DIY Solar Energy Projects?

[ERD50]

As I mentioned in the weather thread, I'm always amazed that in the middle of our cold winter here in N IL, the surface of the south-facing siding on our house will be over 100F. Seems like we ought to be able to capture that heat.

samclem linked this article:

The $1000 Solar Water Heating System

and of course, I spent a good part of the day on the site instead of doing my taxes. I agree with samclem that there are some good aspects to the design (the 12 Gallon capacity PEX heat exchanger inside, near the standard water heater).

Like samclem says, though it is tempting to use this heat for the house, it probably makes better payback sense to heat water with it, as that is a year-round need. A few things that are de-motivating me though...

1) I analyzed my gas bill for a few summer months - after you subtract out the fixed costs, I only spend ~ $13-~19 per month on gas to heat our water. And I'm overdue for a replacement water heater, which will be slightly more efficient (and this is the lower cost, lower efficiency model, no premium for efficiency that I wouldn't need with the solar system anyhow).

2) That article mentions $1,000 cost, not including time. If I assume it provides 90% of my hot water needs, that is an over 7 year payback (assigning 4% opportunity cost to the $1,000). Not too bad really, on pure economic terms except...

3) you end up with a custom, somewhat 'tweaky' system. Who really knows how reliable this will be? Who is going to fix it if something goes wrong? Unless I'm there to do it, I can't imagine what a HVAC guy would charge. I imagine most of these guys are replacing parts on units they are familiar with - being faced with a system like this would surely throw them for a loop.

4) Resale value - I expect this would decrease the value of my house. I can't imagine that too many buyers would like the idea of a handmade 150 gallon tank in the crawlspace, a bunch of wiring, pumps and plumbing, and a big panel on the side of the house. All to save $15 a month?

5) While I think the article is on solid ground with their heat exchanger design (the PEX tube holds 12 gallons of domestic water, so it's OK if it takes some time for it to absorb the heat from the circulating solar heated water), I really wonder about the engineering of those solar panels. As samclem mentions, aluminum in contact with copper over the long run? And how do they determine the optimum pipe diameter, spacing, etc. If this isn't engineered properly, you are wasting money on this part of the unit. Maybe there is info elsewhere.

6) Freezing - the thing is a pretty good 'failsafe' design, but as samclem points out, a stuck relay could keep that pump going and allow things to freeze. A series relay on a timer so can only run during daylight hours would provide some added protection. One system used a solar PV panel to run the pump - that seems pretty good (cost?) - it can only run when the sun is shining.

Now, if this was sized to provide 90% domestic water heat in winter, there would be excess heat in the warm months. If that could be turned into electricity with a stirling engine, maybe it could all work out. More complications/cost.

To avoid all those issues - I'm more attracted to my original thoughts - just a hot air collector to warm the house. No liquids, fewer complications, but I'm not sure of the payback (only used part of the year), which I think would be OK if done on new construction.

$350 Solar Heating Thermosyphon Collector

Bottom line, I ought to just figure out how to conserve $15/month in utility costs. That would probably be far easier.

-ERD50

 

[Dimsumkid]

I can comment on item 5) aluminum over copper. My house in Chicago was built in 1941 and had hot water heat before I switched to forced air. They used a combination of radiators and convectors (think baseboard, but only 2 ft long and ran horizontally). These used the same combination of aluminum fins over the copper tube. I never saw any degrading of the copper when I removed the convectors after 55 years. I also had a baseboard heating unit that utilized the same concept. I found this link about convectors so you can get an idea:

Home and Garden | Add Hot Water Convector - Heating - Do It Yourself

 

[ERD50]

Maybe the copper to aluminum is OK, but outdoors in humidity/dew might be different story, I dunno.

I looked a little closer at the other more passive approach to heating the home with solar:

$350 Solar Heating Thermosyphon Collector

He calculates (I'm not exactly sure how), that he is getting 130,000 BTUs per sunny day from that 20x8 collector. It helps efficiency that he is heating a workshop from very cold (30-40F) temps up to 60-70F. In a home you would not have such a high thermal delta, so would get less efficiency from it.

