Ejector pump variable solar solution

I had mentioned in on thepage about pumpsthere was a solution to get solar thermal to work with ejector pumps, and that if I didn’t post about it to remind me. In the past week or two a few people have asked about the solution to this problem

The reason I didn’t post it at the time is because the solution I found was in a payed for paper I purchased so I couldn’t just copy.

Basically, the problem with solar thermal steam powering an ejector pump is that ejector pumps generally have small operating ranges whereas solar energy is highly variable.

The solution is to use a valve system that accumulates steam and only releases the steam into the when the right pressure is reached and shuts off when the steam falls back below.

Each cycle then inputs steam at the right pressure into the steam ejector. Presumably there are losses associated with starting each cycle, but these could be minimized by accumulating enough steam so that each cycle is longer.

The valve system the aforementioned paper described was fairly simple. Pressure accumulates in the boiler, and is blocked by a valve with a weight on it. The weight applied pressure on the top of the valve. Below the valve there is a diaphragm on which the steam pressure acts. When the pressure on the diaphragm increases enough to push up the weight, the valve opens allowing steam into the steam ejector (which they had designed a simplified version of). When the steam pressure reduces, the weight overpowers the diaphragm and the valve closes.

This would a simple DIY method of building such as valve, but commercial solutions also exist using the same idea of with a spring instead of a weight.

In the paper they had some calculations about efficiency of the system. They were using only flat plate collectors to produce the steam and estimated about a 5% efficiency. With Solar Fire Concentrator much hotter steam can be produced and so the efficiency should be much higher using a similar system.

The steam ejector they built had two adjacent chambers. Steam is injected into one chamber and pushes the water into another chamber where it is times that most of the steam condenses in the second chamber thus also pulling the water. One way valves allow the water to flow from one chamber to the other and the out of the system. I don’t know if this qualifies as a steam ejector since it doesn’t really use the venturi effect, but it’s the same basic idea and can be built low cost in a DIY setting (whereas a real ejector pump would be difficult to build DIY, but may definitely be worth to buy when possible).

Of course, solar energy "fuel" is free so the efficiency doesn’t matter so much. The steam of course heats the water, which may be good or bad depending on the situation. A situation where this would be good is if the pump is placed in a green (the solar concentrator outside of course), and the water could be pumped into holding tanks inside the green house which would provide warmth to the green house. Water for cold use can moved to an outside tank, though both warm and cold water might have to be filtered before use on plants or people (as warmth may invite bacteria). Definitely some practical experimentation would be needed to judge what impact of this warmth would be and how best to deal with it.