Grid tied - or not!

[clnpwrman]

I really like the concept of the panel mounted inverters to feed directly into the grid. Problem is; when the grid goes down, so does solar generation. Is anyone aware of off the shelf hardware that can power ones house without batteries when the grid goes down? I have some gulf cart batteries acting like a super UPS for the computers, refrigerator, etc. But now I want to add some solar panels with inverters that will keep me going in an extended power outage. In the case of a grid melt down, I would like the panels to continue to suppy AC power even if the batteries eventually failed. I know it's technically possible, but I would rather buy then build.

Thanks for your help.

[solar_dave]

Grid tie inverters need a voltage and frequency reference to operate, I think they also don't they take well to not having a place to sent the power to, so,if you could use a generator for the reference or a battery inverter neither will like being back fed.

[mike95490]

I really like the concept of the panel mounted inverters to feed directly into the grid. Problem is; when the grid goes down, so does solar generation. Is anyone aware of off the shelf hardware that can power ones house without batteries when the grid goes down? I have some golf cart batteries acting like a super UPS for the computers, refrigerator, etc. But now I want to add some solar panels with inverters that will keep me going in an extended power outage. In the case of a grid melt down, I would like the panels to continue to suppy AC power even if the batteries eventually failed. I know it's technically possible, but I would rather buy then build. Thanks for your help.

Xantrex XW MPPT 80 Amp 600VDC Charge controller.
our host sells them http://www.solar-electric.com/xaxwmp80amp6.html a bit expensive, but so is re-stocking a moldy fridge. The charge controller, 48V worth of batteries, and a 48V inverter, and you are set. The bigger the batteries (up to about 700AH worth) the longer the runtime. And the more expense to pay when replacing the batteries at year 7.

[BB.]

Pretty much, you should start with measuring and documenting your current power usage. A Kill-a-Watt meter (or similar) is great for measuring plug-in appliances. And there are whole house type units (like T.E.D.) that are useful too (especially if you have A/C, electric hot water, etc.).

After you have done that, then look at what you can do for conservation... The usual like adding a lot more insulation, double pane windows, Energy Star Appliances, laptop computer vs desktop, turning off entertainment systems when not in use, etc... All can help.

Now you are at the point of looking at solar energy... If you are here to purely save money. After all of the conservation, go with Grid Tied and, possibly, a backup genset (propane, natural gas, diesel, gasoline, etc.) sized to your loads.

For generators, it is easy and not very expensive to install a 10kW whole home genset. However, when you see them sucking down 1-2 gallons per hour just to run a few lights and a refrigerator (most of the time), they get scary expensive to operate very much and difficult to supply fuel for more than a day or so without a large fuel cache.

A smaller genset which can supply power 12-18 hours a day on a couple gallons of fuel a day (like a Honda or Yamaha ~1,600 watt inverter/generator) is usually very practical for emergency backup power.

If--You need to go off grid (very rural area that is the last to receive power after an ice storm, preparing for other things), then you can look at either a pure off grid power system, or a Hybrid inverter system that does both grid tied and off grid (does need a battery bank)...

But with any off grid system, the price of power is not cheap (hence why we suggest starting with conservation first). For example (very rough numbers):

• $0.10 to $0.20 for Utility power
• $0.15 to $0.30 for Grid Tied power
• $0.45 or so for Hybrid Power (when running on utility power, solar/battery power available for backup)
• $1-$2 per kWH for Off Grid power (and usually generator power)

Remember that batteries age and don't really last much longer than 6-15 years or so... And the electronics should be budgeted for replacement about every ~10+ years.

Which gets us back to conservation--The less power you use in the first place, the less you have to spend on Solar and/or emergency backup power.

-Bill

[Lee Dodge]

But with any off grid system, the price of power is not cheap (hence why we suggest starting with conservation first). For example (very rough numbers):

• $0.10 to $0.20 for Utility power
• $0.15 to $0.30 for Grid Tied power
• $0.45 or so for Hybrid Power (when running on utility power, solar/battery power available for backup)
• $1-$2 per kWH for Off Grid power (and usually generator power)

-Bill

I have estimated the electricity cost amortized over 25 years for three grid-tied systems installed here in sunny Colorado, and have come up with much lower electrical costs than what you have provided, namely, $0.064/kWh, $0.080/kWh, and $0.082/kWh. These estimates are for two different utilities that have different rebate strategies. Details of how the costs were computed are provided at http://www.residentialenergylaborato...v_systems.html, especially Tables 1 and 3. Have I underestimated maintenance costs? I have assumed one inverter replacement over 25 years (at 12.5 years).

These costs include all applicable rebates, and some folks would argue that the rebates should be left out. My response is sure, but then I need to compare the costs with electricity generated at nuclear plants that do not include the subsidy of the Price-Anderson Nuclear Industries Indemnity Act, and so forth for the other electricity sources. I see no advantage of being overly conservative in estimating solar energy costs, but rather support the most accurate estimates possible based on actual prices paid.

May I assume that the cost for hybrid power is so high due to the cost for batteries, including replacements every 7 years or so, and the hybrid inverter, plus a small penalty to keep the batteries topped off?

[BB.]

I have estimated the electricity cost amortized over 25 years for three grid-tied systems installed here in sunny Colorado, and have come up with much lower electrical costs than what you have provided, namely, $0.064/kWh, $0.080/kWh, and $0.082/kWh. These estimates are for two different utilities that have different rebate strategies. Details of how the costs were computed are provided at http://www.residentialenergylaborato...v_systems.html, especially Tables 1 and 3. Have I underestimated maintenance costs? I have assumed one inverter replacement over 25 years (at 12.5 years).

