Doing a Starter Solar PV System

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Now that you have assessed your energy needs, determined the amount of sun available and the size of your battery storage; you are ready to put it all together into a solar PV system. We are going to put together a simple starter solar PV system which you can add to later. We are going to divide this into 4 parts:

A. Energy source (PV modules)

B. Energy storage (utility or battery)

C. Energy processing + protection
(controller, fuses, disconnects, inverters, instrumentation, etc)

D. Total Estimated Cost

A brief note on costs: PV systems typically range between $8 - $30/watt depending on variables such as location, # PV panels + orientation, system design + configuration, varying energy loads, etc; and ever-changing market supply + demand and technology. This range is an average – you can build less or more costly PV systems. We will provide very rough estimated costs for this system at the end of each section.

‘~’ before our cost estimates, means it is an ‘approximate’ number.

We will build a 12 Volts DC (direct current) system. It will power your lights or other simple appliances. You can expand it to about 3 times its size without having to change major components.

We discussed PV panels in Section 5. For this starter system, we will use one 50 watt PV module per household person. You can decide how many panels you will need depending on the electrical loads you want to power: see Section 5b.

For this starter system, each person will have about 250+ watts (5+ hours of sunlight per day) available to use each 24 hours. This uses peak solar power input = there will be substantially more in the summer and less in the winter. Also, if you live in the South or South west you’ll have more solar input than if you live in the north or if you have more cloudy days. How much solar energy each panel collects will depend on where it is located, the tilt angle, and system characteristics. For this starter system we will assume that there are 3 persons and specify 3 solar PV panels.

PV panel tilting: In northern latitudes the rule of the thumb for optimal wintertime solar panel tilt angle is the latitude plus 15 degrees. For most of North America this means your PV panels should have a tilt of 45-65 degrees from horizontal (flat). There are many other tilting considerations when mounting solar PV panels. Wind shear, summertime vs. spring/fall equinox, etc.

We will estimate the cost for each PV panel to be ~$400
(see our Solar Panel Center for current panel prices)

For this starter system we are assuming no utility tie-in and a totally independent PV system using on-site battery storage. We talked about net metering and battery systems in Section 5B, page 14.
If you opt for a Trojan L16 battery, you’ll need at least two for a 12VDC system (each L16 is 6VDC). For more cloudy day energy storage you may want to upgrade to 4, 6, or 8 L16’s later on. We will be using 2 – L16’s for this starter PV system.

We will estimate the cost for each battery to be ~$250
(see our selection of batteries for current prices)

The basic function of solar PV controller is to regulate and provide optimal current from the solar PV array to the batteries or utility grid. The controller provides many functions:

1. Regulates PV array current to batteries
2. Prevents overcharging of batteries
3. Compensates for temperature variations
4. Compensates for various battery charging states
5. Can step-up or step-down voltage as needed
6. Provides Low-voltage disconnects
7. Protection and auto-resets on short circuits

Controllers can have a variety of output devices. Whether LEDs, digital displays, audible sounds or others; they can easily tell you the status of your PV system. Controllers are sized according to maximum array charging current. This is readily available from your PV panel spec sheet or manufacturer or distributor.

Many PV systems use readily available low-voltage automotive and RV/marine type fuses. These range between ¼” blade fuses, ‘SEA’ fuse blocks, Class ‘T’, ATO/ATC Powerhouse Fuse blocks; or other in-line fuse holders. Safety disconnects are needed for total system shutdown in case maintenance or repair work needs to be done; and for over-current protection. Circuit breaker protection are needed for all electrical loads.

There are also DC battery and load switches available to disconnect the battery system from your electrical loads and to switch between various battery arrays.

It is essential to have a knowledgeable electrical engineer or contractor design and install proper fuse and disconnect protection.

All connections should be properly terminated, soldered and/or sealed from outdoor and indoor elements. NEC codes must be followed – they are minimal requirements – not design criteria!

Of course you will need extensive wiring and terminations (connection points) for all of these components. You will also need to provide electrical connection to your lighting loads, and will want to replace your current lights with more energy efficient ones.

Most American appliances are designed to run on 120VAC (alternating current voltage) at 60Hz (cycles per second) . Other countries may use 230-250VAC and 50Hz. Most renewable energy systems (solar, wind, hydro, etc) produce 12-48 VDC (direct current voltage). In order to power these appliances from a renewable energy source, an inverter is needed to convert the VDC to VAC.

An inverter is a device that electronically changes the low-voltage DC power to the standard high-voltage AC power required by most appliances.

Over the last few years, inverters have greatly improved. They are now quieter, more efficient, have a low ‘sleep mode’ power consumption, have better waveforms and have come way down in price. Most inverters manufactured in the last 5-10 years have between 88-97% efficiencies. Most inverters produce VAC using a modified sine/square wave. These inverters may emit electrical noise and interfere with radios, TVs, telephones, etc. A true sine wave inverter would avoid this, but would also be more than triple the price of a modified wave inverter.

We recommend you consider these minimum inverter features:

1. Reliability and safety
2 . Low battery voltage protection
3 . Over current protection
4 . Reverse polarity protection
5 . Thermally activated cooling fan
6 . Automatic ground switching

1. Reliability and safety

This is the most important requirement for an inverter (heck – for just about anything!). Most major inverter manufacturers that have been in business more than 10 years produce a reliable and safe product. Another way to asses this is to look at how the inverter is packaged and shipped. Reputable manufacturers know that packages can get shredded and trashed and provide extra foam molding and packaging protection.

2. Low battery voltage protection

This protects your battery system from excessive discharge. Some manufacturers provide an adjustable setting: A high setting allows the user to leave for an extended period while leaving security lights, refrigerators, etc. on without fear of harming the battery system due to discharge. A low setting on this may allow for a deeper discharge for special batteries that can handle it.

3. Over current protection

Should a high current suddenly be present, this will provide some protection from inverter failure.

4. Reverse polarity protection

In case of an inadvertent reversal of + and – wiring, or some other polarity failure, this feature will provide some protection from inverter failure.

5. Thermally activated cooling fan

When the inverter gets too hot, this feature will automatically provide a stable temperature allowing the inverter to continue doing its job.

6. Automatic ground switching if needed.

This feature is needed if you have an RV or marine PV system – it is strictly prohibited by NEC for residential and commercial application. Automatic ground switching disconnects the inverter’s internal VAC grounding when the inverter is hooked to a RV or shore (marine) remote power source. See the grounding section (page 19) for more information about why this is essential.

From a simple voltmeter to sophisticated computer controlled multi-digital displays, there is a variety of instrumentation available for your starter PV system. We recommend a minimum of a simple digital voltmeter showing your battery voltage. Depending on your needs and sophistication, you may want to include a shunt ammeter telling you how much energy your PV panels are generating and/or how much energy you are using.

We will estimate the cost of a controller to be ~$200;

various fuses/disconnects/ circuit breakers to be ~$80,

wiring and terminations to be ~ $100,

one 1000 watt inverter to be ~$300,

one voltmeter to be ~$40.

(see www.solarhome.org for current prices)

From each of the above sections our total estimated cost is :

3 solar panels @ ~$400 each = ~$1200.

2 L-16 batteries @ ~$250 each = ~$ 500.

1 – Controller/fuses/inverter/voltmeter = ~$ 720.

TOTAL = ~$2,420.*

Approximate cost/watt for starter system is $16 (2420/150w)

*This is an estimated minimum price for these materials only. You will need to add labor costs, permits + inspections if needed, electrical load wiring, etc. Your actual costs will also vary depending on changes in these components’ prices, availability, freight and taxes. Please see www.solarhome.org for current prices.

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