Re-Thinking My Off Grid System

Rngr275 · June 2012

Thanks to many of you here I had been leaning towards a 48V, 2-3Kw PV with battery back up (Size undecided 1-2 daysautonomy probably) and a generator (probably a decent Honda or similar) as a start to get my feet wet. I was figuring that this would be a decent system to handle my expected daily power requiements (3-5Kwh as calculated using my most excellent Kill-a watt). As a side not my family screams and runs when I have it in my hand looking for something to measure its wattage use!:D

An installer had propsed: 24V, 2Kw PV, 1000Ah battery back up and a generator. This was a proposal and completely open to changing.

After thinking about all of the above it hit me that I had not thought about some other things that I like and will want to do. In a nut shell I have some wood working equipment (nothing real big) but big enough that it would definately have a real impact on my power/energy use when I fire things up from time to time (table saw, band saw, radial arm, etc). Damn I'm an idiot for not thinking about this... but anyway.

So now I am thinking about something like this... and again I would like your input/HELP!

Similar to my first set up 3-5Kwh for typical usage ( Shop not included), 48V system, 2-3Kw PV with battery back up (1-2 days say ~ 600Ahr or so) but then step up to a little more robust generator like a 5-8Kw diesel. I could use the generator as needed to keep the batteries healthy, maybe time my shop work near the end of the charging cycles so as not to impact the battery charging, or just fire it up for shop/laundry/heavy load days. Or use the generator stand alone when needed to feed the shop power. I know they are more expensive but looking at a Perkins or Isuzu I could get a 5-8Kw one for $5-7K. It also gives me peace of mind in case I need to run it for a long period of time if needed since they are more rated for continuous use.

Also, looking ahead can I place this generator 100ft from the house in my barn? That would keep it out of the weather, make it not so noisy for the house. But in the house will be all of the PV system (inverter, charger, battery bank).

What do you gents think?

Ralph Day · June 2012

Re: Re-Thinking My Off Grid System

100 feet from the house will work. It'll be outputting 240vac no doubt, so not a problem with the right wire. Running at 1800rpm makes for a quieter generator. Mine is in an insulated shed, 130 feet from house, exhaust directed away from house, and it is less noisy than my neighbour's 2cyl 24hp lawn tractor which is 400 feet away running for 3 hours at a time. (genset is 10kw Nissan diesel). You can even outfit your engine with a hospital grade muffler to further quiet it's running noise.

My gen shed is not overly large so I had to put a dedicated barn type fan in to exhaust the heat thrown off during running...not a big deal. Does your barn have hay/straw or any residue of same? Could be a fire hazard.

Ralph

Rngr275 · June 2012

Re: Re-Thinking My Off Grid System

No hay/Straw it will actually be used as our garage (was the Amish buggy barn). Can 240VAC feed the inverter/charger?

Eric L · June 2012

Re: Re-Thinking My Off Grid System

"Can 240VAC feed the inverter/charger?"

Some can, yes; depends on the make and model.

From your description, it sounds like the shop tools can be seen as an opportunity load; i.e., there won't be many or any days where you HAVE to run the table saw, e.g. If so, you can wait good sun conditions and do as you suggest; using the tools in the afternoon on sunny days.

I've run a table saw, chop saw, drill press, etc. on my 4.1 kW pv system this way using a Magnum 4448 PAE inverter (240 VAC output and input for charging). It hasn't been a problem, although my usage has been light.

I would carefully balance the cost of those more expensive generators you are considering against the (possibly considerable) extra pv panel capacity you could buy with similar money. There are a lot of factors to weigh here, including your location and sun conditions, but having a larger pv array relative to your battery size may allow you to do a lot of 'opportunity loading'. That has been my experience, at any rate.

vtmaps · June 2012

Re: Re-Thinking My Off Grid System

Here's my advice... Build your system (panels and battery) for your domestic needs, but make sure your inverter is large enough to handle your shop needs. Get a small high quality inverter generator (such as honda eu2000). Get a battery charger that can be powered by your generator.

When you need to work in the shop, start up the generator and battery charger. You can now use tools that draw more than the generators output. You are using your big inverter/charger as an inverter, and using a separate charger at the same time.

I find that most shop tools are used intermittently. Thus you may be charging 1600 watts (honda eu2000) for an hour or two, while occasionally drawing 2000 or more watts for a power tool.

The advantage is that you have a lower investment in generator, panels, and battery. This idea is called "the DC concept" by Victron. read about it here:
http://www.victronenergy.com/upload/documents/Book-EN-EnergyUnlimited.pdf

--vtMaps

stephendv · June 2012

Re: Re-Thinking My Off Grid System

Eric L wrote: »

I would carefully balance the cost of those more expensive generators you are considering against the (possibly considerable) extra pv panel capacity you could buy with similar money. There are a lot of factors to weigh here, including your location and sun conditions, but having a larger pv array relative to your battery size may allow you to do a lot of 'opportunity loading'. That has been my experience, at any rate.

Ditto what Eric suggested. An industrial continuous rated genset like perkins/cummins etc is about the best you can buy. But no matter how reliable, they will require maintenance and more importantly FUEL! $7k worth of solar can make a substantial contribution to your energy requirements, and requires close to no maintenance and is expected to last 25+ years.
A small backup genset is always handy, not only to augment battery charging in bad weather but also as a redundant power source in case something on the AC side fails. I replaced my 1500rpm diesel monster with a small petrol honda in January. So far it has 1 hour on the clock

Rngr275 · June 2012

Re: Re-Thinking My Off Grid System

That is why I love this site. Makes sense to me. Plan on using the shop periodically at best. All my equipment is 110AC. Radial arm saw is probably biggest draw... would a 2000W Honda handle that alone (if I wanted to just power that)? Sorry I don't know the wattage.

