New to Solar : Figuring out how much system we need

[jellybellyma]

Hi, totally new here, I've been reading the posts, and I have to say its all way over my head!

My husband and I are thinking of trying to install a solar system on our roof to help cover our electricity bill. I just can't figure out how to figure out how many panels, and how many watts per panel we need.

Going off my last Consumers Energy bill, in the last year we have used 14471 kwh, which averages out to about 1200 kwh a month. (we are going to make some changes to our consumption, eliminating a freezer, weatherstripping, etc to also help.)

What watt/amp panels do we need to produce this? We have a large, due south facing roof, and we live in Northern Lower Michigan.

We will stay grid-tied, as I am hoping that the excess energy that would be produced in the summer months would offset the greater consumption in the winter months for heating.

Researching prices, we want to do it ourselves as much as possible, (my husband is very handy around the house, as am I, (I think).) I'm thinking we may need to start small, and have something we can expand as we go.

Help is appreciated! Thanks!

[Airstream]

Why do you want to do this? There is no savings when you are trying to compete with a already-connected public utility; their buying power delivers power for 15 or 20% of what photo voltaic solar delivers!

The situation to start from is stressing conservation in your household - getting a handle on minimums needed and still live comfortably. That will give you the winning perspective from the start...

"Learn more about your solar resource by exploring these Web sites:"

http://www.nrel.gov/rredc/

http://rredc.nrel.gov/solar/calculators/PVWATTS/version1/

[DamonHD]

Indeed: we used to use what you (OP) do now per month and were able one way or another to cut that by ~80% over about the last year or so, without giving anything up.

I hope we can come in at under 2000kWh (ie 2MWh) consumption this calendar year, and it's looking plausible, see: http://www.earth.org.uk/saving-electricity.html

We do solar as well, and hope soon to generate more than we use over the course of the year, but that will never pay itself back from reduced electricity bills: our motivation is carbon-footprint reduction.

Cutting out waste is about 5x to 10x cheaper per kWh than generating with solar PV.

Rgds

Damon

[jellybellyma]

Why do we want to do this? I will admit that our reducing our carbon-footprint is not the main motivator or factor.

The main reason we are looking into solar power, is that we have a large family, and the present economical situation, along with a possible looming recession/depression has us scared. My husband is the sole bread-winner in our family, and jobs here are very scarce. He was lucky to get the job he has, and its looking as if he may not have it much longer, as the auto-makers he trucks for are moving the plants out of the country. If he loses his job (as we expect he will, and soon), being self-reliant for our electricity will go a long way to keep us afloat, as well as helping take care of our family, until another job is available.

[SteveCH]

You can do this yourselves. Maybe. I did. However, I am off-grid and always have been. The grid-tie is a good compromise for people who are, for whatever lifestyle reason/need, cannot cut back enough on their elec. usage to make PV viable [because the sytem you would have to design and install...and purchase!...would be lots and lots of money. Well into the tens of thousands.] The problem, for you, with grid-tie is that you are connecting and interacting with the commercial electrical supplier and that creates all manner of requirements that will almost certainly need a professional installer to do, plus to satisfy the inspectors. Not that I want to discourage this, but you need to realize the costs involved. As I said, I am not grid-tied, but from the reports I've read by people who are, they reduce their electicity bills, yes, but it can take a pretty long time to pay back the costs of getting into it. Speaking simply of money outlay here and what you can expect to get back and when. Remember that the cost per Kw of the elec. you are buying is much less than the cost per Kw of what you'll be making from the sun [cost of the system you install] and the money you "make" by selling excess back to the grid will be based on the very much lower cost of their production.

On the other hand, you want some security and if you can cut back your usage [a lot] and increase your home's efficiency, if you get into a finacial situation where the electric bill is critical, you can have a pv system that will give you electricity, perhaps even not-grid-tied, sort of like an emergency gasoline generator but PV instead. This will entail, obviously, running the wiring from the batteries/controls around the house, not a huge thing but a lot of work. This is just one other option to consider.

As to your thoughts for an expandable system, that isn't too difficult. You can always add more solar panels. What you should consider is when it comes to the controls for the panel array, go ahead and buy a large controller than you think you will need or you'll add panels later and keep having to improve/beef-up your controller, breakers, etc. every time, which would waste a bunch of money in the long run. I have added to my system probably five times over 20 yr., and I wish I'd done that....

