All-Renewables Observatory - feasibility

[pmrid]

I'm gradually weaning myself off the grid. But because I don't have an electrical or electronics background, I have to be quite frank about what I don't know. I suspect I'm not alone either in wanting to be more off-grid and lacking that sort of background. So I thought I might propose a sticky thread to deal with all things renewable as it applies to our hobby (obsession).

To kick it off: I've had a grid-connected system for 6 or 7 years now and still have the benefit of the early and bigger rebates that were offered. So my domestic power bills are currently fairly negligible. That will change with time since the unit prices are always going up and new connectivity fees and charges are being added and are also on the way up. And the rebates are not indexed. In time I may have to go fully off-grid.

But for the moment, the next area I have targeted for a full conversion to renewables is my observatory. But I'm struggling to get my head around the various equations that determine the sizing of the system I need.

I have recently made an impulse buy of a small wind-solar system (1 x 400 watt turbine and 200 watts of panels with a controller but no inverter). I also already have 3 x 105 AH deep cycles 12 VDC batteries I can connect.

My existing 500 watt Sine-wave inverter will be way too small so I am reconciled to having to replace that among other things.

In my obs I have several scopes on their own piers. It is not unusual for me to have at least 2 of them working at any given time (night-time only of course) and there are various internal lights etc in the warm room, a separate little IBM linux-based micro system running some music. All computers and mounts/scopes/cameras are currently sitting behind their own UPS. In a wholly offline system those UPSs may no longer be necessary (I suppose).

An important reality to keep in mind these days is that there is often (usually) a fair time between imaging opportunities. That is fairly seasonal of course. Over recent years, I've not had much imaging between about November and April. And even in winter, I usually only image a week either side of the new moon. So there are often long periods during which the system is not consuming much if any electricity. When I am using it, however, it will often run 4-6 hours at a time. And in winter, add some extra demand for running dewstraps etc.

Has anyone already been down this road? I'd sure be grateful for some guidance.

Peter
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[glend]

Peter my single pier observatory is off-grid now. Because I make regular dark site trips I already had all the 12V gear I needed to take the astro equipment off-grid. When I built my observatory I laid in a single 10amp AC cable from my shed solar system inverter, the rest of the power requirements in the observatory use standard 12V supply from my dark site batteries which I keep in the observatory and which are charged by the shed solar system during the day. The key element of my system is 500W of solar panels on ground mounts dedicated to charging (through a 30A MPCC charger) my shed battery bank ( 4x 100ah Deep Cycle batteries) with a 5000W Sine wave inverter. The single most energy hungry device in my observatory is the DSLR camera cooling system (12V, 6ah on max cooling), and this is powered off the inverter in the shed or via the observatory batteries depending on which adaptor is used. My observatory laptop runs off the AC feed from the inverter, or its nine hour internal battery. As long as you don't want a fridge, coffee makers, etc in the observatory it is pretty easy.

I looked at wind turbines but they are expensive and relatively low output and almost exclusively three-phase AC output requiring a controller as well. In NSW there are regulations regarding their use which make it almost impossible in residential areas - separation distances, noise, etc. I could not make a case for wind; but if you lived on a rural property I guess they could be useful.

[pmrid]

Hi Glen. looks like you've got a well-balanced system.
My flirtation with a wind turbine may all end in tears! I accept this. Particularly since the unit I bought is only quite small- 400 watts with a swpt area of only about 1.5 square meters. But I'm in a rural location with good SE and S winds a lot of the time and an average wind speed of between 5 and 6 mps. So I ought to get some charging benefit from it. And with a couple of solar panels to augment it, and long intervals between actual power usage, I ought to be able to keep 300 AH of batteries fully charged most of the time.

This could be a fine example of "famous last words " but I'm hoping there is a balance in there somewhere.

I have an extra couple of smaller solar panels and a 30A charge controller so I can always throw those into the equation and add a second charging source for the batteries, increasing the solar input to about 300 watts.

I'm more concerned about the inverter. I see a 5000 watt pure sine wave will run to about 3 grand. That is probably 10 times more than the power I would expect my obs to consume in a year - making it a dubious investment.

I think I'll start small and see if I can set up just one of my scopes to run off-grid and use that as a tester for a larger system. I hope my 500 watt psw inverter will be uo to that sort of load. We'll soon see.

Peter

[DavidTrap]

Peter, I'd be surprised if you actually use more than 500w across your entire system. I can run my rig up at Leyburn and not drain a 100Ah battery during a night. I only use a 20w panel to recharge, but it's not an issue when I'm only up there once a month at most.

Have a look at the software that comes with your UPS, it may be able to tell you what the load of your system is?

