Can I do solar power?
by William Papolis, Wednesday Mar 28, 2007 5:54PM EST
Increasing Power – "Grid-tied" System (without batteries)
Oh well, it seems we can’t say “bu-bye” to the utility company just yet. Digging deeper on Mr. Solar’s web site we discover the CE20180SB Clean Energy Grid Tied System (3.6kW) for about the same cost $22K. The main difference with the “Grid tied” system is "No batteries"! Since it doesn’t look like we will be able to generate power for all our needs and have extra power to store in batteries for later use, "no batteries" isn’t too much of an issue now!
System = CE20180SB
- Total Power = 3.6 kilowatts (with 13.8% solar panel module efficiency)
- Total roof space = 2500 sq feet (required)
- Total Cost = $22,407.00
Here are the details ...
| Mr. Solar 3.6 kW "Grid-Tied" system (CE20180SB) | |||||||
|---|---|---|---|---|---|---|---|
| Description | Qty | Unit Cost | EXT Cost | Unit Ship Wt. | EXT Ship Wt. | ||
| 180 Watt Solar Modules, 13.8% efficiency (Sharp-180) | 20 | $925.00 | $18,500.00 | 37.5 | 750 | ||
| Sunny Boy 3.8 kW Inverter c/w LCD (SB3800ULCD) | 1 | $2,410.00 | $2,410.00 | 98 | 98 | ||
| Mounting Hardware | |||||||
| Unirac 180" mounting rail | 4 | $253.00 | $1,012.00 | 34 | 136 | ||
| Unirac top mounting clamps, size F | 4 | $25.00 | $100.00 | 3 | 12 | ||
| Circuit Breaker | |||||||
| Circuit breaker 600Vdc, 30 amp outdoor rated (HU361RB) | 1 | $265.00 | $265.00 | 10 | 10 | ||
| Misc Accessories | |||||||
| 10 Meter MC Output | 6 | $30.00 | $180.00 | 8 | 48 | ||
| TOTAL | $22,407.00 | 1,038 lbs. | |||||
Source: Mr. Solar (Mar. 2007)
Looking at this table let's note a few things:
- Solar panels @ $925 per panel that generate 180 watts yields at unit cost of $5.13 per watt
- The solar panels represent 83% of the total cost of the system
- With "no batteries" the weight of the "Grid-Tied" system is 33% of the "Remote" system
- Shipping costs are not included and will likely add ($500+?) to the total system price
- Labour is not included either and a good rule of thumb is 20% of the system cost
Using similar assumptions as in our previous example:
- The typical American home consumes 31.3kWhrs per day
- A 3.6 kilowatt “Grid-Tied” system will generate a maximum 3.6kW per hr in direct sunlight
- Average daylight is 6 hrs/day, however, since we are mounting our solar panels on the roof, facing in a fixed direction, I estimate we can only count on about half those hours - 3 hrs per day
SOURCE: US Department of Energy (2005) and US National Renewable Energy Laboratory
Now the results ...
Maximum Daily Output = 10.8kWhrs per day = 3.6kW x 3hrs
Percent of daily requirements = 34.5% per day = 10.8kWhrs / 31.3 kWhrs
Well, that's a little better, 35% of our daily requirements. To install this system we need over 2500 sq feet of space on our roof, which for most of us, won’t be possible. Our roofs just aren’t that big. During the day any unused energy will feed directly to the grid and credit us “one for one”. At night, we will be able to buy energy as we need it. At the end of the month, all credits and debits are added, and hopefully we can see a 35% reduction in our electricity bill.
Hmm … how come solar power can’t meet our energy needs? It seems we have some constraints on building a home based system:
- Space for panels on the roof
- The price
Space for panels on the roof
The “Remote” system required ~1500 sq feet. The “Grid-Tied” system required ~ 2500 sq feet. When you consider the average sized home is 2,349 (includes main floor and upper level) it doesn’t make sense that there will be 2,500 sq feet on the roof. I currently live in a 2,100 sq foot home and we have:
- 525 sq feet - facing South of prime solar power space (good for 8 months, most of the day)
- 525 sq feet - facing North (good for 4 months, most of the day)
- 160 sq feet - facing East (good year round, half the day)
- 160 sq feet - facing West (good year round, half the day)
- Total = 1,370 sq feet on the roof
On average, homes just aren’t that big. SOURCE: ABC News (Dec 2005)
The price
A solar panel system is expensive and clearly we will only deliver a portion of our energy needs. In our example above, if we are saving 35% on a typical home, how much money is that per month?
Assuming ...
- $.15kWhr per hr = the per kilowatt cost of electricity in my neighborhood
- 31.3kWhr per day = average electricity usage per day
- 30 days = amount of days per month
- 35% = power savings per month
Monthly Electricity Savings = $50 per month = ($.15kWhr * 31.3kWhr * 30 * 35%)
So if we are saving about 30% per month, that works out to about $50/month in savings.
Extrapolating these figures into the future we can expect savings of:
Savings per year ...
- $600 per year = $50 * 12 months
- $6,000 per decade = $50 * 12 months * 10 years
- Breakeven ~ 37 years (or ~ 40 years with interest cost at current energy prices)
Note: these results don’t include interest, time of day discounts that are available in some neighborhoods, nor do they factor in the future increased cost for electricity.
When you consider typical home ownership length is 5 – 7 years (SOURCE: Home Insight), breakeven is in the distant future.
How about when you sell your home, will we re-coupe the investment? Will the new owner share the same enthusiasm for the solar panel system to pay the full value? Likely not! The new owner may view the system as "nice, but also a problem", likely he will only be willing to pay a fraction of the cost. Until solar power systems become pervasive, like water heaters, selling it with your home might be a “tough sell”.
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