Grid tied - or not!

Re: Grid tied - or not!

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

Re: Grid tied - or not!

Lee Dodge wrote: »

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.residentialenergylaboratory.com/comparison_of_pv_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