I would really like to have backup power at my house, but I'm not currently willing to pay $10k to install a propane fueled generator that would then require $4/gal propane to run it. It turns out that gets pretty expensive pretty quickly. What to do instead?
Alternatives to the Grid
Off the top of my head, I think the following could be alternatives:
- Backup generator
- Large-scale battery storage system
- Solar system
- Wind system
- Combined wind/solar system
- A big hole (Potential energy conversion system)
Let's explore each in turn.
Backup Generator
I'm pretty lazy and would just want my house to work in the event of a short-term grid collapse. I'd be looking for a whole-house backup generator. For my 400 amp service, I'm probably looking at $10k in capital costs (based on my initial discussions and research) and then more for on-going maintenance to ensure it actually comes on when I want it to. It'd be more compelling if it were a combined heat and power (CHP) application, but that is not easily integrated into my house.
Some believe backup generators to be a bad idea. I tend to agree. Expensive and might not actually be there when you need it to be. I'd prefer a simpler solution.
Large-scale Battery Storage System
I'm not an expert here, but it appears that large-ish scale batteries are costing on the order of $600/kWh of storage. I use around 2,000 kWh during a non-summer month. I'd be looking for something to last me at least two days. So for that (on average) we are talking about:
2,000 (kWh/month) / 730 (hours/average month) * 48 hours = 131.5 kWh
So for that size battery, it would cost (just for the battery):
$600/kWh * 131.5 kWh = $78,900
Wowsers. That's a big hurdle for something that will be used quite infrequently. No. Not going to work. And that is before any of the balance of plant costs (e.g., electrical connections, installation, maintenance).
Some have suggested that battery costs are going to decline steeply in the coming years down to $200/kWh and there have been sitings of Volt battery packs as low as $144/kWh. The latter sounds like some dumping and the former sounds optimistic given that Tesla's retail price for their larger battery pack is $517/kWh. But even at 1/4 the cost, the above battery system is still expensive at almost $20,000. Maybe some start to see that as reasonable, but I'm not sure that I do.
Solar system / Wind / Combined Wind/Solar
I'm combining all of these because they share the same weaknesses. You just don't know for sure if they will be there when you need them. These won't really work unless you combine them with a battery system. The advantage of the combination would be that you can reduce the size of the battery by the amount of "guaranteed" output from your combined wind/solar system in addition to offsetting your power usage under normal operating conditions. The downside is that the cost per kWh of residential scale solar and wind is quite high. Well above the 10¢ or 11¢ that I'm currently paying Dominion. I think that this would work if I lived in the middle of nowhere and didn't want to pay to connect to the grid in the first place, but I'm already there.
Potential Energy Conversion System
I'm talking about something here that I have no idea about, pretty much just making things up. Bear with me, they are good ideas :) First off, I'm not talking about installing a
new section of road in front of your house and harvesting energy of the passing cars. Though, if you could get away with it and have a reasonably busy road in front of your house, it might be a great idea. I'm thinking about two ideas: car ramp and a suspended (very heavy) weight.
Car Ramps
The idea is reasonably simple. I think there is a good chance the power could go off tonight, so when I get home, I park my car in a very specific spot in the driveway. I then raise the vehicle. In the event that the power goes out, the vehicle starts to descend, its potential energy being converted into electrical energy powering the house. This is the concept in graphical form:
Let's do the math to see what we've got here:
6,078 lbs * 6 ft = 36,468 ft-lb * 3.76616097 × 10-7 kilowatt hours/ft-lb = 14 Wh
The problem here is that I'm short by a factor of 10,000. So despite me wanting it to work, its just not going to. There just isn't much here unless we can dramatically increase the weight or the distance. My car isn't going to get any heavier (thank goodness - an Expedition is super heavy as it is).
Big Hole - Gravity Power Module
As shown
here, I could, with just a six meter diameter hole, have ~ 9 MWh of energy at my house. Presumably this could scale down measurably, given that I would only need about 1/8 of a MWh (1/72nd the amount of power). So maybe only a 1 meter whole would do the trick. But we'd still have to drill down 500 meters. That is a long ways, but we could double the area of the hole to half the depth. I'm sure it would work if the concept was developed enough for commercial adoption, but its not going to be cheap in the short-run.
Conclusion
At this point, there really doesn't seem to be any cost-competitive back-up systems to the grid. This may be a compliment to the engineering that has gone into central station power-based systems, but I think that it is the current reality. However, how might the environment change, if only on the margin over the coming years? Might be interesting to think about.
Residential Thermal Solar: This already makes sense and yet people aren't using it (widely) to offset energy usage otherwise. Natural gas and power are too cheap. This will be a much bigger deal when (if) gas and power get substantially more expensive.
Residential PV Solar: This will absolutely explode when the unsubsidized cost per kWh of solar is roughly equal (and has the prospective chance of being lower with future fuel cost increases) to the local power company. Many will jump at the chance. A few changes will make it even more compelling. When we cross the threshold of 5% to 10% of residences have solar systems, the real estate community will figure out a way for them to get recognized in the sale price of the house. Changes to the residential rate structure may make this point in time bleed out 50 years or so (we get charged a variable price for many fixed costs - as people drop off the grid or reduce their variable consumption with no change in the fixed costs - the structure will have to change - see the pain that is predicted in California in the next couple of years). I'd still rather have a solar stirling engine in the front yard. Talk about yard art.
Electric Vehicles: If I already have an 85 kWh battery pack in the form of my car, maybe my backup system is my car(s). Two of them would more than cover my two day costs. Still doesn't address the (electrical) cost of starting motors, but there are likely capacitor-based solutions to this.
Wide-Spread CHP: If I could have a mini-turbine in my furnace where the exhaust was being used to heat my air as well as my hot water, and do it at a reasonable price, I would.
Freewatt looked like a system that could have fit my needs, if the company hadn't gone away. Somebody else will do it. If it costs 50% of the current projected costs ($25k), I might be willing to pay the 200% premium over a normal furnace. Not a whole-house backup circuit, but it'd run the furnaces and refrigerators and some lights. That'd (probably) be enough.
