://www.hotwater.com/products/residential/gas.html

GAMA ratings of some residential gas water heaters (PDF):
http://www.gamanet.org/gama/inforesources.nsf/vAttachmentLaunch/BD9C57BA8477D8E185256E9000606CD0/$FILE/4-06-gas-cwh.pdf

Unless things change dramatically somewhere—I am currently leaning towards just replacing my current tanked gas water heater with another one. Possibly look at the Condensing Type and see how much they cost.

Lastly, if I were to choose a Solar or even a condensing type hot water system, when to install… Wait until the hot water heater fails and take two or more weeks to find a contractor, parts, time, permits or try to install ahead of time and convince wife that replacing our perfectly good water heater with something that costs 3x-10x our current water heater to save $15 a month is a great deal…. Hmmmmm.

Oh well---the search continues...

-Bill

Brock · May 2006

Re: Solar Hot Water / Heating...

Do you have a basement? We just got a water to water heat exchanger. It is all copper, 5 feet tall and 3 inches in diameter with copper wrapped around the outside. What you do is put this in your drain line and run all the cold water through it. I am completely amazed at how much heat this recovers, we can run the shower for an hour straight (2 adults and 3 kids all in a row) and it never drops temp on a 40 gallon 40,000 btu natural gas heater. It raises our well water from 52F to 75F, so the water going in to the heater is at 75F and the cold water on the shower is also at 75F so you don't need to add as much "hot" to get it to the correct temp. Actually when I take a shower (water just barely on) the heater might never come on or if it does will warm up and cycle off.

http://gfxtechnology.com/

We did have an electric demand water heater and that low flow really bugged me since the rate at which I had the shower running wouldn't kick it on and once set if someone used water someplace else the temp would drop and then spike again, not to fun.

If I had to do it again I would get a 20-30ish gallon well insulated 40k BTU unit.

System2 · May 2006

Re: Solar Hot Water / Heating...

i installed (literally , with some help on the gas) a tankless a couple yrs ago, works great. is saving us gas but with a corresponding increase in gas prices i cant really see that in the bill. around here people say solar hot water clearly pays for itself and can make hot water even on a overcast day with new technology. i am a victim of hype though, and have no data other than hearsay. i didnt read this whole thread sorry if im repeating

niel · May 2006

Re: Solar Hot Water / Heating...

brock,
i do have a basement and i thought about your idea with the waste water heat recovery, but i'd have a problem with implementing it here because the waste water pipe is vented to the outside air by law. on winter days there will be more cold air in that pipe than warm waste water that would pass through so i don't see the feasability with it cooling more often than heating the water. the only way i see it to be feasable would be to put an s or p trap on that 8in black pipe to isolate it from the outside air. oops i forgot it's vented just before the curb too so there's no way. there is a p trap prior to the street to prevent the main sewerline from gassing us out. :roll: how did you get around that or isn't yours vented?

BB. · May 2006

Re: Solar Hot Water / Heating...

Hi Brock,

No, I don't have a basement... Homes around here (near SF, CA) rarely have basements (plus, I have a high water table).

I know that you are in an area that gets pretty cold, so any bit of energy you save can help a lot. I saw your post on the coiled cold water/shower drain heat recovery device and I thought that was a great place to put it...

I did some work on my home last year, including redoing the bathroom and that would have been the time to install the device. I did see the web site for the copper coiled unit (not cheap)--but was thinking about how much of a pain it would be to route back to the cold water inlet on the water heater and figured it would not be worth it--I just kick myself for not thinking of installing it on the cold side of the shower faucet--a stroke of brilliance by you.

Mattl,

From what I have read, unless you are making really hot water (or are in a very cold climate), the "standard" glazed & insulated flat plate collector should produce about as well (if not slightly better).

