two-speed with solar panels

[semenzato]

Is there really a difference between "negative head" and "vacuum"? As I see it, unless there is still positive head at the top of the panels, the water on its way down is pulled by gravity and produces a "suction" at the top. By suction I mean a pressure lower than atmospheric. If the system is sealed, that negative pressure "sucks" the water up from the inlet. But if there is a valve, the suction will make the valve open. As I said, it's possible that the valve will stay closed with a small amount of suction, but eventually it will open, and I would imagine the margin to be too small to be of use.

Thanks!
Luigi

[mas985]

Is there really a difference between "negative head" and "vacuum"? As I see it, unless there is still positive head at the top of the panels, the water on its way down is pulled by gravity and produces a "suction" at the top. By suction I mean a pressure lower than atmospheric. If the system is sealed, that negative pressure "sucks" the water up from the inlet. But if there is a valve, the suction will make the valve open. As I said, it's possible that the valve will stay closed with a small amount of suction, but eventually it will open, and I would imagine the margin to be too small to be of use.

Thanks!
Luigi

Yes there is a difference between negative head and a vacuum. The primary difference is the reference. Vacuum usually refers to pressure below atmospheric or negative PSI. Your solar valve on the roof will not release until the pressure in the pipes is below atmospheric which requires the pump to be off and water to be draining out of the pipes. This causes suction.

However, with the pump on, there is a net positive pressure within the pipes usually between 10-20 PSI above atmospheric pressure (i.e. your filter PSI reading). This keeps the valve closed. So while the water going down the pipe offsets the water going up the pipe, this is called static head, there is still a substantial positive pressure to keep that valve closed. There just isn't any head added to the system because of elevation. The only pressure difference is the dynamic head loss experienced in pipe and solar panels. The water falling simply makes it such that less pressure is needed to push the water up the pipes.

The easiest way to see this is when the solar is first turned on. You will see the PSI rise substantially and then after the pipes are filled, the PSI will drop slightly but still higher than without solar.

So in formula terms:

Filter PSI Solar on = PSI Solar off + PSI elevation Rise - PSI elevation fall + PSI Dynamic Head Loss Panels and Pipe

PSI elevation Rise - PSI elevation fall nets to 0 so there is no PSI impact due to elevation.

[rilesworld]

I have been trying to learn a little more about solar options and have a couple of basic questions.

Can you use PV solar panels to heat your pool? I guess I thought that you either had a PV system that generates electricity that can create units that can be sold or you have a "water heating" system that just creates hot water. Is that accurtate?

It seems like having solar for heating the pool is beneficial early and late in the year to extend the swim season, but does anybody use their system for anything during all those other months? I know during peak summer it seems like you can use it to cool your pool, but what about all that sun during the summer and winter months? Just curious.

Some of you that have a PV system. What size system do you have and how much energy are you able to generate over the year?

Thanks,

Riles

[mas985]

I have been trying to learn a little more about solar options and have a couple of basic questions.

Can you use PV solar panels to heat your pool? I guess I thought that you either had a PV system that generates electricity that can create units that can be sold or you have a "water heating" system that just creates hot water. Is that accurtate?

You could use them to generate electricity and then run an electric heater but that would be very inefficienct. The better bet is to use the electricity to run the pump and then use passive solar for heating.

It seems like having solar for heating the pool is beneficial early and late in the year to extend the swim season, but does anybody use their system for anything during all those other months? I know during peak summer it seems like you can use it to cool your pool, but what about all that sun during the summer and winter months? Just curious.

Really depends on where you are. Most of the year, I use the solar to keep the pool between 85-90 degrees. There is onlyabout three weeks in the summer where I don't need it. Also, you need to add more heat if you don't use a solar cover. Although our days here in CA can get quite hot, the nights seem to be fairly cool and that is when you lose a lot of heat.

Some of you that have a PV system. What size system do you have and how much energy are you able to generate over the year?

Thanks,

Riles

Some thoughts.

[cleancloths]

A PV system generates electricity, what you do with that electricity is up to you. CA like NJ has some very good incentives to install PV. PV provides electricity year-round - so I find it a much better use of my roof space. My 54 panel system generates over 12,000 kwh per year.

[tphaggerty]

I second mas985. My controller stays on all summer. After it rains or we have a few cold nights, it will kick on, even in July & August.

Extending the season isn't anything to sneeze at, though. We opened about 3 weeks ago, the water in now 85+. We will swim until almost the end of October in 80+ water. No one else, and I mean no one, will do that around us (unless they get solar!!)

[cleancloths]

I second mas985. My controller stays on all summer. After it rains or we have a few cold nights, it will kick on, even in July & August.

Extending the season isn't anything to sneeze at, though. We opened about 3 weeks ago, the water in now 85+. We will swim until almost the end of October in 80+ water. No one else, and I mean no one, will do that around us (unless they get solar!!)

I've done it for years in Northern NJ with my heatpump. The key issue is more of using a solar cover then how you heat. The heat loss in April/May and Sept/Oct at night is HUGE if you don't use a cover.