- Planning A Solar PV System For Home And Small Business

Planning a Solar PV system for home and small business:

Before we begin, first and foremost – you need to figure out if your site can accommodate a solar pv array so that it operates at or near its rated efficiency. If your site conditions (roof of your home or business, backyard, etc) will limit the electricity production even by 20-25% – everything else is irrelevant and solar is probably not for you.

Step 1 – Determining if your site can accommodate a solar photovoltaic system

Southern Exposure:
Solar PV systems operate by converting sun light into electricity, so the first thing they require is enough sun light through-out the year, with as little obstruction or shading as possible. If you plan to use solar system that will be fixed (usually a roof mounted solar array), you will need to position it so that it faces South. In this case your solar PV system will collect as much sun light as possible, as the sun will move from East to West.
During the year, the sun is positioned very different, depending on the season – in the summer the sun is up high and in the winter it is very low. You need to consider this as this has a potential to make your system very inefficient. Solar Pathfinder is used by solar professionals to determine the position of the sun during the year and to find any shading that will obstruct the sunlight to the Solar PV Panels. Using a pathfinder you could determine weather it makes sense to have a solar system installed at your location and if you would need to remove some of the shading – eg. cut down some trees or move your neighbor’s house 20 feet to the left .

It is unlikely that a homeowner will have a Solar Pathfinder handy, but using just common sense, you can get a good idea if you have to much shading or if your location is perfect for the installation of a Solar PV system.



Angle or slope for solar panels:

Depending on where you live or plan to install your solar system, an angle or incline of the panels may have a significant effect on electricity production. For example, in New England the sun is at about 20 degrees to the earth surface and at about 45-50 degrees during the summer. If you plan to have a fixed solar systems installed in CA or at the similar longitude, ideal angle for your panels would be 30-32 degrees. As you above down south, the sun is higher in the skies so it is better to lower the angle of solar panels. At equator, solar panels can lay flat on the ground and will get maximum electricity production. At north or south pole, they should stand up vertically.

Size of your roof:

If you plan to have a ground-mounted solar system, this will be irrelevant as there is usually enough room to have a decent size systems installed. If like most other people you plan to have solar panels installed on your roof, depending on the number of Kilowatts you plan your future solar system to be, you may need a considerable roof area. If you have a large roof and you are thinking about metal roof, a Roof-Integrated Solar PV System such as standing seam metal roof with Uni-solar panels is a very good choice providing you with a long lasting roof and slick-looking yet efficient amorphous-silicon thin-film solar panels. This babies require more space to produce the same amount of electric power, but are a better choice from the perspective of roof / solar system longevity and integration.

Lets assume that now you have performed a site inspection and determined that it would make a good place to have a solar systems installed. Maybe you will have to trim some trees, but over all, you have a decent size south facing roof with a good 35 degrees angle and no or very little shading going from east to west.


Step 2 – Figuring out the size (in Watts) of your future Solar PV System:

This will surprise many people, but solar PV systems are priced in Watts or Kw – NOT in Sq. Ft. Every second person calling us about Solar Roof, asks me: “how much is solar per square foot”. Truth is – I can’t answer this question and frankly, no one can. The question it self is wrong, but here is the right answer: Cost of solar will be determined by the system size measured in KW. Here I will explain how many kilowatts of solar you may need or want, and below you can find out how much it will cost.

How many Kilowatts do I need?

This is actually simple, but pay attention to the theory behind it all. Electricity production of your solar system depends on how many “sun-hour-days” you have in your area. In Massachusetts and surrounding states (Connecticut, Rhode Island, Southern NY) we have an average of 4.2 – 4.5 hours of sunlight (sun hours) per day annually. This accounts for rainy and cloudy days as well as long, sunny summer days and short winter days.