In our area, about 30+ years ago (during the first oil shocks) people came around our area to sell passive solar hot water systems (the ones with the tank at the top of the collector). And they sold these to folks that lived on the coast (where I was born and raised) where we get 5-7 days of fog/overcast a week. I always associated the "solar" folks with con-artists from that point on...

I now live a few miles inland and have a reasonable number of nice sunny days. However, my home has a smallish roof that I chose to cover with solar PV panels last year... I don't have any really good places to install one or two 4'x10' collectors (that is close to my hot water/plumbing and has good sun--I would just have to cantilever them off the edge of my 2nd floor roof), and because my garage is already small enough that adding additional water heater/storage tanks is also less than ideal for me.

I am kind of with you Mattl, I am not sure that spending a lot of money to hang an ugly pair of panels off the side of my home is going to be acceptable (at least, until natural gas is 10x what the price is now).

Solar Hot Water should be still be an OK deal--but it appears not to be for me at this time. The lack of a good looking sunny panel mounting location for my home, plus the lack of space that I would want to dedicate to hot water storage probably points me towards just getting a very efficient natural gas tanked hot water heater.

If I wanted to use my excess solar PV panel capacity (tied in with my Time Of Use electric metering) probably would let me install a small(sh) electric instant hot water heater on the inlet to my normal gas hot water heater. Just a little plumbing and wiring, plus a timer (to only allow it to run during off-peak hours). However, the drawback is that I have "budgeted" the extra electricity for some sort of electric vehicle (I hope) in the next few years--and I would then just have to turn off the electric pre-heat for my water heater--waste of money to install the electric pre-heat in the first place.

Has anyone seen a gas water heater that also included an electric heating element so I could do both without a lot of added costs? I have seen solar hot water system tanks with an option for an electric backup heater...

According to this link:

http://www.gamanet.org/gama/inforesources.nsf/vAttachmentLaunch/BD9C57BA8477D8E185256E9000606CD0/$FILE/4-06-gas-cwh.pdf

Many of the gas water heaters lose around 1,000 BTU/Hour whereas the most efficient gas water heater can be down in the 250 BTU/Hour range.

It seems:

$ of gas = $1.65/Therm * Therm/100,000 BTU * 24 h/day * 30 day/month * 250 BTU/Hr

$ of gas/month= $2.97 per month for standby losses for a 250 BTU/Hr heater

$ of gas/month = $11.88 for a 1,000 BTU/Hr heater (average thermal loss for other brands)

Or, I would be saving about $9 / month or about $1,080 bucks over ten years to install a well insulated (low standby) tanked water heater. I would save another $360 over 10 years if I went tankless... The $1.65 / Therm price was my historical peak (for last winter). Now it is around $1.25, and has averaged under a $1 per therm.

My old gas water heater is rated at 263 therms/year or about $36 per month (at $1.65 / therm... I would guess that this is roughly correct). So, about 1/3 of my money appears to be just keeping the tank warm.

Now, how much does a Polaris 34 or 50 gallon hot water heater cost? These units are also intended for hydroponic heating--so they have pretty high input BTUs (130-150,000 BTU vs 40-50,000 BTU for an average tanked water heater). So, I am guessing that the Polaris units are not going to be cheap (and way over kill for hot water for the average home).

There is an AO Smith 50 gallon gas water heater that only has 70,000 BTU input and 364 BTU/Hr heat loss...

There are not a lot of options for condensing type domestic hot water heaters. I guess that if they spend that kind of money for a water heater, they want something extra (like space heating and/or high recovery rates for commercial use) to justify the cost.

Not a solar solution yet (at least, for me)... Now to find out how much one of those babies costs.

