Wednesday, October 31, 2007

Are You Ready for a Winter Emergency?

Winter is almost here, and that brings back memories of last years extended power failure. It was obvious at the moment the failure occurred that this was going to be a worst-case scenario. With sub-freezing temperatures outside, I knew it wouldn’t be long before it would be unbearably cold inside. Fortunately I had plenty of corn on hand for the corn-burning stove, and electricity available from my small off-grid photovoltaic (PV) system. We survived the first night comfortably, but I knew the PV system would not be able to keep up with the electrical demand of the stove.

That power failure taught me a valuable lesson. When the grid fails, you use the systems you have, not the ones you wish you had. And although that may sound obvious, you’ll understand the significance of that statement once you’ve experienced it for yourself. You’ll find yourself wishing you had installed eight PV panels instead of four, and you’ll wish you had a bigger battery bank. As you make do with what you have, you’ll vow to make the needed upgrades before the next emergency.

My PV system was too small to supply the electrical needs of the stove and the chest freezer last winter, so I purchased a small gasoline-powered generator. I was fortunate in that the electrical outage was spotty, and I only had to drive one mile to find a source of gasoline. With winter approaching once again, this is a good time to assess preparedness.

When last-year’s power failure occurred, I had 2 PV panels (170-watts of PV), while now I have four panels (340-watts of PV). I still have the same amount of batteries, a total of 420ah. In practical terms this means that I can charge my batteries faster, but I have no more storage capacity than I did last winter. Based on my previous experience, I should be able to run the stove for at least 8 hours, but I may be able to fully charge the batteries with only one day of sunshine. Previously, it has taken two days. This means, of course, that I could have as much as eight hours of heat per night, every night, as long as the sun shines during the day. That’s great progress, but I obviously need to do much more.

I’ve recently replaced my 20-amp charge controller with a 60-amp one, paving the way for additional solar panels. I’m very pleased with my 1100-watt sine wave inverter, so no upgrades are needed in that area. My goal before the end of the year is to add at least one more panel, and another 210ah of battery capacity. In addition to the electrical demands of the corn stove, being able to run the chest freezer means that I can keep food from spoiling. Additionally, I’ll need lights, the ability to charge a cell-phone, and the limited use of other household appliances.

Because my system will remain small in the short term, I need to incorporate other strategies in the event of an extended power failure occurring in the winter. Closing off unused rooms is one way I can cut back on heating. I can use an electric blanket, and therefore tolerate cooler indoor temperatures as I sleep. Instead of running a refrigerator, I'll place perishables in an ice-chest, and use an energy-efficient chest freezer. While these inconveniences are annoying, at least I can remain relatively comfortable in my home. Some of my neighbors had to abandon their homes during last-years power outage. With each system upgrade, living through an extended power failure becomes less of an annoyance.



d said...

Hi SJ,

Yes: once bitten, twice prepared.

I don't anticipate significant outages here in the stockbroker belt round London, though Russia has the EU by the short-and-curlies for a lot of our natural gas supply, from which the UK generates something like 2/3rd of its electricity for example, and gas shortages may mean peak-time electricity brown-outs and a huge jump in the gas price mid-winter as before.

So I have been looking at new more efficient freezers and fridges as a matter of interest, and one big store had only C-rated chest freezers, but A-rated (and one A+-rated) upright fridge-freezer. Our current one at home is ~2kWh/day for ~270l; the new efficient uprights were half the power consumption (claimed) for the same capacity.

But if I thought that power failures were going to become common, and the weather not cold enough just to leave perishables outside in the shade or a shed as an impromptu larder, I'd consider beefing up my pilot PV system to be able to at least power an efficient 12V DC cooler box.

And I've made a little progress understanding what would be needed to install a ground-source heat pump to replace most of our natural gas use. Not quite as expensive as I had feared, though since gas is cheap, and the heat-pump eats a lots of electricity, probably not worth doing unless gas gets very expensive or unreliable.



rowan langley said...

Dear John,
I have just been sent a link to your site and blog. I think we are of a similar mind.

I have been building up my system a bit like yours, it is now at the end of its third year of growth. Like yours it started off doing the low powered stuff and grew as funds permitted. The battery bank expanded to 7.2 KWh last spring and a 2.4 KW inverter went in on fifteenth of may,the same day our prime minister said something like we could not do without nuclear power, renewables couldn't do it on their own. Since then, a grand total of 2 KWH has been drawn from the grid, the rest from solar. The most recent electricity bill came to zero.

Here are some links which you might like to put on the site :

d said...

Hi SJ,

I did a bit more work on pricing up the heat-pump stuff:

The end figure is ~GBP50k (ie ~USD100k at the moment) for my London house to be a net exporter or neutral for mains electricity and to replace mains natural gas with the heat-pump. I think it is reasonable to assume at least a 20+ year equipment life, but I'm still checking.

This solution will NOT work without the grid (ie in a power cut) as costed since the grid is the cheapest storage available, though you could adjust it to run from battery power if need be, with maybe 3kWh/day of battery storage to cover outages, eg ~500Ah@12V down to 50% discharge if I've done my sums right. (Note that our current mains gas heating will fail when mains electricity does.)