Sunday, April 05, 2009

First Look at Ecopower Operation

It has almost been a year now since the generator was installed in the basement, and there are more data points to analyze than there is time to do it. The photo shows the engine from the side view. First let's review the motivation for buying this thing and then see how it has performed.

The decision to purchase the co-gen unit goes back to late 2006 shortly after the geothermal was installed. Geothermal is a great heating device, but the power usage is high. In New England, geothermal peak power is in the winter, and if everyone went to geothermal for cooling, the power peak would be in the winter instead of in the summer as it is now. That is pretty much true across the USA, although it gets hard to use geothermal for cooling in the deep south due to the high ground temperature. I'm digressing.

The concern was the large power requirements and dependence upon the grid for heating needs. Given a choice, I'd choose the domestic power grid over heating oil supplied by foreign providers who don't seem to care for us, which is why we went to geothermal in the first place. The geothermal unit sizing still required second-stage heating, and moving from heating oil to propane (natural gas is not available at our house still) was a better choice, and with a co generation unit, I'd get both heat and power and a fuel source that is about 70% domestic instead of about 70% foreign.

So, why not more solar. Definitely, more solar would be better, but the largest problem with solar, aside from the cost which is becoming less and less of an issue, is its intermittent nature. Solar power has a fixed generation schedule with frequent interruptions. These interruptions are difficult to forecast as the behavior of clouds is rather hard to predict. The other difficult problem is that these solar outages can extend for a couple of days, so there is some need for something other than solar (or lots of power and heat storage) to help smooth out the rather jagged production.

The other reason is the gross inefficiency of the electric grid. With close to 70% of the energy lost as waste heat, there is good reason to be generating power close to where heat is required, and residential heat is a large fossil fuel consumer, so generating power at the residential level has the potential of recapturing the heat lost in power production. In terms of cost, it is a trade-off between building a small number of large-scale power plants that are 30-50% efficient versus a larger number of small-scale generators that are 95%+ efficient. Historically, the large-scale system has dominated for a variety of reasons, not all of them rational, but with the semiconductor revolution of the 1980s, it is my opinion that the micro-generation paradigm is more efficient, potentially cost-advantageous, and definitely better in terms of energy security.

The following figure shows the amount of generated daily power from June, 2008 through March, 2009. The big gap in October is due to a computer outage, so daily Ecopower files that are normally available were not saved.

Notice in the figure there are three main periods. When the system was started, it was put in a maximum power generation mode. The amount of power generated was limited by how fast the heat could be dissipated. No system was installed to dissipate excess heat other than losses from the water tank, because it was not really cost-effective to do so (I may be changing my mind on that). Starting in late July, in an effort to reduce operating costs, we switched it to water heating and second-stage space heating mode only, so the Ecopower only ran when hot water (or second-stage house heat) was needed, and the average daily power was reduced as a result. It ran in this mode until the end of 2008.

At the beginning of 2009, the unit was switched to first-stage heat. The problem with this mode is that the generator is not sized to the heating needs of the house. It comes at a maximum 5KW power generation capability, and to meet the standard design criteria for house heating needs, it would have to be 2-3 times larger than it is. When thinking about the size of generator I wanted, 5KW seemed to be about the right size to match up the with geothermal needs and about what I'd want for backup power in case it was necessary. An important point is that with a co-generation unit, one still wants a second stage heating source for the very cold days. Otherwise, the unit required will be way too large for the local power needs.

Two points after 2009 are worth mentioning. The drop shortly after the New Year was a result of a discovered propane leak, so we shut off the Ecopower until it was fixed. The second one at the end of February was over a vacation and the house heating needs were dramatically reduced. The rest of the variability is mainly explained by changing temperatures and the required heating needs.

Currently, I think 5KW is too much given our plans and our current other equipment, but for now, it is still too little to heat the house by itself. We found this out shortly after switching to the cogen unit running by itself with no geothermal heating, for it was not enough to keep up with the heating load, and the house slowly became colder. For the colder days, I've come up with a compromise which is to put part of the house onto geothermal and part on co generation. This happens when the average daily outside temperature is near freezing or colder as seen in the next graph.

In this graph, we plot the average daily power generation versus outside temperature (which is recorded every 15 minutes by a thermometer outside the house and read by the Ecopower computer). Each dot represents one day. Remember that zero degrees Celsius is 32 degrees Fahrenheit. Only the days from August, 2008 are included. The important features are (1) the lower boundary where the Ecopower is used for hot water and 2nd stage heating needs, (2) the upper boundary where the limit is the 4.7KW power capability, and (3) the sloping boundary on the upper right where the Ecopower is used as first-stage heating. Above 15C (60 degrees Fahrenheit), there is no space heating need and the Ecopower is used only to make hot water. For the points in between the 3 boundaries, the heating was a combination of Ecopower and geothermal.

There have been a few issues with operation, but that will have to be discussed in another post. Bottom line is that most of the issues have been resolved, and the Ecopower is now running well and represents yet another step down for us in terms of fossil fuel usage and another step in the direction of energy security.

The next question is how best to operate the generator by itself and/or with the geothermal. This is not an easy question to answer, and it is one of the problems I'm working on now.



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