Need a solar system to fully power my home

Re: Need a solar system to fully power my home

Maggie,

My first suggestion is to spend your money on conservation measures first... I don't know where you live, or what type of home you have, how many live with you, what the summer/winter weather is like, etc....

Basically, a Grid-Tied Solar system installed (the simplest and, usually the best, for 90% of the people out there in the USA), will cost you around $0.25 per kilo-watt-hour to run for 30 years. If you get rebates (like California's ~$3.00 or so per watt rebate), you may drive the costs down to $0.14-$0.17 per kilo-watt-hour. And you have to "pre-pay" (or take out a loan) to purchase the install the solar equipment (my system, call it 300 kWhrs per month, was ~$21,000 cash up front, after rebates). You can do better if you look around (or maybe not, it all depends)...

Right now, I pay about $0.11 per kWhr (E-1 PG&E, baseline useage under ~300 kWhrs per month). And, my electric power, while pretty high, has not change price for years. So, my $0.14-$0.17 a kWhr from solar is still more than I pay for power today--it is not saving me any money right now---I installed the system to protect against future price increases, and to allow me to charge an Electric Vehicle in near future (power for me, at the higher rates can be $0.30 t0 $0.51 per kWhr if I am over 1,000 kWhrs per month).

So, you really need to:

A) Where do you live and is your bill larger or smaller than average? (your power company can tell you this)
What do you use your electricity and gas (oil, etc.) for (AC, hot water, cooking, home heating, etc.)
C) Do you have appliances over 10 years old (if yes, replacing them can save 1/3 to 1/2 of your bill).
D) Do yo have 1. Attic insulation, 2. double pane vinyl windows, 3. wall insulation, weather stripping, etc...
E) What is your power bill (amount of energy used and price per kWhr/Therm/gallon/etc. Per month/winter/summer/etc.
F) Do you have something to measure your power for each major appliance (fridge, tv, AC, etc.)--suggest a kill-a-watt meter. Cheap (~$34) and pretty simple to use:

http://www.amazon.com/gp/product/B00009MDBU

G) Once you have identified your most "costly" energy loads, look at replacing with Energy Star appliances (high efficiency), add missing insulation, and, in some cases, replacing an old AC system with a Ground Sourced Heat Pump (good for places that get very hot or very cold).

G) If you are thinking about going solar, does your home/property have a good location for several hundred square feet of solar panels with, at least 9am-3pm of good south facing exposure with no trees/homes/etc. blocking (especially in the winter when the sun is low).
H) Is your first concern Electric or Gas bills? Frequently, using solar hot water heating for a swimming pool, domestic hot water, and/or home space heating, is more cost efficient than going with Solar Electric at first (Solar Electric systems usually have much less maintenance though when compared with solar hot water systems).

As an example about spending money to save money for conservation... Say you get 5% return on your money in the bank and you have $0.10 per kWhr energy costs. You have a load that uses and average of 100 watts (0.100 kWatts) of electricity an hour (like your fridge), day in and day out.

Cost per year = 0.100 kW * 24 h/day * 365 d/year * $0.10/kWhr = $87.60 per year.

Break even expense = $87.60 per year / 5% interest per year = $1,752 spent to save 100 watt load per year...

Say your old fridge was 200 watts per hour 1,752 kWhrs/year (or 146 kWhrs / month) and a new fridge was only 100 watts per hour (or 876 kWhrs per year), if you spent less than $1,700 for a new refrigerator, you would be saving money...

I hope that this helps you... Do you have more questions?

-Bill

Re: Need a solar system to fully power my home

Ed,

I am not at all sure that I understand what you are asking... At first, I thought you were asking about Natural Gas pricing--but if you are doing something yourself, it seems that you may be asking about solar irradiation numbers of 4 kWhrs per day per square meter (not cubic meters)...

So, I will take a stab that you are asking about solar irradiation numbers. I got my US information from:

http://rredc.nrel.gov/solar/pubs/redbook/

You can look up California, and I used San Francisco... Roughly, my numbers are from 3.5 to 6.8 kWhrs per sq. meter (December/July) for Latitude and flat plate collectors...

However, there are a lot of issues that seem to make these numbers less than ideal to predict your results... For example, in San Francisco, there are areas in the western part of the city that don't see any sun at all during the entire summer (clouds, fog, followed by clouds). Other areas (eastern parts in the older sections of the city) are quite nice.... So, I don't know where they get these numbers.

Also, the Photo Voltaic Solar Panels are very sensitive to temperature. If you are in a warm climate (not even hot like where you are at) and roof mount them--you can derate their daily output by 75% or more. (also, I had a wet/cloudy winter and generated much less power than predicted by the tables).

