Can I do solar power?
by William Papolis, Wednesday Mar 28, 2007 5:54PM EST
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The quick answer is yes! Don’t stop reading though, because it’s a “qualified yes”. Now, what do I need to generate solar power? How much will it cost? How much power will I be able to generate? Will I be able to store some power for use at night? Can I sell power back to the grid? How much will they pay? What’s the bottom line? Is it worth it to set up "my own home system"? |
For this article we will consider a "Remote" System that includes batteries for power storage, and a “Grid-Tied” system without batteries. We will discuss the advantages and disadvantages of both systems and come to a final recommendation. We have a lot of questions to answer, so let’s get started. The first thing you need to do is get out your chequebook, because a solar power system isn’t cheap!
Typical cost and some assumptions - "Remote" system (with batteries)
Surfing around the internet and I discovered Mr. Solar located in Cockeysville Maryland. Their web site is a good example of a solar system retailer, but I do encourage you to shop around and consider systems from at least 3 other vendors before you make your final decision.
Let’s consider Mr. Solar’s top end "Remote" system, the RPS-8-AC. Why? Well, we want to be off the grid, right? Perhaps we can say “bu-bye” to the electricity company and their bills. Well let’s see …
System = RPS-8-AC
- Total power generation = 2.1 kilowatts (with 13.3% solar panel module efficiency)
- Total roof space = 1,500 sq feet (required)
- Total Cost = $20,996.00
Here are the details ...
| Mr. Solar 2.1 kW "Remote" system (RPS-8-AC) | |||||||
|---|---|---|---|---|---|---|---|
| Description | Qty | Unit Cost | EXT Cost | Unit Ship Wt. | EXT Ship Wt. | ||
| 175 Watt Solar Modules, 13.3% efficiency (175-PC-RPS) | 12 | $805.00 | $9,660.00 | 40 | 480 | ||
| 4kW Inverter (SW4048Plus) | 2 | $2,150.00 | $4,300.00 | 125 | 250 | ||
| 40 amp Load Controller (C40) | 1 | $130.00 | $130.00 | 6 | 6 | ||
| GEL Batteries (UB30H) | 24 | $170.00 | $4,080.00 | 78 | 1,872 | ||
| Mounting Hardware | |||||||
| Unirac 144" mounting rail | 3 | $190.00 | $570.00 | 25 | 75 | ||
| Unirac top mounting clamps, size D | 3 | $22.00 | $66.00 | 3 | 9 | ||
| Unirac high profile tilt legs | 3 | $150.00 | $450.00 | 22 | 66 | ||
| Fuses & Circuit Breakers | |||||||
| 10 circuit fused combiner (TCB-10) | 1 | $240.00 | $240.00 | 10 | 10 | ||
| 10 amp fuse for TCB-6/TCB-10. Pack of 10 (TCF10) | 1 | $25.00 | $25.00 | 2 | 2 | ||
| Circuit breaker c/w enclosure 175 amp/125 Vdc (DC175) | 1 | $285.00 | $285.00 | 16 | 16 | ||
| Circuit breaker 175 amp/125 Vdc (GJ175) | 1 | $162.00 | $162.00 | 3 | 3 | ||
| Circuit breaker 60 amp/125 Vdc (CD60DC) | 1 | $240.00 | $240.00 | 10 | 10 | ||
| Battery Accessories | |||||||
| Battery interconnect, 4AWG/12" (BI4-12) | 18 | $10.00 | $180.00 | 2 | 36 | ||
| Battery interconnect, 4AWG/20" (BI4-20) | 10 | $15.00 | $150.00 | 4 | 40 | ||
| 10' AWG battery cables 2/0 (BC10-2/0) | 2 | $103.00 | $206.00 | 15 | 30 | ||
| 5' AWG battery cables 2/0 (BC5-2/0) | 2 | $63.00 | $126.00 | 12 | 24 | ||
| Battery Temperature Sensor - 35' (5 m) cable (BTS-35) | 1 | $28.00 | $28.00 | 1.5 | 1.5 | ||
| Misc Accessories | |||||||
| Bonding Block (DCBB) | 1 | $60.00 | $60.00 | 3 | 3 | ||
| Output Wiring Kit 10AWG, 25' (OPWK-10-25) | 1 | $30.00 | $30.00 | 14 | 14 | ||
| 10 Meter MC Output | 6 | $30.00 | $180.00 | 8 | 48 | ||
| Stacking Interface for two SW Inverters (SWI) | 1 | $36.00 | $36.00 | 2 | 2 | ||
| TOTAL | $20,996.00 | 2,989.50 lbs. | |||||
Source: Mr. Solar (Mar. 2007)
Looking at this table let's note a few things:
- Solar panels @ $805 per panel that generate 175 watts yields at unit cost of $4.60 per watt
- The solar panels represent 46% of the total cost of the system
- Components related to batteries reperesent about 40% of the total cost
- The batteries represent over 60% of the weight of the system
- Shipping costs are not included and will likely add ($1000+?) to the total system price
- Labour is not included either and a good rule of thumb is 20% of the system cost
Now let's calculate how much power we can generate.
First some assumptions:
- The typical American home consumes 31.3kWhrs per day (or 938 kwhrs per month)
- A 2.1 kilowatt "Remote" system will generate a maximum 2.1kW 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 (or 3 hrs per day)
SOURCE: US Department of Energy (2005) and US National Renewable Energy Laboratory
Now the results ...
Maximum Daily Output = 6.3kWhrs per day = 2.1kW x 3hrs
Percent of daily requirements = 20.1% per day = 6.3kWhrs / 31.3 kWhrs
Based on our assumptions we can expect to generate only 20% of our daily requirements.
Hmm … this isn’t as good as I was hoping. Perhaps there is a way to make it better. What are some options:
- Use less power, or use power more efficiently (and for many of us this is likely very possible)
- Install on a flat roof with axis tracking. (The ability to rotate to always face the sun)
- Install more panels at additional cost
It seems clear that with this "Remote" system only meeting 20% of our daily requirements it isn’t designed to fulfill ALL the needs of the typical modern day house with standard applicances: fridge, stove, washer, dryer, dishwasher, water heater, toaster oven, microwave, lights, garage door openers, TV’s, computers and other electronic devices.
Let’s now consider a more powerful system, but we will need to make a major concession to achieve a better result!
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