posted 12 years ago
I think the setup Dave suggested would be a very good choice -- as long as slow and steady will work well for your water demands. That way you'd move water to your cistern whenever there was both water and sunlight available, and with gravity you can use it whenever you need it.
The slope has been described as "gentle" and elsewhere as a 35% slope (or is that 35 degrees?)...I'm not sure 35 degrees would count as gentle (at least if I was climbing a long slope on a hot day!) A 35 degree slope is like an 8/12 roof pitch (a little steeper, actually); for every 12" forward, you have to climb 8" upward, or for every 1 meter ahead, you'd have to step up ~67 - 70 cm. If 35 degrees is the case, then 50 meters forward, would equal about 33-35 meters straight up, so the lift would be around 110'
Other things to consider, or just good info to record here for others seeking solar pumping options (some already stated above):
> a solar direct (or PV-direct) pump only moves water when there is daylight available -- cloudy = slower, and bright sun = faster. These pumps can tollerate the higher voltages produced by solar panels -- for example, a "12 Volt" PV-direct pump can usually take up to 20 or 21 volts input from the solar panels, while a 12 volt battery-based pump might only work from about 10 volts to about 15 volts.
> Some are low-cost, and some cost $ thousand$
> Lift and flow requirements determine how much OOMPH you need, and how much money you'll need to spend.
> There are very good PV-direct pumps that don't need batteries, and some have pretty advanced controllers with MPPT tracking (solar nerd speak for higher efficiency), and even linear current boosters (more solar nerd stuff, but a good option), while some just hook directly to the wires from the solar panel(s).
> A battery-mediated pump allows you to turn the pump on and off if the need for water is sporadic, or if you need to pump water when there may be no sunlight available.
> Submersible slow-start pumps are mounted under water an push the water up -- these are fairly expensive, but there are very good ones that last for many years (like Grundfos). Some are AC and some are DC.
> Submersible diaphragm pumps, like the SureFlo 9300, work well, but require routine maintenance (clean & replace screens, etc...)
> Controls: If you have a water tank you want to fill -- especially one at some distance from the pump -- you do not usually need to run wires all the way to and from the tank to turn the pump on and off. A float valve can be attached to the end of the hose or pipe up at the tank, and when the tank is full, that closes off the end of the pipe. The pump doesn't know this, so it keeps pumping, and the pressure in the water line rises... A pressure-activated switch can then cut off the power to the pump (from a battery, a solar panel, or even an inverter or the grid). In this way, the only long and expensive thing is the water pipe, and the electronics are all right near the pump and solar equipment. I have a Shurflo 9300 pump run by two 80-watt solar panels that pump water some 1700 feet (lift is only about 60') to a series of large tanks (about 1200 gallons total). The tank end has a float switch, and the pump end has a pressure switch. Pump and switch are in a little pump house that looks like a large dog house, with the panels on the roof.
> Solar panels charging batteries usually need a charge controller, and these can be simple and cheap, or pretty darned expensive.
> An inverter is only needed when you need AC power.
> Solar panels tend to change a little in voltage with changes in temperature (colder = higher voltage, and hotter = lower), but change in amperage with brightness of the light (all other things being equal).
> When you get info/prices/designs from many solar professionals, some may use the term solar "module" to mean what most people would call a solar "panel".... which can be confusing. In solar geek-speek, a number of solar cells make up each framed solar "module", and a number of solar modules in an array make up a solar "panel".... Most people still call 'em solar panels, but in case it comes up...
> ALL solar panels work best with ABSOLUTELY NO shading. SOME solar panels with an amorphous or "thin film" design will tolerate shade better, but all will produce more power in direct sun with no shading. For monocrystalline or polycrystalline solar modules, shading is a really really big deal -- see Shading.
> Shading: Shading = BAD for solar. Mono-and polycrystalline solar panels are greatly affected by just a wee bit of shade, and when solar panels are wired together in an array (say you have 12 solar panels wired in 3 strings of 4 panels in series), when one solar panel is affected, it usually affects all the others in that string, too. The actual amount of power loss depends on how the cells are wired inside the panel and what part(s) of the panel are shaded, but 5% shading can lead to a 95% loss in power produced!!! Absolutely worst is a sharp-edged line of shading across the width of a solar panel, like a shadow from even a single branch or a wire that's close enough to make a sharp-edged shadow. That's like clamping a hemostat or vice across a hose -- it cuts off nearly all the power. Any other panels wired in series with that one (and farther away from the controller or batteries) will also be reduced dramatically. For long strings of panels in high-voltage arrangements (like grid-tied PV) the "pinch point" caused by shading can also get very hot, and can even burn the building down! CiS and other amorphous solar panels get around quite a bit of this, but then, they aren't the ones available at fire sale prices, either. Take-home message: trim the branches or weeds that cause shading or mount the panels where shading is absolutely minimized.
I hope these solar pumping terms are found helpful by someone. My own little solar pump is a ShurFlo 2088 12-volt pump that I run off a 12-volt marine battery charged by an old and ugly 50-watt Arco panel that somehow survived a house fire, and was eventually replaced by a new solar array, plus a Morningstar Sunguard-4 charge controller. The solar panel keeps the battery charged up, and I use the pump occasionally to top off a 300-gallon water tank about 85' away from a pond, and ~18' higher in elevation, which we keep on hand for gravity feed watering of annual raised beds during dry conditions (because the pond eventually goes dry). The pump sits near the edge of a pond in a waterproof plastic container, and only has to suck the water up about 3' before pushing it uphill. A check valve is used to help the pump keep its prime, but this pump is self-priming; the flow check valve just saves a lot of time (and battery power) waiting for the hose to fill and for the water to arrive at the cistern. This pump has a built-in pressure switch with a little room for adjustment, but I usually just run it while working in the gardens, and manually switch it off when I'm ready to leave (I don't have a low-voltage disconnect installed to protect the battery).
Hopefully all this stuff can be used by someone, even though Dave found a good solution for Alex already.
Clear skies,
Brad Vietje
Newbury, VT