[Rob Beckers]

Hi Jelly,

Since nobody seems to answer your question about figuring out how much PV it takes, here goes:

The daily average number of sun-hours for your general area is 4.1 hours/day (that's the number for Traverse City, it won't change much for a wide area around). That means 1 kW of PV modules should make around 4.1 * 1 = 4.1 kWh/day of electricity. In the real world there are losses (dirt on the modules, temperature losses, inverter losses), so a reasonable number is 70% of this, or 0.7 * 4.1 = 2.87 kWh/day. This assumes the modules have sun from 9am until 3pm (and in mid-winter at least from 10am until 2pm), and are mounted facing due south at the optimal angle for year-around production, which is your latitude (or 43 degrees for you, it doesn't matter if you're off by a bit, production does not go down much for small angle changes). You can do the same calculation for other locations, just substitute the daily average number of sun-hours for the location. The above is for grid-tie, in case of battery charging or for a very hot climate I would derate by more than 30%.

So, to recap, 1 kW of PV will net you 2.87 kWh/day on average for your location (more in the summer, less in the winter, this is an annual average measured over multiple years). Just in parts (panels, inverter, racks) you're probably looking at around at least $6/Watt, or $6K per kW. To generate 13,000 kWh per year means you need just over 12 kW in PV on the roof, or an investment of around 12 * 6,000 = $72,000 if you buy the parts and do the work yourself (yes, it's that much!). Now you know why energy savings is the best investment, and why it is so hard to compete with the electrical utility...

-RoB-

[zeusmorg]

 Your best bet when it comes to SAVING money is to conserve, and if then you still feel the desire to become self-reliant with Renewable energy, your costs will be lower, needing less overall.

A good site to investigate for how to conserve on energy, not just electricity but heating and cooling and water use, hot water heating etc.. is:

http://builditsolar.com/

 Also you will find resources here for conservation. You will be amazed at the things it's possible to do to save on energy by a small or no outlay of cash.

 I'm not knocking your wanting to become self-reliant it is a noble idea, but an expensive one.

[jellybellyma]

Thank you to Steve, Rob and Zeus, you not only provided the information I was seeking, but also some information that was just as pertinent, if not more so. We'll be doing more research as I go, and I'm also looking into wind power and/or hybrid systems as well. We are working to learn to conserve energy, and how to cut our usages drastically, but my husband and I still feel the need to at least have a clue as to what we are getting into with all of this.

Again, thanks so much to all of you!

Jelly

[Yyrkoon]

As a person who lives off grid completely, and loves generating power for 'free', I would have to agree with several other posters here in saying that there is no such thing as a free lunch. One of the commentators here already laid out the pricing much better than what I could, however I would like to add my 2 cents.

Like at least one person said already, the power company can supply you with power much cheaper than you think you can supply it to yourself. So viewing things from a short term perspective, you would actually be losing money. Long term, you end up paying your electricity bill in advance. PV panels can last a very long time, and baring inverter/controller failure over time, you still have to buy new batteries every 5 years or less. OR learn how to rejuvenate batteries on your own, which still costs money. Anyhow, very long term you may come out ahead, but it would not be likely.

Our battery bank right now consists of 9 12v marine deep cycle batteries. ~1200 ah(amp hours), lets us(two people) run two laptops, and several lights during the day, and through the night. We must have sun from 11am - 3PM for these batteries to charge fully for this cycle to continue. Cost of these batteries was ~$700, and we want/need many, many more. We are also located in E Arizona where the sun shows very good. Still, you can not count on it always being there for you.

Charge controllers 2x Xantrex C60's. ~$150 each. Not much else to really say here, they do a good job.

3. x 200W PV panels, currently not hooked up, but cost ~$650 each.
   
44. x 60W PV panels (only 16 currently hooked up) free! Given to us by a radio station where my friend works as an Engineer. The 16 we have hooked up currently give us roughly 40amps while the sun is shinning, and we usually hit full charge around 3PM.
    
    

Other necessities are a 30KW generator for pumping water, and to power 220v devices($5000 at a steal), a propane refrigerator for ~$1000 new, a propane hotshot water heater for ~$700, and a pressurization system for the water, so we have running water inside(do not recall the cost off hand).

So, all in all we're talking $9650 to live completely off grid 'reasonably' comfortable, while getting very good deals on the generator, and free panels(over 2KW of panels for free is something that will not happen for most). All that, and we still can not use our main desktop computer systems for more than short periods of time. My pride and joy gaming computer (which is actually very modest compared to many out there) will drain this battery bank in 2-3hours . . .

