The most inexpensive way for LARGE Solar Storage

[mechster]

Hello, I'm new to the forums.  I would like some insight on safe solar storage.  I've done quite a lot of research on this for cheap ideas for long term safe storage and thought of a system I would use.  I'm looking for extra knowledge of problems that could occur with the system I am planning on building with a new house build.  Also to help people think up an inexpensive way to do solar storage.

- I am going to put parabolic mirrors to track the sun on my roof with pipes running through them, in the pipes will be oil ( I haven't decided what type of oil yet, maybe you could give me an idea ).

- I'm going to install a control system ( maybe reliable controls ) to control the output oil temperature to 390 Deg. C.

- The oil will go down to a room with a very large cylindrical cement casing, covered in insulation.  In the cement structure will be sand or salt ( the cheaper one of the two ), the oil will discharge it's heat into the sand or salt.

- That heat will be extracted later when needed for in floor heating, DHW (Domestic hot water) heating, heat pump loop heating and electricity.  Therefore this mass has to be big.

- Extracting heat for in floor heating, DHW, and the heat pump loop heating is straight forward, but for electricity it is not, as many of you may know, it is quite difficult to get electricity out of heat with a cheap method.

- Here is what I thought up, I would use thermoelectric modules.  I'm looking to cover an area of 50 cm x 50 cm, with approximately 60-90 modules ( I would need the test the modules before buying them in large quantities). These modules will then be placed against a heat exchanger extracting heat from the sand and the opposite side of the module will be against a cooling side.  The cooling side will be feed by glycol from stored cooling provided by the PV solar.  I will incase them in a container and create a vacuum to avoid too much heat leakage.


PROS and CONS

PROS

- Safe
- Most simple in design
- Most inexpensive storage to all the other systems out there
- Less parts
- Less parts to wear, corrode, or fail.


CONS

- Inefficient electrical use
- I don't know the breakdown of oil, but it may need to be changed after a few years.



That is my idea of the system I'm going to build,  I have looked thoroughly at HHO storage, H2/O2 storage, flywheel storage, battery storage, molten salt storage, kinetic water storage, use of a stirling motor and kinetic storage in general.  Most of these ideas are very expensive in the long run and have to many parts involved.  I wanted to simplify the system as much as possible and keep it cost effective.

When I build the system (maybe in 2 years time, I need to design the house around this) I will definitely post everything I'm doing on youtube for everyone in the world to use it, if it is feasible.

Let me know what you think

Mechster

[Peter K]

Hi mechster
I like the idea of mirrors & tracking the sun, I'm doing it with Solar Heliostats we call Sunflowers.
I've made 20 so far as prototype / proof of concept, & instead reflect the energy to a fixed focal heat exchanger that will use Hot Air so there will be no liquid leaks & loss of function. The heat storage will be " rocks " Halibuton Granite " is locally available in smooth fist size rocks, the space between them will allow the Hot Air to flow around them & exchange heat. for insulation
Rockwool of 1 ft thickness, air manifold can direct heat where needed, modular Heliostats can be added if more energy is required.

Regards
Peter

[MarkE]

Hello, I'm new to the forums.  I would like some insight on safe solar storage.  I've done quite a lot of research on this for cheap ideas for long term safe storage and thought of a system I would use.  I'm looking for extra knowledge of problems that could occur with the system I am planning on building with a new house build.  Also to help people think up an inexpensive way to do solar storage.

- I am going to put parabolic mirrors to track the sun on my roof with pipes running through them, in the pipes will be oil ( I haven't decided what type of oil yet, maybe you could give me an idea ).

- I'm going to install a control system ( maybe reliable controls ) to control the output oil temperature to 390 Deg. C.

- The oil will go down to a room with a very large cylindrical cement casing, covered in insulation.  In the cement structure will be sand or salt ( the cheaper one of the two ), the oil will discharge it's heat into the sand or salt.

- That heat will be extracted later when needed for in floor heating, DHW (Domestic hot water) heating, heat pump loop heating and electricity.  Therefore this mass has to be big.

