Solar System Design: What to Know Before You Start

Proper solar system design is essential to ensure successful and safe do-it-yourself photovoltaic systems that generate the maximum amount of power. Check out these tips for planning a DIY solar power system to get started.

| December 2014

The sun's energy is free and abundant, but planning a solar power system to utilize this energy can be a daunting task. DIY Photovoltaic Solar Power for Homeowners (CreateSpace, 2014), by Doug and Jennie Ostgaard, is a resource for any homeowner interested in custom solar system design. Plenty of photos and schematics illustrate the entire design and build process, along with the solar energy and electrical load calculations the Ostgaards used to determine the necessary scope of the project. The following excerpt is from chapter 3, “Designing for Solar Energy.”

Before beginning our DIY solar power system, an evaluation needed to be done to determine the amount of solar energy available at our site and our power requirements. We needed to calculate what size system would get us close to our target and be the most cost efficient with optimum payback period. There were many design requirements and options in PV systems that needed to be evaluated. For example, should we use wood or steel frames? We found it is best to layout questions and variables first. After that, we could proceed in a logical path forward to capture the best system for the lowest price and fastest payback.

Solar System Design Requirements:

Listed below are the basic design requirements we used for our system. While we will explain our requirements, we also include comments to you the reader — to help with your own requirements. We believe these requirements are best for a robust survivable system. With these requirements, even when the power grid goes down, the system will be up and running.

1: Reliable and renewable energy.

Renewable free energy was the key driver for us. The alternative was to use carbon fuel reserves whose price will skyrocket as dwindling supplies are exhausted. Using renewable resources also allows us to do our part to take care of the earth (Genesis 2:15).

2: Off-grid with grid-tied option.

Off-grid has no connection to power grid. If we were off-grid, we would need to produce all of our electricity.  Being off-grid would save us 11 cents per kWh which is the cost of purchasing our electricity from the local utility company. However, if we were on-grid we would receive all of our power from the power grid and sell our PV produced power to the utility company. The utility company would then subtract what we produced from what we purchased from them.

Originally we intended to do a mix with part of our home off-grid, and part of our home on-grid. However, the utility company representative explained that this was inefficient. With this mixed/partitioned system, in the summer we would have all the electricity we needed. However, any excess power would be wasted. In the winter we would not have enough power and would need to purchase electricity. He suggested we be totally on-grid with off-grid capability. Our excess power could then be banked at the utility company and withdrawn (from our power account) when our production was low and our demand was higher. We appreciated the explanation and decided to go with their recommendation.

1/23/2015 7:00:05 PM

Hi GA – Great comments and clarification on a Bimodal Solar Electric ('PV') System. We agree that this is the best way to go and with the most flexibility and grid independence.

1/23/2015 5:48:27 PM

re: Comment about "The utility company representative explained that this was inefficient. With this mixed/partitioned system, in the summer we would have all the electricity we needed. However, any excess power would be wasted. In the winter we would not have enough power and would need to purchase electricity. He suggested we be totally on-grid with off-grid capability." Ironically, the utility rep. is correct! This describes a Bimodal Solar Electric('PV') System which is both "On-Grid" + a "Back-up PV Power" systems in one system. With a Bimodal solar electric system you get two types of PV systems in one complete PV system, and the "best of both worlds" with the most of efficiency of 'Grid-tied' operation + back-up power without normally using your energy storage! Normally, 'Grid-tied only' operation will power house loads, and send excess power to utility. (Energy storage part, usu. a battery bank, will be on 'stand-by' while in 'send/sell-only' mode.) If the grid fails, then the Hybrid inverter system (usu. automatic) will transfer(isolate grid input) and then use only 'Off-grid' mode of your PV power system (array + and energy storage power for your dedicated ('critical') house AC loads your desire to have during 'emergency' power outages! If you decide to live completely off-grid later, you can add to a hybrid PV system as needed (more array and/or, gen-set, energy storage capacity, etc.), disconnect utility power, then connect all house loads desired to live within your 'means'(daily PV production) to produce all your electricity using only the sun! True Independence! (with responsible power usage & correctly sized PV system for all weather!) GA

12/16/2014 1:57:34 PM

Thank you for your question Rita. We highly recommend saving up for the system so you do not have to borrow money. Our book should be helpful for this – chapter 7 offers energy savings ideas for the home. We saved significantly on electricity (about $100 a month) using these ideas. If you save for the system first, a payback like 8.5 years (which is what we got and write about in our book) is not an issue – after payback, you will have it paid for and should be saving or making money in the future. In our state, we have an 18 cent per kWh green energy subsidy. You will want to see what is available in your area. Being cautious about TV ads for solar is wise. For example, the cost of Hyper X-2 panels, in our opinion, turn out to be about twice what we paid using Solar World SW 240 panels (see our earlier comments). Our book provides the cost breakdown and discusses panels and equipment needs. After the 30% federal rebate, our cost for our system was about $22,000. You could reduce this cost by building a smaller system (ours was a large 8 kW system) and by buying SW 240 or smaller panels (or used panels) – perhaps something around 68 cents/Watt versus the 99 cents/Watt we paid. Additional savings can be gained by buying four golf cart 12 volt batteries (perhaps from Costco) and then upgrading batteries in the future when you can afford it. An additional savings of about 30% on panels would be to build only two of the three frames (which we used). You could add a third later if desired. The estimated savings from this would be about $4200. This cost includes one charge controller. With one less frame and four batteries only, the cost could probably be reduced down to about $17,000 after a 30% federal rebate (for an on grid/off grid system) Do-it-yourself saves a lot of money. Our system, we estimated, would have cost $70,000 if we hired it done. Please feel free to email us at our website -

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