Remotely monitor and disconnect off grid PV/Hybrid system - is this possible?

[beastman]

I am doing a a research project (and I'm a newbie!) and I need to know if its feasible somehow to disconnect a PV array (and possibly a wind turbine) from the batteries storage should that need needed for safety reasons, to prevent any possibility of damaging the batteries.
Firstly I'd imagine a correctly designed system would have the wind turbine dumping any excess load to something like a water tank to prevent this and a charge controller would do the same for the PV array, however how effective is this likely to be?
I ask as the building is likely to be unoccupied for around 7 days, in every month and its in a fairly remote location so it is crucial that the system is fail safe and that the batteries (or whatever else may go wrong) don't overheat and get ruined, or worse still burn the place down.
Is it just sensible to disconnect all appropriate systems when leaving the building empty for a week, or can as I was hoping, can the system be left connected safely so it can take advantage of the zero demand for a week and recharge the batteries fully?
The building can be connected to a 3G wifi modem so I was hoping there was a fancy way of monitoring the system remotely via the web and if necessary shut things down.
thanks

 

[Worcester]

Properly designed systems are designed to cope with battery failures, overcharging etc.

The scale and type of controls and measures depends upon the generation and storage capacities.

PV systems are by their nature controllable on their output, small wind however usually dumps to a dump load, basically a heater exposed to the outside air. Depending upon wether you are AC or DC focussed with your generation depends upon how it is all done.

A 1 kW PV system and a 1.5 kW wind turbinw would often just go through a pair of DC charge controllers, with automatic switch on of a genny when insufficient power, PV is just automatically switched off and Wind dumped to heaters aka dump loads. The DC acts as the storage and then converted to AC through an inverter.

Larger systems are typically AC led and use Inverters, and charge controllers such as the Sunny Island product.

The simple answer is yes, with a properly designed system it's feasible, and safe to leave them running and charging the batteries.

And yes web based monitoring is very straightforward so long as you choose the right products in the first place.

 

[beastman]

Properly designed systems are designed to cope with battery failures, overcharging etc.

The scale and type of controls and measures depends upon the generation and storage capacities.

PV systems are by their nature controllable on their output, small wind however usually dumps to a dump load, basically a heater exposed to the outside air. Depending upon wether you are AC or DC focussed with your generation depends upon how it is all done.

A 1 kW PV system and a 1.5 kW wind turbinw would often just go through a pair of DC charge controllers, with automatic switch on of a genny when insufficient power, PV is just automatically switched off and Wind dumped to heaters aka dump loads. The DC acts as the storage and then converted to AC through an inverter.

Larger systems are typically AC led and use Inverters, and charge controllers such as the Sunny Island product.

The simple answer is yes, with a properly designed system it's feasible, and safe to leave them running and charging the batteries.

And yes web based monitoring is very straightforward so long as you choose the right products in the first place.

Thanks for alot the reply. Sounds like your happy there no realistic chance of something catastrophic happening. Apart from perhaps storing batteries slightly away from the main building (assume this is a potentially good idea as long as the storage is well insulated to keep them at a reasonable temperature) in case of a fire hazard is there any other things that should be done to ensure nothing will go bad in the week the site is unattended?

 

[Worcester]

Definitely put the batteries in a safe place (fumes can be explosive!!)
You would also want to double check on the wind turbine braking system for strong winds, on smaller turbines these are often the weak point and a run-away turbine can be an expensive failure. If you are not going to be there and there is likely to be enough sun to top up the batteries, you might want to lower it down assuming it's on a hydraulic mast.
The PV system should be just fine!!

 

[beastman]

I am thinking say in the colder months when the solar hot water system was of little use, if I had a daily power need of say 15kw could the excess power from both the turbine and a little from the PV (obviously not much from the PV in winter) be dumped in a decent sized water tank for later use for space heating? This is on the assumption I don't have a massive and perhaps oversized and expensive battery store to store that unused energy.


Is that in theory a daft idea or could it in fact be a viable use of the energy gained whilst the building is unoccupied and have lots of free hot water when going back to the site a week after being unoccupied? Would it be totally inefficient?

 

[Worcester]

If your looking for efficiency you should consider a heat pump to build up heat in a thermal store - it would have to be pretty large store as it will be at a lower temperature, though the volume would make up for it. Also make sure it is incredibly well insulated and then use that once again via a heat pump to supply when you need it. (Old Dairy Chiller store - well insulated, stainless, steel... )

Ideally of course you would be generating hydrogen for re-use later, the technology is not there yet though...

Check out what David Nicholson-Cole is doing here: Charging the Earth - Solar! It will give you some food for thouight.

 

[beastman]

If your looking for efficiency you should consider a heat pump to build up heat in a thermal store - it would have to be pretty large store as it will be at a lower temperature, though the volume would make up for it. Also make sure it is incredibly well insulated and then use that once again via a heat pump to supply when you need it.

Check out what David Nicholson-Cole is doing. It will give you some food for thouight.

Love that website and whole idea. Definitely alot there that could be useful in the future. One wee problem, I think from the suggestion you gave, is that it crucially needs an underground heat pump system and underfloor heating. Not that I'm against them but for the purposes of this project I can't use either of these. In view of that does my idea have any legs?
thanks

 

[Worcester]

Air source heat pump (air to water) and then water (thermal store) to water should work fine.

 

[beastman]

Love that website and whole idea. Definitely alot there that could be useful in the future. One wee problem, I think from the suggestion you gave, is that it crucially needs an underground heat pump system and underfloor heating. Not that I'm against them but for the purposes of this project I can't use either of these. In view of that does my idea have any legs?
thanks

Sorry cant do an air source heat pump either! Sorry I'm being a pain now.

 

[Worcester]

Consider adding solar thermal then - just be careful which ones can cope with a power cut. Check out Surface Power | The Worlds Most Efficient and Powerful MCS Approved Solar Hot Water System

 

[beastman]

Consider adding solar thermal then - just be careful which ones can cope with a power cut. Check out Surface Power | The Worlds Most Efficient and Powerful MCS Approved Solar Hot Water System

Yes I was thinking dumping the load to perhaps say a separate water tank so in a week of the building being empty there would be loads of hot water ready to use which the SHW water system in winter wouldn't be able to do. Would also save using the biomass boiler.
However I have worked out, with the help of the Sustainable Energy Without The Hot Air book it - it takes 5kWh to heat 110 litres from 10 degrees to 50 (ie bath temperature). If a 5kW wind turbine is pushing out say 300 kWh a week (when the building is empty) then thats, in theory, enough power for 60 baths/6600 litres. That would need an underground tank then? Are my figures right?

 

[Worcester]

from recollection an MCS certified 5kW windturbine will set you back £30k-£50K installed ......