-Bill

System2 · May 2006

Re: Solar Hot Water / Heating...

i just read the thread and a few of your points on tankless , you can get one with no pilot (mine is the smaller hydro electric start: starts up from the water pressure itself) , they do not use 2-3times (overall) the gas (thats the whole point and why they are widely ised for over a decade in europe), i did not need a larger gasline or exhaust,

re: time to heat up, it is slightly, and i mean slightly, longer than it takes to run the cold out of the pipes with a tank. its all copper heat exchanger and gets real hot real quick. the overall savings of having no standbye heating/pilot for the 95% of the time we dont need hot water is a clear advantage.

in general they take getting used to though as you say, and yes, i was down once for almost 2 days waiting for parts.(partly because the plumber was a moron) id see if you have any authrorized service centers for the bosch in your area, you might! i do but they didnt call back.

pressure is sometimes an issue in certain faucets, my lowflo showerhead still works though.

BB. · May 2006

Re: Solar Hot Water / Heating...

Hi Matt,

When I typed about a tankless using more gas--I was talking about instantaneous gas requirement--not gas used over time.

Yes the tankless heaters are very efficient (use less money to heat a gallon of water). However, because there is no tank, the heater needs to supply the entire amount of hot water volume required (typically a few gallons per minute). So, where a tanked 40-50 gallon water heater uses ~40-50,000 BTU/Hr gas flame, a tankless heater, a tankless heater will require 100,000-200,000 BTU/Hr (or 2x to 4x the amount of gas per hour). This can require a, new, larger gas line and a new/larger vent than you would normally have available for a tanked water heater (depends on existing installation--you don't have to change the gas line, but it will limit the amount of hot water/gpm that the heater can put out). And, a large tankless unit may need a second external vent line to bring in combustion air too... All adding to the costs and complexity of changing from a tanked to tankless water heater.

Also, may need special venting (such as stainless steel) because the low temperatures may condense water in the existing flue--causing rust or your brick chimney to be attacked by the acidic water... All of these are issues for my, older, home.

Regarding the "problems" that I read about--the delayed hot water and hot/cold/hot problems were reported for Bosch/AquaStar's new 250sx unit that can output around 5 gallons per minute of hot water (2x the smaller unit capacity). I did not read about or experience that issue with the older simple (and smaller) mechanical tankless water heater overseas...

I hate to pay somewhere around $1,500 to $2,000 to run my own experiment. At this point, if I get a new condensing hot water heater, it appears that it will only use around $2-$3 a month (at $1.65/therm) for standby heating losses--and it is somewhat more efficient than the tankless water heater in heating the water... Of course, I would have many of the same installation issues with a new condensing water heater too (need a new PVC/Plastic flue, possible make-up air vent to outside, and possibly larger gas line than I have now because of the larger burner--of the several brands I have seen so far)... And the condensing heaters have electronics and a fan--more points that can fail--just like a tankless heater...

If I can't figureout where to install a solar panel on my home (that does not look like a poorly done installation), I am tending towards a new condensing tank style water heater (at least, until I find the price for one those puppies) as the couple of bucks a month for heat loss is not too bad (even if the rates double again).

-Bill

System2 · May 2006

Re: Solar Hot Water / Heating...

i have the little one: one major task and 2 mionor heating tasks, works completely fine for us. it was only about $700, i have this one:
http://www.popularmechanics.com/home_improvement/smart_consumer/1274946.html

BB. · May 2006

Re: Solar Hot Water / Heating...

I thought about that one too... Not too expensive, smaller than my current tanked heater and no standby losses.

We don't really use much hot water either (mostly just the one low-flow shower and the standard kitchen/bath sinks and a Fisher & Paykel washer that uses very little hot water).

Perhaps, I will try that and see if the family adjust... That size and function of unit is what my wife grew up with in Taiwan so she may already be OK with that.

From reading about the 250sx, It sounds like the typical issue of throwing too much hardware/software at a problem and missing some basic customer preception issues (never happens with real-life engineering/marketing :-P ).

-Bill

Brock · May 2006

Re: Solar Hot Water / Heating...

Niel, yes ours is vented to outside. But since it is in the basement and the vent is three stories up not much cold air get all the way down there. The thing is no water is running through the outside part unless water is running through the drain. So unless I am taking a shower the water is just sitting in the tubing. I suppose it potentially could cool the ½ gallon or so below 52F, but the extra heat I gain on just one shower would more then offset the smaller amount of heat I lost because of the venting.