Most households in the US consume on average 750 kWh (kilowatt-hours) per month. Assuming a 4.5 sun-hour-day in your area, 1 Kilowatt solar pv system should produce 4.5 kilowatt-hours of DC electricity per day. Per month it will produce 135 kWh DC. Now this DC electric current has to be converted to AC, so that your home appliances could use it. Inverter takes care of this part, as well as making your solar panels working at optimal production. However as any electrical device it has resistance sou there will be power losses. Average modern inverter loses 3% of electricity due to resistance, while total power loss can be as much as 7-10% or more, depending on how well or poorly your system was designed.



Basically to become completely independent from your Utility company you will need produce about 750 kWh of AC electricity. With 4.5 sun-hour-days you will need 6 kW solar PV array (5.83 kW to be exact, but bear in mind that this is all relative) which is optimally designed and is placed in optimal location – no shading, perfect angle, etc. This is the best case scenario. So what size solar system will YOU need? When considering installing a Solar PV system, you as home or business owner will need a to know the future size of your solar system in kW ( 1 kilo watt is 1000 watts) and the cost associated with this solar system. You also need to establish your current annual electricity usage and decide if you want to reduce or completely eliminate the use of electricity that you purchase from your utility company. First, gather your electric bills for the last 12 months, record your total electricity consumption – the number of kW-hours, and your the total amount you had to pay, excluding any late fees and other miscellaneous fees. Divide your total cost by the total number of kWh – this will give you real cost per kWh.

For example, in Massachusetts, average cost of electricity for residential use is 19-24 cents per kWh, and 15-17 cents per kWh for commercial use. Both are set to increase by 20% in near future, as announced in April 2008, by local utility companies.


Designing a Solar PV system, tailored for your need

To make best use of your solar system, you will need to capture as much sun-light as possible, therefore the best location to place your solar system is on the south-facing side of the roof. You also want them to be installed at a certain angle – about 20-30 degrees.

Assuming the 4.5 hours of sun per day, a 1 kW Solar PV system will produce 4.5 kWh per day, and 135 kWh in a 30-day month (4.5 x 30 days). Please keep in mind that the energy produced is in DC volts, and when it goes through the conversion into AC, you lose about 20-25% of that electricity.

Average household electric consumption is 750 kWh per month for a single family home. To cover 100% of this consumption with solar electricity, you will need about 8 kW solar PV system. 135 kWh DC x 8 = 1080 kWh – 10% = 972 kWh AC at 100% production output of solar panel. Note that ALL solar panels loose an average of 0.5% of production output per year, or 10 % through its 20-year warranty period.



Average residential solar installation is 2-4 kW system which usually eliminates 50-70% of electric power that you purchase. However those installations are still dependent on additional electricity. Commercial solar installations can range from 10 kW to over 1 MW (1 megawatt = 1000 kW).

Commercial Solar PV systems can supply power to the building they are installed on or they may be a so called solar farm – or a solar power plant supplying electric power directly into electric grid.

CMR Solar Energy Integrators concentrates on smaller, roof-top solar installations for individual home or business use. Solar farms topic goes way beyond the scope of this guide, and is considered a power utility for taxes and other purposes.


Step 3 – How to choose equipment for your solar system:

This is the most difficult part, as there is no right answer to this question. However there is a general guideline to follow, which will help you choose the longest-lasting and best performing solar panels, inverter(s), control units, production monitors, etc.

This part of our solar guide will be the most confusing part also, as I will go over equipment and the solar systems sizes and how to pair different components and to get the best solar pv rebates, all at the same time.

Lets begin: to avoid as much confusion as possible, we will pretend that we are designing a 3 KW solar system for residential installation, in Massachusetts. Some of the variables will be different for your state, but this will be a good reference point for you.

Basic metrics for choosing solar equipment (or any electronic equipment for that matter) is such that you don’t want to be an early adaptor. You want to buy a 2nd or even 3rd generation stuff (inverter for example), which is a very safe bet that all the bugs of first / second generations were worked out and equipment performs at maximum efficiency.

