Inverter Recommendation

Re: Inverter Recommendation

Mike,

When you go with solar--are you looking to Grid Tied to the utility mains, or are you going to keep this system separate (run a few small loads/or just keep for backup power after storms)?

Do you want automatic generator starting? Or just use a small manual start unit?

At this point, I would look at the Xantrex Prosine 3kW / 24 volt inverter/charger. It is larger than you want, but includes True Sine Wave output, AC Transfer switch, a Power Factor Corrected battery charger, and remote battery temperature sensor. They have a 2kW version also, but it is only available in 12 VDC input.

Unfortunately, they appear to be difficult to get at this time--You will have to call NAWS directly for availability.

I like this as a "small" inverter/charger as it has several items that are missing from many other brands... Power Factor Corrected battery charger works very nicely with generators--reduces the amount of current (Volt*Amps, VA, VAR) that the charger takes when charging. Also has a battery temperature sensor which makes for a bit faster and more reliable charging--especially if the battery bank experiences a wide range of temperatures.

The Xantrex XW hybrid inverter/charger like would be great (above, plus 120/240 VAC split phase power), Grid Tied capable (sell the solar power back to the utility--much more efficient at getting a return on your solar array--if supported by your local utility--and then eligible for various rebates). Generator control option, etc... However, I would bet that this would be 2-4x as much as you really wanted to pay.

Regarding a pure backup/UPS like function (with solar panels and/or shifting loads with Time of Use billing plans)... Very roughly, you batteries will last 1/2 as long when cycled daily vs just sitting in standby/float applications (emergency backup power). The Grid Tied / Hybrid XW system allows you to still use the solar panel array power without cycling your batteries (they remain at float and the inverter feeds energy to your house/utility mains when the sun is up).

-Bill

Re: Inverter Recommendation

Sounds like you have a good handle on the problem.

Do you need a transfer switch (UPS function)?

Also, you could look at making the system from piece parts (inverter + charger + transfer switch)...

I agree with using a small system. For emergency power, using a backup generator that is too large can just suck fuel down like no-tomorrow.

Personally, I picked a Honda eu2000i because it is still pretty fuel efficient down to 400 watts or less (~15 hours on 1.1 gallon tank of gas). Also, it is quiet enough to use in a residential neighborhood.

Get a typical 5kW or larger unit, and you can be running a 1/2 gallon per hour (no matter how small the loads) and need 5-10 gallons of fuel per day to ride out the outage.

So--I would look at your power needs, and pick a genset size + fuel that makes sense for your situation (gasoline, propane, natural gas, diesel, etc.).

Then you can size the battery bank / inverter / charger to efficiently load your genset---Many times, a hybrid type system works well. A larger diesel generator + good sized battery charger and bank allows you to properly load the generator during charging and then you run for awhile with the generator off from your battery bank.

For me, I am both cheap and limited in the amount of fuel I can store + how much noise I can make (quiet suburban neighborhood).

I have natural gas--but plan on my "long power outage" to be the result of a large earthquake--which could knock out the gas--so I need some sort of alternative fuel anyway.

Diesel, and "prime mover" rated gensets are usually much larger than my average power needs (fridge, freezer, few lights, radio, laptop, etc.)... So, I am kind of stuck with a light portable genset (like the Honda "eux000i" family. Plus I am not sure how well a the smell of diesel drifting among the houses would fly.

For a step up in standby power would be an RV generator pack (many are available used from wrecked RV's). I have a friend that mounted a small Onan natural gas fed unit for his emergency power needs.

If you have larger loads (A/C, well pumping)--perhaps two gensets, one small, one large. The larger can be a cheaper unit that only runs when you have the heavy loads.

Because, I my planning, fuel storage/consumption is critical--I look at efficiently loading the genset (typically 50% rated power, the "eu" down to 25%) for optimum fuel usage. And I try to avoid power conversions... For example, to charge your battery bank from a genset:

• 0.80 charger eff * 0.80 batt eff * 0.85 inverter eff = 0.54 overall eff...

So, I could waste almost 50% of my fuel usage just to charge now and use power later...

If I was looking to use a small genset (like the 1,600 watt Honda), I think that the 3kW prosine is a bit large... And I would look at picking some smaller piece parts to make up the standby system.