One of the other ideas I have been toying with is an un-insulated tank that the well water would sit in first, just to let it come up to room temp. This of course would only help in summer or when you need cooling and again depending on incoming water temp might not help much.

Bill, fortunately my main drain passes within a foot of the water heater and cold lines to the bathroom and water heater so plumbing was relatively easy, but in my sister-in-laws house the main drain is at the opposite end of their home from the incoming water so it would really bea pain to plumb.

Bill as I am also on time of use I did exactly what you thought of after my disappointment with the smaller inline electric water heater. I just plumbed it in front of the water heater and had it only run off peak. Right now natural gas is cheaper then off peak so I don’t electrically pre-heat water, but last summer off peak was about 25% cheaper then natural gas. Check
http://www.hearth.com/articles/47_0_1_0_M7.html
to see which is cheaper for you.

I am still with you though; a tank less unit verses a good condensing tank version, the standby losses are a small portion of the actual gas used. While the actual efficiency of heating the water will likely play a larger role in the overall consumption of gas.

I blame you for making me think of getting a better water heater

niel · May 2006

Re: Solar Hot Water / Heating...

brock,
mine is the same way right down to the number of stories to the house except that there's plenty of cold air going through mine to the vent located lower in altitude before the street.

Brock · May 2006

Re: Solar Hot Water / Heating...

I am confused, (nothing new) you have the normal vent in the roof and another one lower? Mine just connects on the lower end to the sewer lateral so I don't think I would get a lot of air flow though it, but if you have two "outlets" then I would imagine more air would be likely to move through it.

niel · May 2006

Re: Solar Hot Water / Heating...

brock,
you're getting the picture right. if you were to follow the sewer line from the street it goes under my sidewalk and starts up towards the house.(house is on a semi-steep slope) it passes through a p trap and then there's a vent. from there it continues into the house and upward. one segment actually goes into the back where there's a drain so it can have airflow from that too as the pipe is leaking out the water from that p trap. the stack is the 8in black abs and has a large vent for that, but it also has a few smaller branch vents from the kitchen and bathroom areas that were put in too. that inspector really liked venting. :roll: i did some of this work and some was the plumber as the whole stack was replaced going up through the house. the sewer line was partially replaced outside the house and that was lots of fun for me as i was the one who dug down 7ft at one end and about 3ft on the other. i did the majority here too with the plumber doing where it was to connect to the section going into the street. i would have done it all myself, but that's another nightmare story i try to forget.

Frank · May 2006

Re: Solar Hot Water / Heating...

BB: another strategy is to use a preheat system. Not sure if you're off-grid but if you have excess PV you can install a DC heating element in a 40-50 gal. tank and use that to preheat water going to your regular heating setup. If you install solar hot-water that can also be used to preheat. There's various ways to make it work. You can use a small stand-alone PV panel to drive a DC pump (we use an El Cid) to circulate a glycol solution and that runs through a tube-in-tube heat exchanger that operates on thermosiphon principle.

BB. · May 2006

Re: Solar Hot Water / Heating...

Good Morning Frank,

Yes, during the summer I have about 10 kWhrs of excess capacity per day of solar--And during the winter, because I am Grid-Tied/Time of Use/and Net Metered, I even have a few 10's of dollars if extra cash too (even with lightly using a couple of portable space heaters). And because my net metering is over one year, I can move my summer peak into winter too.

However, I got the extra capcity to power an EV and some AC (eventually), so I did not really want to spend the extra bucks and power on heating the water. Because I don't have a lot of extra free space to throw an extra water tank for temporay use, I even thought of installing an (small/undersized) electric in-line tankless water heater (I have natural gas here) that I would manually turn on when I had excess power/money on my bill. Anyone know of if a smaller tanked or tankless water heater (like for a sink), can be placed in the main hot water line (for a home with single low-flow shower) without too much pressure drop from high water flow? It might be worth the $200 for a sink-type electric heater to do this even short term (it will probably be a few years before a nice urban electric family car is available again).