I try to be "conservative" with my estimates. I usually use 20 year system life (planning on living in one place for 20-35 years is probably not reasonable for most people) + replace the inverter (and other electronics) every 10 years. Also, if you are at higher elevations with good sun--you will do a lot better with solar PV systems than sea level with morning/evening fog, etc... Also, I did not take into account rebates (Federal 30% tax credit, any local credits, taxes, etc.). Also, I am not convinced there is a good return on investment if you sell your home (some may pay a bit extra, others may want the array stripped from the home).

Equation wise, pretty simple:

• (cost of installation + cost of repairs + taxes - credits/rebates) / (20* yearly power generated--or used for off grid system)

I don't use the cost of money--but it is arguable that inflation is running at least 8% per year even though savings/loans are much less at this point.

These costs include all applicable rebates, and some folks would argue that the rebates should be left out. My response is sure, but then I need to compare the costs with electricity generated at nuclear plants that do not include the subsidy of the Price-Anderson Nuclear Industries Indemnity Act, and so forth for the other electricity sources. I see no advantage of being overly conservative in estimating solar energy costs, but rather support the most accurate estimates possible based on actual prices paid.

That is fine--And why I always try to list my assumptions and cost estimates when I do a detailed plan. For some folks, their costs will probably be less... For others, their costs will be more.

One issue I have with counting on State PUC rules (such as 1 year net metering), is that they can change dramatically over time (and with different governments). FITs (Feed In Tariffs) which are funded out of government coffers and tax rebates/credits are also highly politically charged and may be dramatically reduced in the near future.

May I assume that the cost for hybrid power is so high due to the cost for batteries, including replacements every 7 years or so, and the hybrid inverter, plus a small penalty to keep the batteries topped off?

Yep, cost of inverter + AC charger + Batteries + replacements (average batteries every 8 years, good batteries every 15, really good batteries every 20 years). If you cycle power through the battery bank, you have to add efficiency of 80% for flooded cell batteries, 85-90% efficiency for battery charger + 90% or so for AC inverter (0.8*0.85*0.9=~58% efficiency for time shifting power using AC mains only--not solar--Which add a lot to the power bill).

Of course, there is the possible utility FIT/Billing Plans which can dramatically affect overall return... Some will pay Peak TOU and let you buy off peak Time Of Use power (mine does). Others may only pay you for avoided energy costs (may be 50% of base power rate)... And others add minimum power purchases/billing fees/etc. which can keep costs high for people with energy efficient homes/lifestyles that may not use much power in the first place.

In the end, the numbers are just to get people's mind around where their costs may be before they have done any detailed planning/costing. Since everyone is different (as well as their homes, utility plans, location, etc.)--I certainly encourage people (with our help here--if they wish) to work out their own costs of various power options.

-Bill

[ggunn]

I really like the concept of the panel mounted inverters to feed directly into the grid. Problem is; when the grid goes down, so does solar generation. Is anyone aware of off the shelf hardware that can power ones house without batteries when the grid goes down?

The short answer is no. You cannot power your house from PV without batteries.

The reasons are somewhat complex, involving the difference between time based demand and production power curves, but it boils down to no. There is no free lunch.

[silvertop]

I always tell people that conservation is 1st, that being said, grid tie has the most bang for your buck. For the most part when the sun is out your making electricity...sellling electricity. Where I am located, if we have a wind storm/snow storm expect 2-3 days without power, a generator would have fixed this too , but I wanted a way to be more independent and I had a love of and background in solar electric. Soooo... grid tie if you can , conserve, and if you are at roads end and see the neighbor turning around for the third day and the garbage hasn't been picked up for two weeks consider off grid battery systems. We grow our own trees and heat entirely with wood; have been mortgage free for 12 years and really do enjoy having energy independence.

[2manytoyz]

I have no interest in grid tie. The first reason is as you've mentioned. Grid goes down, no power, despite having solar panels on my roof. The second reason is the power company requires special hardware, inspections & permits, then doesn't pay the same rate for the electricity being sent back to them as the user would pay to use the electricity. They make money taking and selling electricity. The payback would be a very long time.

I live in FL. Power outages are a way of life here. Hurricanes, tropical storms, summer storms, lightning, blah blah. Any/all can take down a section of the grid from a period of hours, up to 18 days (in 2004 in my home town). The main reason I have solar is for emergency power of critical systems in my home.

What I've done at my last house, and working to do at my present home, is to have a stand-alone system. 1000W solar array connected to a 900AH battery bank. Two 1800W inverters handle all the loads easily. Some items (fridges, A/V gear, etc) will automatically transfer over to the alt-power setup when the grid goes down. Other items run exclusively from alt-power (indoor/outdoor lighting, security systems, computer systems, etc).

By running items exclusively from power I produce, I cut the middle-man out of the equation, and I have power no matter what's going on with the grid.

We've been sitting at home, watching a TV show on the 46" HDTV, living room lights on, etc, and the wife asked what the chirping noise was in the other room. Turns out the power had gone out, and an UPS was squawking on a grid powered outlet. Hardly noticed the outage.

Wife also asked if we needed to buy batteries for flashlights. I asked her why, she replied for hurricane season. "Honey, our lights never go out..."

http://2manytoyz.com/gridless.html

Since you already have golf cart batteries, you have a place to start. You can add solar panels, a charge controller, and an inverter to achieve your goal. You can pay someone to come setup a system like this for you, or DIY. I'm a geek, and find this type of project fun.