Wednesday, November 25, 2009

Our New Grid-Tied PV System -- First Sun

The new PV system we have been working on putting in is up and running.  There are many pages of detail and a hundred or so pictures that go through the whole planning, design and installation process in mind numbing detail here...
Sections on performance and economics of the system are also included.


The system is a 2150 watt grid-tied system.  It uses the new micro-inverter approach from Enpahse -- so, each PV panel gets its own small grid-tie inverter.

The panels are ground mounted with our own mounting racks. 

We did the whole installation ourselves, and I've tried to include enough detail to be helpful to anyone who wants to install a PV system of their own.  I've tried to cover not only the details of the component installs and wiring, but also the stuff like deciding on what kind of system, locating the panels, doing a solar site survey, and going through the permiting and net metering process.  It should be enough reading to put you to sleep for a week of nights.


It was a technically interesting and fun project -- not having any previous experience with solar electric stuff, I learned a lot. 
But, the economics are also interesting.  Basically, the system cost was right near $10K or $4.65 a watt -- after rebates this gets down to $6.5K and $3 per watt.  Better than what I was expecting.  The $ saving per year if you pay 10cents a KWH would be $300, or about a 5% return on the $6,500 -- tax free and energy price inflation protected.
Not so bad, but when you compare our PV to well thought out conservation/efficiency projects, or to DIY solar heating projects its comes out a very very distant 2nd -- some examples in the Economics section.

I've fallen behind in getting other projects that people have sent in up, but now that the PV is done, I plan to catch up right after Thanksgiving -- so, keep the projects coming in!


Sunday, November 15, 2009

Heat Pump Water Heaters

I added a couple new entries in the Heat Pump Water Heater Section

The first is a Tom Gocze video that describes installing a Geyser Heat Pump Water Heater -- a good video -- informative and funny in places.  Tom is a long time friend of Build-It-Solar and has contributed a lot of helpful information.  He does some radio and TV work in Maine, so if you are in place where you can get these, they are very good.  Tom knows renewable  energy well, and has a good, practical approach to energy matters.


Heat pumps in general remove heat from one place and "pump" (transfer) it to another place.  For the heat pump water heater, the heat is removed from the household air and transferred to the water in the water heater tank.  The efficiency of the whole process is about 200% (that is they have a Coefficient of Performance (COP) of about 2).  This compares to a regular hot water heater which has a heating efficiency of nearly 100%.  In addition, during the summer they have the added benefit that they provide some free air conditioning -- that is, they cool and dehumidify the household air some. 

The cost of the units are around $700 to $1400.  Some of them (but not all) qualify for the 30% federal tax rebate, and some states may also offer some incentives.

On the down side the cool air they provide, which is a plus in the summer becomes a negative in the winter.  In the winter the cooled air has to be heated back up by your space heating system, and this is a cost.  It seems to me that in effect it will reduce the efficincy back to about what a regular electric water heat is for the winter.  
This paper on a Building America demonstration home shows a way to hook up the heat pump water heater in such a way that in the summer, the cooling air is used to cool the kitchen area, but in the winter the ducts are switched around so that the heat pump air is taken from the crawl space and does not cool the house air (or at least not as much).  This seems like a worthwhile improvement, but does complicate the installation.

Does anyone have any ideas on a winter hookup that would not steal warm air from the house?  Seems like there ought to be a way to do this?

From a carbon emissions point of view, I get these numbers -- the
- Regular electric water heater:  1.5 lbs CO2 per KWH heat out
- Heat pump water heater: 0.75 lbs CO2 per KWH heat out (COP of 2)
- Regular NG gas (EF0.65):  0.75 lbs CO2 per KWH heat out
- Tankless NG gas water heater (EF0.85): 0.6 lbs CO2 per KWH heat out

So, they are substantially better than a straight electric water heater, about the same as a conventional gas water heater, and not quite as good as a tankless gas heater.
These numbers are based on the 1.5 lbs of CO2 per 1 KWH of electric power (the US grid average), and 0.5 lbs of CO2 per 1 KWH of heat output from NG.


Friday, November 13, 2009

New Idea for Heating Domestic Water

Energy Alternatives has come up with a new design for heating domestic water.  Their design pipes water/antifreeze through several PEX pipes that are suspended in the attic ridge roof vent. 

The water heated by the PEX tubing is passed through a heat exchanger coil in a domestic water preheat tank.  The domestic water is preheated in this tank before it goes on to the regular water heating tank.

No real data is given on performance, and I suspect that for many climates, this is a three season heater at best, but it does offer an interesting alternative to solar, and it keeps the external look of the roof unchanged.

One article suggests that the cost of a 40 ft section of the PEX ridge vent assembly might be around $300, and that a full kit including the preheat tank with heat exchanger might be about $3100.

Here are some thoughts about DIY implementation of the ridge vent design that could (I think) be done for less than $1000 -- maybe substantially less.

Thanks very much to Chris for finding this and suggesting it!


Thursday, November 12, 2009

Heat from Composting Biomass

I've been collecting material on the idea of extracting heat from compost piles and adding it to this section...

At first, this was a "that's kind of interesting" idea to me, but it has become more and more of a "that might really work" sort of idea.

Basically these schemes (there are several shown) start with a carefully constructed, large pile of biomass.  The biomass heats up as it goes through the composting process.  Pipes running through the pile pick up heat which can be used for domestic water heating and/or space heating.  Some schemes simultaneously collect bio-gas, which can be used for cooking fuel or even running a vehicle or generator.

Marc's compost furnace under construction.

A lot of work was done on this in the 70's by Jean Pain in France.  The section has some good descriptions of Pain's work, including two newly added videos (thanks to Curbie for these).

Marc's compost furnace work is very interesting, and includes some results from his first winter of operation.

The MB-Soft work in this area is interesting, if a little hard to decipher.

The New Alchemy papers are also quite good.

The attraction of this approach to me is that it holds the promise of a carbon neutral way of generating useful amounts of heat over long periods of time.  Some of the Pain piles are said to have been still generating useful heat after 18 months.  It is quite a bit of work to build one of the structured compost piles and set up the heat extraction plumbing, but then you may be able to get useful heating from the pile for an entire heating season.
The efficiency is claimed to be of the same order as burning the biomass -- maybe even a little better.  In many cases, the biomass can be material that would just be left to rot in place.

Does anyone have more useful information on this area?
Any thoughts on how useful and idea this might be?


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