As for the AC, it would be just a small room unit--but I added wall/floor insulation, double pane windows, operating skylight, CPF lights, energy star appliances, ceiling fans in bedrooms, etc.--and, so far, found that the home has been much better in hot weather then the years past--so, either I probably won't need the AC, or global warming has really cooled our weather here.

-Bill

Brock · May 2006

Re: Solar Hot Water / Heating...

Bill for something like that the cheapest way to go might be to just add a 2.5-10 gallon 120v electric water heater in front of the gas one. If you have extra power it will heat up the water to temp and if your drawing water it will continue to heat it. But once the small tank is up to temp it will just shut off. The advantage is it will heat the small tank no matter if your drawing water or not and could be used later. You could do the same thing with a 20 or even 40 gallon tank, it would just take up a lot more room.

System2 · May 2006

Re: Solar Hot Water / Heating...

fwiw the aquastar had no probs with my lowflo shopwerhead until the filter got clogged from the working on city water pipes, easy to clkean the filter. not sure its the best thing, with your extra power id go electric too especially if tankless. i wonder how many kwh's you'll need for the ev and what your driving habits are.

BB. · May 2006

Re: Solar Hot Water / Heating...

The EV would be around 0.5 to 0.333 kWHrs per mile. I do a lot of around town driving (kids) so an EV with a solid 20+ mile range is OK. I have Time of Use metered power, so charging outside the noon-6pm weekdays saves me money. There is the issue that if you go over baseline here (around 300kWhrs per month), they really start cranking up the kWhr costs (from $0.08 per kWhr to $0.21-$0.31 per kWr--if you have to charge during the day in the summer, and you are over 900 kWhr/month, you are in the $0.51 per kWhr--running a Honda generator is cheaper). During the summer, I have around 200 kWhrs a month to "burn". During the winter, it is less (Net Metering here allows me to bank for a 1 year period--Oct-Sept. for me).

Don't have the EV yet, going tankless (or small tank) electric is a good place to put the excess Solar PV generation for now--but I would like to go solar hot water and not worry about watching the bill so that I end up at $0.00 in the utility bank at the end of the year (or have to pay high penalties).

I bounce around on the gas tankless hot water--but that does use gas and the solar would conserve resources (and get the utility more out of my pocket).

I would have to probably install the Electric Pre-Heat for several years before I would get my money back--not sure when (or if) the EV cars will be around sooner than that.

I looked at the GEM EV (25 mph max)--it seems to be one of the more capable units out there, but by the time you add doors (winter), taxes and such, you are at $10,000+ for a $#&% 25 MPH 30 MILE RANGE GLORIFIED GOLF CART.

http://www.gemcar.com/asp/e4.asp

I have 500' to 1,000' hills to climb in my daily (once or twice per day) around town use (2 mile grades). Has anyone any experience with the GEM like EV cars on what happens to their range while driving around hilly country?

-Bill

System2 · May 2006

Re: Solar Hot Water / Heating...

"The EV would be around 0.5 to 0.333 kWHrs per mile."

What is the kwh consumption when you turn on the heating in the winter or air conditioner in the summer and/or the headlights on at night and what does the range decrease to in those situations? /s At $3.00 per gallon and 30 mpg, a dino fueled vehicle's fuel cost is $.10 per mile. At the high end of your time of day metering you could be paying (using your numbers) .5 kwh/mile X $.51kwh = $.255 per mile.

To put it in perspective, a PV system with (30) 100 watt panels at a 75% overall efficiency with 4 hours average daily insolation = 3000 X .75 X 4 = 9kwh / .5kw per mile = 18 miles per day. Using the commonly quoted $10 per watt installed cost, that PV system would cost $30,000 to drive 18 miles per day. Ouch.

