First, solar, like wireless, should be still viewed as a technology of last resort in most cases. It raises costs, causes aesthetic concerns, creates installation issues, and increases complexity. If you can wire, you should wire. That said, if you have to install a camera in a location where there is no infratructure (power or communications) then wireless and solar may be your best options.
Second, you must look at power conservation as much as power generation. The difference between 10 watts and 40 watts is the difference between a small, attractive and cost effective system and a large, ugly, expensive system. Be prepared to make compromises in order to move to a solar powered system.
Before I go into the specifics of sizing and configuring a solar powered surveillance system, I wanted to share with you a related story that illustrates my points on a larger scale.
Solving the Wrong Problems
Our local school district just undertook what seemed on the face of it to be a great project to install solar at the high school and various elementary schools around town. The project is known as a PPA or Power Purchase Agreement. This is where an installer provides all of the installation of equipment for "free" in exchange for a purchase agreement where the school promises to purchase the power from the panels installed for the next 30 years at a fixed rate. The installer generates power for the school on site and sells it to the school. Surplus power is sold on behalf of the school to the local power utility in order to off set the cost of the solar panels.
|Massive Solar "Carports" being built for "free"|
My political commentary: The school district didn't have to seek any approvals for the project, since they were not undertaking a capital project, but rather just committing to buy power from a "utility" and all of the equipment was "free". Of course "free" means that it is paid for by tax incentives, credits, and other direct government subsidies that come from agencies hidden from public scrutiny. The cost of the project to the school district is $14 million over the life of the contract which is reflected as electricity costs. But as an operating expense, it did not require any review.
The entire viability of the project is dependent on reverse metering sales of electricity back to the local power utility at rates assumed to be much higher than today. If the market stays flat or competition from other schools doing the same thing heats up, then they could lose millions, or have to take draconian measures to conserve energy in order to make ends meet. This also does not figure in the increased consumption that more computers in the classroom would required or depletion in solar cell efficiencies over time (in other words in the outer years, when you expect to have the most net benefit, the solar panels are their least efficient).
And of course the actual cost to the tax payer of the project is much higher than "free". The subsidies incurred for the project can run as much as 70% of the capital equipment costs. But since the subsidies are paid out of different government budgets than the schools it is impossible to hold anyone accountable to pull the spider web in. So we as tax payers are really overpaying for power by about $9.8 million and taking a large risk that the school will run out of capacity in later years.
Solar makes sense if you design for solar from the start, avoid inversion (converting from DC to AC), use power efficient equipment, and plan for capacity growth in the future.
Building the Right Solution
My main point from the story above is: when undertaking a solar project, plan for solar. Pick your cameras with power consumption in mind, pick your wireless routers with power consumption in mind, pick your storage solution with power consumption in mind, then size your solar system to fit the need.
Lets start with a simple perimeter parking lot camera. This camera is remote from any power or communication and needs to use long distance (2km) wireless and solar. There is a requirement for good facial detail, for criminal prosecution, and we need always on situational awareness.
|Solar Insolation Map Shows Peak Solar Hours per Day|
|A conventional surveillance|
system requires a big solar system
|A small scale solar power solution |
runs a system that is well designed
If you design the system for low power consumption, then you can size the power generation for small scale too.
What about Cellular?
Now, say you have to go way off the beaten path. You want to put your camera where you only have 3G cellular, but you need live real time streaming, you want high definition so you can see who is causing trouble.
Using conventional thinking you might use a PIR motion detector to trigger the camera to come on for a short time, transmit its video and then turn off again. The problem is that you only get low resolution and you only get it for a short time. Try now running a microNVR with the same low power camera and a 3G modem. Again, at less than 12 watts total, you could run this solution all day on two panels. The microNVR can record at high resolution 24x7 and using transcoding software we can send high quality, high frame rate video for situational awareness over 3G.
Again, design the system correctly and the power requirements can be small, the solar panels can be small,