- Extracting heat for in floor heating, DHW, and the heat pump loop heating is straight forward, but for electricity it is not, as many of you may know, it is quite difficult to get electricity out of heat with a cheap method.

- Here is what I thought up, I would use thermoelectric modules.  I'm looking to cover an area of 50 cm x 50 cm, with approximately 60-90 modules ( I would need the test the modules before buying them in large quantities). These modules will then be placed against a heat exchanger extracting heat from the sand and the opposite side of the module will be against a cooling side.  The cooling side will be feed by glycol from stored cooling provided by the PV solar.  I will incase them in a container and create a vacuum to avoid too much heat leakage.


PROS and CONS

PROS

- Safe
- Most simple in design
- Most inexpensive storage to all the other systems out there
- Less parts
- Less parts to wear, corrode, or fail.


CONS

- Inefficient electrical use
- I don't know the breakdown of oil, but it may need to be changed after a few years.



That is my idea of the system I'm going to build,  I have looked thoroughly at HHO storage, H2/O2 storage, flywheel storage, battery storage, molten salt storage, kinetic water storage, use of a stirling motor and kinetic storage in general.  Most of these ideas are very expensive in the long run and have to many parts involved.  I wanted to simplify the system as much as possible and keep it cost effective.

When I build the system (maybe in 2 years time, I need to design the house around this) I will definitely post everything I'm doing on youtube for everyone in the world to use it, if it is feasible.

Let me know what you think

Mechster

In order to store thermal energy, you want to be able to isolate all conduction and radiation paths as much as possible.  Vacuum is the best insulator, air is next.  Silvered glass is an excellent reflector.  This is why water heaters are built the way that they are.  390C is pretty hot.  Are you going that high in order to try and reduce your thermal storage mass?  How much energy do you want to store? 

If you want simple, then store at under 100C using conventional water heater tanks.  The main disadvantage is the volume you will need.

[mechster]

Wow, thank you guys for your information.  Thank you, I really do appreciate your responses.

I was run out of another large solar forum by Harassment from the members for mentioning any new ideas.

MarkE - You're right, I was way out of my league thinking I could handle 390 C, it would be unsafe to be handling that kind of temperature for anyone starting this kind of stuff.  I thought maybe 150 C of water in a pressurized water tank would be ok, but I looked at pressurized water tanks (because water is the best for storing energy), but they are very expensive.  Almost $ 5k for a 400 gallon tank, 2 of them would achieve the same capacity at a huge bed of sand, but that's a huge price tag.   

PeterK - I love your idea, I'm lucky where I live on a Island in Korea where they have a lot of Basalt Rock in supply.   

                    Density       Heat C    Energy Density
                     kg/m3       kJ/kg K   kJ/m3 K
water             1000         4190        4190
Sand              1682         830          1396.06
Basalt Rock    3000         840          2520
Granite          2700         790          2133
            
I don't know if my calculations are spot on, but the energy density of basalt rock seems pretty good.  I really like the idea of a Heliostats, as it kind of looks like an ornament. 

Do you think the modular heliostat would take up less space?  My last question, how did you move the air through the system at high temperatures.

Thank you again, I'm going to do some more research on heliostats.  This would be a cool build

http://energy.gov/sites/prod/files/2014/02/f7/csp_review_meeting_042513_kutscher.pdf

Mechster

[MarkE]

Leakage is a big issue.  If you go with storing in rock, then you will need to come up with a vessel design of your own that has really low leakage.  That's maybe good if you want to experiment.  water heaters work really well as long as you hold the temperature below boiling which you can manage with a bypass around your outside source to storage heat exchanger.  There is lots of kit for this sort of stuff that is well proven.

Thermo electric may sound appealing until you look at the cost per Watt and the need to keep 300C material around to have any efficiency at all.  As much as I hate to say it, but a NG fired generator is the cleanest night time solution.  A high quality Diesel would be the next choice.