If you can find somebody near you that has a system and they have some monthly figures throughout the year, it will make it much easier to predict what your proposed system will do.

Not trying to throw a wet blanket on Solar Power--just trying to help set reasonable expectations.

Is this what you were asking about?

-Bill

Re: Need a solar system to fully power my home

Thanks Jim,

Duhhhh, I had a blond moment. Yes, the lat/lon location is right on the top of the page in big numbers. Right about at the north tip of one of the runways almost on the shore of the SF Bay.

SFO is more sunny than much than western San Francisco. However, 7 miles south (where I live) has fewer cloudy periods and is much warmer. And, technically, SFO is not even in San Francisco but 7 miles south of the city.

-Bill

Re: Need a solar system to fully power my home

Pretty nice site!

Interesting in that is shows about a 10% difference between the west and east stations. I would have expected a larger difference--but you can't argue with actual measured numbers. Hmmm

Using their numbers, and a 3kW system (like mine)... They are estimating, roughly between 3,600 and 4,000 kWhr/year... I am about 16 miles southeast of San Francisco (near the shore of SF Bay) and my roof mounted (facing SSE ~155 degrees true) PV system will produce around 4,700-4,800 kWhr in one year (est., my first year anniversary is 9/5/06.

Are my numbers above, below, or average for my installation? Don't know.

-Bill

Re: Need a solar system to fully power my home

Thanks for the links...

Hmmm... Looking at the Urban School in SF, they are using 37 kW right now (9am on a Wednesday) with, apparently no students for the last few weeks (according to their calendar). Would be nice to see power usage closer to their weekend amounts (which still seem high for an empty set of classrooms).

-Bill

Re: Need a solar system to fully power my home

I went to their web site and looked at the calendar for summer--no activities or summer school listed for most of the summer.

My location, I am right in the middle of the City of San Mateo (a mile south west of the intersections of highway 92 and 101).

I do have a 3.5 kW grid tied system and it has been turned on since September of '05. It appears, to be relatively on track for generating 4,500-4,800 kWhrs for the year. The installer predicted 5,300kWhr/year. So, the system is performing about 10% or so less than designed (we had a very cloudy/wet winter--would I average more? Don't know--ask again in 10 years). From the design of the panels (and their thermal deratings), the Inverter, orientation on my roof, etc., I think that everything is working just fine. I did not automate any data collection (burning power with a computer for solar data collection seemed to be counter productive to conservation)--I just take the daily readings (kWhrs generated) by hand. I don't really know what I would do with more data.

What I was really wondering about was more the "average weather" and how we are doing this year vs other years. Although, in a way, it really does not matter too much. The amount of sun that I get today is it... No more and no less. I can't do anything about the weather so I am just along for the ride.

What I am really trying to do is help people understand that Solar, while nice, is not quite the same as turning on a light switch or opening the gas valve. It is a product of nature (and physics) and therefore don't expect miracles from a solar installation. If it is very cloudy weather for a week, that power is lost forever. If you put in twice as many panels as you need, sometimes you will have way more power than you can shake a stick at. And, at other times, you will still not have enough without some other form of backup--or just going without.

I chose grid-tie for my home even though I really would have like the battery backup for here (California designed brownouts and earthquakes)--but Grid-Tie was best for me. Batteries cost money, need servicing, a place to put them, and can only store a few days of power. PG&E (via the Cal PUC), basically made PG&E a 1 year unlimited storage battery for my power--all at the costs of less than $6 per month (assuming that I am a zero or net generator of power over 365 days). I also chose Time of Use metering (peak power is noon-6pm Mon-Fri. $0.29 vs $0.09 per kWhr during summer).

For $900 and a few gas cans, I can ride-out any of the short term emergencies that may come.

The only way I can make my system any better would be to cut down/back a couple neighbors' trees and rotate my house from ~155 to 180 degrees (due south).

Overall, you can actually do a lot of engineering predictions, and they usually workout pretty well... But people don't really like the answers (same as in business when marketing and engineering start talking past each other).

For example, we have one thread about camp cooler and solar--planned on only using a 50 watt panel, but engineering the solution showed that a 230-300 watt panel would be needed (and at $5 a watt or so per panel, that is a big cost adder). Another was the sailboat thread... Wanted to generate all the power with solar panels. Engineering said that it would not really be satisfactory only using the existing panels--suggest looking into alternative energy sources/conservation. And today's race note's comment that 3 days of clouds is forcing electron rationing.

It is just the nature of the problem and expections. If you set expections correctly, solar is a great solution. If people try and under-design a solution (and, many times, lack of maintenance) to save money (and/or if the result of high-pressure sales tactics)--they will not be happy.