Cheers,

Bad Apple

BB. · May 2006

Re: Solar Hot Water / Heating...

The "GEM" type vehicle is around 0.333 kW/mile (if I remember correctly--the RAV 4ev is around 0.400 kWh/mile--depending on who is driving).

30 miles is about 10 kWatts. With solar, during the summer with a 3 kWhr Grid-Tie system, I am generating about 16 kWhrs (month of May average) and using 8 kWhrs or less... Leaving me 8 kWhrs per day. Also, during the week, part of that energy is being credited at $0.09 per kWhr off-peak, and $0.29 per kWhr peak (Mon-Frid, noon to six--call it 6kWhr*5 days = 30 kWhr * 0.29/0.09 = 96 kWhrs pk credit for off-peak charging vs 30 plus the 5*8 + 2*16 = 72 kWhr/week = 168 kWhrs per week total off-peak credit that I would be getting if flat rate charging). Month of April I got a 26.88 credit to use anytime between October 2005 and September 2006 (my current credit through April is $61). And I have not spared the electric use--probably several hundred "extra" kWhrs were used during winter for space heating a couple of rooms and dehudifying inplace of running my gas heater more.

My 3kW system generated about 500 kWhrs during May, and 134 kWhrs during January (really wet/cloudy winter for use, plus I have some tree shading in winter). If I paid my "normal" electic bill of ~$26 per month, the system would:

generate around 4wk*168kWhr/week (May) = 672 kWhrs Using Time of Use / Pk generating/off-peak charging
or 2,000 miles a month (May)
for the GEM (0.333 kWhr/mile) or 65 miles per day (30.5 days per month).
My system has 20x 175 watt BP 4175 modules (3,500 watts marketing rated numbers).
December (very bad month) = 134 kWhrs => 13.2 miles per day (no time of use--just raw power--winter spread is not much anyway)

My system cost per kWhr, after rebates, and assuming that I used every watt generated over 30 year life (yes, retail price before rebate was ~$29k) is about $0.14 per kWhr.

25 mpg city driving car @3.20 per gallon = $0.128 per mile
.333 kWhr/m 4 passenger GEM @ $0.14/kWhr = 0.04662 per mile

Realistically, you could argue that with some service (replace inverter once) and such, $0.17 per kWhr. Interest on money lost, not all power used, etc.--call it 2 x $0.14 = $0.28 per kWhr => ~$0.09 / mile for the GEM.

Off-peak charging costs me $0.09 per kWhr => $0.03 per mile (solar panels keep me from hitting above base rate (home use + charging car) charges with PG&E which does get in the $0.17 to $0.30 per kWhr if I did not have solar and needed to run my home and charge a car too.

If you want to see what a guy who really loves the EV does over time... You can visit:

http://darelldd.com/ev

He has a RAV 4ev and used to have the GM EV1... The Rav 4ev has AC and heat--the AC is not that much of a load (couple Kwatts per hour?) when you look at the RAV 4v and a 40kWattHr battery pack (if I recall correctly--just giving rough numbers here--look up later if interested in details). Yes, you can't go quite as far with lights, heat, AC and such, but it is only in the 10% loss on trips, not 50% loss (at freeway speeds, you can only go about 2 hours anyway). Just sitting in the driveway, you can run the AC for something like 20 hours before needing to recharge the battery pack.

Still not convinced I want to spend $10k for a special purpose vehicle when I can spend about twice as much for a Prius that can take me anywhere--A plug-in Prius with 10-20 mile electric only range--that would be interesting....

-Bill

Brock · May 2006

Re: Solar Hot Water / Heating...

I am so with you Bill! Darell told me at SHOT that Toyota is working on a plug in Prius. Their target date was 2008, but who knows if they will really make one or not.

