Saturday, January 24, 2015

Electricity Generation and Off-grid for Low Energy Houses

I was recently involved in two low energy house projects and they were both on rural, undeveloped land.  In these cases, I always ask, is it cheaper to have on-site generation and storage, or is it cheaper to be grid-connected?  Actually, I even ask this question all the time in the city, every time I get my electricity bill - the delivery charges are frequently higher than the electricity charges.

So dimensions of the question go like this:
  1. It is often something like $10k to $20k to create a new grid connection for a rural property.  Wouldn't it be nice to put that money towards electricity storage or on-site generation/both?
  2.  Sometimes there is a microFIT project involved - so if we are going to sell solar electricity to the grid, then we need the grid connection anyways
  3. Electric vehicle - If we are going to have an electric vehicle, then we are no longer purchasing gasoline, but must instead supply additional electrical energy to our vehicles as well as our house - well, do the math and you'll probably find that net zero may often be practical for our houses, but net zero including our transportation? - that can be quite an additional load, depending on how much one travels, or plans to.  While the vehicle can act as a big battery for the onsite storage of electricity, everytime I look at vehicles storing energy for the house, I come up short - either for the house, or for the vehicle - so in terms of timing, this option has yet to prove viable.
  4. Microgrid stability - In one project, there is kind of a significant computer activity in the house.  This owner is looking seriously at back-up generation, but one also needs a transition system - like a battery bank or an ultracapacitor bank  - basically a UPS that gives the generator the few seconds needed to come online in a black-out.  This house is also in a valley, so the back-up generator will be perfect to run pumps for flood protection - Even though we are in a big city, power outages frequently come when there are big rains.
    If we need back-up-generation AND the grid connection is costly, why not forego the grid connection altogether?
  5. Finances:  In one instance, the bank decided what to do, rather than the buyer of the land - The bank's position was this:  Build all services - septic, water, and grid connection, or we won't lend you the money to buy the land. - Sheesh!  They must not have heard of solar PV!  
This question always fascinates me - I get to go out looking for off-grid technologies.  So today I came across this on Gizmag: - the power pallet.  This is a machine which eats biomass, and makes heat and electricity, and it is smallish - relative to many biomass machines.  it produces about 20kW, and costs about $30,000.  Kind of attractive if a grid connection costs $15k and  back-up generator $10k.


  1. The attraction will be user-specific, akin to the attraction of a hobby. Especially if your situation demands a backup generator ($15k). Given the need, why would you be spared the requirement for a spare just because you installed a biomass machine? Are biomass machines so fail-safe?

  2. That should have been $10k back-up generator... If that is the need then the cost comparison is $40k (30 + 10) plus ongoing maintenance and feeding, versus $25k (15 +10).

  3. A passivhaus or passive house is low energy home constructed by eco refurbishments in London with quality construction techniques and rigorous designs.

  4. I assume this problem is now solved by Tesla power wall :-)