DT

[pmrid]

Hi David,
thanks for the tip. I did that. Interesting but, like to "Curate's Egg " , it is only "good in parts ". [ Google that! Interesting bit of trivia].

The UPSs are Belkin 1400VA line interactive models. There is a Belkin Automatic Power Management software which is very much a network administrator's tool - scheduling, self-testing etc. But it does include a "load " figure but with no explanations. I ran it up on 2 systems, one a full i7 desktop with the Titan mount running and SX imaging train. System reported 9% load. The other was a low-power i7 Gigabyte Brix running an EQ8 with QSI imaging train. That one reported 6% load.

Since the 1400VA Belkin says it has an 840 watt output capacity, I am assuming for the moment that this is what the "load "refers to. The Gigabyte Brix for example only drawn 65 watts of juice at 19 VDC so that is starting to look about right.

So I am taking some comfort from those figures even though I'd like more explanation about the specifications of the UPS, that just isn't anywhere to be found.

I miss the days of printed User Manuals!

Peter

[ZeroID]

Yup, you're right., 9% and 6% respectively is about right. ( My wife sells all this sort of stuff so I get to see lots of it ).

Our 3kVA shows less than 10% for the whole TV, Sound system and PC unless I give the volume a big tweak up.

[glend]

Mounts don't use much power at all, most are around 2AH max when slewing at highest speed. It's camera power where you really need the AH. Whether its a cooled CCD or a Cooled DSLR, you can require up to 6AH especially if using motorised focusers, filter wheels, etc and that alone is going to mean probably a 100AH to run imaging all night (that's what I use at my dark site).

If you want grid independence for your observatory then add up all the load elements and size it on that basis. Do not discharge a deep cycle battery more than about 60% (on a voltage basis).

[ZeroID]

Bit more info for you, checked with wife cos I wasn't 100% sure. Your Belkin UPs is only running at about 60% efficiency, very low. 840 watts output from 1400 kVA input is not great.

Newer and I guess a bit more expensive units run at better than 90%, some as high as 97%. 90% would give you about 1250 watts and a lot less heat.

If you are going off grid totally just go to battery and solar panel for your 12volt supply, far more efficient. If you require higher volts for a laptop then there are automotive voltage converters that use inverter circuits to give 240VAC to run the laptop when the battery gets a bit down. Auto shops have them.

A UPS requires a 240VAC input to charge the batteries which you will then convert back to 12 VDC mostly. Line interactive will not deal well with Solar panel 12-24 VDC > 240 VAC inverter input. Unstable and input voltages will give it a lot of grief.

[pmrid]

Thanks Brent. This is proving to be quite a learning experience.
The use of an inverter as a 240 VAC source feeding a UPS seems to be out then. That raises the question then why bother with putting a UPS into the power train at all since it is primarily there to deal with " grid" issues that won't be there in an off-grid system? Power spikes, outages, brownouts, surges, price increases :D
peter

[glend]

I saw no need for a UPS in my system. If you have a battery bank which is charged by solar panels and distributes load as 12V DC via the Mulitpurpose Charge Controller (MPCC) and as AC via a bank attached inverter then you effectively have everything you need. You can get MPCCs which handle solar, and wind turbines inputs.
As far as the inverter is concerned you will need to provide a fusible link protection between the battery bank and the inverter +12V supply. Also I highly recommend a battery disconnect switch to isolate the the battery bank (in professional bank installations each battery would have an isolation switch), and an IPS switch to isolate the solar panels from the MPCC. This way you can work on any segment of the system while it is 'live' by isolating the others. Suggest you look at Whitworths online (its a boating supply business with retail outlets) as they have all the 12V stuff you need. The MPCCs are availble on ebay.
Finally, I am of the view that 'everything should have two purposes', and thus I can remove batteries from the bank (and this can be done live if you know what your doing) and install them in my camper when I go to the dark site. I leave two batteries on the bank and two go into the camper for my dark site supply. My camper has its own solar charge controller, and I carry a 80W solar panel to provide continuos daytime charge and supply to the camper bank, and a portable 120W fold up system for back up and to charge the smaller batteries I take for the scope equipment, heaters, etc, (40AH) and (21AH) respectively. I can extend the camper battery bank via an Anderson plug & cable off the camper to the camera cooling system. I have a small inverter in the camper to supply AC for charging tablet, phone, etc, and Laptop battery for imaging.
So when you build your system, consider the design if you intend to go out to a darker site at some point, as this will potentially save you some money by avoiding additional purchases or dual purposing items.:thumbsup:

[pmrid]

Thanks again Glen. Point of information: what is an IPS switch. That's a new one to me.

Peter

[glend]

Peter it is just a weather proof switch, needed if it is to be mounted outside. Similiar to the ones used to isolate roof top solar panels on the extenal wall of house.