The most important question about a PV installation is its purpose: what you you want to do with it and when. From what I've read here, it seems you want a backup in case of power failures (which seem to happen mostly in winter IIRC). I'm not sure that this is practical with solar power. A solar array large enough to keep batteries charged in winter would probably produce much more energy in the summer. What are you going to do with that? Additionally you would be using your expensive panels and batteries only relatively rarely. For power outages in the winter it would probably be easier to ditch the solar panels use the grid to keep the batteries charged that would give you some spare power in case of an outage.

There are several other scenarios to generate electrical power in winter, considering you are already burning wood;

• The waste heat from your woodstove could power a small heat engine that in turn would drive a generator.
• Slightly more complicated but still old and well-understood technology, you could go for a small steam engine combined with a generator. The waste heat produced that way could be used to heat your home.
• Or you could slap some thermoelectric generators onto your wood stove.

Second, if you want to regulate an electrical system, you need to know about electronics. Both batteries, PV panels and other generators need electronics to regulate them and keep them working efficiently and avoid damage.

Third, batteries are chemical reactors and need to be managed as such. With lead-acid batteries you want to keep an eye on battery acid levels and specific gravity, as well as the condition of the plates.

Because of our core leftist philosophy, seemingly high outage rates in the North Woods, easement questions and the cost of burying a line 1700' from the road, we went in to the building process with a serious commitment to off-grid. We became members of the Midwest Renewable Energy Association, attended at least a dozen seminars, and subscribed to Home Power Magazine to educate ourselves in hopes of building a modest, properly-sized 1200kw off-grid system ourselves. We bought 9 15 watt panels and 3 batteries and practiced for two years on reduced demand, finally living in our shed for 6 months while the house was being built. This project can be done, if you are willing to literally "learn to be an installer", as by definition, you will be installing sophisticated components you can't afford to ruin by "wiggling in". There is no short-cut, and for us, the choice was between getting a homestead up and running in a year or learning a new profession. Sad as it is, until it becomes "plug-and -play", it seems unlikely that a homeowner has the money, time and skill to pull it off, but you are welcome to try. The components amount to about $13K; having someone do it for you makes it $26K, and that put it well beyond our resources, if not sanity. The final deal-breaker is the batteries. Spending $8-10K on a battery bank that, even if you do everything right, will end up a biohazard somewhere in ten years, is not a value proposition we chose to entertain. And then you get to buy some more. Before you scorn the grid-tie: it is popular for a reason. We plan to eventually go that way, as we did resolve the easement issue and pony up for the buried line @ $12 a foot over 500' as our solution. Sorry if that seems bourgeois. Now, solar thermal is another story...

I had similar sentiments when I read this book a little while back--quick read, but not a lot of DIY info.

One more idea to add to Roland's: if you had a way to store water at the top of a hill (like a pond or series of barrels), you could use excess juice from the solar panels to pump water uphill. Then use a small-scale hydropower system to get the electricity when you need it. http://www.green-trust.org/hydro.htm

It looks like you've already done some research on microhydropower though, so maybe I'm missing something. I suppose the initial investment for solar and pumps and microhyrdo would be pretty high...

@Jake: hydro is nice, but the energy density sucks because gravity is a relatively weak force. 1 kWh (which is not much) equals 3.6 MJ. The potential energy of mass is m·G·Δh. Having 25000 lb (11339.8 kg, 14.8 cubic yards) of water flow down 100 vertical ft (30.5 m) only yields 3.4 MJ, and that doesn't factor in conversion losses. The average household in the USA uses around 30 kWh every day. A small household might use around 5 kWh/day, but to create even that would require a huge amount of water or a large drop.

So stored hydro is only viable if you have a huge reservoir, and/or a large vertical drop. Building a suitable reservoir is a complex and expensive undertaking. And there are safety issues to consider; you wouldn't want to have people living downhill in case the reservoir fails.

Hi All,

A friend of mine heated his factory in NH with solar.

A couple of rolls 0f solar passing stuff on a kludge frame along the south side of his factory. When he observed it got hotter there, he added a plenum at the top and had more heat during the day.

Next he added some scrap metal suspended in the middle. It heated up and rose and made the plenum air much warmer.

Next he added solar energy storage to his system. Rocks !! in the bottom. They heated up during the day and added more heat.

About this time each year he had to open the windows to let the heat out!

So who needs high tech?

John

@Roland: A little math always makes things clearer, so thanks for that. But from your example, 25000 lb of water is about 2975 gal, or about the size of a (12' diameter) above-ground swimming pool. That doesn't seem intractably huge, even if you have to have several pools-worth. What made me think of stored hydro as an option is Joel Salatin's farm, which is relatively flat toward the front end of the property and rises up into the mountains toward the back. He's got a series of ponds built up in the mountains that fill up just from rainwater. He uses the water for irrigation (if I remember correctly), but the ponds are way bigger than five swimming pools (and would probably yield more than 100 feet of head to his hypothetical generator), so it seems like a similar setup could potentially power a small homestead for a couple days.

Admittedly, I don't know much about building and securing reservoirs, or if there's even a suitable location on Anna and Mark's property. But even if it's an expensive undertaking, batteries aren't so inexpensive themselves, and the reservoir wouldn't need to be replaced every 10-20 years. If only water were a little more frictionless and gravity a little stronger.

@jake: Suppose you want to store enough water for a power outage of a week, a daily use of 5 kWh and a total conversion efficiency of 50% with the aforementioned drop of 100 ft. That would grow the 2975 gallons into 2975·5·7/.5 = 208250 gallons or slighly over a thousand cubic yards. A large tanker truck is in the order of 11600 gallons, so that's around 18 big tanker trucks parked uphill.

Constructing a reservoir of that size is not a job for amateurs; one would have to find a suitable spot (preferably some kind of high and steep valley, so you only have to build one retaining wall instead of several) and be able to deterimine if the local geology is suitable to build a reservoir there. The weight of the water and the forces on the dam are factors to take into account. Building a dam in such a remote and inaccessible location is a challenge in itself, starting with getting a bulldozer or an excavator to their property.

The thing is, we basically haven't found a cheap and safe way to store renewable energy at a high density and with good efficiency yet.

While it is easy to use e.g. use solar or wind power to split water into hydrogen and oxygen, storing the hydrogen is something else entirely. Compressing it it relatively easy, but then you're dealing with up to 5,000 to 10,000 psi tanks. And a gas which is explosive in air in a wide range of concentrations (between 4% and 75% by volume), which burns easily and with an invisible flame. So you'd better be very sure that whatever enters the compressor is pure hydrogen! Suck 5% of air into that compressor and you have an explosion waiting to happen.

@Bill: according to this page, in the period 1999-2003 in the USA, 99.2% of the lead in lead-acid batteries was recycled. I think that's an impressive number. Especically in a country like the USA which doesn't have a good reputation for recycling.

All those coummunist pinko lefites who advocate PV & wind generated juice always overlook the lost investment potential of shelling out $20-30K up front for the systems. If that money were invested instead in something safe like a Dow-linked fund, they'd have lost out on something like a $80K return over the 20 yr life of their system while only saving $20K in energy costs, and then they'd have to shell $30K out again for another 20 yrs of power.

The good socialist thing to do would be to let the govt regulated, centalized monopoly power company produce the energy for everyone. The only time the alternatives are a good alternative is when you're so far off-line that the cost of running a line is very much greater than the cost of the system.

BTW- as Roland points out, Pb/acid batteries are not really hazardous when recycled properly. And the more efficient Li batteries require materials available almost exclusively from China. Can we trust them to keep supplying that at reasonable prices?