I'm looking for a product that I'm sure I saw here: a galvanised post, like a short lamp-post, that comes with a solar panel, wind generator and a weatherproof box for storing battery, charge controller, etc in. I think it was a couple of grand, but don't recall if that was USD, GBP, EUR or what. I'm sure I didn't imagine this product and that it really does exist, but my Google-fu is failing me.
Sorry if it's not obvious, the intention is to mount a couple of APs in the cabinet.
DIY is cheaper.
Look for galvanized HD fence post.
Use two weatherproof boxes as venting battery will eventually damage the other electronics.
Without going into the metical details a larger solar panel vs a wind gen is typically best unless you're locating this in an area that has consistently steady winds of 10 mph or higher.
What you're looking for is called a "wind solar hybrid". For example:
Most of the wind power system vendors also sell hybrid systems. The reverse is not usually the case. You could probably build your own, but finding and sizing the controller might be a problem. I'm not a big fan of vertical rotors, but if you don't care about efficiency, they're fine.
Reminder.... if it moves, it breaks.
Hybrid is rediculous. Calcs and logic follows.
A "couple of access points" might have an average power requirement of about 10 watts. To make it through a 24hr day, you would need to draw: 10 watts * 24 hrs/day = 240 watt-hrs/day With a non-tracking solar insolation of about 4.0 (for central Calif), the solar cell would need to be: 240 / 4.0 = 60 watts That's one typical solar panel.
To make it through a 24 hr day, the battery will need to power the access points through the equivalent of 20 hrs/day. To avoid killing a gel cell, you don't want to discharge it more than about 20%. 20 hrs/day * 10 watts = 200 watt-hrs/day 200 watt-hrs / 0.20 = 1,000 watt-hrs total capacity. For a 12v system, that's a: 1000 watt-hrs / 12v = 83 Amp-hrs battery The nearest usable size would be 85A-hr:
What the wind generator would add to the system is the ability to charge at night[1]. With only an average of 4 hrs of equivalent sunlight per day, a night time charge would perhaps double that at best. That would reduce the size of the solar cells to half (30 watts) and reduce the size of the battery by requiring it to run only
16 instead of 20 hrs per day. That results in a smaller 67A-hr battery.Generally, adding a wind generator is a win in terms of size, but not complexity or reliability. If the wind forgets to appear on several consecutive nights, you've got a big problem. Same with the sun hiding behind clouds. If the one appears but not the other, you still get a charge. However, this does not allow you to assume that BOTH will appear on schedule, meaning that you have to use the original calculations, with the 60 watt solar panel, and the 85A-hr battery. It's cheaper and easier to just get a bigger panel and bigger battery, than to add wind power.
Incidentally, I built a spreadsheet for such calculations:
Starting values are for a single WRT54G.
[1] There is no benefit in wind charging during the day, when the solar panel already has the battery charged to 100%.
Right. I'm looking at about 2.2 for this location, 55 degrees north. The APs would be a Ubiquiti Picostation 5 and 2, the data sheets for which both suggest max power consumption of 4W each, so 10W gives us a litle margin. However planning for the worst case of 0.5, I'd need 500W of solar power [source:
OK, so why a gel-cell instead of a deep-cycle?
This isn't a particularly remote installation, it's just that the cost of digging a trench to lay power is considered to be too disruptive to operations by the customer. Ironically, not laying a cable increases the power requirements, because there would be fibre going in with the power, so the 5GHz AP is for backhaul.
This is just a feasibility study really; the customer has already suggested a generator which seems like madness to me, so I'm trying to think of something more sensible. If I understand correctly, a 1000WHr battery would power 8W of APs for about four days. Being required to swap a battery every four days isn't as much of an obstacle in this case as it might be in others.
It's the south-west of Scotland. The sun rarely appears from behind the clouds. If it could be powered by drizzle, we'd be sorted.
Thanks for your thoughts as ever.
You have wind I think , not having been to the UK in 30 years but I remember Scotland being blowing and wet and very much so around my ancestors growth sites I should think a small wind generator of around 200 watts on a light tower or building , perhaps a solar cell and a decent deep cycle would pull it up ? Perhaps the solar is optimistic :)
Good radios.
Solar isn't going to work. Not enough direct sunlight. Check the maps for average wind speeds.
Price. Gel-cells are generally more available and cheaper. Deep cycle "solar" batteries would be better because they can be discharged to a lower level. They also have more (non-sintered) lead, which means they generally last longer. Note that deep cycle refers to the (solid) composition of the lead plates, while gel-cell refers to the composition of the electrolyte. There are batteries that combine both solid plates and gel electrolyte. For example:
Incidentally, a sloppy but effective way to choose batteries is by weight. The heavier the battery, the more lead, the better for deep cycling.
However, some care is required to obtain a full lifetime:
"When new, a deep-cycle battery may only have about 75 percent capacity. Formatting as part of field use will gradually increase performance. Apply a gentle load for the first five cycles to allow a new battery to format." More:
The problem with generator based SMALL installations is that generators are frequently used to "quick charge" the batteries. Run the battery almost flat, and then rapidly recharge them with the generator. That's a great formula for premature battery death.
Wrong. That would mean running the 1000 watt-hr battery to total discharge. Battery will not like that.
Let's use 10 watts instead assuming you want to run the system solely on battery for about 4 days: 10 watts for 24 hrs = 240 watt-hrs/day 1000 watt-hr battery / 240 = 4.2 days So, you need to DELIVER about 1000 watt-hrs for 4 days. Assuming you use my figure of not running the battery down to below about 80% of full charge, the total battery size would be: 1000 watt-hrs / 0.20 = 5000 watt-hrs If this were a 12v battery, that would be a: 5000 watt-hrs / 12V = 416 Amp-hrs size battery. Of course, you could drop the charge level to below 80% and obtain more runtime or use a smaller battery, but that will kill the battery more quickly. Note that this is a rather crude calculation which more closely resembles the best case scenario instead of reality. Use my spreadsheet, or other solar/wind calculators online to get more realistic numbers.
I've never been there, but I can imagine the problem. Wind power seems like a better alternative.
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