Grid vs. Off-Grid

[D.I.M.1]

Once again I'm showing my complete lack of knowledge for this field:
What is grid and off-grid?

How are they different?

Which is better?

How are they used?

How do they function?

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My only goal in life is to get my questions answered myself before they get answer and I can't tell anyone.
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[GreenPowerManiac]

Grid: Power supplied by electric utility company

Off-Grid: Your own supplied electricity system cut off from Grid

Which is better ? Obviously not paying the utility company for something that can be created FREE. Well, you have to fork over tens of thousand of dollars in some cases to go off grid.

We all know how Grid systems are used.

There are partial Grid/Off Grid systems. My friend has a 1kw Solar array fed into an inverter and wired up directly to the telephone pole.
Off Grid systems depend on the amount of electricity they produce.

How do they function ? Someone else can answer that one who can more appropriately answer it.

[BB.]

Xantrex has a quick explanation about the major types of home solar power.

The big issues are function (do you want to "save money", "be green", have emergency power, or you don't have utility power...

Save Money--first spend money on conservation. It is almost always cheaper to save electricity vs making it.

Going Green--Grid Tied power (solar panels connected to a special GT inverter that can synchronize with grid AC power) is the cheapest and most cost effective method of making power at home. With good sun and government rebates/credits--it can actually be cheaper than utility power in some states. Bascially, think of a GT Inverter like an AC battery charger that can 'recharge" the electric utility (push power to the utility and spin the meter backwards).

Emergency Power--Is "off grid" power. Solar panel to charge controller to battery to DC/Load and/or Off-Grid Inverter. This is actually the most expensive use of solar power. System sits unused until power is needed (a few days or weeks per year). For most people, a simple gasoline genset would be a better investment. Usually need a backup genset anyway to help in bad weather.

Off-Grid power. Making your own power (same as off-grid) but using it over 9 months of the year (3 season cabin, remote home, etc.). Usually sized a bit larger to reduce genset use to near zero for 9 months of the year. May still need some backup genset use to charge batteries during winter.

Hybrid Solar power. Basically a UPS for your home. Solar panes, charge controllers, batteries, and a special inverter that can be a GT Inverter (work with grid) and be an Off Grid inverter (no AC power, grid down). Basically a large UPS for your home.

Cost of power (very rough cost estimates):

$0.10-$0.30 per kWhr for grid power
$0.15-$0.30 per kWhr for Grid Tied Solar
$0.20-$0.45 per kWhr for Hybrid Solar (GT+Emergency power)
$1.00-$2.00+ per kWhr for Off-Grid power (9+ month usage a year)

Making your own power is expensive--and if something breaks, you pay to fix it. Utility power is hard to beat. Batteries add a huge expense--both for the batteries, and their replacement every 3-10 years or so. And, battery+inverter+charge controller have more losses (less efficient) than a "simple" GT system.

-Bill

[mshen11]

indirect question on cost.

youve mentioned batteries are 3-10 years
how long does inverters, controllers, wires last? assuming indoors and you leave them alone, always on.

[BB.]

I don't know (not in the business)--but my guess is 5-15 years on average for the electronics. Electrolytic Caps and fans are typical weak points. Thermal cycling and high temperatures are another big killer...

I used to qualify computer disk drives back in the 1980's--and two weeks in a thermal chamber cycling every 4 hours between min/max operational temperatures would kill 80% of the vendors (at the time)--mostly popping components off the board and breaking solder joints. Good drives/mfg.--I never got them to fail thermally.

Regarding temperatures--The Engineering Rule of Thumb is for every 10C increase in temperature, you cut the life by 1/2... 30C increase is 1/2*1/2*1/2=1/8th the life. Also works the other way, cooling by 10C would double life.

Keeping your equipment+batteries cool and in stable temperatures is 1/2 the battle.

Xantrex (and others probably) have a 10 year warranty on the GT Inverters (used to be 5 years).

Wiring (in conduit) should last the life of the building. I don't know how long UV rated/stable wire is "supposed to last" in sunlight. My home's utility drop is UV rated and all twisted in a bundle--so I would hope it would last the life of the installation.

Solar panels, that are not damaged or mfg. faults--should last 25-40 years (crystalline silicon panels are supposed to only have ~80% output after 20-25 years--Solar Guppy has posted before that "good panels" seem to output 100% of their power even decade(s) later).

Also--long panel life means that you may need a new roof with 40+ year rated roof covering. You don't want to install the panels on an old roof.

-Bill

[mshen11]

[Regarding temperatures--The Engineering Rule of Thumb is for every 10C increase in temperature, you cut the life by 1/2... 30C increase is 1/2*1/2*1/2=1/8th the life. Also works the other way, cooling by 10C would double life.]

assuming 10 years (5-15 years average) is the baseline... what is the baseline temperature to work off these general calculations? 20C?

[PhilS]

indirect question on cost.

you've mentioned batteries are 3-10 years
how long does inverters, controllers, wires last? assuming indoors and you leave them alone, always on.

I have some experience here, having used inverters and battery banks for over 25 years and solar panels for ~20 years.

Man, I gotta knock wood here: I've never had an inverter or controller fail. The first inverter I bought was a Heart Interface high efficiency 2000w MSW. I replaced it a few years ago with a better one, closer to TSW (or is it PSW?). It was powering my water pump, and motors don't like MSW, so when the pump burned out I moved a Xantrex SW2500 to that circuit, and bought a Magnum to replace the Xantrex.