But even if I'm generous, and figure 100,000 BTUs (one Therm) per day average (not all days are sunny either), I'm paying ~ $0.58 per therm for Nat Gas ( for round numbers, I'll assume it's a near wash between my furnace efficiency and the % of sunny days - that's probably also generous), so that would only save ~ $17/month, maybe $87/season? 4~5 year payback?

I just don't think I could get 20x8 of collector on my south facing walls that wouldn't get shade part of the day, and $350 seems cheap to me, there's a good amount of labor in that.

But again, in new construction the labor/materials wouldn't be that big an issue, these could replace the siding. I'd do it if I were building new and had a good south wall for it.

For comparison of other ways to save money - consider a furnace that costs $3,000 to buy and have installed. If you think about maintaining/repairing it to get a few more years use out of it, at around the 15 year point that is ~ $200 a year amortized, and you avoid the opportunity cost of tyeing up that $3000 (~ $120 at 4% long term). At $320/year, I'm Ok with an occasional repair to keep the furnace going another year or two. My blower motor seems slightly intermittent - got a replacement for $100, and a new draft inducer is about that. Assuming the heat exchanger doesn't go (can you DIY replace those?), it makes sense to put the money into it.

-ERD50

 

[samclem]

Yes, most of these DIY solar projects share some traits:
-- They have attractive payback periods only if your energy costs are high (e.g. you heat water or air with electricity or propane) and if you don't count the labor costs.
-- You'll have a one-off design that only one homebuyer in a thousand is going to want to mess with. They probably detract from the home's value.
-- The neighbors won't be happy. The projects generally don't look sleek.
-- Many (especially the ones that use liquid for heat transfer) have subtle engineering shortfalls that could considerably reduce their service life. It's up to the builder to find the glitches.

These projects could be fun for the person who enjoys tinkering. They probably make the most economic sense for rural houses where utilities are expensive, the neighbors don't see/care if you put up a panel somewhere, there's plenty of room around the house, and resale value won't be much affected because a person buying a rural property will expect some "unique features" and be more willing to go with it or rip it out without a thought.

The PV system Nords has built works out well because it's a hobby for him (scrounging for parts, engineering, installation, troubleshooting, etc) and because utility costs and govt incentives are high where he's located.

For the average suburbanite who doesn't want to tinker, conservation has a better payback with less hassle than these energy capture schemes. As energy costs climb, that might change, but to gain wide acceptance outside of the soldering-iron club, they'll have to be standardized, easy to install, and priced attractively.

 

[Tesaje]

From what I have read, the 2 most cost effective and efficient solar energy captures are water heating and passive solar heating. The south windows in my very non-solar house still significantly heat the rooms in the dead of winter on sunny days with below zero temps. A house designed for it works a lot better.

It seems that radiant floor systems with solar water heating can be very cost effective for new construction. A lot of tear out to retrofit that.

Methods to turn it into electricity have losses in efficiency just like petro fuel electricity systems do.

There are certainly a lot of use efficiencies to reduce power use that can be incorporated. My gas company charges a higher rate if I use less so that sucks. I replaced my old gas water heater with a high efficiency electric and noticed only $10 a month more. It was a better choice than replacing with a gas one.

 

[Dimsumkid]

I was wondering if this would be a good alternative to the posting from a week or two ago where the electric radiant floor heat for just the basement was costing them $500/mo in MN? I think it would be a great modification project for them. No monthly utility costs and can use the almost free heat.

 

[samclem]

I was wondering if this would be a good alternative to the posting from a week or two ago where the electric radiant floor heat for just the basement was costing them $500/mo in MN? I think it would be a great modification project for them. No monthly utility costs and can use the almost free heat.

I don't think we ever figured out the root problem with that installation, but we thought maybe there was no insulation under the slab. It would take a lot of collector area to make up for that heat loss.

 

[Dimsumkid]

I don't think we ever figured out the root problem with that installation, but we thought maybe there was no insulation under the slab. It would take a lot of collector area to make up for that heat loss.

I don't think we ever did hear back on it. Just thought for $500/mo, scrap the electrical cost, switch over to solar only,lay it on top of the basement floor with insulation. Even get a professionally installed solar unit should cost less than 1-2 years of added electrical use of the current system in there. At the very least, you'll get heat in the basement while the sun is powering vs. nothing at all.