-Bill

Re: Inverter Recommendation

From my post in the Ham Radio thread:

This guy wrote something that I pretty much agree with (with my limited education):

To answer the specific question of the OP, it depends upon the application. Military electronic hardware, save for acceptable commercial-off-the-shelf (COTS) components, area built to specific interface standards like MIL-STD-464 (Electromagnetic Effects Requirements for Systems), MIL-STD-461 (Requirements for the Control of Electromagnetic Interference Characteristics of Subsystems and Equipment), and MIL-STD-2169 (Classified) (High Altitude Electromagnetic Pulse Environment). The latter is probably most pertinent to the question, and for obvious reasons unavailable to the public at large. However, the ugly truth about high altitude EMP is that no amount of shielding, save being buried deep under hundreds of feet of rock or dirt, is really adequate to protect sensitive microelectronics. By their nature, the electronics are delicate and sensitive to small levels of excess voltage, and it is nearly impossible to make a practicable sensor, communication system, or avionics control that has to interface with the outside world and yet is adequately isolated against large pulses.

High altitude EMP (HEMP) devices produce three distinct regimes of pulse, referred to as E1, E2, and E3. Microelectronics are most sensitive to E1, which is due to interaction of x-ray and gamma ray radiation with the rarified upper atmosphere and the geomagnetic field resulting an a nearly coherent, widely distributed pulse, sort of like a very large free electron maser. In more dense atmosphere where the the rays are rapidly absorbed and don't have much length to deflect, this pulse is serious attenuated, and the amount of damage done but the physical effects of the blast (shock and thermal wave) would likely make E1 effects moot. E2 is more like static electricity, and can typically be shielded by using a protected ground or faraday cage type shielding. E3 is energy that is stored in the Earth's magnetic field (similar to that which comes from coronal discharges and solar flares) and will cause longer term disruption and very high voltage spikes in large arrays like power grids; again, not much of a threat to microelectronics.

So, from my point of view, the solar flares produced relatively low frequency changes in magnetic fields... Probably would take structures on the size of miles or 10's of miles to capture the energy (1/4 wave length or larger?).

Here is a wiki entry for geomagnetic storms:

Electric grid When magnetic fields move about in the vicinity of a conductor such as a wire, a geomagnetically induced current is produced in the conductor. This happens on a grand scale during geomagnetic storms (the same mechanism also influences telephone and telegraph lines, see above) on all long transmission lines. Power companies which operate long transmission lines (many kilometers in length) are thus subject to damage by this effect. Notably, this chiefly includes operators in China, North America, and Australia; the European grid consists mainly of shorter transmission cables, which are less vulnerable to damage.[12]

The (nearly direct) currents induced in these lines from geomagnetic storms are harmful to electrical transmission equipment, especially generators and transformers — induces core saturation, constraining their performance (as well as tripping various safety devices), and causes coils and cores to heat up. This heat can disable or destroy them, even inducing a chain reaction that can blow transformers throughout a system.[13][14][15] This is precisely what happened on March 13, 1989: in Québec, as well as across parts of the northeastern U.S., the electrical supply was cut off to over 6 million people for 9 hours due to a huge geomagnetic storm. Some areas of Sweden were similarly affected.
According to a study by Metatech corporationI][URL="http://en.wikipedia.org/wiki/Wikipedia:Citation_needed"]citation needed[/URL][/I, a storm with a strength comparative to that of 1921, 130 million people would be left without power and 350 transformers would be broken, with a cost totaling 2 trillion dollarsI]not specific enough to [URL="http://en.wikipedia.org/wiki/Wikipedia:Verifiability"]verify[/URL][/I.

By receiving geomagnetic storm alerts and warnings (e.g. by the Space Weather prediction Center; via Space Weather satellites as SOHO or ACE), power companies can (and often do) minimize damage to power transmission equipment, by momentarily disconnecting transformers or by inducing temporary blackouts. Preventative measures also exist, including digging transmission cables into the soil, placing lightning rods on transmission wires, reducing the operating voltages of transformers, and using cables that are shorter than 10 kmI][URL="http://en.wikipedia.org/wiki/Wikipedia:Citation_needed"]citation needed[/URL][/I.

I do not believe that an off-grid solar array, backup generators, inverter, etc., would be susceptible to a solar flare event.

For grid tied systems--there may be a risk of damage from surges on power company transmission lines entering the home electrical system (guess on my part).

-Bill