One installer that I did talk to gave me a rough estimate of $5K for 1KwPV installed with a top mount. But I can reduce a large amount of that by doing much of the work.

I have seen (Some where) that all things considered a rough estimate of the out put of a 1Kw panel would be ~2.5Kw a day (includes losses and 3hrs sun I think). Is that a reasonable#?

vtmaps · June 2012

Re: Re-Thinking My Off Grid System

Rngr275 wrote: »

would a 2000W Honda handle that alone (if I wanted to just power that)? Sorry I don't know the wattage.

Not long. The honda is 1600 watt continuous, but can go higher for awhile. The similar Yamaha is rated a coupe hundred watts higher. --vtMaps

Eric L · June 2012

Re: Re-Thinking My Off Grid System

Radial arm saw is probably biggest draw... would a 2000W Honda handle that alone (if I wanted to just power that)? Sorry I don't know the wattage.

Can't say without knowing the wattage it uses. But consider if you had a set-up like vtmaps suggests above you'd be able to supplement the generator's output with the pv output and/or battery power to bridge the gap (if any). His proposal sounds like a cost-effective way to get some extra power when needed.

One installer that I did talk to gave me a rough estimate of $5K for 1KwPV installed with a top mount. But I can reduce a large amount of that by doing much of the work.

There are so many variables it's hard to judge these estimates (and does it include all equipment, even batteries?). Just for reference, my 4.1 kW system with a relatively small 360 amp-hour battery bank (48 volt) cost me $2.76/watt installed recently (I did all the work, but that number does include all major components). So it may be possible to get the price lower, but without knowing all the particulars of your installation it's hard to say. I would certainly suggesting pricing out a system yourself though, and start with a 48 volt system, given your plans.

Cariboocoot · June 2012

Re: Re-Thinking My Off Grid System

Since the saws are intermittent use but high current demand (especially when cutting wood - I measured a few; it's around here somewhere on the forum) I would run them from the inverter and just leave the gen for boosting the batteries back up afterward.

1 kW of PV will produce about 2 kW hours AC on a sunny day with 4 hours of good sun.

Rngr275 · June 2012

Re: Re-Thinking My Off Grid System

Thanks to all!

Once this is done and installed everyone is invited over for a beer (Homebrew).

Prattsburg area Cariboocoot:D

BB. · June 2012

Re: Re-Thinking My Off Grid System

By the way, many times it is better to have several gensets... A smaller/more fuel efficient for day to day use. And a larger/cheaper genset for occasional high power needs.

And spend the bucks to get a good genset for which ever one you will be running longer--With good sound insulation. Nothing like being embarrassed every time you run your genset because it bothers people blocks around (and making your "quiet" farm life a nightmare).

A small eu2000i type genset will run ~9.5 hours on a gallon of gasoline while running a 400 watt average load. A 5-10kW genset will run the same load on about 1/2 - 1 gallon per hour (or even more) for fuel.

While the Honda eu family gensets are "throw away" type engines--With good maintenance and a bit of luck, you should get ~2,000 to even 6,000 hours (one user here with a eu1000i genset) of use from one.

-Bill

Cariboocoot · June 2012

Re: Re-Thinking My Off Grid System

Rngr275 wrote: »

Prattsburg area Cariboocoot:D

(À la Maurice Chevalier) "Ah yes; I remember it well!:

Vic · June 2012

Re: Re-Thinking My Off Grid System

Have read that the Honda EU gensets (at least for the USA) have a 20 minute Surge rating, unlike inverters, or inexpensive non-inverter gensets. I did ask a Honda dealer to confirm this, and got a call back indictaing that this was correct (some have said 30 min Surge). FWIW.

Agree with BB Bill, about having several gensets. A large HD diesel is nice if one has a fairly large system, and one or two Inverter gensets works great. The genset that is used most here is still the lil Honda EU 1000is. It weighs about 30 lbs wet -- easy to carry and runs small pumps, drills, saws, auto battery charger and so on. It will NOT run a large worm drive saw, or almost any table saw etc, but is sure handy for smaller jobs away from AC power. Also use use larger EU gensets on the Grid In terminals of inverters. This allows using a HD genset on the Gen terminals, and the more fuel stingy inverter gen on the grid terminals. (this trick does not work so well on SW series inverters when they try to regulate charhe volatge ...). Vic

Cariboocoot · June 2012

Re: Re-Thinking My Off Grid System

Of course you can buy two Honda EU2000i's and hook 'em together for 3200 Watts of power.

stephendv · June 2012

Re: Re-Thinking My Off Grid System

Given that you're likely to expand in the future, I think the inverters you buy now should be versatile enough to cope with what you throw at them down the road. In addition to going 48V straight off the bat, it would be good if the inverters are parallelable so that you can increase peak power if needed by adding more inverters. Another nice feature of some of them is "generator boost" or gen support or gen assist or some such, which basically means that you can configure them to assist the generator, e.g. gen of 4kW and inverter of 4kW means you can draw 8kW. Not all inverters support this.

Re-Thinking My Off Grid System

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