Another example, around here, a lot of people installed domestic hot water systems.... On the coast where there is fog and trees--people did not get much heat and fog rotted many of the systems. On the sunny side of the hill, many used plastic domes which crazed and darkened in relatively few years. Again, giving solar a black eye. But you could go down to Scotty's Castle in Death Valley and see a properly build (locally designed and maintained around 1930's) solar hot water system that worked well for many years.

p://www.oldengine.org/members/levans/dv/dv11.html (photo of Scotty's Castle Solar Hot Water installation)
http://www.oldengine.org/members/levans/dv/ (rest of the shots around Scotty's Castle/Death Valley--Old Iron)

In the end, I chose I my first major solar project to be solar electric because, 1) I could charge an electric vehicle--I hope--in the near future, and 2) because I wanted something that would last several decades without much maintenance. I was not sure solar hot water (gas was about 1/2 or a little more of my utility bill) would meet that requirement (even though, it should be much cheaper to install solar domestic hot water wrt to utility costs).

-Bill

Re: Need a solar system to fully power my home

Earthquake wise--I am not too worried about the solar panels. I just changed the roofing shingles and there is 1/2 or 5/8 structural plywood underlayment for the whole roof (new earthquake code requirements when re-roofing). Also, mounted on metal frames.

If the panels get totaled--I am already in a world of hurt. If you remember, many of the homes in the earthquake were destroyed when either the first floor collapsed (soft story) or from fire.

And, I just found out that our local utility is changing all of their gas service from iron pipe to somesort of tough plastic line. Plus, they are adding a flowrate shut-off valve (if house pipe is broken, the gas flows at full volume, and the internal valve slams shut until the flow is stopped (and the gas back pressure bleeds off). So, there is a new anti-fire measure coming over the next 10 years for everyone in California with natural gas.

The big issue with Grid-Tied Solar, is that the inverter will not supply any power if there is no utility power--and I don't think it will work with a generator either (for various reasons). I would like to get an Outback MX60 controller and a few batteries--but the typical Xantrex Grid-Tie runs from 195-600VDC... The MX60 shuts down above 135VDC and fails above 150VDC. Can't just through a cut-over switch into my arrays--I would have to rewire too. Hence, just a generator for now.

Don't know anything about the Haman school... But if you look at the numbers, right now (10:30am) they are getting 3,898 kW peak... And the panel temp is around 117 degrees F. That is about what I would expect it to produce... [as I am typing this, is is now 4,025 watts output; edit: and now 4,153 watts at 11am--probably pretty close to peak power]

My 3.5 kW system highest peak I ever saw (not logged, just walking by and looking) was 2.998 kW peak (inverter limits to 3.0 kW peak). And, typically is around 2.5 to 2.7 kW on a nice summer or spring day... The cooler the weather, the higher the power supplied for equal sun. So, for the Haman School, I would have expected nominal power to be (including inverter eff of 94% for my system):

4.9kW *2.5kW/3.5kW= 3.5 kW typical peak in hot weather... And 4.2kW peak on cooler days...

Temperature is a big deal for these solar panels. And the STC ratings are quite a bit higher than you would expect in any nice weather above 70F.

Jim (Crewzer) did this and found that the SF site was right at the north tip of one of the main runways at SFO airport. Yes, sunnier than some parts of SF, less sunny (buy much cooler) than San Mateo.

To see what temperature different panel configurations do to actual outputs, Xantrex has a nice support site for their Grid Tie inverter family:

http://www.xantrex.com/support/gtsizing/index.asp?lang=eng

You can see there is STC (panel manufacturer ratings), PTC (numbers use by California PUC for rebate base numbers) and CEC (PTC - Inverter Eff and limits). CEC is what CA gives the rebates on.

Pick Solar Panels "BP 4175", Inverter "GT3.0" and look at 2 strings of 10 panels and you will have my system.

So, unfortunately, 60-70-75% output is not an indication of poor system design--it is more a function of site, time of day, temperature, weather, and overall efficiencies.

I always thought it would be neat to sell a 6" solar cell with a small data logger that you could just throw on a roof for a month (or even 1 year) to actually give site specific performance. And sprinkle a few of these around a city or on people's home who are interested in solar. In reality though, simple charts, and estimates are about as accurate and can give you answers with a few minutes or an hour of work.

In the end, for Solar, it is usually expectations that need to be adjusted, and not the equipment. Cheaper and more efficient panels would be great for everyone--but I would not hold my breath for anything like that in the near future. Demand is just too high right now, it cost lots of money to make a panel that can withstand 30+ years of weather (thermal cycling is a real killer for any sealed element), and there is only so much you can get from Silicon and a little doping.

-Bill