What I would suggest as a start is that you and your husband find a kill-a-watt P4 power monitoring device(s)(these can be found online for ~$15 each on sale), plug all your electric devices into them, and start making choices on what you can do without. After that look into buying lower powered devices where it makes sense, especially if you use computers a lot.

Also, if you could somehow get a very good deal on a PV array, and isolate some of your most power hungry devices from your grid, running said devices off of batteries. You would save more money this way, than dumping this electricity back into the grid. But again, solar equipment cost can be very. very high . . .

[Yyrkoon]

Whoops, forgot to mention our 3KW modified sine wave inverter ran us around $600 (at the time this was a very good deal). So . . .over $10,000, not counting the minor odds and ends such as the welding cable to tie the batteries into the inverter, cable ends, etc.

My point here of course being; Even 'on the cheap', the cost is still high.

[Airstream]

Solar electric panels are about 12-15% efficient converting sunlight into usable energy. Solar heating panels can be 70-80% efficient - in Michigan mixing those two types may be the smartest money spent, doing solar hot water & solar hot air plus some PV electrics to get the most $$ worth from each dollar spent.

I've tried to write this up 3 or 4 times already and never got the angle I wanted quite write, err right, written, whatever... Remember the "bulk-of-system" frames, trackers, wiring, combiner boxes, disconnects, inverters, batteries are going to be a large expense - perhaps equal to the solar panels themselves.

Yyrkoon's $10,000 earning 4% interest is $400 income - in our Minnesota electric utility rates that $400 equals 3200 kilowatt hours worth of utility power, or 8.75Kwh per day. (4% interest chosen at random, your mileage may vary)

To equal that amount of PV generated electricity from the 5 average peak sunshine hours in a day requires 1,750 watts of solar panels, which sell for around $5 per watt new, so I am describing a $8750 investment in panels to do something with your savings cash now earning interest to offset 'burned' monies spent on utility power.

Now keeping some liquidity in your new PV investment, being able to cash out, means being able to resell the panels if/when the need arises. With 25 or 30 year warranties on mono or polycrystalline PV panels they do not take large depreciation hits until 6-10 years (Avoid thin-films as they don't hold their resale value) so you may get $3.50 or $4.00 a watt back. Small to midsize panels always command best prices on eBay & Craigslist.

The smartest original buying also calculates in the shipping charges, there is a spot where the panels shipping carton length x width inches invokes a surcharge that doubles or triples shipping, or even forces it to truck freight - keeping them on the smaller side makes reselling them easier as shipping won't be a deal killer then. Save the original packing materials. A quick search on several online sellers shows the shipping rate jump happening around 100 watts panel size, this varies with man'f construction, cell efficiency etc. but you get the idea...

The concept of buying to resell in the future is not a bad one - if you agree with the lifestyle and want to enlarge your system in the future it may be easiest to sell and start fresh, there will always be people wanting to add to their systems piecemeal.

[Airstream]

Inevitable missed idea - They literally don't know how long a top-name 30-year panel will last, 30, 40, 50 years?

So buy the best; BP - Sanyo - Sharp - Kyocera - etc., do not be drawn in to 'no-name' cheaper panels if you can avoid it. Don't be in a rush and a good deal will come along... and they will hold their value longer too!

[Yyrkoon]

Panels that were given to us are ~25 years old, so the radio station probably got their investment back, but that was not why they were bought(top of mountain . . . no power . . .). Anyhow, they do not know how long these panels will last, but we are presuming they will out live us at least.

After a little more thinking last night, it dawned on me that perhaps saving money is more important right now, with the economy the way it is. If things end up the way I see it very easily could, your dollar is going to be worth more in the very close future. If the stock markets tanks, we're in for some very interesting financial times . . .

[WineGuy]

Evidently you are concerned about money (who isn't). Like many of the other posts say, producing your own power is not cheap. In most situations, especially in Northern Michigan, you first need to look at not wasting energy, then producing heat (instead of electricity) cheaply.

Two words here:

Weaterize, and solarize.

Insulate, calk, make some insulating window treatments etc. Make sure you are not loosing heat (money out the window).

Next, try some simple solar projects. My brother built an attached greenhouse using scrap storm windows, 2x4s and two inches of foam insulation. On sunny days he opens the kitchen window to the greenhouse and uses a small solar powered fan to move the air. He has black painted metal roofing inside the greenhouse to gather the heat.

Search online for simple solar projects. They should be easy to do, cheap, and provide quick payback. The greenhouse probably paid for itself the first cold week.