But I got twenty years from that Heart Interface and now it just sits in the garage. It was still operational when it was replaced for better technology.

I have a Xantrex Prowatt 2000w inverter in shipment now, to replace a Prosine 1000w inverter. No problem with the Prosine except that I added a mini-split air conditioner and I want to power it from our "lights and entertainment circuit", but the 1000w inverter isn't powerful enough. The Prosine is still working great and has been on most of every day for years.

I've bought solar panels every few years since the late eighties/early nineties. When I buy panels, the purchase always includes a controller (duhh). I now have 4 controllers (C60, two MX60s, an FM60) not counting the original C30 that I moved to our RV. I've made 6 panel investments. None have failed. All are producing as much power as they did when new (it'll be another thread that I explore the firmware revision of the FM60, which doesn't produce as much power in a day that the MX60 did on that same solar array).

I'm on my third battery bank -- 12 T-105 -- and I expect something over 8 years from a set. I have two "desulfators" (one on each end of the bank) but cannot verify that they do anything at all.

SOOOOOOOOO... my experience is that this stuff doesn't wear out or fail very often, if at all.

Phil

[BB.]

Don't know for sure... When I was designing other equipment--we assumed 95F for office and 122F for industrial.

Check the vendor specs... Some have quite low enviromental (I have seen 95F in times past). I would suggest a minimum of 50C/122F equipment rating if it will be installed in a garage/shed/outside.

-Bill

PS: Regarding what Phil says--I would hope that my system lasts longer than 5-10 years too... However, I would also have money in the bank (savings) to be able to replace/repair and failed components too.

Whether they fail from age, poor design, water leaks, or lightning strikes--the equipment will need to be repaired. And that adds to the overall life cycle costs.

The $$$/kWhr price estimates are based on retail pricing, 20 year system life, and with one battery set change out at 10 years.

Equipment may last longer than 20 years, and you may spend 2x as much money for a 2x longer lasting battery bank ($$$ does typically equal longer battery life--assuming the batteries are treated well), no interest, taxes, depreciation taken into account... While solar panels may last 40+ years--after 20 years, I am not even going predict the world will be around--let alone worry about "present value/future worth" calculations.

The numbers are estimates to help guide you to the appropriate solution for your needs. Obviously, they are just SWAGs (scientific wild a$$ guesses) and you should do your own due diligence regarding your proposed system.

If you have some numbers (cost, life, power usage, location where installed, etc.)--the basic math is pretty straight forward.

Do not look at solar RE power as an "investment" in the value of your home... From other discussions here--Grid Tied systems really only have value to the person who installed them. People may pay some fraction of the value of the RE System when they purchase a home so equipped--but others buyers will be "afraid" of the system and its "unknowns" and may discount the price of a home equipped with GT.

Similar issues with Off-Grid systems too... They have little residual value (equipment is obsolete, no parts; batteries are old, etc.).

[PhilS]

I mis-spoke in my previous post.

I HAVE had a controller fail ... but I don't count it as a "failure", I count it as defective design and/or construction:

http://www.wind-sun.com/ForumVB/showthread.php?t=1779

Phil

[Photowhit]

While I don't have the 20+ years of background that PhilS has I;ve been off grid most of the last 10 years. In that time i Have had one controller failure a small scs unit that lived 5 years for me inland and 2 years on my sailboat and 3-4 years on my dad's pontoon boat before failing, pretty good for a saltwater enviroment the last half of it's life.

I've also had an inverter failure, a cheap no name quasi sine wave (not a true sine wave but lots of steps) Likely I could have saved it if I paid more attention to it, The cooling fan failed and I just opened it up and ran a small fan over it continuously. worked that way for @ a year before releasing the magic smoke. I hadn't paid much for it and got what I paid for. it liked it's input voltage 22-30 volts so every month it kicked out when I did an equalizing charge, so perhaps that helped shorten it's life. I had already purchased a never used Prosine 1800, a better option as it lives outside.

I do buy lots of used equipment. about 8 years ago I paid @$2 a watt for 3 - 55 watt French Photowatt panels made in the late 70's, when I moved 3 years ago they were producing @ 80% of their rated value (sorta, at least functionally with a 60 charge controller, measured amperage off of a Trimetric, it's rated 18+ volts could have been reduced, measure input over 2 hours at solar noon. New panels are often in this range!)

I have an old 30 amp SCSII (don't think thats correct but close) charge controller that is close to the same vintage as the panels, that was functioning fine when taken down 3 years ago for the move.

While off grid, I have no backup generator, so I, Like PhilS, have spares of most anything I need, it comes with growing a system and may be the single biggest uncalculated expense.

With bargain hunting, and installing the system my self, I figure I'm about as cheap as a home system can get. BB stated that "Grid connect" going green, I think this is an important point as most off grid systems will not produce and use as much energy as it takes to create the panels and recycle the batteries. I find lots of people who think I'm "going green", and I don't doubt that having and maintaining an off grid system I use a lot less energy than grid connected people, only in this way is an off grid system green.

I'm not saying it can't be cost effective, if you have a long run to grid connect, or very high user fees (local Elec. charges $25 per month, here before you buy any elec. or I would be grid connected)