Bad Apple good observations, my off peak rates are .0488 and I would be willing to bet I could push a RAV4 to .25 kw per mile ($.0125/mile) , but even assuming .5 kw / mile at $.05 that is still $.025 per mile and I think anyone would be hard pressed to get a ICE to really get 30mpg city or $.10 a mile But you are correct if electricity gets above $.2 to $.25 range gasoline is cheaper strictly talking $ spent. Then again as gas goes up so dose electricity and I would be willing to bet in a 100 years from now electricity will be far cheaper then gas, at least in the ratio it is in now. And to top it off I can't make my own gas no matter how hard I try, but I could generate my own electricity. Although I have made bio-diesel

for my VW diesel.

BB. · May 2006

Re: Solar Hot Water / Heating...

Electricity from a central power plant is actually not that efficient--Only, roughly, 1/4 of the heat burned in the fuel actually makes it through to your home (IIRC about 1/2 of the electricity is loss in distrbution). Looking at my power rates for E1 (normal residential rates... Baseline is around 300 kWhrs per month for a gas heat/hot water home):

http://www.pge.com/tariffs/pdf/E-1.pdf

Total Energy Rates ($ per kWh)

Baseline Usage $0.11430
101% - 130% of Baseline $0.12989
131% - 200% of Baseline $0.21981 (R)
201% - 300% of Baseline $0.30292 |
Over 300% of Baseline $0.34648 (R)

UNBUNDLING OF TOTAL RATES
Energy Rates by Component ($ per kWh)

Generation:
Baseline Usage $0.03614 (I)
101% - 130% of Baseline $0.04317 (I)
131% - 200% of Baseline $0.10701 (R)
201% - 300% of Baseline $0.16603 |
Over 300% of Baseline $0.19696 (R)

Distribution:**
Baseline Usage $0.04082 (R)
101% - 130% of Baseline $0.04938 |
131% - 200% of Baseline $0.07546 |
201% - 300% of Baseline $0.09955 |
Over 300% of Baseline $0.11218 (R)

Transmission* (all usage) $0.00879
Transmission Rate Adjustments* (all usage) ($0.00031)
Reliability Services* (all usage) $0.00293
Public Purpose Programs (all usage) $0.00703
Nuclear Decommissioning (all usage) $0.00038
Competition Transition Charges (all usage) $0.00462
Energy Cost Recovery Amount (all usage) $0.00437
Fixed Transition Amount (FTA)** (all usage) $0.00684
Rate Reduction Bond Memorandum Account (RRBMA)** (all usage) ($0.00216)
DWR Bond (all usage) $0.00485

Boy, I sure don't like the use more, progressively pay more type billing... Like going to CostCo (or Sam's Club), purchasing in bulk and paying 3x as much as going to the corner market. Can't tell what the "real cost" of any thing is...

-Bill

Brock · May 2006

Re: Solar Hot Water / Heating...

Wow, 300kw per month seems low to me. I would imagine most people are well above baseline.

I agree that overall load should have nothing to do with cost. I can understand peak loading, say you use 500kw at one time because it would cost them more to beef up lines overall. And I can understand time of use, it cost them more to buy or generate power at 4pm on a hot sunny summer day. But to pay a higher rate just because you use more? Seem like everything is cheaper in bulk, not the other way around, hummm, is there something I am missing?

BB. · May 2006

Re: Solar Hot Water / Heating...

Yes,

You are missing the years of Jimmy Carter as president trying to reduce energy consumption... That is when this all got started. In the "olden days", even for home use, your charges per kWhr were moderately reduced as your usage went up.

Remember, our temperature here is probably 40-80 F through the whole year--and most people here heat with gas (baselines associated with that too).

http://www.weather.com/weather/wxclimatology/monthly/graph/94403

Not like where you live--remember, "they" are trying to force everyone into baseline. I can make baseline electricity very easy, baseline gas is a bit harder for me.

-Bill

Solar Hot Water / Heating...

Comments

Categories