You also want to get UL rated equipment, or your electrical inspector will never sign off on the permits. A good example of such inverter is the Sunny Boy 2500, which is a 3rd generation, tried and true work horse which also offers one of the best expandability and efficiency. This is not to say that other inverters are bad – you should use the 2nd/3rd generation metric and do your due diligence.



You also need to keep in mind that average life-span of the inverter is 7-10 years while it’s cost is up there (on average you can expect to pay just under $1 per watt of the inverter’s capacity). If you plan for a big solar system, it is better to have many smaller inverters than one big inverter. If a small inverter dies, others are still performing, and your system is only partially down and it is a LOT cheaper to replace one $3000 unit, out of 5, than one $15000 unit.

For our hypothetical solar system we will choose one of the more simple inverters from Sunny Boy, rated at 3000 or 3500 watts. There is never and exact number of watts produced and in the first year, your Solar system WILL produce about 10% more than its rated capacity. You want to utilize that and also don’t want to “overload” your inverter: this is a little confusing – inverter will only accept as much electricity as it’s rated capacity – not more, so anything extra will just disappear.

A slightly larger inverter will allow for some future expansion of your solar systems.


Cost of Solar PV systems:

National average cost to install a Solar PV system ranges from $6 to $7 per watt or $6000-$7000 per kW DC (direct current) of solar system installed, with smaller installations being at the top for this price range due to fixed costs such as equipment, setup, installation, permits and paperwork.

Most expensive component of the solar PV system are the solar panels themselves, however equipment such as inverter (which converts DC into AC and feeds it into your meter) also add considerable amount to a smaller size PV systems.

Fortunately the price tag is not your actual cost, as many states have a wide range of rebates for solar PV installations as well as federal tax credits, available for both commercial and residential systems.

As systems get larger, the cost per watt is lower. A two (2) kilowatt system may cost between $16,000 and $20,000 ($8.00 to $10.00 per watt), while a five (5) kilowatt system may be installed for as little as $35,000 ($ 7.00/watt). All of these prices are figured before the rebates or tax credits. The final cost may be as low as $2.50 per watt (or $12,500 for a 5 kW system) depending upon which incentives your utility may offer.


ROI and pay-off period for Solar PV

Return on investment is a very popular metric because of its versatility and simplicity. That is, if an investment does not have a positive ROI, or if there are other opportunities with a higher ROI, then the investment should not be undertaken.

The return on investment formula:

ROI = (Gain from Investment - Cost of Investment) / Cost of Investment

It is more instructive to think of solar as an investment that yields an annual return, much as a bank savings account provides interest.

A solar PV system may generate savings that would equal an annual Return on Investment (ROI) of 7% to 15% per year at today's electric rates. These savings is not taxed as would be the interest earned from a bank savings account. Thus you would have to find a bank account or investment yielding 14% to 28% to equal the return on a solar electric system.

No matter what ROI your system would generate, this is ultimately a choice about how you will be buying your power - not whether or not you will be paying for it!

The State of California will help you buy a solar electric system. The California Public Utilities Commission will pay you a lump sum rebate up front or monthly for five years based upon the actual performance of the system. The amount of the lump sum rebate is calculated by using an online tool ( created to take into account module and inverter efficiencies, tilt and orientation, shading and local weather to produce an Expected Performance Based Buydown (EPBB).

The rebate was administered by the California Energy Commission (it was called the Emerging Renewables Program or ERP) but the program was extended and altered on January 1, 2007 (it is now called the California Solar Initiative or CSI).

In prior years the rebate had been as high as $4.50 a watt but was summarily reduced to $2.50 in 2007. As of June '09, the rebate level for Edison customers has dropped down to a maximum $1.90 per watt.

The rebate paid is now reduced by the degree of shade measured on the panel's surface, the tilt and orientation as well as the inverter efficiency.

On July 1, 2009, the rebate was again reduced by using newer performance ratings for solar panels that were mostly lower than in the past. Many other factors are involved in this complex calculation as well. //Top..


CMR Integrators - Solar Energy
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San Ramon, CA 94583
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